Germination characteristics of two yellow bluestems, Bothriochloa ischaemum (L.) Keng

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Germination characteristics of two yellow bluestems, Bothriochloa tschaemum (L.) Keng.

Munda, Bruce David, M.S.

The University of Arizona, 1993

U MI 300 N. ZeebRd. Ann Arbor, MI 48106

GERMINATION CHARACTERISTICS OF TWO YELLOW BLUESTEMS, Bothriochloa ischaemum (L.) Keng.

by Bruce David Munda

A Thesis Submitted to the Faculty of the

DEPARTMENT OF PLANT SCIENCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN AGRONOMY AND PLANT GENETICS

In the Graduate College

THE UNIVERSITY OF ARIZONA

1993 2

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

^ Albert K. Dobrenz ? Date Professor of Plant Sciences 3

ACKNOWLEDGMENT

My special appreciation goes to Dr. Albert Dobrenz for without his guidance, support, and never ending enthusiasm I would have never completed this thesis. Extended appreciation to Dr. K.C. Hamilton and Dr. Bruce Roundy for guidance, advice, and willingness to serve on my graduate committee for such a long time. Thank you to my committee members and other researchers I have had the pleasure to work with at the University of Arizona for stimulating my desire to learn more.

I acknowledge the Soil Conservation Service for allowing me the time and facilities to pursue an advanced degree. My appreciation to the Plant Materials Program for developing my interest in plants and ecological processes and challenging me to become a better agronomist and ecologist.

I thank Maggie and our children, Mikel and Byron, for their support and tolerance during those stressful periods over the past 8/4 years. 4

TABLE OF CONTENTS

LIST OF ILLUSTRATIONS 6

LIST OF TABLES 7

ABSTRACT 8

INTRODUCTION 9

LITERATURE REVIEW 12 Germination 12 Seed Appendages 19 Seed Respiration 26

MATERIALS AND METHODS 30 Experiment 1 31 Experiment 2 32 Experiment 3 34 Experiment 4 35

RESULTS AND DISCUSSION 37 Experiment 1: Comparison of Ganada and P.I. 237110 at three constant temperatures 37 Percent Germination 37 Time to 50% Germination 40 Experiment 2: Comparison of respiration rates for Ganada and P.I. 237110 under four osmotic potentials 43 Experiment 3: Comparison of Ganada, P.I. 237110, Vaughn sideoats grama, and Cochise lovegrass 46 Percent Germination 46 Time to 50% Germination 46 Experiment 4: Comparison of Ganada, P.I. 237110, cane bluestem, Vaughn sideoats grama, and Arizona cottontop across three seed conditioning treatments 50 Percent Germination 50 5

TABLE OF CONTENTS - continued

Time to 50% Germination 53

SUMMARY 57

REFERENCES 59 6

LIST OF ILLUSTRATIONS

Figure Page

1. Mean total germination for Ganada and P.I. 237110 yellow bluestem averaged across three constant temperatures of 15.6,21.1, and 32.2°C 38

2. Mean total germination at three constant temperatures for Ganada and P.I. 237110 yellow bluestem 39

3. Time to 50% of total germination for Ganada and P.I. 237110 yellow bluestem 41

4. Seed respiration rates for Ganada and P.I. 237110 yellow bluestem for four osmotic potentials (0, -0.4, -0.8, and -1.2 MPa) 44

5. Mean total germination for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, and Cochise lovegrass at an alternating temperature of 35°C (8h) and 20°C (6h) 47

6. Time to 50% of total germination for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, and Cochise lovegrass 49 7

LIST OF TABLES

Table Page

1. Mean total germination for control, brush, and caryopsis treatment for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, Arizona cottontop, and cane bluestem 52

2. Time (incubation days) to 50% of total germination for P. I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, Arizona cottontop, and cane bluestem for three seed conditioning treatments 55 8

ABSTRACT

Germination responses of P.I. 237110 and 'Ganada' yellow bluestem (Bothriochloa ischaemum (L.) Keng.) were compared in four experiments. P.I. 237110 had the highest total germination for all seed conditioning treatments. At the lowest temperature (15.6°C) P.I. 237110 did not germinate and Ganada had a low total germination. P.I. 237110 and Ganada require high (>20°C) incubation temperatures for optimum germination. Seed conditioning treatments did not significantly increase total germination for P.I. 237110 or Ganada. The caryopsis treatment gave the highest percent germination for all germplasm except Ganada. P.I. 237110 had the fastest time to 50% germination for all seed conditioning treatments. Seed conditioning did not significantly affect time to 50% germination for P.I. 237110 or Ganada. Ganada had significantly higher respiration rates than P.I. 237110 at 0 and -0.4 MPa but not at -0.8 and -1.2 MPa. Respiration rates for both germplasm decreased as osmotic concentrations became more negative. 9

INTRODUCTION

Irrigated agriculture is of major economic importance in the Southwest. Unfortunately, it has relied on a finite natural resource-groundwater. As water tables have dropped pumping costs have increased and the quantity and quality of groundwater have deteriorated causing abandonment of marginal farming operations. In 1980 the State of Arizona passed the Groundwater Management Act which restricts groundwater pumping. As farmland was retired from agricultural production the water rights were transferred to another location and use (Cox and Madrigal 1988). Cities, mines, and other water users have purchased farmland and its water rights to assure a supply of groundwater for future growth. To date as much as 50% of the agricultural land between Phoenix and Tucson (2,200 square kilometers) has been abandoned (Jackson et al. 1991). Over 200,000 ha of land in Arizona may be involved in water right transfers (Thacker and Cox 1992).

The USDA Soil Conservation Service Plant Materials Program has been screening plant materials for rangeland revegetation, critical area stabilization, and revegetation of abandoned cropland since 1933. The Tucson Plant Materials Center (TPMC) has evaluated and developed establishment techniques such as pitting, contour planting, and planting into a dead litter mulch for soil stabilization and the establishment of forage and cover for wildlife and livestock on retired or abandoned cropland (Munda et al. 1991; USDA-SCS, Farmers Bulletin No. 1913, Wash. D.C. 1942). 10

Yellow bluestem is a perennial, warm season, C4 bunchgrass (Waller and Lewis 1979) that may have potential for revegetation of abandoned farmland. It was introduced to the United States in the early 1930's from Eurasia and the Middle East. The inflorescence is an unbranched raceme arranged subdigitally on an axis distinctly shorter than the longest raceme (Taliafero et al. 1972). Method of seed production is reported to be apomictic (Christoff 1976). It has been used in revegetation efforts throughout the southern half of the United States. In Southern New Mexico yellow bluestem has been easily established on sandy and loamy soils that were previously vegetated with creosote bush (Larrea tridentata Vail) (Herbel et al. 1973). Most irrigated farmland soils have loam to clay loam surface textures. Revegetation efforts on soil with surface textures of sandy loams or lighter have generally been successful. But, soils with surface textures of loams or heavier have been difficult to revegetate. Yellow bluestem is a perennial grass that is well adapted to clay loam soils.

In 1983 the Tucson Plant Materials Center conducted a comparative evaluation of 13 yellow bluestem accessions. The purpose of the evaluation was to screen existing cultivars and accessions for use in revegetation of abandoned cropland and other highly disturbed lands in the Sonoran desert. The study found P.I. 237110 was superior to all other accessions in regards to percent stand, forage production, drought tolerance, and stand longevity (Munda 1987). P.I. 237110 was also planted at Three Points, AZ. on retired cropland. This accession was evaluated as one of the best performers in relation to percent stand and production under limited irrigation. P.I. 237110 11 was collected from the A1 Khars area of Saudi Arabia in 1952 and received at the TPMC in 1954.

The objectives of this experiment were to evaluate the germination characteristics of P.I. 237110 and 'Ganada' yellow bluestem, along with four other warm season grasses: Arizona cottontop (Digitaria californica Henr.) canebluestem (Bothriochloa barbinodes (Lag.) Herter) 'Vaughn' sideoats grama, (Bouteloua curtipendula (Michx.) Torr.) and 'Cochise' lovegrass, (Eragrostis lehmanniana Nees X E. trichophora Coss & Dur.). Total percent germination and time to 50% germination are parameters which will be used to compare germination characteristics. The last objective of this research was to determine seed respiration for Ganada and P.I. 237110 yellow bluestem in relation to osmotic potential. 12

LITERATURE REVIEW

Germination

A high germination rate is a key characteristic for the successful establishment of various plants adapted for seeding in semiarid environments (Coyne and Bradford 1985; Weaver and Jordan 1985). Wright (1971,1975) felt three characteristics were required for grasses to be used in revegetation of arid lands; high germination, seedlings must have high emergence, and the plant must be able to establish under stressful environments. Roundy and Call (1988) indicated that germination, seedling vigor, reproduction, and ability to tolerate drought, variations in temperature, grazing, and salinity are desirable characteristics for revegetation species.

Wright (1975) established an extensive breeding program to develop grass species with the above characteristics. Several cultivars have been released through this program and include: 'Sonora' black grama (Bouteloua eriopoda Torr.), 'SDT' blue panicgrass; 'Catalina' Boer lovegrass (Eragrostis curvula var. conferta Nees), and 'Kuivato' and Puhuima' Lehmann lovegrass (Eragrostis lehmanniana Nees). Unfortunately many of the above cultivars are not used due to lack of available seed and poor performance in rangeland seedings. Adequate field testing is necessary to document plant performance and determine proper planting procedures. 13

Time to 50% germination was used by Wright (1980) to determine germination rate of several genotypes of blue panicgrass (Panicum cmtidotale Retz ). He determined that germination rate was positively associated with seedling emergence and establishment in blue panic. Rate of germination and seedling survival for Cochise lovegrass and sideoats grama were evaluated across various wet/dry sequences by Frasier et al. (1984). They found that sideoats grama germinated during the first initial wet period but the seedling died when exposed to a 5 day dry period. Cochise lovegrass germinated much slower and had higher survival rates following the 5 day dry period versus sideoats grama. Frasier et al. (1985) evaluated five warm season grasses for emergence and survival over six combinations of wet dry cycles. He found that Lehmann lovegrass required 3 or more consecutive wet days for significant emergence. Based upon the success of Lehmanns lovegrass for reseeding arid lands maybe its characteristics should be evaluated such as; high dormancy, requirement of prolonged wet period (indicating a slow germination rate) and high fluctuating temperatures to initiate germination. Major and Wright (1974) indicated that if seed germinates too rapidly, under rangeland conditions, the seedlings may not establish due to rapidly changing and stressful establishment conditions. They suggested that seed with dormancy (slower germination) characteristics would increase its potential for seedling establishment. Regulating the amount of seed to germinate over time would "expose the potential of seedling establishment to a broader array of environments in time and space and increase the probability of establishment" (Major and Wright 1974). 14

Seed appendages may also cause dormancy through chemical inhibitors or acting as a physical barrier impeding imbibition. Ahring et al. (1975) found that oil from the bracts of two Asiatic bluestems significantly retarded germination and seedling growth. He found that heat drying degraded the active compounds and recommended drying the rough seed prior to planting to increase the probability of stand success. Drying, moistening, and alternating temperatures have been found to promote germination and break dormancy (Griswold 1936, Harrington 1923).

Grasses belonging to the Andropogoneae tribe have glumes, bracts and a sterile floret attached to the grass spikelet (Hitchcock 1971; Gould and Shaw 1983). These enclosing seed structures may interfere with absorption of water and gas exchange and may contain a germination inhibitor (Crocker 1906; Evenari et al. 1942; Nazarenko and Djadjun 1934). Burton (1939) found that the physical removal of the lemma and palea of dalllisgrass (Paspalum dilatatum Poir.) and bahiagrass (Paspalum notation Flugge.) served the same purpose as acid scarification for increasing germination. Removal of seed appendages (lemma and palea or glumes) has increased germination for Urochloa pullulans Staph. (Akamine 1944); rice (Oryza sativa L.) (Roberts 1961); sideoats grama (Sumner and Cobb 1962); and reed canaiygrass (Phalaris arundinacea L.) (Vose 1962). The glumes surrounding the caiyopses of Dichanthium annulatum (Forsk.) Staph, and Bothriochloa intermedia A. Camus have been shown to be involved in the delay of germination (Ahring and Harlan 1961a,b; Ahring 1972). Ahring and Harlan (1961a) has shown that freshly harvested yellow bluestem seed 15 required 65 days, in an optimum environment, for maximum germination to occur.

Germination occurs in three phases; rapid uptake of water or imbibition, a lag phase where there is a leveling off of water uptake, and another period of rapid water uptake marked by radicle elongation (Vertucci 1989). During imbibition water moves into the seed along a wetting front, as the outside cells become hydrated they expand and create tremendous pressure on the inner dry cells. This stress is controlled by three factors: initial moisture content, temperature of the medium, and rate of water uptake (Vertucci 1989). The first two factors are environmentally controlled while the third factor is controlled by inherent properties of the seed plus the environment.

Temperature, rate of imbibition, and initial moisture content of the seed affect germination and seedling vigor (Haferkamp et al. 1977a and Vertucci 1989). When seeds with a low initial moisture content are imbibed rapidly at high temperatures there is little decline in germination vigor. However, if dry seeds are subjected to rapid imbibition at low temperatures vigor has been strongly reduced. But, with slow imbibition, there are few deleterious effects at low temperatures (Vertucci 1989). Haferkamp et al. (1977b) found that germination of Lehmann lovegrass could be improved by priming, oven-drying, scarification, or pre-chilling on moist substrate. Newly-harvested Lehmann lovegrass seed exhibits high dormancy. Haferkamp et al. (1977b) found that the pretreatments abraded the seed coats 16 causing an increase in moisture imbibition and subsequent increase in germination.

Dormancy is another condition that has significant impact on germination. Warm season grasses generally exhibit less seed dormancy than many cool season grasses which may possess a long dormancy (Sapahkevich 1961). Seeds are normally ready for dispersal at the end of the wet season when environmental conditions may still be favorable for germination but will rapidly become unfavorable for seedling growth and establishment. Therefore, many species, especially those from drier habitats, are innately dormant (Fitter and Hay 1991). The term "dormancy " is used to describe two inactive conditions. The first is a result from an unfavorable environment while the second is internally imposed by a metabolic block or inhibitor. Germination inhibitors develop with the maturation of the seed on the maternal plant (Ahring 1972).

There are three basic types of dormancy; innate, induced, and enforced. Innate dormancy or primary dormancy prevents germination during development and maturation of the seed on the mother plant (Tran and Cavanagh 1984). Primary dormancy is found in the ripe dispersal unit and is of survival value for the species while induced dormancy is important for seed survival and longevity (Roller et al. 1962). An example of innate dormancy is a seed with an impermeable coat such as legume seed. Induced or secondary dormancy is represented by a seed that continues its dormant condition when the seed has been imbibed under conditions unfavorable for germination. 17

Thornton (1945) concluded that accumulated hydrolytic products act as inhibitors in primary and or secondary dormancy. Enforced or imposed dormancy is characterized by a seed's ability to germinate immediately upon removal of the environmental limitation (light temperature, or available moisture). Some desert species have a specific light requirement before germination can occur (Koller and Negbi 1966). Schultz and Kinch (1976) found that dormancy in western wheatgrass (Agropyron smithii Rydh.) was reduced when the seed was exposed to red light or left in complete darkness- increasing the germination percent. Wright and Baltensperger (1964) studied the germination requirements for black grama and found that germination was more rapid in the dark versus light conditions but highest germination occurred when an alternating temperature and light were used.

Germination can be measured by three parameters: maximum germination achieved, germination rate, and uniformity of germination. Weaver and Jordan (1985), based on the Maguire method, evaluated germination using the following equation : CRG = [En / E(Hxn)] x 100 where: CRG = Coefficient of Rate of Germination n = The number of seeds germinating at a given hour (H) H = The hour, counted from the hour of sowing. The larger the CRG, the higher the rate of germination. The CRG is equivalent to the reciprocal of the Mean Time to Germination in hours multiplied by 100. Therefore, as used by Weaver and Jordan (1985) one can calculate the approximate time to 50% germination by: (1/CRG) x 100. 18

Tucker and Wright (1965) evaluated three methods for estimating rapidity of germination or time to achieve 50% germination. They evaluated the Maguire (1962), George (1961), and Regression Index Method (I) and found that only the I method expressed time to 50% germination in a measure of time. The one negative aspect of this procedure is for rapid germinating species (over 50% in the first 3 days) the I value would be negative. The I method determined the 50% germination point by "fitting a least squares regression line to the cumulative germination counts" (Tucker and Wright, 1965). The formula for the RI method is: I = (N/2 - a)/b, where I = Index of rapidity of germination N = total cumulative germination, a = the intercept and b = slope of the line.

Another method of evaluating germination is the use of a Germination Speed Index (GSI): GSI = (Nj/Di + N2/D 2+ + Njo/io) IP where N is the number of seed to germinate each consecutive day, D is day and P is the cumulative number of seed to germinate by the tenth day. Percent germination data were converted using the arcsin transformation (Robinson 1986).

Bewley and Black (1986) measured germination uniformity using the equation: 19

CUG = Xn/L[( t' - t) xn] where CUG = coefficient of uniformity of germination, t' = mean time to complete germination, t = time in days, and n = number of seeds germinated on day t. The higher the value the greater the uniformity of germination.

Seed Appendages

In nature seed appendages assist in dispersal and placement and enhance the probability that a seed will germinate and establish. Generally, it was thought that seed appendages were for dissemination purposes only (Peart 1981). However, Booth and Schuman (1983) found in their studies of winterfat (Eurotia lanata (Pursh) Moq, Ceratoides lanata (Pursh) J.T. Howell) that the pubescent bracts enclosing the embryo acted to position and anchor the seed.

As man has domesticated wild crops he has bred or selected those genotypes that offer the least problems in harvesting, cleaning, and sowing (Harlan 1992). During the early to mid 1900's there was a great need to revegetate large areas of natural ecosystems to restore forage production for livestock grazing and to reduce soil erosion (Roundy and Call 1988). Native species were tried, but in the arid Southwest these seedings had veiy poor success. Introduced species, such as Lehmanns lovegrass, performed exceptionally well (Cox et al. 1982). The success of Lehmanns lovegrass was partly due to the fact that it was easy to sow, propagate and condition with conventional fanning equipment. Thus, allowing seed growers to 20 produce large quantities of high quality seed at an affordable price, unlike most of the native species. Booth (1984) has shown that normal seed processing techniques damage the embryo of winterfat. Many attempts have been made to seed fluffy-seeded species using coatings or a pelleting process to assist in distribution of the seed. In most cases pelleted seeds had little or a negative effect on germination and plant establishment (Hull 1959). However, Kocher and Stubbendieck (1986) found that broadcast seeding with coated seeds aided in seed distribution. Today, technology has improved and equipment is now available that can harvest, condition, and sow seeds that have fluffy or chaffy appendages.

Various authors have used different terminology to describe seed and their appendages. Was the unit a seed, disseminule, fruit or a propagule? A term was needed that would describe the function and characteristics of the seed unit. Booth (1987) used the term "diaspore" to define the structure that serves to disperse seed and may have a mechanical and/or chemical function to contribute directly to seed germination and seedling establishment. The term "diaspore" was first used by Gove (1981).

Diaspores can be described in terms of seven functions; seed dispersal, seed positioning, anchoring, hydraulic conductivity, seed protection, chemical transfer, and regulation of seed respiration.

Seed dispersal can be obtained by several modes which include: wind, water, gravity, animal or insect, self dispersal, and man. Many papers have 21

been written on the forms and function of appendages and diaspores. Gutterman et al. (1967) evaluated the dispersal mechanisms of Blepharis persica (Burm.) Kuntze. He found that seed dispersal of this species was controlled by water, termed hygrochasy. The diaspore of this species is a capsule that is enclosed by sepals which remain closed until wetted. As the capsule ripens the septum dries creating a tension, locking the capsule, until it relaxes by absorbing water. When the septum is released the capsule explodes dispersing its seed.

Wind is also a dispersal mechanism for many species in the Compositae. Sheldon and Burrows (1973) studied the dispersal efficiency of the pappus of composite fruits. They found that dispersal efficiency was determined more by the pappus geometry than by the size ratio of pappus to achene. They also found that dispersal distance was increased with increased wind velocities and increased height of fruit release.

Animals are good dispersal agents for many species, including mesquite (Prosopsis velutina Woot.), Xanthium saccharatum (Wallr.), and filaree (Erodium botrys (Cav.) Bertol). Filaree was introduced into the central valleys of California from livestock that were introduced by early Spanish colonists (Young et al. 1975).

Seed positioning was evaluated by Gutterman et al. (1967) study of Blehparis persica (Burm.) Kuntze. They found that the coat of the dry seed was covered with multicellular hairs that were appressed to the seed. When 22 wet these hairs became erect and raised the seed to a 30 - 45 ° angle to the soil surface so that the soil and seed micropyle were in contact, maximizing the potential for water uptake by the seed. Peart (1979) studied the diaspore functions of six grass species: Danthonia tenuior (Steudel) Conert., Dichanthium sericeum (R.Br.) A. Camus., Dichelachne micrcmtha (Cav.) Domin., tanglehead (Heteropogon contortus (L.) Beauv. ex Roem et. Schult.), Schizachyrium fragile (R.Br.) A. Camus., and Stipa verticillata Nees ex Sprengel. All of these species were awned with a callus that had antrorse hairs. In various evaluations of removing portions or all of the seed appendages it was found that the orientation and position which assured good seed soil contact was altered resulting in reduced germination rates. Peart determined that the attachment scar had higher initial water uptake rates compared to the micropyle. In some cases the hilum can act as a one-way valve, opening in dry air to permit water vapor loss but closing as humidity rises. Imbibition can only occur after a prolonged immersion in water which normally occurs during the wet season (Roller and Hadas 1982). Peart also evaluated the role of hygroscopically active awns in locating microsites. He found that removal of the awn significantly reduced the number of diaspores finding microsites, but removal of the callus did not have an effect. It was also shown that the sharp callus with antrorse hairs assisted in the movement of diaspores and in the location of soil cracks while blunt callus did not assist. Peart (1981) evaluated two species, Aristida vagan Cav. and Microlaena stipoides (Labill.) R.Br., which had rigid awns and barbed antrorse callus. He found that the rigid awns and the sharp callus orientate the falling diaspores so they will land with the callus penetrating the soil or entering soil 23

cracks or crevices. Peart (1981) also found that those diaspore positions which maximized soil diaspore contact had the higher germination and establishment rates.

Functions for seed anchoring include: holding the seed in place, not allowing dispersal agents to move the diaspore and acting as a counterbalance to assist the radicle in penetrating the soil. Gutterman et al. (1967) used the term myxospermy to describe the process of the seed appendages sticking the seed to the soil. The long bract hairs of winterfat and mucilaginous coatings are good examples of myxospermy. Peart (1979, 1981) has shown that antrorse hairs on the callus play an important role in anchoring the diaspore and provide a counter to the force of the radicle pushing into the soil.

Another anchoring function has been shown to include the hygroscopic active awns of several grasses, shrubs and forbs. The active awn has been shown to assist in the movement and planting of the diaspore into soil cracks and crevices where better seed-soil contact can be made and evaporative loss from the seed is reduced (Peart 1979, Thurston 1960, Harper et al. 1965). Young et al. (1975) showed that the hygroscopic active awn of filaree aided in diaspore movement on bare soils until the diaspore movement would lodge in the soil and then its twisting action would drill the diaspore into the soil. The mechanism of self planting also aides in the protection of the diaspore by reducing seed evaporation, predation and may provide protection from damage caused by fire (Lock and Milburn 1971). 24

Litter fixation is an additional anchoring methodology used by Russian thistle (Salsola kali var. tenuifolia Tausch, Salsola iberica Sennan and Pau). Bush muhly (Muhlenbergia porteri Scribn.) once occurred is extensive stands in southeastern Arizona, but now is generally found in or around the base of shrubs and trees (Gould and Shaw 1983). Bush muhly may use litter fixation as an anchoring methodology. As the inflorescence disarticulates from the plant wind or other dispersal agents may lodge it in surrounding shrubs, providing a 'safe site' for germination and seedling establishment.

Appendages can increase hydraulic conductivity by increasing the amount of surface area for water absorption. Seeds that have a smooth seed coat or can secrete a mucilaginous coating can increase their seed-soil contact and improve the hydraulic conductivity between the seed and the soil (Koller and Hadas 1982). Young et al.(1970) found that seed appendages such as: hairs, pappus, awns and or mucilage improve water conductivity by sticking the diaspore to the soil. On the other hand, the hydraulic conductivity of achene pappus decreases its effectiveness as a dispersal agent under high humidities (Sheldon and Burrows 1973). In many respects the hydraulic conductivity functions of appendages and diaspores also serve to position and anchor seeds. Hygroscopic awns of Avena fatua L. and Danthonia penicillata (Labill.) Palisot orient and bury their seeds (Sheldon 1973).

Appendages also protect the diaspore from predation, herbivory, and dehydration of the embryo and precocious germination. Awns of many perennial grasses like tanglehead, and threeawn (Aristida sp.) reduce their 25 palatability and can cause livestock injury (Humphrey 1970). The thick seed coats of legumes reduce the absorption of oxygen and water by the embryo. This restriction not only promotes dormancy but protects the embiyo from desiccation in harsh environments. Chemicals extracted from bitterbrush (Purshia tridentata (Pursh) DC.) seed have been shown to reduce some insect predation (Booth 1987).

Aqueous extracts from the diaspores of creosote bush and white bursage {Ambrosia dumosa (Gray) Payne) have been found to contain chemicals that inhibit germination. Although, with winterfat and greasewood (Sarcobatus vermiculatus (Hook) Torr.) it was found that imbibed seeds, from the diaspore, contained significantly higher concentrations of calcium and magnesium (Booth 1987) and this influx of cations improved seed imbibition, germination and seedling growth of winterfat.

"Seed coverings may impose seed dormancy by preventing or significantly limiting oxygen from reaching the seed embryo" (Booth 1987). Mechanical, heat, and hot water scarification have been shown to break dormancy by removing or abrading seed coverings allowing increased respiration and water imbibition. Seed conditioning may be adjusted to achieve a desirable rate and total germination, based on planting site environment, to optimize germination and establishment. 26

Seed Respiration

Woodstock (1965) proposed that respiration rates during germination could be used as a tool to characterize seedling vigor. Abernethy et al. (1977) and Ching and Kronstad (1972) also evaluated respiration as a means to determine seedling vigor. Abernethy et al. (1977) evaluated respiration rate for light and heavy seed weights of blue panicgrass to characterize the relationship between seed weight, respiration rate and seedling vigor. They found that higher respiratory metabolism produced increased rates of ATP formation which resulted in larger and more vigorous seedlings. They found that the heavy seed-weight selection had higher root and shoot growth versus the light seed-weight selections. However, when they compared the results on a unit seed-weight basis there were no significant differences between light and heavy seed-weight selections. Higher metabolic rates in the heavy seed-weight selections may be due to larger amount of substrate and mitochondria per seed versus a genetic influence. Voigt et al. (1987) also demonstrated a positive relationship between seed size and vigorous seedlings.

Respiration, during seed imbibition, may be defined as the process of oxygen consumption during active metabolism with byproducts of CO2 and water. During imbibition seed respiration progresses through three phases. These are; Phase I where respiration rises rapidly with a sharp increase in O2 consumption, Phase II where there is a lag or stabilized O2 consumption and 27

CC>2 production, and Phase III where there is a sharp increase in O2 consumption and CO2 production (Bewley and Black 1986).

There are three metabolic pathways believed to be active in imbibing seeds. These are glycolysis, the pentose phosphate pathway, and the citric acid or Krebs cycle. In Phase I there is an activation and hydration of mitochondrial enzymes through the Krebs cycle and the electron transport chain (Bewley and Black 1986). Simon (1984) suggests that glycolysis is the major metabolic pathway during the early stages of Phase I. He concluded that mitochondrial activity is rate limiting during the onset of imbibition and that the limiting factor is in the electron transport chain (Simon 1984). During phase II the seed is fully hydrated and all preexisting enzymes have been activated. There is a reduced rate of O2 consumption which may be caused by restriction of O2 uptake by seed coats or other seed structures. Another reason for the lag phase may be that the glycolic pathway may be diverting Krebs cycle acids for its fermentation process rather than use in the Krebs cycle or the electron transport chain. Generally, germination is thought to be complete between Phase II and Phase III because the radicle begins to protrude from surrounding structures. Phase III is characterized by a second rapid consumption of O2 which is attributed to development of new mitochondria and respiratory enzymes in the cells of growing plant tissue. A potential contributing factor may be the actual increased exposure to O2 through the punctured seed coat (Simon 1984; Bewley and Black 1986). 28

Seed germination under osmotic stress has been used to determine or evaluate a species ability for germination and/or establishment under drought and or saline conditions fRoundy 1983; Roundy et al. 1985; Allen et al. 1986). Polyethylene glycol (PEG) solution is commonly used as a substrate to control water potentials during seed germination experiments (Emmerich and Hardegree 1990, 1991; Young et al. 1983). PEG when compared to mannitol and sucrose has been shown to have minimal effects on the accumulation of proline and amino acids in seed tissue (Cress and Johnson 1986). PEG because of its high molecular weight cannot pass through the cell walls and reduces the hydraulic conductivity effects of the solution-seed contact and the germination medium (Heydecker 1967; Emmerich and Hardegree 1990). There are several molecular weights of PEG. PEG-6000 has been perferred because at given concentrations, vj/, increases linearly with temperature (Michel and Kaufinann 1972). PEG has also been used for osmotic priming of seeds and has been shown to increase the rate of germination and increase the percent germination at sub-optimal temperatures (Adegbuyi et al. 1981).

The cultivars Cochise, Ganada, and Vaughn are frequently used for range and critical area revegetation. Currently, the Tucson Plant Materials Center is comparing the accessions P. I. 237110, P.I. 216101, and 9003705 for use in revegetation of abandoned cropland and rangeland in the Sonoran desert. 29

Seed characteristics such as: time to 50% of total germination, total germination, and seed respiration have been used by numerous researchers to determine establishment potential under arid conditions. To date no one characteristic has shown to be effective in predicting a plants ability to establish over a wide range of environments. MATERIALS AND METHODS

These experiments were conducted from the fall of 1991 to the spring of 1993. The study was divided into four experiments. Experiment 1 evaluated time to 50% germination and total percent germination of two germplasms, P.I. 237110 and Ganada yellow bluestem at constant temperatures of 15.6, 21.1 and 32.2°C. Experiment 2 was designed to measure the respiration rate of P.I. 237110 and Ganada yellow bluestem, at osmotic concentrations of 0, -0.4, -0.8, and -1.2 MPa using polyethylene glycol (PEG) 6000. Experiment 3 evaluated time to 50% germination and total percent germination of four germplasms: P.I. 237110 and Ganada, Vaughn sideoats grama, and Cochise lovegrass. Experiment 4 was designed to measure total percent germination and time to 50% germination. Germplasm consisted of P.I. 237110 and Ganada, Vaughn, 9003705 Arizona cottontop, and P.I. 216101 cane bluestem. Experiment 4 included three seed conditioning treatments: seed harvested with Woodward flail vac seed harvester retaining all seed appendages (control), seed conditioned to retain the glumes and/or lemma and palea using the Westrup brush machine (brush), and seed conditioned to caryopsis using the Woodward air seed shucker (caryopsis). In experiment 4 a lighted seed purity table was used to select florets with a caryopsis.

Polyethylene glycol (PEG) 6000 was the osmotic agent chosen for the respiration study to reduce the water potential of the respiring seeds. The PEG solutions were prepared by dissolving appropriate amounts of PEG 6000 31 into distilled water and the water potential checked with a Westcor model 5500 vapor pressure osmometer.

Experiment 1

This experiment involved two germplasm sources: P.I. 237110 and Ganada yellow bluestem. All seed was conditioned to caryopsis using a Viking hammer-mill with a 3/32 screen at 450 rpm's and processing the material using a office clipper with a number 1/20 mesh screen for the top position and a 38 X 38 mesh screen for the bottom position. The air adjustment was .25 open.

Three constant germination temperatures were chosen: 15.6, 21.1 and 32.2°C. A Seedburrow dual chamber germinator was used for the 15.6°C and 32.2°C temperatures and a Burrows single chamber germinator was used for the 21.1 °C temperature. Light was constant. Each germplasm was replicated four times for each temperature. Clear plastic petri dishes (100 X 15 mm) were used with one sheet of Whatman number 1 filter paper. One hundred seeds of each germplasm were used in each petri dish. The 100 seed lots were obtained using an "Old Mill Co." model 850-2 electronic seed counter. Three ml of distilled water was added to each petri dish.

The 21.1°C temperature treatment was started on 30 May 1990 while the 15.6°C and 32.2°C treatments began on 1 June 1990. Counts were made each day and ended on 8 June 1990. A seed was considered germinated and 32

removed from the dish when the radicle was > 2 mm in length. Seeds that developed a fungal growth were removed and considered nonviable. Total percent germination and time to 50% germination was calculated for each germplasm. Total percent germination was determined by dividing total number of germinated seeds by 100. Time to 50% of total germination was determined by developing a graph which showed cumulative germination (Y axis) by time (X axis) and estimating the time to achieve 50% from the graph.

Analysis of variance was used to statistically evaluate the data for significant differences between germplasms and temperatures. Duncan's New Multiple Range Test was used to analyze the means germplasm and temperature at a 0.05 level of probability. Interaction between means was analyzed using Least Significant Difference (LSD) at a 0.05 level of probability.

Experiment 2

PEG 6000 was mixed with distilled water at ratios of 0, 182,228, and 332 g 1-1 for 0, -0.4, -0.8, and -1.2 MPa, respectively. A vapor pressure osmometer was used to precisely measure each osmotic concentration. Additional PEG or distilled water was added to adjust solutions to the desired osmotic concentrations. The germplasm used was P.I. 237110 and Ganada yellow bluestem. Seed for each germplasm was conditioned down to the caryopsis using the Woodward air seed shucker and separating the chaff from the caryopsis using a 'Dakota' seed blower for 60 s at an air setting of one. A 33

clear plastic petri dish (100 X 15 mm) with one sheet of Sargent Welch 9 cm filter paper was used. The filter paper was dried in VWR 1645 oven for 20 min at 80°C . A 0.5 g seed sample for each germplasm was placed into the petri dishes. Three ml of each osmotic concentration was applied to the appropriate replication and each dish was sealed with masking tape. A randomized complete block was used with four replications of each treatment. Each replication was placed on individual germination trays. A Burrows single chamber germinator was used at a temperature setting of 8 h at 35°C and 16 h at 15°C. Light was constant. Respiration was measured 3 days after initiation of the experiment. A closed system was used to measure respiration. A Beckman model 865 infrared gas analyzer was used to measure changes in CO2 concentration. Petri dishes were placed inside a sealed chamber and gases circulated through the analyzer at a rate of 1 L min- 1. A dark cloth was placed over the sealed chamber to eliminate any photosynthetic activity and subsequent use of CO2. A Heath Schumberger model SR-205 chart recorder was used to plot the change in gas concentrations. Chart speed was 2.54 cm min-* and the sensitivity of the chart recorder was 0.776 mg L"1 . Respiration rates were measured by calculating the slope of the line for each measurement. Each dish was oven dried at 80°C for 2 h, weighed and the respective weight of the filter paper + dish + PEG was subtracted from the total weight to give the seed weight. The final respiration rate was calculated as mg L~* of CO2 per g of dry seed weight per min derived from the slope of the line and the dry weight of the seed. 34

Analysis of variance was used to statistically evaluate the data for significant differences between germplasm and seed conditioning treatments. Duncan's New Multiple Range Test was used to separate means at the 0.05 level of probability. Interaction between means was analyzed using Least Significant Difference (LSD) at a 0.05 level of probability.

Experiment 3

In this experiment four germplasm sources were used: P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, and Cochise lovegrass. All seed was conditioned to caryopsis using Woodward air seed shucker and a Dakota seed blower for 60 s to separate trash from the caryopsis. Clear plastic petri dishes (100 X 15 mm) were used with one sheet of Whatman number 1 filter paper. One hundred seeds of each germplasm was used per treatment. Three ml of distilled water was added to each dish. A Burrows single chamber germinator was used at an alternating temperature of 35°C for 8 h and 20°C for 16 h with constant light. Seeds were considered germinated when the radicle was > 2 mm in length and removed from the dish. Germination counts were made each day for 21 days. Total percent germination, and time to 50% germination was calculated for each germplasm. Time to 50% of total germination was determined by developing a graph which showed cumulative germination (Y axis) by time (X axis) and estimating the time to achieve 50% germination from the graph. 35

Analysis of variance was used to statistically evaluate the data for significant differences between germplasm and temperature. Duncan's New Multiple Range Test was used to separate the means at the 0.05 level of probability. Interaction between means was analyzed using Least Significant Difference (LSD) at a 0.05 level of probability.

Experiment 4

Three seed condition classes were used: 1) control-as recovered from the Flail-Vac seed harvester, 2) seed appendages such as hairs, awns and glumes were removed using a Westrup brush machine and 3) removing all seed appendages leaving only the caiyopsis using a Woodward air seed shucker. Species used in this experiment were: P.I. 237110 and Ganada yellow bluestem, 9003705 Arizona cottontop, P.I. 216101 cane bluestem, and Vaughn sideoats grama.

Germination was conducted using clear plastic petri dishes (100 X 15 mm) and Whatman number 1 filter paper 9 cm in diameter. Three ml of distilled water and 50 seeds of each treatment was added to each replication. Additional water was added to maintain a moist filter paper. A randomized complete block design with four replications of each germplasm and seed conditioning treatment was used. A Hoffman model SG 30 dry germinator set at an alternating temperature of 35°C for 8 h and 20°C for 16 h was used for this experiment. Light was on continuously. Seed counts were made for 10 consecutive days. A seed was counted as germinated and removed when 36

the radicle extended beyond the coleorhiza and /or if the plumule (or coleoptile) was > 2 mm long. Dishes were checked at 7 a.m. and 4 p.m. for germinated seed the first 7 days and then every 24 h for the final 3 days. At the end of the experiment all non-germinated florets were dissected to determine percent fill. Percent germination was determined by dividing the number of germinated seed by the number of viable florets. To control fungus, Daconil-2787 WDG (90% A. I.) was used at a concentration of 0.5 g 100ml"! The Daconil solution was used only if signs of fungus were apparent. Distilled water was used for the majority of the experiment. Seeds that developed fungal growth were removed and considered nonviable.

Total percent germination and time to 50% of total germination was used to compare germination characteristics. Time to 50% of total germination was determined by developing a graph which showed cumulative germination (Y axis) by time (X axis) and estimating the time to achieve 50% germination from the graph.

Analysis of variance was used to statistically evaluate the data for significant differences between germplasm and seed conditioning treatments. Duncan's New Multiple Range Test was used to separate the means at the 0.05 level of probability. Interaction between means was analyzed using Least Significant Difference (LSD) at a 0.05 level of probability. 37

RESULTS AND DISCUSSION

Experiment 1: Comparison of Ganada and P.I. 237110 at three constant temperatures.

Percent Germination

Across all temperatures Ganada had significantly (P>0.01) higher total germination than P.I. 237110, 69 and 61%, respectively (Figure 1). Germination for both germplasm was significantly (P< 0.001) different among temperatures. Mean germination percentages for both germplasms increased significantly as temperature increased (Figure 2). Temperature and germplasm interactions were non-significant (P>0.37). Indicating that both germplasms had similar reactions at each of the temperatures. Ganada and P.I. 237110 require high temperatures for optimum germination. At 15.6°C there was no germination for P.I. 237110 and Ganada required 6 days to initiate germination and reached less than 15% total germination. P.I. 237110 had a higher total germination at day 1 than Ganada for 21.1 and 32.2°C. At day 3 Ganada's total germination equaled or exceeded P.I. 237110. P.I. 237110 appears to have a higher initial germination rate than Ganada at 21.1 and 32.2°C.

Ahring (1972) has shown that yellow bluestem germination percentages are significantly increased when germinated without seed 38

75 r

GANADA PI 237110 GERMPLASM

Figure 1: Mean total germination for Ganada and P.I. 237110 yellow bluestem averaged across three constant temperatures of 15.6,21.1, and 32.2°C. Means with same letter are not significantly different at the 0.05 level of significance. 39

100 J 90 ••

80 •• e z 70 -• o 60 50 •• 40 •• 30 -- o43 20 -• B 10 •• 0 -- + 32.2 21.1 15.6 TEMPERATURE (C)

Figure 2: Mean total germination at three constant temperatures for Ganada and P.I. 237110 yellow bluestem. Means with the same letter are not significantly different at the 0.05 level of significance. 40

appendages and under an alternating temperature of 20/30°C. Cole et al. (1974) evaluated the optimum temperature for germination of sideoats grama. He found that an alternating temperature of 20 and 30°C produced maximum germination. Butler (1985) evaluated buffelgrass (Cenchrus ciliaris L.) germination across five temperatures and found that maximum germination percentages occurred with an alternating temperature of 20/35°C or at a constant temperature of 25°C.

Time to 50% Germination

Ganada and P.I. 237110 had significantly (PO.OOl) different time requirements to reach 50% germination. Ganada required more time than P.I. 237110 to reach 50% of total germination. As temperatures increased both germplasm required less time to reach 50% of total germination. Both germplasm sources had a significantly (PO.OOl) different germination response to temperature. Approximate time to 50% of total germination for Ganada was 7.33,1.68, and 0.98 days for 15.6, 21.1, and 32.2°C, respectively (Figure 3). For P.I. 237110 the approximate time to 50% of total germination was 1.7 and 0.78 days for 21.1 and 32.2°C, respectively (Figure 3). There were significant differences between Canada and P.I. 237110 at 15.6 and 32.2°C and no significant differences at 21.1°C. At 21.1 and 32.2° C P.I. 237110 reached 50% of total germination faster than Ganada. P.I. 237110 requires less germination time than Ganada under hot incubation temperatures. PI 237110D GANADA

^ N o VI >; On < ., a 00 7.33 w Q 'O H z oN-N •• m 1.7 1.68 s CN 0.78 0-98 O 0 s O J* 15.6 21.1 32.2 TEMPERATURE (C)

Figure 3: Time to 50% of total germination for Ganada and P.I. 237110 yellow bluestem. Comparison of all means LSD(0.05) = 016. 42

Rapid germination has been suggested by Wright (1980) and Koller and Negbi (1957) as a desirable characteristic for establishment under stress environments. On the other hand, Major and Wright (1974) suggested that dormancy and or a slow germination rate were desirable for establishment under environments with limited, sporadic moisture and high temperatures. Rapid and uniform germination is a desirable characteristic for cultivated plants Harlan (1992) and may provide a competitive edge in a wildland setting if favorable environmental conditions are of adequate duration for rapid germination and plant establishment. 43

Experiment 2: Comparison of respiration rates for Ganada and P.I. 237110 under four osmotic potentials.

Dark respiration rates averaged across four osmotic potentials show that Ganada has a significantly (P>0.02) higher rate than P.I. 237110 with 66.1 and 45.6 mg L~1 g~l min"l, respectively. Respiration rates averaged for both germplasms were significantly (P<0.001) different. Mean respiration rates averaged for both germplasm were 160.1, 57.4, 3.3, and 2.6 mg L~1 g~* min"l for osmotic potentials of 0, -0.4, and -0.8 MPa, respectively. There were no significant differences between -0.8 and -1.2 MPa.

Osmotic potential and germplasm interactions were significantly (P>0.04) different. Ganada had significantly higher respiration than P.I. 237110 at 0 and -0.4 MPa. At -0.8 and -1.2 MPa P.I. 237110 had higher respiration rates than Ganada but the differences were not significantly different (Figure 4). Decreasing respiration rates with increasing osmotic concentrations follows results by Bar-Adon (1974). He found that as sodium chloride concentrations increased respiration of alfalfa (Medicago sativa L.) decreased. Figure 4 shows a steady decrease in respiration for P.I. 237110 and Ganada. However, the -0.8 and -1.2 MPa readings for Ganada show zero at -0.8 and then a slight increase in CO^ production at -1.2 MPa. • 0 • -0.4 • -0.8 • -1.2

200 r 179.6

140.5 g 150 - - 1—HH 100 84.1 Oh VI e W 50 •• 30.8 0 0.8 6.6 4.5 0 - GANADA PI 237110 GERMPLASM

Figure 4: Seed respiration rates for Ganada and P.I. 237110 yellow bluestem for four osmotic potentials (0, -0.4, -0.8, and -1.2 MPa). Comparison of all means LSD (0.05)= 34.3. 45

Kittock and Law (1968) found a positive correlation between respiration and seedling vigor for wheat (Triticum aestivum (Host) MacKey) seed. Higher seed respiration rates may be associated with greater seedling vigor and increased probability of plant establishment. In this experiment and based on the above information, Ganada would be the logical choice for reseeding efforts. However, work at the TPMC has indicated that P.I. 237110 has higher percent stand ratings and higher rates of biomass production (Munda 1987). Dobrenz et al. (1993) evaluated 11 cotton cultivars for seedling respiration rates and germination percentage. They found that those cultivars which had the highest germination rate had the lowest respiration rates. This negative correlation suggests that a low respiration rate may be a useful tool for evaluating seedling vigor and seed quality. Especially, if seed lots of test material are of equal purity and percent germination. 46

Experiment 3: Comparison of Ganada and P.I. 237110, Vaughn sideoats grama, and Cochise lovegrass.

Percent Germination

Mean total germination was significantly (PO.OOl) different for all germplasm. P.I. 237110 had the highest total germination (98%) of all tested germplasm (Figure 5). Ganada was significantly lower than P.I. 237110 even though the same seed lot from experiment 1 was used. Two factors may explain the variation. First, the seed lots were 2 years older and there may have been a decline in seed viability. Second, the incubation temperature was 35°C and may be above Ganada's optimum temperature for maximum germination. Ganada and Cochise were not significantly different from each other but had significantly lower germination compared to P.I. 237110 and Vaughn. Vaughn had the second highest germination (94.3%) and was significantly different from all other germplasm. The high germination of Vaughn sideoats grama at 35°C supports findings by Cole et al. (1974) that sideoats grama has a wide temperature band (22 to 37°C) for optimum germination.

Time to 50% germination

Time to reach 50% of total germination was significantly (PO.OOl) different for all germplasm. Approximate time to 50% of total germination 47

100 T

95 + £ Z ONH 90 +

75 -I llllli mi millllfll 1 — 1 "••••''inn—.iii. h .lU.iliNiiiiiiliiiisiuUiMlUmlllillij 237110 VAUGHN GANADA COCHISE GERMPLASM

Figure 5: Mean total germination for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, and Cochise lovegrass at an alternating temperature of 35°C (8h) and 20°C (16h). Means with same letter are not significantly different at the 0.05 level of significance. 48 for P.I. 237110, Ganada, Vaughn, and Cochise were 1.49,1.63, 1.37, and 2.4 days, respectively (Figure 6). P.I. 237110 had the second fastest time to reach 50% of total germination and was significantly faster than Ganada. In comparison with experiment 1: P.I. 237110 and Ganada required longer incubation times to achieve 50% total germination and Ganada had lower total germination while P.I. 237110 had a higher total germination. Suggestions for the above differences are: older seed lots and, in the case of Ganada, a potential decline in seed viability, and a different incubation temperature (constant 32.2°C vs. an alternating 35 and 20°C). Temperatures above 32°C may reduce Ganada's germination while appearing to increase germination for P.I. 237110. Vaughn had the shortest time to 50% of total germination which again attests to its ability to germinate rapidly under a wide range of temperatures. However, by day 3 P.I. 237110 had exceeded Vaughn for total germination. Cochise had the slowest time to 50% of total germination with 2.4 days or 58 h. Weaver and Jordan (1985) determined that Cochise had one of the fastest germination rates of the lovegrass species. Achieving 50% germination in 42 hours, which was much faster than germination rates in this experiment. Suggestions for the differences are: seed lots vary in their viability and germination capacity, and they used a constant temperature of 20°C compared to an alternating temperature of 35 and 20°C. In this experiment higher temperatures and less viable seed may have reduced its germination. • COCHISE • PI 237110 • GANADA • VAUGHN

(S ts • •

m ©

COCHISE PI 237110 GANADA VAUGHN GERMPLASM

Figure 6: Time to 50% of total germination for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, and Cochise lovegrass. Means with the same letter are not significantly different at the 0.05 level of significance. 50

Experiment 4: Comparison of Ganada and P.I. 237110, cane bluestem, Vaughn sideoats grama, and Arizona cottontop across three seed conditioning treatments.

Percent Germination

Mean total germination for the three seed conditioning treatments was significantly (P<0.001) different among the germplasm sources. Total germination was 96.8, 89.7, 79.9, 79.8, and 70.8% for P.I. 237110, Ganada, Arizona cottontop, Vaughn, and cane bluestem, respectively. Different seed lots for P.I. 237110 and Ganada were used for this experiment compared to experiments 1 and 3. P.I. 237110 had the highest germination rate for all germplasm and was significantly higher than Ganada. The incubation temperature (35°C) used in this experiment may be too high for optimum germination of Ganada. Arizona cottontop exhibited high germination as compared to findings by Tapia and Schmutz (1971). They evaluated Arizona cottontop at a germination temperature of 25°C and had low germination (<6%). They attributed these results to age of the seed and not the incubation temperature. Seed conditioning was not mentioned in the article.

Mean total germination for all germplasm showed that seed conditioning treatments were significantly (P0.001) different. However, the caryopsis and brush treatments were not significantly different. The control had significantly lower germination. The caryopsis treatment had the highest 51 percent germination followed by the brush machine and control with 89.7, 85.7, and 74.8%, respectively.

Germplasm and seed conditioning treatment interaction was significantly (P>0.004) different (Table 1). All germplasm had increases in percent germination as severity of seed conditioning increased. Seed conditioning treatment had little effect on total germination for P.I 237110 and Ganada. Little difference was found between the conditioning classes which indicates seed can be used with or without seed conditioning as long as it is dried so potential germination inhibitors are volitalized. Cane bluestem and Vaughn sideoats grama had the highest germination increases as seed conditioning increased. Cane bluestem did not have a significant increase in germination from the control to the brush treatment. These results suggest the potential of a germination inhibitor within the seed appendages. Vaughn had significant germination differences between the control and all other seed treatments. For Vaughn, seed conditioning which retains part of the seed appendages (glumes or lemma and palea) can be used to minimize damage to caryopsis without reducing total percent germination. The brush treatment retained the lemma and palea around the caryopsis. These results suggest the germination inhibitor must be in the glumes or outer bracts. Arizona cottontop had significant increases in germination from the control to the caryopsis treatment with the brush treatment not significantly different from the other seed treatments. Table 1: Mean total germination for control, brush, and caiyopsis treatment for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, Arizona cottontop, and cane bluestem.*

GERMPLASM SEED CONDITIONING TREATMENT

CONTROL BRUSH CARYOPSIS

CANE 58.8 70.3 83.3 BLUESTEM ARIZONA 71.8 82.3 85.8 COTTONTOP GANADA 90.5 92.8 85.8 P.I. 237110 92.8 98.5 99.0 VAUGHN 60.3 84.5 94.5

* Comparison of all means LSD (0.05) =11.89 53

Removal of the cotton-like pubescence from Arizona cottontop seed improves its handling and seeding characteristics and it appears not reduce its total germination.

Removing all seed appendages increased mean germination for all germplasm. Mean germination of P.I. 237110 and Ganada were similar for all seed conditioning treatments. Ahring and Harlan (1961a) found that germination of yellow bluestem was increased with the removal of the seed appendages. Ahring (1972) and Ahring et al. (1975) have shown that inhibitory substances in the bracts were in part responsible for inhibiting germination of fresh seed. Seed used in this experiment was at least 4 months old which may be of adequate time for the inhibitory substances to have volitalized.

Time to 50% Germination

Mean time to 50% of total germination was significantly (P<0.001) different for all germplasm. Cane bluestem and Vaughn sideoats grama were not significantly different from each other with 2.9 and 2.7 days, respectively, to reach 50% of total germination. Vaughn, Ganada, and Arizona cottontop were not significantly different from each other with 2.7, 2.4, and 2.4 days, respectively, to reach 50% of total germination. P.I. 237110 was significantly different from all other germplasm and had the fastest time (1.3 days) to reach 50% of total germination. 54

Time to 50% germination was significantly (PO.OOl) for all seed conditioning treatments. The caryopsis treatment had the slowest time (2.99 days) to reach 50% of total germination. The brush treatment required an average of 2.4 days to reach 50% of total germination. The caryopsis treatment was the fastest requiring 1.6 days to reach 50% of total germination.

The interaction between germplasm and seed conditioning treatments was significantly (PO.OOl) different. Cane bluestem had the second slowest time to 50% germination for all seed conditioning treatments (Table 2) with the brush significantly slower than the control. Potential germination inhibitors within the seed appendages may partially explain the slower times for the control and brush treatments compared with the caiyopsis treatment.

Time to 50% of total germination for Arizona cottontop decreased with increasing severity of the seed conditioning treatment. There was no significant differences between the control and brush treatments. Due to the fluffy nature of this species it would desirable to devise a system that could remove the appendages without damaging the caryopsis, reducing viability, and maintain similar germination characteristics as non-modified seed. The brush machine treatment appears to obtain these desirable features. Based on limited information, storing brush machine treated seed indicates little to no reduction in shelf life. Experimental results show brush machine treated seed 55

Table 2: Time (incubation days) to 50% of total germination for P.I. 237110 and Ganada yellow bluestem, Vaughn sideoats grama, Arizona cottontop, and cane bluestem for three seed conditioning treatments.*

GERMPLASM SEED CONDITIONING TREATMENT

CONTROL BRUSH CARYOPSIS CANE 3.0 3.8 1.9 BLUESTEM ARIZONA 2.9 2.6 1.6 COTTONTOP GANADA 2.5 2.6 2.2 P.I. 237110 1.5 1.2 1.1 VAUGHN 5.1 1.8 1.2

""Comparison of all means LSD (0.05) = 0.69 56 has a minimal decrease in time to 50% of total germination but an increase in total germination compared to the control treatment. Seed treatments did not significantly affect the germination of Ganada (Table 2). These results indicate that one could use any type of conditioned seed and potentially achieve the same results. P.I. 237110 had no significant differences between seed conditioning treatments. Time to 50% of total germination decreased with increasing seed conditioning severity. P.I. 237110 had the fastest time to reach 50% of total germination for all germplasm and seed conditioning treatments. Like Ganada, it appears you could use any type of conditioned seed and achieve similar results. If rapid germination is the key to plant establishment than P.I. 237110 should excel in revegetation practices. However, if slow germination is the key then this species should be used were supplemental moisture can be provided to assure establishment. The control treatment for Vaughn sideoats grama had the slowest time to reach 50% of total germination out of all the germplasm and seed conditioning treatments. The brush and control seed conditioning treatments for Vaughn were significantly different. The amount of time to reach 50% of total germination decreased as seed conditioning severity increased (Table 2). Brush and caryopsis seed conditioning improved overall germination for Vaughn and greatly decreased the time to 50% germination. Vaughn's increase in total germination due to seed conditioning supports Major and Wright (1974) work which showed that long term dormancy was broken upon removal of floral parts from the caryopses. The brush machine treated seed retained the lemma and palea around the caryopsis. The brush treatment was not significantly different from the caryopsis treatment. 57

SUMMARY

Four experiments were performed comparing six warm season grass species that are being used for range revegetation and erosion control on critically eroding areas. P.I. 237110 yellow bluestem, Arizona cottontop, cane bluestem, and Cochise lovegrass are plant materials developed or being evaluated at the TPMC. Vaughn sideoats grama and Ganada yellow bluestem are released cultivars from the Los Lunas PMC near Albuquerque, New Mexico. Total percent germination and time to 50% germination were measured in relation to seed conditioning treatments. Dark respiration was measured for germinating seed, Ganada and P.I. 237110, exposed to PEG 6000 induced osmotic potentials of 0, -0.4, -0.8, and -1.2 MPa to simulate drought.

In experiment 1, total percent germination was measured for Ganada and P.I. 237110 at three constant temperatures. Ganada had higher mean germination percentage compared to P.I. 237110 for all temperatures. Mean germination increased as temperature increased. P.I. 237110 had a faster germination rate than Ganada at 21.1 and 32.2°C. P.I. 237110 did not germinate at 15.6°C.

In experiment 2, respiration rates for Ganada and P.I. 237110 were compared across four osmotic concentrations. Ganada had a higher respiration rate at 0 and -0.4 MPa. At -0.8 and -1.2 MPa Ganada and P.I. 237110 were not significantly different. Dobrenz et al. (1993) evaluated 58

cotton seedling respiration and germination percentage. They determined that a negative correlation existed between seedling respiration and germination percentage. This information suggests that P.I. 237110 may be the suitable plant for seeding in environments that require fast germination and strong seedling vigor.

In experiment 3, P.I. 237110 had the highest germination while Vaughn had the most rapid germination. Ganada and Cochise were significantly lower in total germination and slower to reach 50% germination compared to P.I. 237110. The high temperature (35°C) may partly explain the germination differences. Vaughn and P.I. 237110 appear to have a wide temperature range for optimum germination. Optimum temperature for P.I. 237110 is between 25 and above 35°C.

Experiment 4 compared the germination of P.I. 237110, Ganada, cane bluestem, Vaughn, and Arizona cottontop using three seed conditioning treatments. P.I. 237110 had the highest total germination for all germplasm and seed conditioning treatments. Seed conditioned to caryopsis had the highest total germination. Caryopsis treatment had the fastest time to 50% germination for all germplasms. Brush treatment had the slowest time to 50% germination for cane bluestem, and Ganada. The control treatment had the slowest time to 50% germination for Arizona cottontop, P.I. 237110, and Vaughn. P.I. 237110 and Ganada showed little difference in time to 50% germination for caryopsis, brush, and control treatments. 59

REFERENCES

Abernethy, R.H., L.N. Wright and K. Matsuda. 1977. Association of seedling respiratory metabolism and adenykate energy charge with seed weight of Panicum antidotale Retz. Crop Sci. 17:563-566.

Adegbuyi, E., S. R. Cooper and R. Don. 1981. Osmotic priming of some herbage grass seed using polyethylene glycol (PEG). Seed Sci. & Technol. 9:867-878.

Ahring, R.M. 1972. The Influence of glume constituents on seed germination in two Old World bluestems, Bothriochloa ischaemum (L.) Keng, and B. intermedia A. Camus. University of Nebraska, Lincoln, Nebraska ( Diss. Abstr. AAD72-27377)

Ahring, R.M. and J.R. Harlan. 1961a. Germination characteristics of some accessions of Bothriochloa ischaemum L. Oklahoma Agr. Exp. Sta. Tech. Bull. No. 89.

Ahring, R.M. and J.R. Harlan. 1961b. Germination studies on the Dichanthium annulatum complex. Oklahoma Agr. Exp. Sta. Tech. Bull. No. 90. 60

Ahring, R.M., J.D. Eastin and C.S. Garrison. 1975. Seed appendages and germination of two asiatic bluestems. Agron. J. 67:321-325.

Akamine, E.K. 1944. Germination of Hawaiian range grass seeds. Hawaii Agr. Exp. Sta. Tech. Bull. No. 2.

Allen, S.G., A.K. Dobrenz and P.G. Bartels. 1986. Physiological response of salt-tolerant and nontolerant alfalfa to salinity during germination. Crop Sci. 26:1004-1008.

Bar-Adon, Moshe. 1974. Seed germination, respiration and mitochondrial efficiency of three alfalfa (Medicago sativa L.) cultivars subjected to NaCl salinity. M.S. Thesis. University of Arizona, Tucson, Arizona . p. 34.

Bewley. J.D. and M. Black. 1986. Seeds: physiology of development and germination. Plenum Press, New York and London.

Booth, T.D. 1984. Threshing damage to radicle apex affects geotropic response of winterfat. J. Range Manage. 37:222-225.

Booth, T.D. 1987. Diaspores of rangeland plants: ecology and management. P.202-211. In G. W. Frasier and R.A. Evans (ed.) Proceedings of Symposium "Seed and Seedbed Ecology of Rangeland Plants", Tucson, AZ. 21-23 April. 1987 U.S.D.A., A.R.S. 61

Booth, T.D. and G.E. Schuman. 1983. Seedbed ecology ofwinterfat: fruits versus threshed seeds. J. Range Manage. 36:387-390.

Burton, G.W. 1939. Scarification studies on southern grass seeds. Amer. Soc. of Agron. J. 31:179-187.

Butler, J.E. 1985. Germination of buffel grass (Cenchrus ciliaris). Seed Sci. andTechnol. 13:583-591.

Ching, T.M. and W.E. Kronstad. 1972. Varietal differences in growth potential, adenylate energy level, and energy charge of wheat. Crop Sci. 12:785-789.

Christoff, M.A. 1976. Apomixis and the polyembryony in Bothriochloa ischaemum (L.)Keng. Genetics and Plant Breeding. 5:71-84.

Cole, D.F., R.L. Major and L.N. Wright. 1974. Effects of light and temperature on germination of sideoats grama. J. Range Manage. 27:41-44.

Cox, J.R. and R.D. Madrigal. 1988. Establishing perennial grasses on abandoned farmland in southeastern Arizona. Appl. Agric. Res. 3:36- 43. 62

Cox, J.R., H.L. Morton, T.N. Johnsen, Jr., G.L. Jordan, S.C. Martin and L.C. Fierro. 1982. Vegetation restoration in the Chihuahuan and Sonoran Deserts of North America. ARM-W-28, Agric. Res. Serv., Western Region, Oakland, California.

Coyne, P.I. and J.A. Bradford. 1985. Morphology and growth in seedlings of several C4, perennial grasses. J. Range Manage. 38:504-512.

Cress, W.A. and G.V. Johnson. 1986. The effect of three osmotic agents on free proline and amino acid pools in Atriplex canescens and Hilaria jamesii. Can. J. Bot. 65:799-801.

Crocker, W. 1906. Role of seed coats in delayed germination. Bot. Gaz. 42:265-291

Dobrenz, A.K., J.C. Silvertooth and J. Martin. 1993. Germination and respiration of cotton seed produced in Arizona. University of Arizona Coop. Ext. Serv., Annual Cotton Report (In Press).

Emmerich, W.E. and S.P. Hardegree. 1990. Polyethylene glycol solution contact effects on seed germination. Agron. J. 82:1103-1107.

Emmerich, W.E. and S.P. Hardegree. 1991. Seed germination in polyethylene glycol solution: effects on filter paper exclusion and water vapor loss. Crop Sci. 31:454-458. 63

Evenari, M., E. Konis and S.B. Ullman. 1942. The inhibitors of germination. Chron. Bot. 7:149-150.

Frasier, G.W., D.A. Woolhiser and J.R. Cox. 1984. Emergence and seedling survival of two warm-season grasses as influenced by the timing of precipitation: A greenhouse study. J. Range Manage. 37:7-11.

Frasier, G.W., J.R. Cox and D.A. Woolhiser. 1985. Emergence and survival response of seven grasses for six wet-dry sequences. J. Range Manage. 38:372-377.

Fitter, A.H. and R.K.M. Hay. 1991. Environmental physiology of plants. 2nd ed. Academic Press Inc., San Diego, CA.

George, D.W. 1961. Influence of germination temperature on the expression of post-harvest dormancy in wheat, p. 15. In Crop Sci. abstracts. CSSA, Madison, WI.

Gould, F.W. and R.B. Shaw. 1983. Grass Systematics. 2nd ed. Texas A&M University Press, College Station, TX.

Gove, P.B., editor. 1981. Webster's Third New International Dictionaiy of the English language-unabridged. Merriam-Webster Inc., Publishers. Springfield, Mass. 64

Griswold, S.M. 1936. Effect of alternate moistening and drying on germination of seed of western range plants. Bot. Gaz. 98:243-269.

Gutterman, Y., A. Witztum and M. Evenari. 1967. Seed dispersal and germination in Blepharis persica (Burm.) Kuntze. Israel J. Botany. 16:213-234.

Haferkamp, M.R., G.L. Jordan and K. Matsuda. 1977a. Physiological development of Lehmann Lovegrass seeds during initial hours of imbibition. Agron. J. 69:295-299.

Haferkamp, M.R., G.L. Jordan and K. Matsuda. 1977b. Pre-sowing seed treatments, seed coats, and metabolic activity of Lehmann Lovegrass seeds. Agron. J. 69:527-530.

Harlan, J.R. 1992. The dynamics of domestication. In J.R. Harlan Crops and Man. 2nd ed. ASA, and CSSA, Madison, WI.

Harper, J.L., J.T. Williams and G.R. Sagar. 1965. The behavior of seeds in soil. 1. The heterogeneity of soil surfaces and its role in determining the establishment of plants from seed. J. Ecol. 53:273-286.

Harrington, G.T. 1923. The use of alternating temperature in the germination of seeds. J. Agric. Res. 23:295-332. 65

Herbal, C.H., G.H. Abernathy, C.C. Yarbrough and D.K. Gardner. 1973. Root Plowing and seeding arid rangelands in the southwest. J. Range Manage. 26:193-197.

Heydecker, W. 1967. Drought hazards to seed germination. Ann. Arid Zone 6:23-24.

Hitchcock, A.S. 1971. Manual of the grasses of the United States. 2nd ed. Dover Publications, Inc., New York. vol. 2.

Hull, A.C.,Jr. 1959. Pellet seeding of wheatgrass on southern Idaho rangelands. J. Range Manage. 12:155-163.

Humphrey, R.R. 1970. Arizona Range Grasses. Revised format 1970, University of Arizona Press, Tucson, Arizona.

Jackson, L.L., J.R. McAuliffe and B.A. Roundy. 1991. Desert Restoration. Restoration and Management Notes. 9:71-80.

Kittock, D.L. and A.G. Law. 1968. Relationship of seedling vigor to respiration and tetrazolium chloride reduction by germinating wheat seeds. Agron. J. 60:286-289. 66

Kocher, E. and J. Stubbendieck. 1986. Broadcasting grass seed to revegetate sandy soils. J. Range Manage. 39:555-557.

Koller, D. and A. Hadas. 1982. Water relations in the germination of seeds. Encyclopedia of Plant Physiol. 12b:401-431.

Koller, D. and M. Negbi. 1957. Germination of seeds of desert plants. Final report to USD A, project no AlO-FS-6, Department of Botany, Hebrew university, Jerusalem, Israel.

Koller, D., A.M. Mayer, A. Poljakoff-Mayber and S. Klein. 1962. Seed germination. Ann. Rev. of Plant Physiol. 113:437-464.

Lock, J.M. and T.R. Milburn. 1971. The seed biology of Themeda triandra Forsk. in relation to fire. Symp. Brit. Ecol. Soc. 11:337-349.

Maguire, J.D. 1962. Speed of germination-aid in selection and evaluation for seedling emergence and vigor. Crop Sci. 2:176-177.

Major, R.L. and L.N. Wright. 1974. Seed dormancy characteristics of sideoats gramagrass, Bouteloua curtipendula (Michx.) Torr. Crop Sci. 14:37-40.

Michel, B.E. and M. R. Kaufmann. 1972. The osmotic potential of polyethylene glycol 6000. Plant Physiol. 51:914-916. 67

Munda, B.D. 1987. Documentation of a plant accession selected for advanced testing- Bothriochloa ischaemum P.I. 237110. USDA-SCS Tucson Plant Materials Center, Tucson, AZ.

Munda, B.D., M.J. Pater and F.A. Archuleta. 1991. Annual technical report. USDA-SCS Tucson Plant Materials Center, Tucson, AZ.

Nazarenko, G.F. and R. M. Djadjun. 1934. Dormancy in seed. Semenovodsto 6:45-46.

Peart, M.H. 1979. Experiments on the biological significance of the morphology of seed-dispersal units in grasses. J. Ecology. 67:843-863.

Peart, M.H. 1981. Further experiments on the biological significance of the morphology of seed-dispersal units in grasses. J. Ecology. 67:425-436.

Roberts, E.H. 1961. Dormancy of rice seed. I. The distribution of dormancy periods. J. Exp. Bot. 12:319-329.

Robinson, D.L. 1986. Recurrent selection for germination salt tolerance in alfalfa. MS thesis. University of Arizona, Tucson, Arizona, p 46-47.

Roundy, B.A. 1983. Response of basin wildrye and tall wheatgrass seedlings to salination. Agron. J. 75:67-71. 68

Roundy, B.A. and C.A. Call. 1988. Revegetation of arid and semiarid rangelands. p. 607- 635. In P.T. Tueller (ed.) Vegetation science applications for rangeland analysis and management. Kluwer Academic Publishers, Dordrecht, Boston, London.

Roundy, B.A., J.A. Young and R.A. Evans. 1985. Germination of basin wildrye and tall wheatgrass in relation to osmotic and matric potential. Agron. J. 77:129-135.

Sapahkevich, P. V. 1961. Dormancy in seeds and the position of flowering plants in the phylogenetic system. (In: Morfogenez rastenii. Plant morphogenesis.) Moskov. Univ.: Moscow. 2: 468-472.

Schultz, Q.E. and R.C. Kinch. 1976. The effects of temperature, light, and growth promoters on seed dormancy in western wheatgrass seed. J. Seed Tech. 1:79-85.

Sheldon, J.C. 1973. The behavior of seeds in soil. J. Ecology 62:47-66.

Sheldon, J.C. and F.M. Burrows. 1973. The dispersal effectiveness of achene-pappus units of selected compositae in steady winds with convection. New Phytol. 72:665-675. 69

Simon, E.W. 1984. Early events in germination. In D.R. Murray Seed Physiology: Germination and reserve mobilization. Vol.2. Academic Press Australia.

Sumner, D.C. and R.D. Cobb. 1962. Post harvest dormancy of Coronado sideoats grama Bouteloua curtipendula (Michx.) Torr. as affected by storage temperature and germination inhibitors. Crop Sci. 2:321-325.

Taliafero, C.M., J.R. Harlan and W.L. Richardson. 1972. Plains bluestem. Oklahoma State Univ. Agricultural Experiment Station Bulletin B-699.

Tapia, C.R. and E.M. Schmutz. 1971. Germination responses of three desert grasses to moisture stress and light. Jour. Range Manage., 24:292-295.

Thacker, G.W. and J.R. Cox. 1992. How to establish a permanent vegetative cover on farmland. University of Arizona, Cooperative Extension Service Bulletin 191051.

Thornton, N.C. 1945. Importance of oxygen supply in secondary dormancy and its relation to the inhibiting mechanism regulating dormancy. Contrib. ofBoyce Thompson Inst. 13:487-501.

Thurston, J.M. 1960. Dormancy in weed seeds. Symp. Brit. Ecol. Soc. 1:69- 82. 70

Tran, V.N. and A.K. Cavanagh. 1984. Seed Physiology-Vol. 2-Germination and Reserve Mobilization. (Australia : Academic Press, 1984) p 1-5.

Tucker, H. and L.N. Wright. 1965. Estimating rapidity of germination. Crop Sci. 5:398-399.

USDA-SCS. 1942. Regrassing for soil protection in the southwest. Farmers Bull. 1913. Washington, DC.

Vertucci, C.W. 1989. The kinetics of seed imbibition: controlling factors and relevance to seedling vigor. Seed Moisture [edited by P.C. Stanwood and M.B. McDonald]. 93-115. CSSA Special Publication No 14. Madison, Wisconsin USA; Crop Science Society of America.

Voigt, P.W., C.R. Tischler and B.A. Young. 1987. Selection for improved establishment in warm season grasses, p. 177-187. In G.W. Frasier and R.A. Evans (ed.) Proceedings of Symposium "Seed and Seedbed Ecology of Rangeland Plants", Tucson, AZ. 21-23 April 1987. U.S.D.A., A.R.S.

Vose, P.B. 1962. Delayed germination in reed canarygrass Phalaris arundinacea L. Ann. Bot. 26:102.

Waller, S.S. and J.K. Lewis. 1979. Occurrence of C3 and C4 photosynthetic pathways in north American grasses. J. Range Manage. 32:12-28. 71

Weaver, L.C. and G.L. Jordan. 1985. Effects of selected seed treatments on germination rates of five range plants. J. Range Manage. 38:415-418.

Woodstock, L W. 1965. Initial respiration rates and subsequent growth in germinating corn seedlings. Bioscience 15:783-784.

Wright, L.N. 1971. Drought influence on germination and seedling emergence, p. 19-44. In Drought injury and resistance in crops. CSSA, Spec. Pub. No. 2. Madison, WI.

Wright, L.N. 1975. Improving range grasses for germination and seedling establishment under stress environments, p. 3-22. In R.S. Campbell and C.H. Herbel (eds.) Improved plants. Soc. Range Manage., Range Symp. Ser. No. 1.

Wright, L.N. 1980. Germination rate and growth characteristics of blue panic grass. Crop Sci. 20:42-44.

Wright, L.N. and A. A. Baltensperger. 1964. Influence of temperature, light radiation, and chemical treatment on laboratory germination of black gramagrass seed, Bouteloua eriopoda Torr. Crop Sci. 4:168-171. 72

Young, J.A., R.A. Evans and B.L. Kay. 1975. Dispersal and germination dynamics of broadleaf filaree, Erodium botrys (Cav.) Bertol. Agron. J. 67:54-57.

Young, J.A., R.A. Evans, R.O. Gifford and R.E. Eckert Jr. 1970. Germination characteristics of three species of Cruciferae. Weed Sci. 18:41-48.

Young, J. A., R.A Evans, B. Roundy and G. ClufF. 1983. Moisture stress and seed germination. USDA-ARS ARM-W-36. Oakland, CA.