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Michael S. Stanghellini and Jonathan R. Schultheis

In 1999 and 2000, a total of 27 diploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] cultivars and advanced breeding lines (hereafter referred to as cultigens) were evaluated for staminate flower and pollen grain production to assess their potential to serve as pollenizers (pollen source plants) in triploid watermelon production systems. Male reproductive output (staminate flower and pollen production) was quantified during the peak flowering and fruit setting phase of the cultigens under field conditions. The number of staminate flowers produced per plant per day, number of pollen grains produced per flower, and total number of pollen grains produced per plant per day (staminate flowers per plant × pollen grains produced per flower) differed greatly among cultigens (for all tests, P < 0.01). Staminate flower production by cultigens differed by year (P < 0.0029) and days within years (P = 0.0225), but pollen production between years by cultigens was stable (P = 0.4841). Total male reproductive output ranged from 134,206 pollen grains per plant per day for `Jamboree' to 321,905 pollen grains per plant per day for `Summer Flavor 500'. These studies demonstrate the genotypic variability in watermelon male reproductive output potential, and may assist growers in choosing a good diploid pollenizer for triploid watermelon production.

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Michael S. Stanghellini, Jonathan R. Schultheis, and Gerald J. Holmes

In 1998 and 1999, a total of 27 large-fruited and 15 miniature-fruited pumpkin (Cucurbita pepo) cultivars were evaluated for adaptation to eastern North Carolina grow- ing conditions. Test categories were yield (fruit number and weight); fruit characteristics (shape, rind and stem attributes); and susceptibility to edema (wart-like growths on fruit exterior), foliar diseases, preharvest and postharvest fruit decay, and viruses. Yields of large pumpkins ranged from over 3,200 fruit/acre (7,907 fruit/ha) for `SVT 4613367', `Autumn Gold', and `Gold Standard' to less than 1,000 fruit/acre (2,471 fruit/ha) for `Gold Rush' and `Progold 200'. For miniature pumpkins, over 33,000 fruit/acre (81,542 fruit/ha) were produced by `Touch of Autumn', `Lil' Pump- ke-mon', and `HMX 5682', whereas `Mystic' and `Progold 100' produced less than 7,000 fruit/acre (17,297 fruit/ha). `Gold Rush', `Howden', and `Progold 510' (large), and `EXT 4612297', `Lil' Goblin', and `Lil' Ironsides' (miniature) appeared the most susceptible to foliar diseases. Preharvest fruit decay ranged from 0% for `Howden' and `EXT 4612297' to over 20% for `Lil' Goblin', `Jumping Jack', `Peek-A-Boo', and `Tom Fox'. Virus incidence on fruit and foliage was low on virus-resistant cultivars ('SVT 4613367' and `EXT 4612297'), and ranged from 4% to 74% for nontransgenic cultivars. Virus incidence and/or severity on foliage and fruit were not related. `Early Autumn' (large) and `Touch of Autumn' (miniature) were the most prone to edema. `Aspen' and `Magic Lantern' (large) and `Baby Pam', `Lil' Goblin', and `Spooktacular' (miniature) were the most susceptible to postharvest fruit decay. Fruit characteristics are discussed in relation to marketability and possible consumer appeal to pumpkins.

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Michael S. Stanghellini, John T. Ambrose, and J.R. Schultheis

The need for alternative [non-honey bee (Apis mellifera L.)] pollinators continues to increase as the number of problems facing the American beekeeping industry increase. One readily available alternative pollinator source is commercially produced bumblebee (Bombus spp.) colonies. From 1997 to 1999, three studies were conducted to compare the pollination efficacy of bumblebee and honeybee pollinators on field-grown watermelon. The experiments documented 1) bee activity periods (the onset and termination of foraging behavior in association with watermelon anthesis and duration), 2) floral visitation rates (number of flowers visited per unit time by individual foragers), and 3) stigmatic pollen deposition (number of pollen grains deposited on stigmata during single bee visits to pistillate watermelon flowers over the course of anthesis). Bumblebees outperformed honeybees in all three comparative experiments. Bombus foragers initiated foraging activity 30 to 60 min before the appearance of the first honey bee foragers. Both bee types continued to forage throughout anthesis once appearing in the field. Individual bumblebees consistently visited two or more times the number of flowers per min than did honeybees (P < 0.0001) throughout the day excluding the initial 30 to 60 min when honeybees did not forage. The number of pollen grains deposited in an initial visit to stigmata by Bombus foragers was consistently greater than for honeybees (P < 0.001). For both bee types, pollen deposition was influenced by time of day, peaking at 0900 hr and then declining until 1200 HR, when the flowers closed. Both foraging rates and pollen deposition favored bumblebees over honeybees regardless of time of day.

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Michael S. Stanghellini, John T. Ambrose, and Jonathan R. Schultheis

The effectiveness of bumblebees, Bombus impatiens, and honeybees, Apis mellifera, on the pollination of cucumber, Cucumis sativus, was compared at the individual bee level. A correlation between the number of bee visits a flower received and the resultant seed set was established. In both cucumber varieties, `Calypso' and `Dasher II', B. impatiens-visited flowers consistently had higher seed sets than A. mellifera when compared at equal visit numbers. This difference between bee types was found to be highly significant.

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Michael S. Stanghellini, John T. Ambrose, and Jonathan R. Schultheis

The effectiveness of bumble bees, Bombus impatiens, and honey bees, Apis mellifera, on the pollination of watermelon, Citrullus lanatus (Thunb.), was compared at the individual bee level. Correlations between the number of bee visits a flower received and the resultant seed set and fruit abortion rates were established. Using `Royal Jubilee' watermelon, B-impatiens-visited flowers resulted in higher seed sets than A. mellifera when compared at equal bee visit numbers. This difference between bee types was highly significant. With respect to fruit abortion rates, no statistical difference between bee types was detected. However, bee visit count was significant. Increasing the number of bee visits received by a flower resulted in a lower percentage of aborted fruit.