and fruit set. An important Requirement for Pollenizer in New Monoecious aspect of the pollenizer is the ability to Hybrid ‘NC-Sunshine’ produce enough staminate flowers to pollinate the available pistillate flowers, and 12% to 15% monoecious - Todd C. Wehner and Rakesh Kumar1 izers are used in the field to pollinate highly gynoecious . How- ever in comparison, 25% to 33% of ADDITIONAL INDEX WORDS. Cucumis sativus, gynoecious, pistillate, pollination, isolation pollenizer is planted to ensure ade- quate pollen supply for triploid water- SUMMARY. Monoecious cucumber (Cucumis sativus) generally produce melon (Citrullus lanatus) production enough pollen for fruit set. The amount of pollen required for fruit set depends on (Fiacchino and Walters, 2003; Walters, the number of pistillate flowers produced by the . ‘NC-Sunshine’ is a new 2005). Therefore, it is important to monoecious slicing hybrid cucumber with a high percentage of pistillate nodes. determine if planting a pollenizer in Because of the high percentage of pistillate nodes, a pollenizer might be required to maximize pollination to get high total and early yield. Hence, an experiment was the field will significantly increase yield conducted at three locations to evaluate the effect of the pollenizer ‘Poinsett 76’ on of ‘NC-Sunshine’. yield of ‘NC-Sunshine’ compared with no pollenizer ‘Gray Zucchini’ squash Cucumber is an allogamous crop (Cucurbita pepo). Differences (P ‡ 0.05) due to pollenizer, location, and the that requires frequent () interaction of pollenizer and location on ‘NC-Sunshine’ yield traits were detected. visit to carry pollen for fertilization. Pollenizer influenced cucumber yield at two of three locations. Results indicated Honeybees (Apis mellifera) and bum- that the pollenizer ‘Poinsett 76’ significantly increased total, marketable, and early blebees (Bombus terrestris) are the yield of ‘NC-Sunshine’. The percentage of early and marketable yield was also main pollinators in (Gajc- higher with the pollenizer ‘Poinsett 76’. In addition, the use of a pollenizer Wolska et al., 2011). The absence of decreased cull yield. Therefore, a pollenizer is needed for monoecious hybrids sufficient pollinators can result in having a high percentage of pistillate nodes. low fruit set and reduced fruit size (Walters and Taylor, 2006). Moreover, reeding for increased yield in pistillate nodes. The has medium pistillate flowers require multiple cucumber has been an impor- dwarf size vines with short hypocotyls visitations after visiting male flowers Btant objective of many cucum- and dark green leaves, and a dwarf- (Stanghellini et al., 1997, 1998). In ber breeding programs since the 1900s determinate plant type (Wehner, 2005). triploid seedless watermelon, 16 to 24 (Staub et al., 2008). Yield of pickling ‘NC-Sunshine’ is a F1 hybrid of NC- honeybee visits are required to achieve cucumber has been improved by breed- 62 (dwarf-determinate, monoecious) · maximum fruit set at a 33% pollenizer ing for disease resistance, as well as NC-63 (dwarf-determinate, monoe- frequency (Walters, 2005). through the use of improved cultural cious). These inbreds were developed Climatic factors have also been practices (Lower and Edwards, 1986; at North Carolina State University. The reported to influence pollen flow Peterson, 1975; Staub et al., 2008; fruit of ‘NC-Sunshine’ have good fresh (Gingras et al., 1999; Whitakar and Wehner, 1989). The increased yield market quality and good keeping ability Bohn, 1952). Wind velocity, temper- of cucumber cultivars has also been with very dark green fruit averaging ature, and other environmental fac- achieved through improvements in 8 inches in length. ‘NC-Sunshine’ is tors may influence honeybee behavior gynoecious sex expression, improved resistant to anthracnose (Colletotrichum thereby affecting pollination; and un- fruit color (improved percentage of sp.), powdery mildew (Sphaerotheca favorable environmental conditions marketable fruit), and direct yield im- fuliginea), and scab (Cladosporium such as extreme temperature, mois- provement (Wehner, 1989). cucumerinum). ture stress, and low irradiance can Although cucumber plants pro- The amount of pollen required result in flower abortion and low fruit duce different sex phenotypes (Staub for fruit set depends on the number of set (Kalbarczyk, 2009). Wehner and et al., 2008), the wild type is monoe- pistillate flowers produced by the cu- Jenkins (1985) reported that the mean cious with staminate flowers appearing cumber cultivar. Generally, monoe- rate of natural outcrossing varied from first, followed by pistillate flowers at cious cucumber plants are planted in 23% to 77% across three locations in later nodes. ‘NC-Sunshine’ is a monoe- the field, and plants produce enough cucumber families. Therefore, it is cious, early maturing, and high yielding pollen for fruit set. Since ‘NC-Sun- imperative to study the effect of pol- slicing hybrid with a high percentage of shine’ produces more pistillate flowers lenizers in different environmental than regular monoecious cultivars, it conditions (locations) and the interac- Department of Horticultural Science, North Carolina might need more pollen for effective tion of pollenizer with location. State University, Raleigh, NC 27695-7609 The research reported in this publication was funded in part by the North Carolina Agricultural Research Service. Units To convert U.S. to SI, To convert SI to U.S., The authors gratefully acknowledge the technical assistance of Ms. T.L. Ellington. multiply by U.S. unit SI unit multiply by The use of trade names in this publication does not 0.3048 ft m 3.2808 imply endorsement by the North Carolina Agricul- 2.54 inch(es) cm 0.3937 tural Research Service, nor criticism of similar ones 25.4 inch(es) mm 0.0394 not mentioned. 1.1209 lb/acre kgÁha–1 0.8922 1Corresponding author. E-mail: rakesh.kumar@syngenta. 1.6093 mile(s) km 0.6214 com. 2.2417 ton/acre MgÁha–1 0.4461

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‘NC-Sunshine’ was planted in field plots with ‘Poinsett 76’ as the pollenizer and ‘Gray Zucchini’ squash as the control. ‘Poinsett 76’ is a mon- oecious slicing cucumber type with excellent color and is resistant to downy mildew (Pseudoperonospora cubensis), powdery mildew, anthracnose, and an- gular leaf spot (Pseudomonas syringae pv. lachrymans). ‘Gray Zucchini’ is an early maturing squash with a bushy habit similar to ‘NC-Sunshine’ and also has long, straight fruit. The objective of Fig. 1. Layout of ‘NC-Sunshine’ cucumber (N) plots in isolation blocks of ‘Poinsett this study is to evaluate the effect of the 76’ (P) cucumber and ‘Gray Zucchini’ squash (Z) pollenizer treatments at three pollenizer ‘Poinsett 76’ on fruit set and locations in North Carolina (Clinton, Oxford-North, and Oxford-South). yield of ‘NC-Sunshine’ cucumber. ‘Poinsett 76’ cucumber was treated as the pollination treatment, whereas ‘Gray Zucchini’ squash was the no pollination treatment. Each isolation block had seven Materials and methods rows where two rows of ‘NC-Sunshine’ cucumber were alternated with a row of Experiments were conducted at pollenizer. Each row represented a plot with 80 plants. Each isolation block had the Horticultural Crops Research Sta- four rows of ‘NC-Sunshine’ cucumber. Pollenizer treatments were assigned their tion in Clinton, NC, and two loca- own isolation block at each location and were separated by 1 mile (1.6 km) to tions at the Tobacco Research Station eliminate pollen transfer between treatments; 1 ft = 0.3048 m. in Oxford, NC, (Oxford-North and Oxford-South) during the Spring The effect of the pollenizer was The effect of using a pollenizer on early 2005. The soil type in Clinton was studied on a new cucumber hybrid fruit production was studied, with fruit a mixture of Norfolk and Orangeburg ‘NC-Sunshine’, which has more pis- harvested from the first harvest treated loamy sand (fine-loamy, siliceous, ther- tillate flower nodes. Field plots of ‘NC- as early setting. mic, Typic Kandiudults) with some Sunshine’ were 20-ft long and 5-ft Analysis of variance procedures Goldsboro (fine-loamy, siliceous, ther- apart (row spacing) with 6-ft alleys at were performed using MEANS and mic, Aquic Paleudults). The soil type in each end. Plots were planted with 100 GLM procedures of SAS (release 9.1 Oxford was a mixture of Helena sandy seeds and thinned to a uniform stand for Windows; SAS Institute, Cary, loam, Vance sandy loam, and Appling of 80 plants per plot. ‘NC-Sunshine’ NC) to determine the effect of pollen- sandy loam. plots were surrounded by two differ- izer on ‘NC-Sunshine’ cucumber yield. Recommended horticultural prac- ent pollenizer treatments, ‘Poinsett Means were separated with least signifi- tices were used for all experiments 76’ and ‘Gray Zucchini’; ‘Poinsett cant difference (P £ 0.05). Location · (Schultheis, 1990). Fertilizer was in- 76’ was the pollen source for highly pollenizer interaction was significant corporated before planting as ammo- pistillate ‘NC-Sunshine’, whereas ‘Gray (Table 1), so locations are presented nium nitrate at a rate of 80 lb/acre Zucchini’ is a squash cultivar and did separately (Table 2). Data are means nitrogen (N), 80 lb/acre phospho- not supply any pollen. ‘Gray Zucchini’ of four replications summed over two rous (P), and 80 lb/acre potassium is a cucurbit with plants about the same harvests. Whole plot effects (location) (K), with an additional 40 lb/acre N size as ‘Poinsett 76’, so they provide were tested using whole plot error (as sodium nitrate) applied at the vine a border effect that is similar. Two rows (replication · location), and subplots tip-over stage. Ethalfluralin at 1.1 lb/ of ‘NC-Sunshine’ were alternated with (replication · other factors) were tested acre preemergence (Curbit; Loveland each row of pollenizer, so that the rows using residual error (replication · other Products, Greeley, CO) was applied for of ‘NC-Sunshine’ were always adjacent factors). weed control. Irrigation was applied to the pollenizer row (Fig. 1). ‘Gray when needed for a total (irrigation plus Zucchini’ was planted to mimic the Results rainfall) of 1 to 1.5 inches per week. competition provided by ‘Poinsett 76’. The total, marketable, cull, early, Honeybees were placed in the field at ‘Poinsett 76’ was treated as the pollina- early marketable, percent marketable, the stage of first flowers opening using tion treatment, whereas ‘Gray Zucchini’ and percent early yields were influ- the recommended rate of two active was the no pollination treatment. enced by both pollenizer and location hives per hectare (Schultheis, 1990). Plots were harvested two times at (Table 1). Pollenizer and location also The experiment was conducted in 2-week intervals. Data were recorded show an interaction indicating that the a randomized complete block design for fruit yield: total, marketable, per- pollenizer responded differently at var- plantedinSpring2005withtwopol- cent marketable, cull, early, percent ious locations. Therefore, data are pre- lenizer treatments (‘Poinsett 76’ and early, early marketable, and percent sented to show the effect of pollenizer ‘Gray Zucchini’) across three locations early marketable. These measure- treatment at each location (Table 2). in North Carolina. There were four ments are important because amount Location differences were detected replications nested in each location. of pollination is reflected on yield. at Clinton and Oxford-South for yield. Treatment combinations were assigned All straight neck and healthy look- The total, marketable, early, and early their own isolation block and separated ing fruit were counted as marketable, marketable yield of ‘NC Sunshine’ by 1 mile to eliminate pollen transfer whereas deformed fruit (crook-necked from plots paired with ‘Poinsett 76’ between treatments as shown in Fig. 1. and bottle-necked) were treated as cull. at Clinton and Oxford-South were

192 • April 2012 22(2) Table 1. Mean square of main and interaction effect in the analysis of variance for yield in ‘NC-Sunshine’ cucumber at three locations in North Carolina. Early Percent Percent Source of Total Marketable Cull Early marketable marketable Percent early marketable variationz yieldy yieldy yieldy yieldy yieldy yieldy early yieldy yieldy Locationx 84,770*** 78,277*** 11,839** 40,470** 40,084*** 1,208*** 221* 488NS Pollenizerw 55,040** 104,503*** 7,861* 87,070*** 85,082*** 1,858*** 1,392*** 1,111NS Location · pollenizerw 14,174* 24,001*** 6,198* 17,903* 13,521* 1,112*** 344** 407* zLocations (main effect): Clinton, Oxford-North, and Oxford-South. Pollenizer (main effect): ‘Poinsett 76’ cucumber was treated as the pollination treatment, whereas ‘Gray Zucchini’ squash was the no pollination treatment. Location · pollenizer is an interaction effect. yTotal yield (tons/acre) = total yield from harvest 1 and 2, marketable yield (tons/acre) = total yield minus cull yield, cull yield (tons/acre) = yield from deformed fruit, early yield (tons/acre) = total yield from harvest 1, early marketable yield (tons/acre) = yield from harvest 1 that is marketable, percent marketable yield (by weight) = (marketable yield/total yield) · 100, percent early yield (by weight) = (early yield/total yield) · 100, percent early marketable yield (by weight) = (early marketable yield/early yield) · 100; 1 ton/acre = 2.2417 MgÁha–1. xTested by error – replication (location). wTested by error – residual error. NS,*, **, ***Nonsignificant or significant at P £ 0.05, 0.01, 0.001, respectively. higher than plots paired with ‘Gray the pistillate flowers early in the sea- in the Oxford-North. Possibilities may Zucchini’ (Table 2). Similar results son, thereby reducing total and early include more bee activity (Dittmar were also obtained for percent early yield; whereas, when plots were sur- et al., 2010; Kalbarczyk, 2009) or more and percent marketable yield. ‘NC- rounded by a pollenizer (‘Poinsett staminate flower production (Atsmon, Sunshine’ plots planted with the 76’), it produced enough viable pollen 1968; Friedlander et al., 1977) on ‘Poinsett 76’ at Clinton produced a for fertilization coinciding with pistil- ‘NC-Sunshine’ in Oxford-North, which higher percent marketable yield and late flower production early in the might have nullified the effect of the lower cull yield than plots paired with season, thus producing high early pollenizer. Environmental factors like ‘Gray Zucchini’. However, no differ- yield. Dittmar et al. (2010) reported high temperature and high light inten- ences were observed in Oxford-South that pollenizer treatments had more sity promote an increase in the propor- for these two traits. Location differ- than 10% and 20% early and total yield, tion of staminate flowers (Friedlander ences were not detected for percent respectively, compared with treat- et al., 1977). Presumably, a high tem- early marketable yield at any location. ments that had no pollenizer in trip- perature may have resulted in adequate In Oxford-North, no significant dif- loid watermelon production. NeSmith staminate flowers in Oxford-North, ferences between pollenizer treat- and Duval (2001) also reported de- hence ensuring ample pollen avail- ments were found for any trait. crease in triploid watermelon yield as ability in plots without a pollenizer. Overall, the use of the pollenizer the availability of pollen decreased and Abundant availability of pollen for pis- ‘Poinsett 76’ produced higher total vice versa. Percentage of early market- tillate flowers produces a high fruit set yield, marketable yield, early yield, able fruit was similar for all treatments. (Adlerz, 1966; Dittmar et al., 2010; and percent early yield compared with This might be attributed to increased Stanghellini et al., 1997; Walters, 2005; no pollenizer. In addition, the use of activity of pollinators or sufficient pollen Walters and Taylor, 2006). However, ‘Poinsett 76’ as pollenizer decreased availability early in the season; therefore, temperature, bee activity, and the num- the cull yield (misshapen fruit) in ‘NC marketable fruit were comparable irre- ber of staminate flowers were not mea- Sunshine’ cucumber. spective of pollenizer treatment. sured in this experiment. Field plots that were not planted Overall in this experiment, re- Discussion with a pollenizer produced more cull sults indicated that growers might Diverse production areas were se- fruit as compared with field plots that not have to use pollenizer in some lected around the main cucumber included a pollenizer. The process of locations, but it is recommended that areas of North Carolina. Some isolation pollination stimulates the ovary to they use pollenizer mixed in hybrid blocks (locations) produced higher enlarge, therefore, fruit set and en- seed to get reliable marketable yield. yield and lower culls when pollenizer largement is dependent upon growth Moreover, use of pollenizer reduces was provided; some were able to regulators produced from pollen and the cull yield (deformed fruit). function the same with or without developing seeds (Hayata et al., 1995). pollenizer. ‘NC-Sunshine’ responded The low amount of pollen available Conclusions positively to the inclusion of a pollen- to pollinate pistillate flowers may have This study demonstrates that the izer in Clinton and Oxford-South resulted in production of cull fruit due production of sufficient male flowers locations. The results indicated that to partial development of fruit tissues with viable pollen is important for fruit the use of a pollenizer increased total, at stem end. Dittmar et al. (2010) set of ‘NC-Sunshine’ cucumber. If a marketable, and early yield while re- reported more than 50% inferior fruit pollenizer is used, cucumber hybrids ducing cull yield. The use of a pollen- in watermelon due to hollow heart in with more pistillate flowers have early izer provided more viable pollen no pollenizer treatment. Fiacchino and fruit set and higher total and marketable resulting in fertilization of more pistil- Walters (2003) observed more de- yield. However, additional studies may late flowers. Since ‘NC-Sunshine’ pro- formed fruit (hollow heart) in water- be carried out to characterize a more duces more pistillate flowers than most melon due to lower pollen availability. suitable pollenizer than ‘Poinsett 76’. monoecious cucumbers, which relates However, cucumber yield was The pollenizer should have distinct to insufficient pollen to pollinate all unaffected by a pollenizer treatment fruit that easily can be distinguished

• April 2012 22(2) 193 RESEARCH REPORTS

y from field cultivar at the time of harvest.

z Other interesting research topics would

. be determining the optimal number of –1

ha plants per honeybee hive and the opti- Á mal ratio of pollenizer to cultivar. yield (% by wt) ford-South). Early marketable Literature cited y Adlerz, W.C. 1966. Honey bee visit num- ber and watermelon pollination. J. Econ. Entomol. 59:28–30.

Early Atsmon, D. 1968. The interaction of 100; 1 ton/acre = 2.2417 Mg

· genetic, environmental, and hormonal

yield (% by wt) factors in stem elongation and floral de- velopment of cucumber plants. Ann. Bot. y (Lond.) 32:877–882. Dittmar, P.J., D.W. Monks, and J.R. Schultheis. 2010. Use of commercial pol- lenizers for optimizing triploid watermelon

Marketable production. HortScience 45:541–545. yield (% by wt) Fiacchino, D.C. and S.A. Walters. 2003.

y Influence of diploid pollenizer frequen- er was treated as the pollination treatment, whereas ‘Gray Zucchini’ squash was the no

l yield from harvest 1, early marketable yield = yield from harvest 1 that is marketable, cies on triploid watermelon quality and yields. HortTechnology 13:58–61. Friedlander, M., D. Atsmon, and E. Galun. 1977. The effects of abscisic acid and other growth regulators on various

Early marketable sex genotypes. Plant Cell Physiol. 18: yield (tons/acre) 261–269. y Gajc-Wolska, G.J., K. Kowalczyk, J. Mikas, and R. Drajski. 2011. Efficiency 0.05.

£ of cucumber (Cucumis sativus L.) polli- 100, percent early marketable yield = (early marketable yield/early yield) P Clinton

· nation by bumblebees (Bombus terrestris). Early yield Oxford-South Oxford-North (tons/acre) Acta Scientiarum Polonorum Hortorum Cultus 10:159–169. y Gingras, D., J. Gingras, and D. Oliveira. 1999. Visits of honeybees (Hymenoptera: Apidae) and their effects on cucumber yields in the field. J. Econ. Entomol. Cull yield

(tons/acre) 92:435–438.

y Hayata, Y., Y. Niimi, and N. Iwasaki. 1995. Synthetic cytokinin-1-(2-chloro-4- pyridyl)-3-phenyl-urea (CPPU)-promotes fruit set and induces parthenocarpy in watermelon. J. Amer. Soc. Hort. Sci. 15.06 a 4.7 b 12.4 a 9.0 a 76 a120:997–1000. 63 a 59 a Marketable 100, percent early yield = (early yield/total yield) ·

yield (tons/acre) Kalbarczyk, R. 2009. Potential reduction in cucumber field (Cucumis sativus L.) in

y Poland caused by unfavorable thermal

x conditions of the soil. Acta Scientiarum Polonorum Hortorum Cultus 8:45–58. 4.4 2.7 2.5 3.9 3.4 5.7 9.8 14.4 Lower, R.L. and M.D. Edwards. 1986. Total yield (tons/acre) 0.05. Cucumber breeding, p. 173–207. In: £

P M.J. Basset (ed.). Breeding vegetable crops. AVI Publishing, Westport, CT. NeSmith, S. and J. Duval. 2001. Fruit set of triploid watermelons as a function of distance from a diploid pollenizer. Hort- w Science 36:60–61. Peterson, C.E. 1975. Plant introductions (0.05) in the improvement of vegetable cultivars. Least significant difference at Data were averaged over four replications and two harvests at each location in Spring 2005, with 80 plants evaluated in each plot. ‘Poinsett 76’Any cucumb two means within a column within a location not followed by the same letter are significantly different at Total yield = total yield from harvest 1 and 2, marketable yield = total yield minus cull yield, cull yield = yield from deformed fruit, early yield = tota pollination treatment. Treatment combinations were assigned their own isolation block to eliminate pollen transfer between treatments. Table 2. Influence of pollenizers on fruit set and yield ofPollenizer ‘NC-Sunshine’ cucumber at three locations in North Carolina (Clinton, Oxford-North, and Ox LSD z y x w percent marketable yield = (marketable yield/total yield) ‘Gray Zucchini’ squash 13.0‘Poinsett b 76’ cucumber‘Gray Zucchini’ squash 25.5 a 25.5‘Poinsett a 76’ cucumber 4.0‘Gray b Zucchini’ squash 24.7 a 18.0 a 18.5 b 16.8 a 9.0 a 19.6 a 14.1 7.5 b a 8.8 a 6.7 b 5.1 16.3 a a 4.4 a 15.3 a 2.0 b 16.3 a 12.3 a 6.9 b 11.2 a 31 13.5 b a 5.7 70 b a 65 a 50 b 79 a 76 64 a a 60 a 49 66 a a 37 b 68 a 67 a 49 a 39 a ‘Poinsett 76’ cucumber 19.7 a HortScience 10:575–579.

194 • April 2012 22(2) Schultheis, J.R. 1990. Pickling cucum- Staub, J.E., M.D. Robbins, and T.C. Wehner, T.C. 1989. Breeding for im- bers. North Carolina State Agr. Expt. Wehner. 2008. Cucumber, p. 241–282. proved yield in cucumber. Plant Breed. Hort. Info. Lflt. No. 14-A. In: J. Prohens and F. Nuez (eds.). Hand- Rev. 6:323–359. book of plant breeding; Vegetables I: Stanghellini, M.S., J.T. Ambrose, and J.R. Asteraceae, Brassicaceae, Chenopodiaceae, Wehner, T.C. 2005. ‘NC-Sunshine’ and Schultheis. 1997. The effects of honey bee and Cucurbitaceae. Springer Science+ ‘NC-Stratford’ slicing cucumber hybrids. and bumble bee pollination on fruit set Business, New York. HortScience 40:1577–1579. and abortion of cucumber and water- melon. Amer. Bee J. 137:386–391. Walters, S.A. 2005. Honey bee pollina- Wehner, T.C. and S.F. Jenkins, Jr. 1985. tion requirements for triploid water- Rate of natural outcrossing in monoecious Stanghellini, M.S., J.T. Ambrose, and J.R. melon. HortScience 40:1268–1270. cucumbers. HortScience 20:211–213. Schultheis. 1998. Seed production in watermelon: A comparison between two Walters, S.A. and B.H. Taylor. 2006. Whitaker, T.W. and G.W. Bohn. 1952. commercially available pollinators. Hort- Effects of honey bee pollination on pump- Natural cross pollination in muskmelon. Science 33:28–30. kinfruitandseedyield.HortScience Proc. Amer. Soc. Hort. Sci. 60:391–396. 41:370–373.

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