Comparative Analysis of Pawpaw Production Data from 2005-2012 A

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Comparative Analysis of Pawpaw Production Data from 2005-2012

A thesis presented to

the faculty of

the College of Health Sciences and Professions of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

Laine M. Greenawalt

August 2016

This thesis titled

Comparative Analysis of Pawpaw Production Data from 2005-2012

LAINE M. GREENAWALT

has been approved for

the School of Applied Health Sciences and Wellness

and the College of Health Sciences and Professions by

Robert G. Brannan

Associate Professor of Applied Health Sciences and Wellness

Randy Leite

Dean, College of Health Sciences and Professions 3

Abstract

GREENAWALT, LAINE M., M.S., August 2016, Food and Nutrition Sciences

Comparative Analysis of Pawpaw Production Data from 2005-2012

Director of Thesis: Robert G. Brannan

Introduction: This study examined fruit production characteristics of different varieties of pawpaw (Asimina triloba) over a period of 8 years. Methods: Plants of 52 varieties of pawpaw (n = 359) were planted at three locations in southwest Ohio from

2001-2006. Fruit were collected and weighed spring 2005-fall 2012. For further analysis, the 52 varieties were divided into two data categories (varieties not belonging to a genetic group and those assigned a genetic group) based on previous research. Differences in average fruit weight (g), yield (g), and harvest length (days) were analyzed among varieties and genetic groups. Pearson’s r was used to identify any correlation between average fruit weight and total number of fruit produced. Results: Significant differences in average fruit weight were found between genetic groups and individual varieties.

Differences in yield and fruit onset were also identified between individual varieties.

Significant differences in average fruit weight and yield were seen between growing locations. Comparison of average fruit weight and total fruit number resulted in a significant negative correlation. Discussion: Results indicate that some pawpaw varieties, or groups, generate significantly larger fruit. Results also indicate that planting location makes a difference in fruit production, although future research is needed to identify specific growing factors. A weak negative correlation between average fruit weight and total fruit number indicates that large fruit sets can lead to decreased fruit size. In order to 4

improve fruit quality and tree productivity, potential pawpaw growers must consider many preharvest factors. These findings add to the limited body of evidence about pawpaw fruit in general and indicate that variety and growing location can significantly affect the ultimate commercial potential of pawpaw fruit. 5

Preface

The manuscript has been formatted to meet the guidelines set forth by the Thesis and Dissertation Services at Ohio University. Chapter 3 contained within this APA- formatted thesis document serves as a prepublication manuscript which follows the structure of the International Journal of Fruit Science.

Dedication

This work is dedicated to my friends and family, who have supported me throughout the

writing process.

Acknowledgments

I would like to acknowledge Dr. Ron Powell, for providing me with the data that made this project possible, and my committee–Dr. Robert Brannan, Dr. Janet Simon, and

Dr. Art Trese, for their continuing support and guidance. 8

Table of Contents

Page

Abstract ...... 3

Preface...... 5

Dedication ...... 6

Acknowledgments...... 7

List of Tables ...... 10

List of Figures ...... 11

Chapter 1: Introduction ...... 12

Overview and Background ...... 12

Statement of Problem ...... 14

Significance ...... 14

Limitations and Delimitations ...... 15

Glossary ...... 16

Chapter 2: Review of Literature ...... 18

Introduction ...... 18

Background ...... 18

Morphology ...... 21

Fruit Characteristics ...... 27

Development of the Pawpaw Industry ...... 32

Commercialization ...... 36

Chapter 3: Comparative Analysis of Pawpaw Production Data from 2005-2012 ...... 40 9

Abstract ...... 40

Introduction ...... 41

Materials and Methods ...... 43

Results ...... 46

Discussion ...... 58

Conclusion ...... 62

Literature Cited ...... 65

Chapter 4: Summary and Conclusion ...... 69

References ...... 72

Appendix A: Descriptions of Pawpaw Cultivars Used in this Study...... 83

Appendix B: Sample Data Collection Sheet ...... 91

Appendix C: 8 Varieties of Pawpaw Excluded from All Data Analysis ...... 92

Appendix D: Means ± SDs for 52 Individual Varieties Included in Data Analysis ...... 93

Appendix E: Pictures of Planting Locations ...... 95

Appendix F: Original Data Recorded by Ron Powell ...... 95

List of Tables

Page

Table 1: Research Questions and Hypotheses ...... 14

Table 2: Proximate Analysis of Common Fruits ...... 31

Table 3: Genetic Grouping of Pawpaw Varieties ...... 34

Table 4: Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for 52

Pawpaw Varieties by Year ...... 51

Table 5: Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for

Three Data Categories: 52 Pawpaw Varieties, Varieties Not Belonging to a

Genetic Group, and Those Varieties Belonging to a Genetic Group ...... 52

Table 6: Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for

Pawpaw Genetic Groups ...... 52

Table 7: Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for

Pawpaw Varieties Not Belonging to a Genetic Group by Year...... 54

Table 8: Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for

Pawpaw Varieties Belonging to a Genetic Group by Year ...... 55 11

List of Figures

Page

Figure 1: North American pawpaw’s native growing range ...... 19

Figure 2: USDA plant hardiness map ...... 20

Figure 3: Pawpaw flower ...... 23

Figure 4: Pawpaw fruit...... 25

Figure 5: Pawpaw chip-bud graft ...... 27

Figure 6: Map of Butler and Adams Counties, Ohio ...... 45

Figure 7: Pawpaw harvest date ranges (from first to last record) divided into quartiles for individual years across all varieties and locations with growing degree days (GDD) as of

August 1 for each year indicated in parenthesis ...... 47

Figure 8: Frequency (f) distribution of average fruit weight (g): (a) all varieties, (b) varieties in genetic groups, (c) varieties not in a genetic group...... 49

Figure 9: Correlation of average fruit weight (g) and total number of fruit collected per tree for 52 pawpaw varieties from 2005-2012 across three growing locations ...... 57

Chapter 1: Introduction

Overview and Background

The pawpaw, or Asimina triloba, is the largest tree fruit native to North America.

It has a vast native growing range that spans 26 states corresponding to U.S. Department of Agriculture (USDA) plant hardiness zones 5-8 (Galli, Archbold, & Pomper, 2007).

The family Annonaceae, to which pawpaw belongs, contains over 2,400 species, all of which are tropical or subtropical except for pawpaw, making the temperate-growing fruit unique. Other commonly available Annonaceous fruits include cherimoya, soursop, and custard apple (Archbold, Koslanund, & Pomper, 2003; Callaway, 1993; Kral, 1960;

Peterson, 2003).

Pawpaws are shrub-like, understory trees that can grow up to 12 meters tall. They have long membranous leaves and maroon flowers that mature in mid-spring and produce clusters of up to nine fruit in late summer to early fall (Geneve et al., 2003; Pomper &

Layne, 2005). However, pawpaw flowers are self-incompatible, making pollination an important factor that could limit commercial possibilities (Bois, 2001; Layne, 1996;

Willson & Schemske, 1980). In addition, the normal bloom period of pawpaw flowers can last up to 4 weeks, resulting in an elongated harvest period in the fall which requires more labor and time intensive harvesting techniques (Moore, 2015; Pomper, Crabtree,

Layne, & Peterson, 2008).

of their distinct tropical flavor. Research has also shown pawpaw fruit have a notable nutritional value high in antioxidants, specifically flavonoids like condensed tannins

(Brannan, Peters, & Talcott, 2015; Watt & Merrill, 1963). These compounds, which are also found in cocoa, grapes and tea, are believed to have beneficial health effects (Bor,

Chen, & Yen, 2006; Donno, Beccaro, Mellano, Cerutti, & Bounous, 2014; Sun, Chu, Wu,

& Liu, 2002). Unfortunately, pawpaw fruit are highly perishable with a shelf life of only

3 days (Archbold et al., 2003; Koslanund, Archbold, & Pomper, 2005a). This rapid decline in fruit firmness is a major barrier to the growth of the pawpaw industry.

In the early 1900s the pawpaw was being considered as a native, North American cash crop for mainstream commercialization (Pomper & Layne, 2005). Over the last century, however, the rise a more globally centered food system resulted in an increased ease of shipping tropical fruits, decreasing the demand for indigenous goods. The final result was that the pawpaw never became recognized outside of local markets (Moore,

2015; Peterson, 2003). Recently, there has been another surge in interest surrounding this remarkable plant. Horticulturalists and hobbyists are working toward the progression of the pawpaw as a commercial fruit crop. The result has been the development of over 60 varieties and advanced selections with desirable characteristics such as large fruit size, firm texture, delicate flavors, and few blemishes (Ames & Greer, 2010; Brannan,

Salabak, & Holben, 2012; Templeton, Marlette, Pomper, & Jones, 2003). Within these 60 cultivars, however, comes great variation in fruit size and yield. Research has yet to determine which varieties of pawpaw would be best for commercial purposes. 14

Statement of Problem

Currently, pawpaw remains in the beginning stages of commercialization and little is known about which varieties of pawpaw are most commercially viable. Data was collected by the North American Pawpaw Growers Association (NAPGA) over an 8 year period in an effort to measure tree productivity season to season, but this data was never analyzed. The objective of this research was to perform a retrospective study on the data described above with the aim of identifying varieties of pawpaw with the greatest fruit yield and largest average fruit weight over a period of 8 years.

Table 1

Research Questions and Hypotheses Question Hypothesis

1. How does average fruit weight differ There will be a significant difference in among all varieties and genetic groups? average fruit weight.

2. How is average fruit weight affected by Fruit size will be significantly affected by growing location? growing location. 3. How is average fruit size related to fruit Larger fruit set will result in smaller set? average fruit size.

Significance

larger commercial farms. It is important to identify which varieties of pawpaw produce the most noteworthy fruit in terms of size and yield in order to help interested farmers select the most profitable trees.

Limitations and Delimitations

The greatest challenge any pawpaw grower faces is determining fruit ripeness.

Currently, no standardized method exists to conclude ripeness and the decision is often left to the discretion of the harvester. The most commonly accepted method is to feel the fruit–fruit that gives slightly under gentle pressure are generally considered ripe. Here, only fruit that had fallen from the tree were measured. While this method is easier than harvesting fruit before they fall, it should be noted that it is not appropriate for pawpaws headed to fresh market due the likelihood of bruising. It should also be considered that wild animals could have consumed some of the fallen fruit before it could be recorded by researchers.

It is generally accepted among horticulturalists that adverse weather conditions, including drought and high winds, can have a negative impact on any crop. Adverse weather was a factor in two of the growing years. Specifically, a drought occurred in

2007 and Hurricane Ike affected weather in 2010.

At the onset of data collection, all fruit were measured individually. However, as orchard size and fruit yields became larger, this method became impractical. As a result, all fruit for a given tree were gathered, counted, and weighed in batches, making average fruit weight the best assessment of fruit size. Little to no data was recorded regarding 16

fruit diameter, fruit condition (i.e., presence of Phyllosticta), tree trunk circumference, tree age, or weather.

Glossary

Agritourism. Any agriculturally-based operation or activity that brings visitors to a farm.

0Brix. Sugar content by weight in a food product.

Carpel. The female reproductive organ of a flower consisting of an ovary, stigma, and style. Can occur singly or as a group.

Climacteric. A stage of fruit ripening associated with increased ethylene production and a rise in cellular respiration.

Condensed tannins. Or proanthocyanidins; polymers formed by the condensation of flavan-3-ols. A type of antioxidant commonly found in grapes and other foods.

Desiccation. The process of drying.

Flavonoids. A class of oxygen-containing aromatic antioxidant compounds that includes many common plant pigments.

Fruit drop. A natural thinning of a fruit set; occurs when a tree has set more fruit than can be physiologically supported.

Fruit set. Expansion of plant ovary in response to hormones following pollination.

Growing degree days (GDD). GDD is a measure of the number of days above a minimum growing temperature, used to predict plant development such as the date that flowers will bloom or a crop will reach maturity. 17

Gynoecium. The female part of a flower consisting of one or more carpels.

High-pressure processing (HPP). A method of food preservation and sterilization in which a product is processed under very high pressure leading to the inactivation of microorganisms and enzymes in the food.

Inflorescence. The process of flowering.

Morphology. Refers to the study of form and structure of an organism including eidonomy, or outward appearance, as well as anatomy, or internal structure. These characteristics determine how an organism grows, reproduces, and is propagated.

Polyphenols. A class of protective chemical compounds found in plants

(antioxidants).

Phyllosticta. A large genus of fungi that cause leaf spots and leaf blights in plants.

Protogynous dichogamy. A biological phenomenon in which female reproductive organs mature (produce gametes) before male reproductive organs. Occurs in plants.

Sepals. Green leaf-like structures that compose the outermost part of a flower's base.

Yield. The full amount of an agricultural or industrial product. 18

Chapter 2: Review of Literature

Introduction

The following is a review of current literature pertaining to the North American pawpaw (Asimina triloba (L.) Dunal), its taxonomy, morphology, fruit characteristics, and past and present industry. The current pawpaw industry is small and confined to local markets. The basis of this review is to examine current evidence for the commercialization of pawpaw fruit.

Background

Taxonomy. The North American pawpaw (Asimina triloba (L.) Dunal) belongs to the order of flowering plants Magnoliales and the family Annonaceae, the largest of the

Magnoliales families. The Annonaceae, or Custard Apple, family contains over 130 genera and 2,400 species of which all are tropical or subtropical. Other popular members of the Annonaceae family include the commercially relevant cherimoya (Annona cherimola), soursop (Annona muricata), custard apple (Annona reticulata) and sugar apple or sweetsop (Annona squamosal), all which produce edible fruits (Callaway, 1993;

Kral, 1960; Peterson, 2003). While all members of the Annonaceae family share similar physical features and fruit production characteristics, pawpaw’s unique features set it apart (Alique & Zamorano, 2000; Brown, Wong, George, & Nissen, 1988; Wills, Poi,

Greenfield, & Rigney, 1984). Of the 130 genera contained in the family Annonaceae, only the genus Asimina grows in temperate climates. Of the eight species contained in the genus Asimina, Asimina triloba is the only cold-hardy representative and the only one 19

to produce a fruit of interest in terms of commercial viability and consumption.

(Callaway, 1993; Kral, 1960; Pomper & Layne, 2005; Reich, 1991; Zimmerman, 1941).

Growing zone. Pawpaw is a fruit-bearing tree native to eastern and central United States

(Pomper, Layne, & Peterson, 1999). The native growing range of the perennial pawpaw spans 26 states from northern Florida to southern Canada and as far west as Oklahoma and Nebraska (see Figure 1). They grow naturally in temperate, hardwood forests and prefer the fertile, well-drained soils of river basins such as that of the Susquehanna and

Ohio rivers (Callaway, 1993; Kral, 1960; Pomper & Layne, 2005). Pawpaw trees grow successfully in USDA plant hardiness zones 5-8, which have hot summers and cold winters (see Figure 2) (Ames & Greer, 2010; Galli et al., 2007; Kral, 1960).

Figure 1. North American pawpaw’s native growing range. Image of eastern United States excerpted from “Atlas of United States Trees, Vol. 4, Minor Eastern Hardwoods,” by E. L. Little, Jr., 1977. Image created by U.S. Geological Survey (USGS), Department of the Interior (1999). Retrieved from http://esp.cr.usgs.gov/data/little/asimtril.pdf 20

Figure 2. USDA plant hardiness map. Excerpted from “USDA Plant Hardiness Zone Map,” by U.S. Department of Agriculture, 2012. Retrieved March 10, 2016, from http://planthardiness.ars.usda.gov

History. Archeological evidence places fossils of Asimina triloba in North

America as early as 56 million years ago (Moore, 2015). Researchers speculate that

Native Americans played a large role in early pawpaw dispersal and may have even cultivated pawpaw, selecting for desirable characteristics and tending select trees. The fruit’s scientific name, Asimina, is thought to have been adapted from the Powhatan word

Assimin, meaning berry or fruit. Pawpaw is mentioned periodically throughout American history (Hormaza, 2014). In particular, in September of 1806, the pawpaw helped provide food for the Lewis and Clark expedition. Clark wrote,

Our party entirely out of provisions subsisting on paw paws. We divided the

biscuit, which amounted to nearly one biscuit per man; this in addition to the paw

paws is to last us down to the settlements, which is 150 miles. The party appear

perfectly contented and tell us that they can live very well on the paw paws

(University of Nebraska-Lincoln Libraries-Electronic Text Center, 2005). 21

Daniel Boone and Mark Twain, reportedly, were also fans of the pawpaw and it is likely that wild stands of pawpaw provided much-needed food for runaway slaves and

Civil War soldiers when rations ran low (Moore, 2015).

More than 120 years ago, pawpaw was identified by the American Horticultural

Society as a fruit of promising potential and, at the turn of the century, pawpaws were sold in large quantities in cities and towns in areas where the trees naturally grew (Ragan,

1888; Reich, 1991). Pawpaw is also mentioned throughout American folklore, and today there are still towns and rivers named after the fruit (Pomper & Layne, 2005). In 2009, pawpaw was named Ohio’s native state fruit.

Morphology

Description of tree and leaves. Pawpaw trees are deciduous and woody with a straight trunk and stems. They are clonal, shrub-like, understory trees that rarely grow taller than 12 meters. The clonal nature of the plant causes trees to grow in clusters through root suckering. Trees grown in full shade tend to be taller, with a horizontal growing pattern and few low-growing limbs. Alternatively, trees grown in full sun have a pyramidal shape and stronger branch angles, making growth in full sun optimal for fruit production.

Leaves are dark green in color, membranous, and grow symmetrically at the end of branches. They are long and drooping, measuring up to 15 cm wide and 30 cm in length. The membranous leaves of the pawpaw differ from other species of Asimina, which are generally leathery in appearance. This difference in leaf texture is most likely due to ecological factors such as the pawpaw’s wetter, mesic woodland growing habitat 22

(Kral, 1960). The straight trunk and tropical-looking leaves of the pawpaw make it popular among landscapers for its ornamental appearance and in 2000, it was voted landscape tree of the year by Better Homes and Gardens (Ohio Pawpaw Growers

Association [OPGA], n.d.). Environmentalists also love pawpaw trees; pawpaw leaves provide the exclusive food for Zebra Swallowtail butterfly (Eurytides Marcellus) caterpillars (Breckenridge, 2014).

These native trees are hardy. The twig and leaf tissue of the pawpaw tree contains natural compounds called Annonaceous acetogenins that have pesticidal and anticancer properties that make the trees resistant to insects and diseases that commonly affect other fruit and nut trees (Bermejo et al., 2005; McLaughlin, 1997; Pomper, Lowe, Crabtree, &

Keller, 2009). Phyllosticta, a genus of fungi, is the only disease known to affect pawpaw.

It causes gray leaf spots and fruit splitting. Anecdotal evidence indicates that some varieties may be more resistant to the fungi than others.

Flowering, pollination, and reproduction. Mature pawpaw flowers are maroon in color, approximately 5 cm in diameter and have an inner and outer layer each made up of three petals and three sepals (see Figure 3). Buds become visible in early spring, before the leaves and flowers mature in April to May resulting in immature fruit starting in June. Flowers can be found on the same tree for several weeks and the bloom period for a pawpaw tree has been known to last up to 4 weeks. This extended bloom period results in an elongated harvest period later on (Finneseth, Kester, Geneve, Pomper, &

Layne, 2000; Pomper, Crabtree, Layne, & Peterson, 2008). 23

A single pawpaw gynoecium (the part of the flower that ultimately produces fruit) contains several ovaries and can result in clusters of up to nine fruit (Geneve et al., 2003;

Pomper & Layne, 2005; Reich, 1991). Like other members of the Annonaceae family, pawpaw flowers show protogynous dichogamy. In other words, the female receptive organ, or stigma, is ready to receive pollen, produced by the male anther, before pollen is mature, preventing self-pollination. In addition, most pawpaw cultivars are self- incompatible and flower fertilization requires pollen from a genetically different tree

(Bois, 2001; Layne, 1996; Willson & Schemske, 1980). Wild fruit stands are rare and less than 1% of wild flowers set fruit (Reich, 1991).

Figure 3. Pawpaw flower. Excerpted from “Blossom Development in North American Pawpaw,” by R. Powell, 2012, OPGA Pawpaw Pickin’s Newsletter, p. 5. Reprinted with permission.

Pawpaw flowers have a putrid odor, dark colored petals and are considered by the

USDA to be fly flowers, or flowers pollinated by carrion-loving insects such as beetles and flies (USDA, n.d.). These pollinators, however, are unreliable and inconsistent growing patterns in the wild are indicative of poor pollen dispersal (Geneve et al., 2003; 24

Pomper, Crabtree, Layne, & Peterson, 2008; Willson & Schemske, 1980). This becomes important when considering the commercial possibilities of pawpaw; pollination as a limiting factor in fruit production could negatively affect fruit yields.

Research done at Kentucky State University has found that hand pollination is most effective. However, for commercialization purposes, hand pollination is not the most viable option. In orchard scenarios, however, researchers note that pollination is not a major issue due to higher plant density attracting a greater number of pollinators (Ames

& Greer, 2010; Pomper, Crabtree, Layne, & Peterson, 2008). It should be noted that hand pollination can lead to an excessive fruit set, which may result in reduced tree growth and limb damage.

Fruit. Botanically considered berries, the oblong, cylindrical fruits can weigh up to 1 kg, making it the largest edible fruit indigenous to the United States. Fruit grow singly or in clusters and have a strong aroma and distinct tropical flavor (see Figure 4)

(Brannan et al., 2012; Pomper & Layne, 2005). Fruit size, shape, and flavor profile all vary among varieties with the average fruit weighing 150-200 g (Pomper & Layne,

2005).

The skin of young pawpaw fruit is green but turns yellow to brownish-black as the fruit ripens. The skin is tough and inedible while the edible portion of the fruit, referred to as pulp or flesh, ranges in color from creamy white to bright orange or yellow and has a custardy texture prone to bruising. Seeds are dark brown, flat, and are aligned in two rows of 12-20 down the middle of the fruit (see Figure 4) (Peterson, 2003; Pomper

& Layne, 2005). 25

(a) (b) Figure 4. Pawpaw fruit. (a) Copied from U.S. Department of Agriculture, Agricultural Research Service. Created by Scott Bauer (1997, February 28). Retrieved March 13, 2016, from http://www.ars.usda.gov/is/graphics/photos/mar97/k7575-8.htm (b) Adapted from “Asimina triloba,” 2016. Created by Clarknova (2004, September 11). Copyrighted free use. Retrieved March 13, 2016, from https://en.wikipedia.org/wiki/Asimina_triloba#/media/File:Asimina_triloba_red_fern_far m.jpg

Propagation. Although mature pawpaw trees have a strong taproot, the root system of pawpaw seedlings is fragile and easily damaged, making them difficult to transplant. Luckily, pawpaw trees reproduce easily through the formation of root suckers and a single root system can cover a quarter of an acre (Bois, 2001; Reich, 1991).

Suckers, or root sprouts, originate from the root system of an existing tree and are genetic clones of the original tree. It is speculated that root suckering is a form of asexual dispersal for the pawpaw, which is unable to self-pollinate due to its protogynous dichogamy. Since pawpaw is easily able to reproduce asexually, wild pawpaw patches often bear little to no fruit, possibly in order to save the plants from the metabolic stress of fruit production. 26

This limited transplant success, in combination with unreliable natural pollinators, has resulted in the development different cloning techniques for use in the propagation of pawpaw for commercial and nursery purposes (Finneseth, Layne, & Geneve, 1996).

Grafting describes five plant propagation techniques where the ends of two plants (the stem with leaf buds, or scion, and rootstock, or trunk) are united to become a single viable plant. Grafting is a propagation technique commonly seen in fruit and nut plants and pawpaw graft readily to any native root stock (Zimmerman, 1941). These include budding and grafting techniques such as whip-and-tongue, cleft, bark inlay and chip budding (Jones, Peterson, Turner, Pomper, & Layne 1998). Budding, specifically chip- budding (see Figure 5), and the whip-and-tongue grafting technique have been found to be most successful in the propagation of pawpaw plants (Pomper & Layne, 2009). These techniques are currently being used to improve existing pawpaw cultivars (Layne, 1996;

Pomper & Layne, 2005).

Grafting ensures fruit quality by decreasing the genetic variation found in wild trees. It also protects the value of a specific variety or cultivar because grafted trees will not produce clonal growth of the same quality. Grafted trees usually begin producing fruit in 3-4 years while nongrafted seedlings can take up to 7 years to bear substantial fruit harvests. However, grafted trees generally live shorter lives than their seedling counterparts do. Researchers are currently working to identify seedling rootstocks that result in the highest establishment rates (Pomper & Layne, 2005). Seedlings have better survival rates than their grafted counterparts, but initial growth is slow and seeds required cold stratification between 90-120 days in order to germinate (Finneseth et al., 1996). 27

Grafted cultivars and wild seedlings are commonly available from nursery sources, although wild seedlings come with the risk of unknown fruit quality (California Rare

Fruit Growers, Inc., 1999).

Figure 5. Pawpaw chip-bud graft. Image created by Ron Powell. Reprinted with permission (personal communication, March 21, 2016).

Fruit Characteristics

Ripening characteristics. Many fruits, including pawpaw, follow ethylene climacterics and undergo physical and chemical changes after harvest (Hall, Wills, &

Graham, 1989; Koslanund et al., 2005a; Shiota, 1991). Peaks in ethylene production and cellular respiration are evident 3 days after harvest (Archbold et al., 2003) and indicate the final physiological process marking the end of fruit maturation and the peak of edible ripeness. Unlike other climacteric fruits, e.g., bananas, pawpaws picked before fully ripe

(green) will fail to ripen fully. Increased soluble solids content (0Brix) is also typical in ripening fruit as the degradation of starch to mono- and disaccharides adds to the 28

sweetness of the fruit (McGrath & Karahadian, 1994). Overripe pawpaw have an intense aroma and flavor that often found off-putting to consumers (Duffrin & Pomper, 2006).

Postharvest, pawpaw undergoes a rapid decline in fruit firmness. This dramatic decline is most likely caused by physiological reactions inside the fruit such as the action of the cell-wall degrading, hydrolytic enzymes (Koslanund et al., 2005a). The enzymes responsible for this postharvest decrease in firmness are cellulose, polygalacturonase, endo-mannanase, and pectin methylesterase (Archbold & Pomper, 2003). Previous research has found that fruit hardness in preripe pawpaw can range from 1-3 kg while the hardness of ripe pawpaw is 0.5 kg. Once harvested, ripe pawpaw soften and become overripe in 2-4 days at room temperature (Ames & Greer, 2010). This rapid decline in firmness is a major barrier to pawpaw commercialization.

Postharvest fruit ripening characteristics are important factors when considering fruit commercialization. Several postharvest preservation techniques have been tested to improve pawpaw perishability. The goal of these packaging and storage techniques is to decrease the respiration rate of the fruit, therefore slowing antioxidant and enzymatic degradation. Under the most simple form of storage, refrigeration, pawpaw fruit will last up to 3 weeks (Ames & Greer, 2010). Current research includes looking at the effectiveness of modified-atmosphere packaging to control ethylene production and extend the shelf life of pawpaw (Galli, Archbold, & Pomper, 2009) and the examination of the efficacy of frozen pulp storage, which maintains flavor components and antioxidant content while extending shelf-life (Harris & Brannan, 2009). Another treatment being considered is high-pressure processing (HPP). Unheated, high-pressure 29

processing is currently being used on foods such as shelf-stable guacamole because it effectively inactivates browning enzymes, kills pathogens, and even pasteurizes food

(Moore, 2015).

Fruit harvesting. Hand labor is still the most common method of harvest for the fresh fruit industry. Harvest season for pawpaw fruit, which varies based on location, can range from mid-July to mid-October and differs among varieties. As with other commercial fruits, this timetable depends on fluctuations in weather and can vary year-to- year. Due to a staggered bloom period in the spring, pawpaw harvesting can take up to 2 weeks and fruit from a single inflorescence can ripen at different times. This variability in harvest time adds to the difficulty of commercializing pawpaw because varying and numerous harvest times require added labor and can ultimately have a negative effect on fruit quality.

Some recognized indicators of fruit ripeness include fruit firmness and soluble solids content (0Brix). Ripe pawpaw fruit should give slightly when squeezed and are easily picked from the tree with little force, similar to a peach. Soluble solids, or 0Brix, is a representation of the amount of sugar contained within the fruit (g by weight). These indicators of ripeness are used to determine harvest times as the ripeness of the fruit upon picking impacts the final quality (McGrath & Karahadian, 1994; Templeton et al., 2003;

Wills et al., 1984). Unfortunately, change in skin color is not a reliable of indicator ripeness, because color varies by variety (McGrath & Karahadian, 1994).

Sensory. Many factors affect consumer consumption of fruits such as the pawpaw including sensory characteristics, health considerations, and indulgence seeking (Tuorila 30

& Cardello, 2002; Yang & Woods, 2013). It has also been found that product taste significantly affects consumption and that a poor first impression can cause consumers to discontinue use (Duffrin & Pomper, 2006; Tuorila & Cardello, 2002). Other factors affecting the consumption of fruit are education level, gender, age group, and income level.

Pawpaw fruit has a tropical flavor most often described as a combination of banana and mango, although fruit flavor, texture, and appearance can vary across cultivars (Brannan et al., 2012; Pomper & Layne, 2005). An untrained panel testing frozen pawpaw pulp described it as sour, bitter, and having a melon taste (Duffrin &

Pomper, 2006), however, research has shown that consumers have difficulty describing tropical fruit flavors, such as pawpaw and papaya, due to similar aromas and tastes

(Brannan et al., 2012). The flesh has a custard-like texture reminiscent of an avocado

(Kral, 1960; Pomper, Lowe, et al., 2009) and ranges in color from creamy white to bright yellow or even orange (Pomper, Layne, & Peterson, 1999). In addition to its tropical flavor, pawpaw has a unique aroma. The distinctive aroma of ripe pawpaw fruit is a result of a high concentration of methyl esters (Galli, Archbold, & Pomper, 2008). This concentration increases as the fruit continue to ripen after harvest, resulting in a strong fruity aroma and flavor that can be unpleasant to consumers.

Fruit quality from wild trees is highly variable and often less appealing when compared to grafted or selected cultivars (Pomper & Layne, 2005). Low-quality fruit have a mushy texture, lack sweetness, and have a have a strong, bitter aftertaste.

Genotypes resulting from selection processes have more desirable characteristics 31

including firm texture, delicate flavor, and no aftertaste (Brannan et al., 2012). The most attractive fruits are those with clear skin, free of dents or blemishes.

Nutritional quality. Pawpaw fruit have high nutritional quality and is an excellent source of vitamins and minerals. It exceeds other domestic fruits, such as apples and peaches, in potassium, Vitamin C (up to 5 mg/100 g pulp), riboflavin, niacin, phosphorus, zinc, copper and manganese (Jones & Layne, 1997; Peterson, 1991).

Proximate analysis shows that the edible portion of pawpaw fruit is mostly water (75%), low in fat (< 0.5%) and high in carbohydrate, mostly from naturally occurring sugars (see

Table 2) (Brannan et al., 2012). Interestingly, the protein content of pawpaw fruit contains many essential amino acids and is a good source of isoleucine, leucine, lysine, phenylalanine, tyrosine, threonine, and valine (Peterson, Cherry, & Simmons, 1982).

Table 2

Proximate Analysis of Common Fruits Pawpawa Bananab Mangob Avocadob

Energy (kcal) 85 89 60 160

Carbohydrate (%) 16.8 22.8 15.0 8.5

Protein (%) 5.2 1.1 0.8 2.0

Fat (%) 0.9 0.3 0.4 14.7 Note. Values per 100 g edible portion. (a) Data from “Agriculture Handbook No. 8 Composition of Foods: Raw, Processed, Prepared,” by U.S. Department of Agriculture, 1963, p. 42. (b) Data from “USDA National Nutrient Database for Standard Reference, Release 28,” by U.S. Department of Agriculture, Agricultural Research Service, 2014. Retrieved from Nutrient Data Laboratory website: http://www.ars.usda.gov/nutrientdata 32

Antioxidant content. In recent years, there has been a surge in popularity of exotic fruits such as the pomegranate and acai berry. Fruit such as these have become well known because the nutritional make-up of these antioxidant-containing fruits are associated with better health. They have been championed by health enthusiasts and the health food industry and can now be found in numerous commercial products including cereal bars and fruit beverages.

Antioxidants are substances that inhibit free radical initiation and proliferation, protecting cells from free radical damage that can cause diseases like heart disease and cancer (Baron, Berner, Skibsted, & Refsgaard, 2005; Johnson & Sinclair, 1979; Kanner

& Rosenthal, 1992). Phenolics are the category of chemical compounds found naturally in foods that include antioxidants. Previous research has shown that pawpaw’s total phenolic content is comparable to that of many other commercial fruits, such as mango, pear or pineapple, as well as other members of the Annonaceae family (Harris, 2008).

The antioxidant class phenolics includes flavonoids, the subset of antioxidants that give fruit and vegetables their color. Predominate polyphenolic compounds found in pawpaw include three phenolic acids and flavonols, namely the flavan-3-ols, (-)-epicatechin, and procyanidin dimers and trimers (Brannan et al., 2015). Interestingly, pawpaw varieties differed in percent of total phenolics including flavonoids.

Development of the Pawpaw Industry

Varieties. As of 1999, there were over 40 recognized varieties of pawpaw, most the result of selections made through horticulture techniques such as grafting (Pomper et al., 2010). Currently, there are over 60. Pawpaw varieties vary in trunk diameter, tree 33

height, fruit size, skin and pulp color, fruit flavor, the number of fruit produced, ripening period, and geographic region of growth. (Pomper & Layne, 2009). Desirable traits include yellow to orange flesh with mild, sweet flavor with no cloying aftertaste, fruit size ≥200 g, few seeds, and uniform fruit shape with no visible blemishes (Ames &

Greer, 2010). Fruit from poor-quality or wild genotypes can have a mushy texture, lack sweetness, and can have a turpentine or bittersweet aftertaste. It is important to evaluate the characteristics of current cultivars to understand what factors determine fruit quality and yield. The consideration of these positive and negative genetic variations can be applied to improve future fruit quality and, therefore, the commercial potential of the pawpaw. Detailed cultivar information allows growers to select varieties best suited to their needs and growing conditions.

Current cultivars. Beginning in 1900, collections of choice pawpaw selections from the wild began to be assembled in orchards by pawpaw enthusiast and scientists.

From 1900 to 1960, 56 pawpaw clones were selected and named. Of the original 56 varieties, fewer than 20 of those original selections remain. Researchers accredit the loss of these cultivars to neglect, abandonment of collections, and the loss of records required for identification (Peterson, 1991). Since 1960, additional cultivars have been selected from the wild and developed through breeding efforts, resulting in more than 60 clones currently commercially available (Jones, Peterson, Pomper, Layne, & Turner, 1998).

Despite the wide number of varieties available, little is known about which varieties have the most commercial potential in terms of the desirable traits above. A full description of cultivars used in this study can be found in Appendix A. 34

Pawpaw cultivars and advanced selections display a high level of genetic diversity compared to other woody perennial fruit and nut crop species such as the avocado, apple, and pear. This genetic base is also larger than that of other members of the Annonaceae family and indicates support for further domestication of the pawpaw

(Pomper et al., 2010). Genetic testing of 28 cultivars and 13 advanced selections indicates that most pawpaw varieties can be grouped into 5 major groups or families (see Table 3).

Table 3

Genetic Grouping of Pawpaw Varieties

Varieties not included in Group Varieties included in current study current study Taylor and Wilson Taylor, Wilson None Susquehanna Zimmerman, PA Golden 1 and 3, 8-20, 2-10, 2-54, 11-13, Prolific, Susquehanna 3-11 Wabash Sweet Alice, Greenriver Belle, Wabash, 9-58, 10-35, 9- Potomac, Rappahannock, 47, Cales Creek PA Golden 4

Wells Wells, Sue, Middletown M. Gordon, 3-21, 7-90, BH-10, 5-5 Overleese Sunflower, Shenandoah, Davis, 1-68, 1-23 Overleese, IXL, Taytwo, Mitchell, NC-1, Rebecca’s Gold Note. Data from “Characterization and Identification of Pawpaw Cultivars and Advanced Selections by Simple Sequence Repeat Markers,” by K. W. Pomper, J. D. Lowe, L. Lu, S. B. Crabtree, S. Dutta, K. Schneider, and J. Tidwell, 2010, Journal of American Society for Horticultural Science, 135(2), p. 146.

Regional Variety Trial (RVT). In 1993, the Pawpaw Foundation joined forces with Kentucky State University researchers to test 10 commercially available, named 35

pawpaw cultivars and 18 advanced selections selected from Pawpaw Foundation orchards. Regional variety trial trees were planted in 15 locations across the United States and China from fall 1995 to spring 1999. Each site consisted of 300 trees; eight replicate trees of each of the 28 selected cultivars. Named varieties included in the trial were:

Middletown, Mitchell, NC-1, Overleese, PA Golden, Sunflower, Taylor, Taytwo, Wells, and Wilson. In addition to the 10 named varieties, 18 advanced selections were also chosen. Advanced selections were made based on superior traits such as fruit size, fruit taste, flesh-to-seed ratio, resistance to pests and disease, and overall productivity on a yearly basis (Pomper et al., 1999). The objective of these plantings was to evaluate commercially available pawpaw varieties in and outside the pawpaw’s native growing range (Pomper, Crabtree, Layne, Peterson, et al., 2008).

As of 2008, two of the 15 sites had been analyzed for climatic factors, growth, flowering, yield and fruit characteristics: Princeton, KY (planted fall 1995) and Frankfort,

KY (planted spring 1998). Plantings at these two sites followed the same block format

(eight trees of each selection) and similar soil conditions. Data collected for each site included trunk cross-sectional area (TCA, cm2); number of fruit per tree; fruit weight (g); cumulative yield (total kg); cumulative yield efficiency (total kg/TCA); average number of fruit per cluster; and, days required for ripening, harvest peak and harvest duration.

Results showed that all variables differed among cultivars including number of fruit per tree, average fruit weight, cumulative yield, and peak harvest period. However, there was a significant positive correlation between tree trunk cross-sectional area (TCA) and the number of fruit per tree. Based on fruit size, yield, and tree availability, researchers 36

recommended the Potomac, Susquehanna, Wabash, Overleese, Shenandoah, NC-1, and

Sunflower varieties for commercial production in Kentucky (Pomper, Crabtree, Layne,

Peterson, et al., 2008). Across the rest of the RVT sites, a lack of funding resulted in no serious evaluation of fruit but did show that pawpaw can be grown in a variety of climates.

Commercialization

Commercialization is the process of making a new product, or production method, available for commerce. The commercialization process has four key components: when, where, how to launch, and whom to target. Pawpaw has great potential to become a cash crop in the United States due to the nutritional value of its fruit, the value of natural compounds found in the leaves and bark, as well as nursery wholesale and retail value.

Early in the 20th century, there was a decided interest in developing pawpaw into a viable fruit crop (Brett & Callaway, 1992). However, around the same time, another popular native fruit, the blueberry, was also rising in popularity and the pawpaw failed to become recognized. Researchers credit this loss to pawpaw’s rapid perishability. Since

1985, many associations committed to the progression of pawpaw as a commercial fruit crop have emerged. These institutions include the Northern Nut Growers Association, the

Pawpaw Foundation, the pawpaw research program at Kentucky State University, the

Ohio Pawpaw Growers Association, and the North American Pawpaw Growers

Association. These associations and programs are working to develop cultivars and promote consumer education programs surrounding the pawpaw (Pomper & Layne,

2005). In 1994, researchers began collecting varieties for the USDA National Clonal 37

Germplasm Repository, or gene bank, at Kentucky State University, a satellite of the

National Clonal Germplasm Repository in Corvallis, Oregon. The goal behind the development of the repository includes germplasm collection, breeding to improve cultivars, assessment of genetic diversity and fingerprinting of specific pawpaw varieties.

Currently, over 2000 accessions, or trees, from 17 states are contained in the Kentucky

State University repository collection (Pomper, 2007b). Maintaining a high level of genetic diversity aids in making genic improvements and recent initiatives have been undertaken to systematically improve pawpaw as a fruit-producing tree and the long term success of the crop (Pomper et al., 2010).

Challenges to commercialization. Pawpaw faces many challenges before it can be appreciated as a commercial fruit crop. Its seeds are sensitive to desiccation propagation requires expensive grafting techniques. Then, even if a pawpaw tree is successfully propagated, pawpaw yields tend to be much lower than other commercial tree fruits with the average yield for top varieties ranging from 10-20 kg of fruit per tree

(Bellini, Nin, & Cocchi, 2003; Pomper, Crabtree, Layne, Peterson, et al., 2008; Reich,

1991). Factors that affect fruit set can be placed into 2 categories: those growers can control, and those they cannot. Uncontrollable factors include natural pollination and weather conditions. Factors growers can control include crop management, plant placement, and the genetic variation within an orchard. In addition to propagation challenges, pawpaw fruit suffers from a high degree of perishability with a short shelf-life of only 3 days. Harvesting and packaging pose additional challenges for the pawpaw as the fruit are nonuniform in shape, size, and harvest period. The last challenge that faces 38

the pawpaw is consumer awareness and researchers agree that consumer education will be required before the pawpaw will be accepted as a mainstream food item.

Commercial potential. Pawpaw is not yet a commercial crop in the United States but has both fresh market and processing potential. (Duffrin & Pomper, 2006; Pomper &

Layne, 2005; Templeton et al., 2003). Pawpaw’s unique nutrient qualities, potential value for bioactive compounds, and ornamental worth indicate that it has the potential to be an up-and-coming high-value crop for farmers in the eastern and central United States

(Pomper & Layne, 2005; Callaway, 1992).

Exotic fruits, like pawpaw, have seen a recent surge in popularity because their nutritional profiles are associated with better health. As a food source, pawpaw exceeds many other common fruits in vitamin, mineral, amino acid, and energy values. Currently, the primary markets for pawpaw are the niche and gourmet markets, which include direct sale items such as fresh and frozen fruit at farmers’ markets and internet sales. There is commercial potential for the fruit’s tropical flavor in processed foods like juices, ice creams, yogurts, and beer (Pomper & Layne, 2009).

Pawpaw trees contain valuable natural compounds with anticarcinogenic and pesticidal properties. Research has shown that a variety of these compounds exist in the trees leaves, bark, and twigs. One compound, Annoaceous acetogenins, is reported to have antitumor properties. Alkaloid compounds found in the seeds, leaves, and bark of pawpaw are reported to have pesticidal properties, making the trees resistant to insects and disease and a good candidate for organic production. 39

Additionally, the market for edible landscape plants is on the rise. Currently, over

40 nurseries sell pawpaw trees, and this number is increasing. Named cultivars are offered as grafted trees in addition to nongrafted seedlings. Grafted trees have been reported to retail for $18.00-$25.00 each (Bratsch, 2009).

Interested growers should consider all aspects of retail agriculture including knowing the consumer, production value, direct sales, processing requirements, creating unique customer experiences and being aware of current trends including agritourism and the local food movement.

Chapter 3: Comparative Analysis of Pawpaw Production Data from 2005-20121

Abstract

This study examined 52 varieties of pawpaw (Asimina triloba), of which 24 fit into previously identified genetic groups, harvested from 2005-2012. Differences between genetic groups and individual varieties were found for average fruit weight,

(AFW), yield, and harvest length between varieties. Differences were found in AFW and yield across locations. A correlation was observed between AFW and total number of fruit (TF). Results indicate that some pawpaw varieties produce significantly heavier fruit, and that planting location can make a difference in fruit production. A negative correlation between AFW and TF suggests that abundant fruit can lead to decreased fruit weight.

KEYWORDS: Pawpaw, Asimina triloba, fruit production, average fruit weight

1 This chapter represents a prepublication manuscript following the structure of the International Journal of Fruit Sciences which has been adapted to conform to Ohio University’s thesis format. Authors are Laine M. Greenawalt with Robert G. Brannan and Janet Simon ((School of Applied Health Sciences and Wellness, College of Health Sciences and Professions, Ohio University, Athens, OH), and Ron Powell (Fox Paw Ridge Farm, Cincinnati, OH). 41

Introduction

The pawpaw, or Asimina triloba, is the largest fruit native to North America. It has a vast native growing range that spans 26 states corresponding to U.S. Department of

Agriculture (USDA) plant hardiness zones 5-8 (Galli, Archbold, & Pomper, 2007). The family Annonaceae, to which pawpaw belongs, contains over 2,400 species, all of which are tropical or subtropical except for pawpaw, making the temperate-growing fruit unique. Other commonly available Annonaceous fruits include cherimoya, soursop, and custard apple (Archbold, Koslanund, & Pomper, 2003; Callaway, 1993; Kral, 1960;

Peterson, 2003).

Pawpaws are shrub-like, understory trees that can grow up to 12 meters tall. They have long membranous leaves and maroon flowers that produce clusters of up to nine fruit in late summer to early fall (Geneve et al., 2003; Pomper & Layne, 2005). However, pawpaw flowers are self-incompatible, making pollination an important factor that could limit commercial possibilities (Bois, 2001; Layne, 1996; Willson & Schemske, 1980). In addition, the normal bloom period of pawpaw flowers can last up to 4 weeks, resulting in an elongated harvest period in the fall which requires more labor and time intensive harvesting techniques (Moore, 2015; Pomper, Crabtree, Layne, & Peterson, 2008).

Moreover, pawpaw trees are exclusive in that they are the only species of the eight in the genus Asimina to produce a commercially viable fruit. These green and yellow fruits are sometimes called the “poor man’s banana” or “prairie banana” because of their distinct tropical flavor. Research has also shown pawpaw fruit have a notable nutritional value high in antioxidants, specifically flavonoids like condensed tannins 42

(Brannan, Peters, & Talcott, 2015; Watt & Merrill, 1963). These compounds, which are also found in cocoa, grapes and tea, are believed to have beneficial health effects (Bor,

Chen, & Yen, 2006; Donno, Beccaro, Mellano, Cerutti, & Bounous, 2014; Sun, Chu, Wu,

& Liu, 2002). Unfortunately, pawpaw fruit are highly perishable with a shelf life of only

3 days (Archbold et al., 2003; Koslanund, Archbold, & Pomper, 2005; McGrath &

Karahadian, 1994). This rapid decline in fruit firmness is a major barrier to the growth of the pawpaw industry.

In the early 1900s, the pawpaw was being considered as a native, North American cash crop for mainstream commercialization (Pomper & Layne, 2005). Over the last century, however, the rise of a more globally centered food system has resulted in an increased ease of shipping tropical fruits, decreasing the demand for indigenous goods.

The final result was that the pawpaw never became recognized outside of local markets

(Moore, 2015; Peterson, 2003). Recently, there has been another surge in interest surrounding this remarkable plant, but the pawpaw remains in the beginning stages of commercialization. Horticulturalists and hobbyists are working toward the progression of the pawpaw as a commercial fruit crop. The result has been the development of over 60 varieties and advanced selections with the most desirable characteristics including large fruit size, firm texture, delicate flavors, and few blemishes (Ames & Greer, 2010;

Brannan et al., 2012; Templeton, Marlette, Pomper, & Jones, 2003). Within these 60 cultivars, however, comes great variation in fruit size, yield and other horticultural characteristics. Research has yet to determine which varieties of pawpaw would be best for commercial purposes. 43

The pawpaw is a unique fruit with notable nutritional value and the potential to become a profitable cash crop in both processed and fresh markets. It is pest resistant and well adapted to the climate and soil of the eastern and central United States, giving it the potential to be a good investment for small farmers or hobbyists unable to compete with larger commercial farms. It is important to identify which varieties of pawpaw produce the most noteworthy fruit in terms of size and yield in order to help interested farmers select the most profitable trees.

Data were collected by the North American Pawpaw Growers Association over an

8-year period in an effort to measure tree productivity season to season, but these data were never examined. The objective of this research is to perform a retrospective study on the data described above with the aim of identifying varieties of pawpaw with the greatest fruit yield and largest average fruit weight over a period of 8 years.

Materials and Methods

Plantings. Data used in this study was collected from trees planted at three locations in southwest Ohio (see Figure 7)–a farm in rural Adams County (coded as

Location 1) and two adjacent plots in Butler County (coded as Locations 2, 3). Trees were grafted in late spring to early summer by grafting cultivar-specific bud-wood onto pawpaw rootstock that had been grown from seed. The plantings at the Butler County locations began in 2001 and were primarily suburban. The Adams County location, Fox

Paw Ridge Farm, was a 3-5 acre plot that contained over 400 individual pawpaw trees all grafted and planted from 2003-2006. All trees were grafted and planted under the direction of North American Pawpaw Growers Association’s President, Dr. Ron Powell 44

of Cincinnati, Ohio. Fox Paw Ridge Farm plantings were organized in three blocks– north, east, and west. The north block, planted first, contained over 200 trees in east-to- west rows (labeled A-F) with 2.5 m between trees. The second block (east) contained four rows running north-south (labeled 1-4) with trees 2.5 m apart. The last block (west) is still being planted, but at the time of data collection contained nine rows running north- south with 3 m between trees. In all three blocks, rows were planted 4.5 m apart. There was notable soil variation between the Butler and Adams County locations. Soil at the

Butler County locations was fine and loamy with good drainage (ideal for pawpaw growth) while soil at the Fox Paw Ridge Farm location was heavy clay (less ideal for pawpaw growth).

Data collection. Fruit were collected by Dr. Powell with the help of volunteers.

Volunteers did not receive extensive training on pawpaw harvesting. Data were recorded by hand in notebooks taken from spring 2005 through fall 2012. Fruit collected included only fruit that had fallen from the tree. Fruit collection was performed twice daily, once in the morning and once in the evening. Fruit for each tree were gathered and weighed collectively using a Cen-Tech Digital Postal Scale (Harbor Freight Tools) and recorded in ounces. Only one weight measurement was taken unless otherwise needed. Data collected for individual trees included variety, tree location, date of collection, total number of fruit collected, and total fruit weight (oz).

Butler County

Adams County

Figure 6. Map of Butler and Adams Counties, Ohio. Adapted from “Adams County, Ohio” and “Butler County, Ohio.” Images created by David Benbennick (2006, February 12). Retrieved March 10, 2016 from https://en.wikipedia.org/wiki/Adams_County,_Ohio#/media/File:Map_of_Ohio_highlight ing_Adams_County.svg and https://en.wikipedia.org/wiki/Butler_County,_Ohio#/media/File:Map_of_Ohio_highlighti ng_Butler_County.svg

Statistical analysis. After obtaining original records from Dr. Powell, data were transcribed to an electronic format by the author and an assistant to assure accuracy.

Independent variables were identified as variety, harvest year, and tree location.

Dependent variables were identified as harvest dates, total number of fruit collected per tree, total fruit (oz), and average fruit weight (oz), calculated as total weight / by total number of fruit. All ounce weights were then converted to grams.

Data were analyzed using statistical analysis software SPSS Statistics 22 (IBM

Corporation, Armonk, New York). Of the 60 varieties for which there were data, 24 cultivars were placed into one of five genetic groups based on findings by Pomper et al.

(2010), which used polymorphic microsatellite marker loci to identify genetically similar pawpaw varieties. The independent variable genetic group had five levels (Taylor &

Wilson, Susquehanna, Wabash, Wells, Overleese). Twenty-eight varieties and advanced 46

selections were not able to be placed in one of the previously mentioned groups because no genetic information was available. These cultivars were grouped and analyzed separately. Eight varieties were excluded from data analysis because fruit collection only occurred once (see Appendix C). Multivariate ANOVAs were used to analyze differences in average fruit weight (g), yield (g), and harvest length (days) between genetic groups

(1-5), ungrouped varieties (group 6), location, and year. If significance was noted at p <

0.05, post hoc tests (Duncan’s Multiple Range Tests) were used to separate means.

Pearson product-moment correlation coefficient (r) was used to measure the relationship between average fruit weight (g), total number of fruit produced per tree, tree yield (g), and harvest length (days). Significance for all analyses was set at p < 0.05.

Results

Harvest duration data for all varieties and years. Harvest dates ranged from late July to mid-October across all years, varieties, and locations, with most of the fruit harvest occurring in September. All most all trees (99%) had a first-recorded harvest date in August or September (64% and 35%, respectively) and less than 1% had a first- reported date in either July or October. The earliest varieties were Shenandoah and

Wilson, with fruit collection dates recorded as early as July 24. The date ranges for fruit collection for each year across all varieties and locations are reported in Figure 7. Harvest length was measured as the first collection day to the last collection day for all trees by year. Overall harvest length per year ranged from 31 days in 2006 to 74 days in 2010.

The average number of harvest days per tree was 19 days. Harvest length for individual varieties can be found in Appendix D. Growing degree days (GDD) are also reported. 47

GDD is a measure of the number of days above a minimum growing temperature, used to predict plant development such as the date that flowers will bloom or a crop will reach maturity. The number reflected is the number of GDD as of August 1 for the respective year.

(2207)

(2195)

(2203)

(2040)

(2063)

(2446)

(2376)

(2587)

Figure 7. Pawpaw harvest date ranges (from first to last record) divided into quartiles for individual years across all varieties and locations with growing degree days (GDD) as of August 1 for each year indicated in parenthesis.

Frequency data for pawpaw fruit weight. The data for average fruit weight from 52 varieties of pawpaw were analyzed. Twenty-four of the varieties were categorized into genetic groups based on Table 3, and 28 of the remaining varieties were uncategorized as no genetic information was available. There were eight varieties, described in Appendix C, that were included in Dr. Powell’s original data, but were excluded from all data analysis because fruit collection only occurred once. 48

Frequency (f) analyses of average fruit weight in the three data categories shown above are presented in Figure 8. A frequency (f) histogram of average fruit weights (g) for all varieties, shown in Figure 8a, displays a positive skew. Shapiro-Wilk’s test (S-W test) of normality shows normal distribution for average fruit weight across all 52 varieties. Of these, 41 individual varieties exhibit normality for average fruit weight; five do not exhibit normality (Glaser, KYSU 2-11, Lynn’s Favorite, Prolific, and SAA

Zimmerman); and six varieties could not be reported because harvest only occurred twice. A histogram of average fruit weights for the genetic groups, shown in Figure 8b, exhibited a slight positive skew. S-W test of normality indicated that three genetic groups

(Taylor & Wilson, Wabash, and Wells) were normally distributed, and two (Susquehanna and Overleese) did not follow normal distribution for average fruit weight. A histogram of average fruit weight for the uncategorized varieties, shown in Figure 8c, displayed the greatest amount of positive skew. S-W test of normality indicated that of the 28 varieties, three varieties did not fall under a normal curve for average fruit weight.

Figure 8. Frequency (f) distribution of average fruit weight (g): (a) all varieties; (b) fruit in genetic groups; (c) fruit not in a genetic group. 50

Analysis of average fruit weight, yield, and harvest length in three categories of pawpaw data: All varieties, varieties not belonging to a genetic group, and those placed in a genetic group.

All varieties. The main effects of location and year were analyzed for average fruit weight, yield, and harvest days among all varieties. No significant differences between the three locations were observed for average fruit weight. Significant differences in yield (F = 69.74, p = .00) and harvest days (F = 66.59, p = .00) were observed for location in the order of Location 3 > Location 2 > Location 1. There were significant interactions between growing year, average fruit weight (F = 5.63, p = .00), yield (F = 3.58, p = .00), and harvest length (F= 4.87, p = .00). The mean average fruit weight, mean yield, and mean harvest length for all varieties each growing year are shown in Table 4.

Table 4

Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for 52 Pawpaw Varieties by Year

Average fruit weight Year (g) Yield (g) Harvest length (days)

2005 121abc ± 43 679d ± 564 5d ± 6

2006 152a ± 48 4134bcd ± 6770 13bcd ± 11

2007 101c ± 47 1254cd ± 1008 9cd ± 6

2008 100c ± 46 5289abcd ± 4837 21ab ± 15

2009 138ab ± 54 9145a ± 9087 25a ± 13

2010 143a ± 61 3013bcd ± 5045 16bc ± 13

2011 122abc ± 55 6027abc ± 8560 17bc ± 11

2012 108bc ± 47 6881ab ± 9080 16bc ± 13 Note. Means within columns with different superscripts are significantly different at p < 0.05.

The means ± SDs for average fruit weight, yield, and harvest days for all 52 varieties (pooled) can be found in Table 5. In total, fruit was collected from 359 trees.

The means ± SDs for average fruit weight, yield, and harvest days for each of the 52 individual varieties can be found in Appendix D. The variety Davis had the largest average fruit weight (244 g ± 95). The variety SAA Zimmerman had the largest gram- weight average yield (18,182 g ± 14,847). The variety KYSU 2-11 had the longest average harvest out of all varieties (33 ± 19 days). The mean ± SD for average fruit weight, yield, and harvest days for each of the five designated genetic groups can be found in Appendix 6. 52

Table 5

Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for Three Data Categories: 52 Pawpaw Varieties, Varieties Not Belonging to a Genetic Group, and Those Varieties Belonging to a Genetic Group

Subset of data Number of Average fruit Harvest length (# of varieties) trees weight (g) Yield (g) (days) All varieties 359 125 ± 55 5317 ± 7565 16 ± 13 (52) Uncategorized 124 111 ± 50 3842 ± 6099 16 ± 14 (28) All genetic 235 132 ± 55 6096 ± 8139 17 ± 12 groups (24)

Table 6

Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for Pawpaw Genetic Groups Genetic group Number of Average fruit Harvest length (# of varieties) trees weight (g) Yield (g) (days) Taylor & 24 92d ± 39 3747b ± 4509 16ab ± 11 Wilson (2) Susquehanna 30 137ab ± 62 7851a ± 10144 19a ± 12 (5)

Wabash (5) 30 98cd ± 36 3570b ± 6000 13b ± 13

Wells (3) 30 112bc ± 48 7449a ± 9634 16ab ± 14

Overleese (9) 119 155a ± 53 6517ab ± 8158 19a ± 13

Note. Means within the genetic groups with different superscripts are significantly different at p < 0.05.

Varieties not in a genetic group. The main effects of location and year were analyzed for average fruit weight, yield, and harvest days for the varieties not placed into a genetic group. Similar to the data presented above for all varieties, no significant differences between the three locations were observed for average fruit weight.

Significant differences in yield (F= 16.68, p = .00) and harvest days (F= 25.13, p = .00) were observed, with Location 1 exhibiting significantly lower yield and fewer average harvest days than Location 3. There were significant interactions between growing year, average fruit weight (F = 2.80, p = .01) and harvest length (F= 2.42, p = .03). The mean average weight, mean yield, and mean harvest days for each growing year are shown in

Table 7.

Table 7

Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for Pawpaw Varieties Not Belonging to a Genetic Group by Year Average fruit weight Harvest length Year (g) Yield (g) (days)

2005 89ab ± 37 404b ± 569 1b ± 0

2006 117ab ± 27 1914ab ± 2104 18a ± 12

2008 75b ± 31 4295ab ± 3401 23a ± 17

2009 116ab ± 46 6841a ± 7418 25a ± 15

2010 127a ± 42 2034ab ± 3723 12ab ± 13

2011 127a ± 65 4358ab ± 7206 18a ± 11

2012 95ab ± 49 4998ab ± 7941 15a ± 17 Note. The year 2007 was excluded from this table because no there were no data for that year in this data category. Means within columns with different superscripts are significantly different at p < .05.

Means ± SDs for average fruit weight, yield, and harvest days from the 25 named varieties and three advanced selections (pooled) included in this study that did not fit in a genetic group is shown in Table 5. Average fruit weights in this group ranged from 68 g

± 10 (LA Native) to 210 g ± 82 (Mango). Gram-weight yield ranged from 99 g ± 12

(Shawnee Trail) to 11349 g ± 10202 (KYSU 8-2). Harvest length in days ranged from 1 day ± 0 (Cullman Late, Lady D, and Shawnee Trail) to 33 days ± 19 (KYSU 2-11).

Varieties included in a genetic group. The main effects of location and year were analyzed for average fruit weight, yield, and harvest days in the varieties categorized into a genetic group. Significant differences were observed for all three dependent variables 55

for both main effects. Location 2 exhibited significantly larger average weight (F= 6.47, p = .03) than the other two locations. Yield (F= 51.40, p = .00) and harvest days (F=

40.24, p = .00) exhibited significant differences in the order of Location 3 > Location 2 >

Location 1. There were significant interactions between growing year, average fruit weight (F = 5.36, p = .00), yield (F = 2.38, p = .00), and harvest length (F= 3.92, p =

.00). The average weight, yield, and harvest days for each growing year are shown in

Table 8.

Table 8

Mean Average Fruit Weight, Yield, and Harvest Length (Means ± SDs) for Pawpaw Varieties Belonging to a Genetic Group by Year Average fruit weight Harvest length Year (g) Yield (g) (days)

2005 133bcd ± 41 783b ± 564 7c ± 6

2006 172a ± 46 5420ab ± 8162 10bc ± 9

2007 107d ± 49 1452b ± 944 10bc ± 6

2008 111cd ± 48 5748ab ± 5371 20a ± 14

2009 149abc ± 55 10343a ± 9769 25a ± 12

2010 151ab ± 67 3537ab ± 5588 19ab ± 13

2011 120bcd ± 48 6966ab ± 9173 16ab ± 10

2012 116cd ± 44 7962a ± 9587 17ab ± 15 Note. Means within columns with different superscripts are significantly different at p < .05.

The average weight, yield, and harvest days for the varieties categorized into one of the five genetic groups (pooled) is shown in Table 5 while the same variables for each individual genetic group is shown in Table 6. Differences of note were observed in two of the three variables: average fruit weight (F= 15.45, p = .00), yield (F= 2.42, p = .05), and harvest length (F= 1.62, p = .17). With respect to average fruit weight, a significant difference was observed between the Overleese group and the groups Taylor and Wilson,

Wabash, and Wells, with fruit from the Overleese group larger on average. A significant difference was also seen between the Susquehanna group and the groups Taylor and

Wilson and Wabash. There was no significant difference between groups Overleese and

Susquehanna. A significant difference was seen in yield between genetic groups in the order of Susquehanna = Wells > Wabash and Taylor & Wilson. No significant differences were seen between groups Susquehanna, Wells, and Overleese. Significant differences in harvest length were observed, however, harvest days only ranged from 13-

19 days.

Pearson product-moment correlation (r) relationship between average fruit weight (g), total number of fruit collected, and harvest length (days). Test was performed for three sets of data (all varieties, varieties not in a genetic group, and varieties in a genetic group), Pearson product moment correlation coefficient r (p < .05) was used.

All varieties. There was a significant negative correlation between average fruit weight and total number of fruit (r = -.21, p < .00), see Figure 9, when comparing all 52 varieties. Average fruit weight was also negatively correlated to harvest length (days) 57

across all varieties (r = -.11, p < .05). Total number of fruit was significantly correlated with harvest days and yield in this data category (r = .62 and r = .90 respectively, p <

.01). Yield showed a significant positive correlation with harvest days (r = .61, p < .01).

There was no correlation observed between yield and average fruit weight.

400 350 300 250 200 150 100 50 0

Number Fruitof Collected per Tree 0 50 100 150 200 250 300 350 400 Average Fruit Weight (g) per Tree

Figure 9. Correlation of average fruit weight (g) and total number of fruit collected per tree for 52 pawpaw varieties from 2005-2012 across three growing locations

Varieties not in a genetic group. For the 28 varieties not placed in a genetic group, there was a significant negative correlation between average fruit weight and total number of fruit as well as average fruit weight and the number of harvest days (r = -.22 and r = -.19 respectively, p < .05). There were significant positive correlations between total number of fruit and yield (r = .93, r < .01), total number of fruit and the number of harvest days (r = .62, p < .01), and yield and harvest days (r = .57, p < .01). There was not a significant correlation between yield and average fruit weight. 58

Varieties belonging to a genetic group. For the varieties placed into one of five genetic groups, a significant negative correlation was found between average fruit weight and total number of fruit (r = -.23, p < .01), similar to the other two data groups.

Significant positive correlations were found between yield and the number of harvest days (r = .65, p < .01), yield and the total number of fruit (r = .90, p < .01), and the total number of fruit and harvest length (r = .63, p < .01). No correlation was found between harvest length and average fruit weight or yield and average fruit weight.

Discussion

Analysis of harvest duration and frequency of pawpaw fruit weight data for all varieties and years. In this study, overall harvest length for 52 pawpaw cultivars ranged from late July to mid-October with the average harvest length for individual trees lasting 19 days. A majority of fruit was collected in September with 50% of the fruit being harvested in September for all harvest years except two, 2010 and 2012. During the period under study, there were 2 years for which there was unusual weather. A drought occurred in 2007. It is possible that the drought was responsible for the short 41-day harvest range, 9 days shorter than the average range (see Figure 7). Hurricane Ike hit

Ohio with 70 mph winds on September 14, 2010. This likely knocked a lot of underripe fruit from the trees, resulting in the fact that 75% of fruit collection occurred by mid-

September. In contrast, median harvest date, i.e., 50% of fruit collection, for the surrounding years 2009 and 2011 fell in mid- to late-September. The year 2010 also had the longest harvest range of 74 days (see Figure 7). 59

Reported for the first time in pawpaw, the average fruit weight over the collection period in the three subsets of data are normally distributed, with a slight positive skew.

Researchers tested the variable average fruit weight for normality and were satisfied.

Varieties belonging to genetic groups showed the least amount of skew while varieties not belonging to a genetic group showed the most. Therefore, the positive skew seen across all 52 varieties was most likely driven by one or more varieties that were not placed in a genetic group. No information about the distribution of pawpaw or other

Annonaceous fruit weight could be located.

The results of this study differ slightly than those reported in the most recent 2008 pawpaw regional variety trial organized by Kentucky State University (Pomper, Crabtree,

Layne, Peterson, Masabni, & Wolfe, 2008), the USDA National Clonal Repository for

Pawpaw in 2008. The variety trial for 28 cultivars reported an average fruit weight of 139 g, almost 15 g heavier than the fruit of this study (124 g). Average harvest duration for the 28 varieties was 22 days, 4 days longer than the fruit for this study (18 days). These differences could be related to a number of factors including growing location (Kentucky versus Ohio), size of the orchard, and varieties sampled. While averages differed, the overall patterns in the data remained similar. The Kentucky State regional variety trial found significant variation in fruit size and yield between varieties as well as lower than average yields when compared to other fruit trees. Tropical relatives of the pawpaw such as cherimoya, sweetsop, and soursop also demonstrate low yields due to limited natural pollination. 60

Analysis of average fruit weight, yield, and harvest duration by location and year. There were no significant differences in average fruit weight between the three growing locations when comparing all 52 varieties and those varieties not belonging to a genetic group, however, significant differences were observed in both yield and harvest length in these datasets. There were significant differences in average fruit weight, yield, and harvest days across growing locations for those varieties belonging to a genetic group. While significant differences were noted, it is challenging to elucidate what caused these differences. Preharvest factors could have a significant effect on fruit production including, but not limited to, soil characteristics (pH or fertility), tree placement, sunlight, and irrigation. Dr. Powell suggests that one possible cause is that soil conditions of Locations 2 and 3 (loam) were more appropriate for pawpaw growth than that of Location 1 (clay). More research is required to determine what environmental factors affect fruit production and harvest duration of various pawpaw cultivars.

When comparing growing year regardless of variety, significant differences were observed at the p < 0.01 level for average fruit weight, yield, and harvest days. This indicates that growing year had an impact on both fruit production and harvest duration.

In comparison, significant differences (p < 0.05) were observed for average fruit weight and harvest days for varieties not belonging to a genetic group but no significant differences existed between yearly yields of this data category. Thus, growing year had an effect on fruit weight and harvest duration, but not yield. For varieties belonging to a genetic group, significant differences were observed for average fruit weight and harvest days at the p < 0.01 level and for yield at the p < 0.05 level of significance. 61

There were 3 years for which events could have affected the data. The year 2005 was the very first year of data recording, and there were fewer trees, so it is not surprising that 2005 had smaller number of fruit than any other year. Weather was an important factor in 2007 and 2010. Values for average fruit weight, yield, and harvest days for 2007 were the second smallest/fewest. It can be speculated that the drought experienced in southwest Ohio during this time negatively affected fruit weight, yield, and harvest length. While 2010 had the potential to be a bumper year (large average fruit weight and longest harvest), a hurricane brought damaging winds to the area in early September resulting in the loss of over 45 kg of unripe fruit resulting in an overall smaller yield.

2010 was also the first year that fruit from the Fox Paw Ridge Farm location were included in the analysis, resulting in an increase in the number of trees.

Overall, no one variety or genetic group can be recommended based on the findings of this study. It is important to note that this study examined only a portion of the commercially available pawpaw cultivars. Large standard deviations across all variables indicate there was a large amount variance within each variety, year and location.

Examination of relationships between variables using Pearson correlations.

A significant negative correlation was observed between average fruit weight and total number of fruit collected in all datasets. This is a strong indication that as the number of total matured fruit increases, average fruit weight decreases. These findings support a generally accepted phenomenon among horticulturalists. This trend is assumed to be linked to the physiologic stress put on a tree through the action of producing fruit and 62

explains why trees naturally “drop” a portion of their set fruit. Hand-thinning has also been modeled as a method of increasing fruit size. However, it is important that the increased costs of hand-thinning are offset by the increased profits brought by larger fruit before it should be recommended to growers (Crabtree, Pomper, & Lowe, 2010; Menzies,

2004).

A significant negative correlation was observed between average fruit weight and harvest length in two of the three datasets (all varieties and ungrouped varieties). This indicates that this relationship is driven by one of the varieties included in the ungrouped category. A negative correlation indicates that as harvest days increase, or harvest becomes longer, average fruit weight declines. No significant relationship was observed between average fruit weight and yield in any dataset.

Conclusion

The specialty produce industry is a niche market that is growing rapidly. Over the last two decades, federal dietary guidelines have continued to emphasize fruit and vegetable consumption. Over the last decade, produce consumption has increased, as has consumer demand for exotic choices. From 1980 to 1992, shipments of tropical produce increased by 500% (Yadava, 1996). More recently, an increase in consumer awareness of the nutritional value and health benefits of exotic fruits and vegetables has led to an increased demand for exotic goods. In order to meet demand, domestic production of tropical or nontraditional horticultural commodities is necessary. Pawpaw is a tropical- tasting fruit with notable nutritional value that is well adapted to U.S. climates making it a fit for this specific market. 63

Sensory analysis of different varieties of pawpaw indicate that fruit firmness, texture, flavor and aroma are all important factors in consumer acceptance (Brannan et al., 2012). In addition to these factors, many in the pawpaw industry believe that large fruit increase customer approval and could warrant a premium price (Crabtree et al.,

2010). While pawpaw variety trials have been undertaken, none included the number of varieties analyzed in this dataset. Further, this study for the first time reports that pawpaw fruit weights are normally distributed, allowing scientists to use parametric statistical procedures with confidence.

This study is limited to the accuracy of its collection methods, which evolved over time along with the size and aim of the project. Recommendations for future research would include data collection regarding fruit appearance (e.g., diameter, length, shape), individual fruit weights, and a record of time between the appearance of flowers to the appearance fruit as well as the time it takes fruit to ripen. Having individual weights would allow researchers to make claims regarding variety fruit weight with greater confidence. Additionally, information regarding fruit appearance and size would help to identify intervariety variability, which has yet to be studied. Intervariety variability could have an impact on the commercial potential of pawpaw in the future. Identifying which varieties are most consistent in fruit weight, size, shape, color, and harvest length, will prove beneficial in the development of a commercial pawpaw industry.

The results of this study help to identify pawpaw varieties that produce fruit with the most desirable traits, specifically larger average fruit weight. Helping potential 64

growers identify varieties with the most commercial value will help establish the pawpaw as a viable native cash crop.

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Chapter 4: Summary and Conclusion

The objective of this research is to perform a retrospective study on data collected by the North American Pawpaw Growers Association over an 8-year harvest period with the aim of identifying varieties of pawpaw with the largest fruit yield and average fruit weight.

In this study, overall harvest length for 52 pawpaw cultivars ranged from late July to mid-October, with the average harvest length for individual trees lasting 19 days. The majority of fruit were collected in September for all years and varieties. Reported for the first time is the frequency distribution of average pawpaw fruit weight in three subsets of data. Distributions satisfied normality testing with a slight positive skew in all three data categories. The results of this study differed slightly from those reported in the most recent 2008 pawpaw regional variety trial organized by Kentucky State University

(Pomper, Crabtree, Layne, Peterson, et al., 2008), which reported heavier average fruit weight and longer harvest duration. These differences probably are related to a number of factors including growing location (Kentucky versus Ohio), size of the orchard, and varieties sampled.

Varieties that were placed in one of five genetic groups had a larger average fruit weight than those varieties for which there was no genetic information, a larger average yield, and a longer average harvest length. Within genetic groups, varieties in the

Overleese group had the largest average fruit weight (155 g) which was significantly larger than fruit from varieties in the groups Taylor and Wilson, Wabash and Wells.

Trees of varieties in the Susquehanna group had the largest average yield and varieties of 70

this group were found to be significantly larger than that of trees in two other groups–

Taylor and Wilson and Wabash. Pawpaw varieties from the groups Susquehanna and

Overleese had the longest harvest lengths, but were found to be significantly different only from the Wabash group. Overall, varieties that belonged to a genetic group had better fruit production in terms of fruit weight and yield than those varieties that did not belong to a genetic group.

While the results of this study indicate that some varieties may be more profitable in orchard or production industries than others, they also indicate that there are many preharvest factors that can potentially affect pawpaw fruit quality, specifically, growing location. Between growing locations there can be variation in soil quality (i.e., pH, nutrient density, etc.), irrigation, drainage, growing temperature, and sunlight, all factors that can impact fruit quality and cumulative yield (Crisosto, Johnson, DeJong, & Day,

1997).

Identifying critical preharvest factors will allow growers to achieve the highest quality fruit. It is recognized that the development of a process by which to effectively determine pawpaw fruit ripeness is necessary for industry success. The current method is to squeeze each fruit by hand, looking for a small amount of give in the fruits pulp, but this is at the discretion of the harvester. Research has shown that a 0Brix is a strong determinant of ripeness and a higher soluble solids content is more popular among consumers (Tuorila & Cardello, 2002). The elongated flowering period of the pawpaw means that fruit ripen at varying times and one-time harvesting is not an option. In addition to the varying ripening times, it is impossible to determine fruit ripeness on any 71

external feature including color. Further research is needed to determine a reliable way to ensure fruit quality and ripeness. As the exotic fruit industry grows, consumer education will be required before pawpaw can become a mainstream produce item. The pawpaw has a strong tropic flavor and aroma; if overripe, it can be off-putting to consumers

(Templeton et al., 2003). In the future, it will be important to educate consumers about how to select the best pawpaw fruit for consumer acceptance.

Specialty produce is one of the fastest growing segments of the produce industry.

Demand and consumption of exotic goods have grown exponentially over the last two decades. Pawpaw is an up and coming fruit crop with the potential to be a profitable addition to new and existing orchards. Its nutritional value and tropical flavor make it a strong candidate for both fresh and processed markets. In order for pawpaw to be successfully commercialized, a stronger grower base must be established. It is important for growers to select and grow varieties that show strong market potential based on the following factors: large fruit size with fewer seeds, acceptable fruit flavor and texture, large yields per tree, and harvest duration.

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Appendix A: Descriptions of Pawpaw Cultivars Used in this Studyabc

Cultivar Description

421 Originally purchased from Hidden Springs Nursery (no longer available). Produces medium size fruit with good flavor but average texture. Trees show average productivity.

Allegheny™ The fruit has medium fleshiness with seeds making up approximately 8% of fruit weight. Pulp texture is moderately firm and creamy with yellow color. Fruit flavor reported as sweet with no aftertaste. Average fruit size less than 200 g. Fruit size benefits from thinning. Selected and trademarked by R. Neal Peterson.

Belle Originally purchased from Tollgate Nursery. Fruit have yellow flesh and outstanding flavor. Not a good producer.

Broad Originally purchased from Hidden Springs Nursery (no longer available). Poor producer with below average fruit quality.

Cawood From Hidden Springs Nursery (no longer available). Late ripening fruit with cream-colored flesh and yellow skin. Produces medium to large fruit.

Cherokee Ridge Collected near Foster, OH. Produces small fruit but is a hardy tree and prolific fruit producer.

Convis Selected from Corwin Davis orchard. Produces largeb fruit with yellow flesh that ripen the first week of October in colder environments (e.g. Michigan).

Cullman Late Collected by Don Cullman in Marysville, OH. A very late fruiting tree, fruit are medium size with good taste.

Danica Seedling purchased from Walt Tuleck of Yellow Springs, OH. Selected for largeness of fruit, but not evaluated for quality.

Davis Selected from the wild by Corwin Davis in 1959 and officially introduced 1961. This tree produces medium fruit, up to 12 cm long, with green skin, light-yellow flesh, and large seeds. Ripens the first week of October (in Michigan). 84

Estil Selected by Nettie Estil in Frankfort, Kentucky. The tree produces large fruit with smooth textured flesh.

Forest Keeling No description available. Glaser Selected by P. Glaser of Evansville, Indiana. Variety produces medium-sized fruit.

Green River Belle The original tree grew near the Green River in southern Kentucky. A wild seedling selected by Carol Friedman in 1998 for its large fruit. Fruit have a firm texture and are similar to PA-Golden in size and shape, but have more seeds and trees are less productive. Little to no instance of Phyllosticta.

IXL A hybrid of Overleese and Davis varieties, this cultivar produces large fruit with yellow flesh that ripen in mid- October.

Kirsten The hybrid seedling of Taytwo and Overleese selected by Tom Mansell in western Pennsylvania.

KYSU 2-7 Advanced selection from Kentucky State University. Planted with permission for evaluation (trial was unsuccessful).

KYSU 2-11 Advanced selection from Kentucky State University. Planted with permission for evaluation. Very late ripening (into October in Cincinnati). Produces small to medium fruit of mediocre taste.

KYSU Atwood™ Released by the Kentucky State University horticulture program in 2009 and is named for Rufus B. Atwood (KYSU president 1929-1962). Fruit have an attractive greenish-blue skin, yellow-orange pulp, and few seeds. Fruit are round, average in size (around 120 grams) with few seeds and medium flavor. Little Phyllosticta reported. Also recognized as KYSU 8-2.

LA Native Originating from Louisiana, this tree is somewhat frost resistant and produces small fruit later than other varieties.

Lady D Purchased from Tollgate Nursery. Medium sized fruit with yellow flesh and good taste.

Lynn’s Favorite A popular variety selected from a Corwin Davis orchard. A mature tree produces large, yellow-fleshed fruit that ripen in mid-October and are not susceptible to Phyllosticta. Won Best Fruit at the 2014 Ohio Pawpaw Festival. A good producing tree with large yields.

Mango A cultivar selected from the wild in 1970 in southern Georgia. Cultivar demonstrates vigorous growth and is a large, productive tree. Produces mostly medium to large fruit with few seeds. Soft flesh and large pulp to seed ratio indicate this variety is a viable option for processing.

Mary Foos Johnson Selected from the wild in Kansas by Milo Gibson. Mary Foos Johnson donated the seedling to the Oregon State agricultural research extension. Fruit are large with yellow skin, butter- colored flesh, and few seeds. Ripens in late September to early October.

Middletown Chance seedling selected from the wild in Middletown, Ohio by Ernest J. Downing in 1915. The variety produces small- sized fruit.

Mitchell Selected from the wild (chance seedling) in Jefferson County, Illinois in 1979. Fruit are medium-sized with slightly yellow skin, golden flesh and few seeds. Fruit flavor is fair with no aftertaste but does have an astringent mouthfeel.

NC-1 A hybrid seedling of Overleese and Davis varieties selected in Ontario, Canada, 1976. Fruit are large with few seeds and yellow flesh and skin. Fruit have good flavor with some aftertaste. Fruit skin is thin, and fruit ripens in early-to-mid September. Less productive than other varieties (average 45 fruit per tree), its early ripening makes it suited for colder climates. Somewhat susceptible to Phyllosticta. 2005 Best Fruit winner at the Ohio Pawpaw Festival.

Overleese Chance seedling selected from the wild in eastern Indiana in 1950. Bears large fruit with few seeds, creamy texture, and fair flavor with some bitter aftertaste. Has a long harvest period ranging from early September to early October. Reported average fruit size of >170g and average tree production of 55 fruit per tree. The parent of other improved cultivars, Overleese fruit maintain quality longer than others. Won Best Fruit at the 2011 Ohio Pawpaw Festival.

PA-Golden 1, 2, 3, 4 Selection of seeds from the George Slate collection by John Gordon in Amherst, New York. Presents small to medium- sized fruit (110 g/fruit) maturing in late August to mid- September. Fruit have golden flesh and skin that yellows upon ripening. Fruit flavor is good with no aftertaste but can have an astringent mouthfeel. Productive trees (up to 65 pounds of fruit per year). Can be seen as PA Golden 1-4, although PA Golden 1 is the most common. A remarkable bloom makes it a good pollinator for other varieties.

Pepper Scion wood from Chris Chmiel of Albany, OH. Supposedly, from the largest pawpaw tree in Ohio. No outstanding fruit qualities.

Pickle From Hidden Springs Nursery (no longer available). Small fruit shaped like a pickle.

Potomac™ Selected by R. Neal Peterson as a seedling of a tree from the Blandy Experimental farm in northern Virginia. Fruit are large (average 235g/fruit) and extremely fleshy (only 4% seed by weight) with a firm, smooth texture and medium yellow flesh color. Moderately productive (average 45 fruit per year). Large fruit are susceptible to splitting due to Phyllosticta. Not ideal for northern climates due to later ripening.

Prolific Selected as a chance seedling by Corwin Davis in south-central Michigan in the mid-1980s. Fruit are large with yellow flesh and ripen late (early October in Michigan). The fruit’s dense but creamy texture allows it to age better than other varieties. Fruit have a good, caramel flavor but can have a bitter aftertaste. Prolific trees start producing earlier than most and tend to be lush and strong growing.

Quaker Delight This variety produces fruit with light colored flesh, creamy texture, and mild flavor. Found by Dick Glaser in the Wilmington College Arboretum, this variety ripens in early September. It won the title of “Best Pawpaw” at the 2003 Pawpaw Festival in Albany, Ohio.

Rana Best Fruit winner at the 2004 Ohio Pawpaw Festival, but has failed to produce quality fruit at the Cincinnati, OH locations.

Rappahannock™ Selected by R. Neal Peterson as a seedling of a tree from the Blandy Experimental farm in northern Virginia and patented in 2004. Fruit exhibit a color-break and skin turns yellow near ripeness around mid-September. In full sun, trees present with a horizontal-to-upright leaf habit, making the small fruit more easily visible. Fruit are small (95g) but have good seed to flesh ratio (3%). Trees are productive averaging 95 fruit per year. May be better suited for southern climates (anecdotal reports).

Rebecca’s Gold Selected from Corwin Davis seedlings in south-central Michigan by J.M. Riley in 1974. Fruit are medium-sized and kidney-shaped with yellow flesh. They have thin skin and soft texture requiring careful harvesting techniques.

Ruby Keenan Variety with medium-sized fruit and excellent flavor. Origin and selector are unknown.

SAA Overleese Selected from Overleese seed by John Gordon in 1982. The variety produces large fruit, rounded in shape, with green skin, yellow flesh, and few seeds. Fruits mature in mid-October.

SAA Zimmerman A seedling selected from seed by John Gordon from the G.A. Zimmerman collection in western New York (1982). Fruit are large, with yellow skin and flesh and few seeds.

SAB Overleese Seedling introduced from Overleese by John Gordon. Produces large, good tasting fruit with yellow flesh.

Shawnee Trail Won 2002 Best Fruit winner at the Ohio Pawpaw Festival. 88

Shenandoah™ Seedling of Overleese selected by R. Neal Peterson. Fruit are (1-7-1) medium-large (150 g/fruit), have few seeds (7% by weight), yellow flesh and a good, mild flavor. Fruit texture can sometimes be chalky but there is no aftertaste. Ripen in September, earlier than most cultivars, and trees produce 80 fruit per year on average. Only slightly susceptible to Phyllosticta. 2009 Best Fruit winner at the Ohio Pawpaw Festival.

Sue Selected from southern Indiana. Small to medium-sized fruit have yellow flesh and skin when ripe. Good-producing cultivar with mild flavor and resistant to Phyllostcta.

Sunflower Wild selection from southeast Kansas in 1970. Fruit are large (155 g/fruit) with yellow skin and butter-colored flesh, few seeds and ripen from mid-September to early October. Fruit have a fair flavor and firm texture. Moderately productive at 75 fruit per year on average. The only variety reported to be self- fertilizing and makes strong rootstock for grafting. Late ripening may not be appropriate for northern climates. Won Best Fruit at the Ohio Pawpaw Festival in 2006 and 2010.

Sunglo Large fruit with yellow skin and flesh that ripen the first week of October.

Susquehanna™ Selected by R. Neil Peterson as a seedling from the Blandy Experimental Farm. Fruit are very large (185 g/fruit) and have few seeds (4% by weight), with medium yellow flesh, and thick skin, making them less fragile than other varieties. Fruit have good flavor with some bitter aftertaste and astringent mouthfeel. Fruit ripen in late September but are less productive than other varieties, only 40 fruit per year on average.

Sweet Alice Selected from the wild as a chance seedling in West Virginia in 1934. One of the oldest cultivars still commercially available. Medium fruit size reported. 89

Sweet Virginia From Tollgate Gardens in Michigan. Seedling found in Marshall, MI. Fruit are medium sized, have yellow flesh and good flavor. Had been somewhat unsuccessful in the Cincinnati area.

Taylor Wild selection from Eaton Rapids, MI made by Corwin Davis in 1968. Trees produce medium fruit (110 g/fruit), up to 7 in a cluster, with green skin and yellow flesh. Fruit ripen in September in Kentucky, but early October in Michigan. Moderately productive at 70 fruit per year.

Taytwo Sometimes spelled Taytoo, the variety developed from a wild selection made by Corwin Davis in Michigan in 1968. Fruit are medium size (120 g/fruit) with light-green skin and yellow flesh. Flavor is good with no aftertaste and creamy texture. Fruit ripen September to October. About 75 fruit per year is the reported average.

Tollgate Fruit are large with yellow flesh and ripen in early October.

Vickey Russel Placed second at the 2004 Ohio Pawpaw Festival, but has not performed well in the Cincinnati area.

Wabash™ An R. Neal Peterson selection made as a seedling from a tree in the Blandy Experimental Farm, MD. Large fruit (185 g/fruit) are fleshy (6% seed by weight) with a texture that is creamy yet firm. The flesh ranges from yellow to orange in color, has good flavor with mild aftertaste. More difficult to graft then other varieties, it is slow to produce fruit and only averages 65 fruit per year.

Wells A wild selection from Indiana made by David Wells in 1990. The variety produces small to medium-sized fruit with green skin and orange flesh. Ripens in mid to late September.

Wilson Chance selection from the wild by John V. Creech in 1985 in Kentucky. Ripe fruit are small, typically 90 grams, with yellowish skin, creamy golden flesh, and mild flavor. Fruit tend to ripen in mid-season. A fast growing and productive variety, its fruit flavor can become unpleasant if over-ripe.

Zimmerman Selected in New York from G.A. Zimmerman seeds by George Slate. The variety produces medium-sized fruit.

Note. Fruit size categories are small (<100g), medium (100-150g), and large (>150g). All trademarked varieties belong to R. Neal Peterson; propagation restrictions apply. Fruit descriptions reported were gathered from multiple sources including anecdotal reports and an informal cultivar tasting. Portions of cultivar information excerpted from a“Pawpaw description and cooking information,” by S. C. Jones and D. R. Layne, 2009, b“Pawpaw planting guide,” by S. C. Jones, R. N. Peterson, T.-A., Turner, K. W. Pomper, and D. R. Layne, 1998, Kentucky State University Cooperative Extension Program, and c“The North American pawpaw: Botany and horticulture,” by K. W. Pomper and D. R. Layne, 2005, Horticultural Reviews, 31, p. 349-377.

Appendix B: Sample Data Collection Sheet

Appendix C: 8 Varieties of Pawpaw Excluded from All Data Analysis

Avg. fruit Harvest Variety Location Year Yield (g) weight (g) Days

Allegheny 2 2012 1338 96 11

Cherokee Ridge 1 2012 522 52 1

Danica 1 2012 1293 68 1

Forest Keeling 1 2012 250 83 1

PA Golden 2 1 2012 692 99 --

Pepper 1 2011 267 67 1

Pickle 1 2011 1089 78 9

Vicky Russel 1 2012 238 79 1

Note: The pawpaw varieties listed in this table were excluded from data analysis because they only occur once (n = 1).

Appendix D: Means ± SDs for 52 Individual Varieties Included in Data Analysis

Average Fruit Harvest Length Variety Weight (g) Yield (g) (days) 421 132 ± 15 722 ± 10 17 ± 6 Belle 125 ± 26 1194 ±934 8 ± 7 Broad 112 ±26 483 ± 419 7 ± 8 Cawood 153 ± 11 667 ± 371 22 ± 4 Convis 74 ± 6 791 ± 565 2.0 ± 1 Cullaman Late 10 ± 20 563 ± 212 1 ± 0 Davis 244 ± 95 1017 ± 946 3 ± 5 Estil 136 ±17 734 ± 392 15 ± 13 Glaser 103 ± 45 564 ± 639 6 ± 10 Green River Belle 106 ± 22 10818 ± 8016 26 ± 15 IXL 121 ± 25 4888 ± 6687 22 ± 17 Kirsten 76 ± 1 337 ± 261 2 ± 1 KYSU 2-11 99 ± 50 8335 ± 9206 33 ± 19 KYSU 2-7 85 ± 27 5216 ± 4041 24 ± 15 KYSU 8-2 141 ± 67 11349 ± 10202 22 ± 12 (Atwood) KYSU Seedling 81 ± 29 2901 ± 2415 22 ± 13 LA Native 68 ± 10 654 ± 146 15 ± 4 Lady D 142 ± 13 822 ± 521 1 ± 0 Lynn’s Favorite 135 ± 55 3791 ± 4471 14 ± 10 Mango 210 ± 83 1321 ± 794 5 ± 6 Mary Foos Johnson 139 ± 80 1234 ± 1476 10 ± 10 Middletown 96 ± 15 1038 ± 119 10 ± 10 Mitchell 117 ± 34 5706 ± 6976 20 ± 14 NC-1 172 ± 43 9550 ± 12791 20 ± 13 94

Overleese 160 ± 49 7208 ± 5151 17 ± 8 PA Golden 1 93 ± 28 11161 ± 8147 23 ± 15 PA Golden 3 92 ± 9 276 ± 26 -- PA Golden 4 107 ± 39 542 ± 473 8 ± 11 Potomac 121 ± 53 427 ± 447 3 ± 3 Prolific 105 ± 33 2132 ± 1169 13 ± 8 Quaker Delight 127 ± 69 2010 ± 2594 7 ± 9 Rana 73 ± 23 281 ± 237 5 ± 5 Rappahannock 72 ± 23 1218 ± 1247 9 ± 7 Rebecca’s Gold 167 ± 59 9953 ± 5296 21 ± 8 Ruby Keenan 79 ± 36 359 ± 405 8 ± 12 SAA Overleese 156 ± 69 472 ± 90 1 ± 0 SAA Zimmerman 170 ± 24 18182 ± 14847 24 ± 10 SAB Overleese 208 ± 75 1021 ± 879 1 ± 0 Shawnee Trial 77 ± 44 99 ± 12 1 ± 0 Shenandoah 153 ± 47 3660 ± 3930 20 ± 10 Sue 96 ± 43 10215 ± 11349 19 ± 14 Sunflower 148 ± 36 10998 ± 11570 25 ± 15 SunGlo 79 ± 14 1514 ± 1295 15 ± 9 Susquehanna 194 ± 76 1846 ± 2392 15 ± 8 Sweet Alice 141 ± 19 792 ± 684 4.5 ± 5 Sweet Virginia 110 ± 26 931 ± 675 12 ± 12 Taylor 119 ± 49 2079 ± 1855 9 ± 8 Taytwo 121 ± 47 3024 ± 3086 13 ± 16 Tollgate 120 ± 27 3853 ± 2141 17 ± 9 Wells 144 ± 46 4672 ± 5779 12 ± 12 Wild 76 ± 1 264 ±156 11 ± 14 Wilson 80 ± 28 4433 ± 5120 18 ± 12

Appendix E: Pictures of Planting Locations

Fox Paw Ridge Farm (Location 1), Adams County, Ohio

Les’s (Location 3), Butler County, OH

Note. All photographs taken by Dr. Ron Powell of Cincinnati, Ohio.

Appendix F: Original Data Recorded by Ron Powell

2005

2006

100

101

102

103

104

105

106

107

2007

108

2008

109

110

111

112

113

114

115

116

117

118

119

120

121

2009

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

2010

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

2011

155

156

157

158

159

160

161

162

163

164

165

166

2012

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

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