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Sandra B. Wilson, Laurie K. Mecca, Judith A. Gersony, Mack Thetford, and Josiah S. Raymer

Because of its weedy nature, extensive use in the landscape, numerous cultivars, and history as an invasive plant in other countries, butterfly bush (Buddleja) was an appropriate candidate to evaluate for seed production and germination in Florida. Seed production was quantified for 14 butterfly bush taxa planted in western Florida (Milton) and central southern Florida (Fort Pierce). Each of the 14 taxa evaluated produced seed. In Fort Pierce, japanese butterfly bush (B. japonica) had the greatest capsule weight and `Gloster' butterfly bush (B. lindleyana) had the second greatest capsule weight as compared to other taxa. In Milton, `Gloster' had the greatest capsule weight and japanese butterfly bush and `Nanho Alba' butterfly bush (B. davidii var.nanhoensis) had the second greatest capsule weights as compared to other taxa. The shape and number of seed capsules per infructescence varied with cultivar. Seeds were cleaned and germinated in germination boxes with and without light at 20/10, 25/15, 30/20 and 35/25 °C (68.0/50.0, 77.0/59.0, 86.0/68.0 and 95.0/77.0 °F). Regardless of temperature or cultivar, light was required for germination. At each temperature, `Nanho Blue' butterfly bush (B. davidii var. nanhoensis) and `Moonlight' butterfly bush (B. × weyeriana) had highest germination rates (63-74%) as compared to other taxa.

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M.M. Peet, C. Clement, and S. Sato

Starting 2 weeks before anthesis of the first flower, tomato cultivars (Lycopersicon esculentum Mill.) differing in heat tolerance were exposed to mild heat stress (31/24 vs. 28/22 °C) at three levels of relative humidity (30%, 60%, and 90%) in controlled environment chambers at the Duke Univ. Phytotron. Pollen development in the anthers was followed cytologically, pollen release was measured at anthesis, and seed production and fruit weight were measured as fruit matured. Fruit and seed development were best at 60%RH and 28/22 °C and worst at 90% RH and 31/24. Seed development was poor at 31/24 °C at all humidity levels. It was also poor at 28/22 in the 90% RH treatment. Low relative humidity had a greater negtive effect on fruit and seed production and on cytological development in plants grown at high temperature. Pollen release was also reduced at 90% RH, with virtually no pollen released at 31/24 °C. Cytological examinations revealed developmental anomolies in pollen in some, but not all cultivars at 90% and 30% RH. Plant height was also affected by the treatments, with much taller plants in the high-temperature, high-humidity treatments.

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Daiichiro Miyajima and Masaaki Nakayama

Composition of capitula and their making by florets of zinnia (Zinnia violacea Cav.) were analyzed to improve seed production. For each cultivar, mature capitula were classified into three types based on shape. A capitulum was made of the accumulation of <20 newly opened florets per day for >15 days. The total number of florets per capitulum was 210 to 330, 220 to 290, and 160 to 240 for the two pumila double cultivars Kumamotonokagayaki and Snowball and for the pompon cultivar Purple Zem, respectively. The numbers of tubular florets were negatively correlated with the numbers of ray florets. Ornamentally superior capitula, which were the basic capitulum types for pumila doubles and pompons, had more ray florets and fewer tubular florets than the ornamentally inferior capitulum (the single-flowered type). Results indicate that maintaining a high percentage of plants with double-flowered capitula may decrease seed yield.

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Daiichiro Miyajima

The seed producing system in viola (Viola ×cornuta) was investigated to improve seed yield and to save labor. In a flower five anthers sequentially dehisced; pollen grains were continuously supplied to the anterior petal, which played a significant role in pollination, throughout the flowering period. Evidence from pollen and ovule number suggests that the species is facultative autogamy. Each flower opened more than 10 days was independent of the success in fertilization and kept seed producing ability during the flower longevity period. Pollen grains also maintained viability during the flower longevity period. Pollinators were indispensable for pollination of viola, but pollination in viola was done by a different mechanism from the typical insect-mediated pollination that sticky pollen grains adhere to the exposed stigmas. Pollen grains, accumulated around the entrance of the stigmatic cavity, entered into the cavity by the movement of pollinators. Although the visitation of pollinators was occasional, solitary bees primarily contributed to the pollination of viola. On the other hand, germination of pollen grains on the stigmatic surface was under 50%. Seed set was much lower than the germination percentage of pollen grains. A viola flower had the ability for additional pollinations and fertilization for some days after the fertilization success in some ovules in the flower. This characteristic suggested that repeated pollination is effective to increase the number of mature seeds in a capsule.

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Kent J. Bradford

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Yu Sung, Daniel J. Cantliffe, and Russell T. Nagata

Lettuce (Lactuca sativa L.) seeds can fail to germinate at temperatures above 24 °C. The degree of thermotolerance is thought to be at least partly related to the environment under which the seed developed. In order to study the effects of temperature during seed development on subsequent germination, various lettuce genotypes were screened for their ability to germinate at temperatures ranging from 20 to 38 °C. Seeds of the selected genotypes `Dark Green Boston' and `Valmaine' (thermosensitive), `Floricos 83', `Everglades', and PI 251245 (thermotolerant) were produced at 20/10, 25/15, 30/20, and 35/25 °C day/night temperature regimes in plant growth chambers. Seeds were germinated on a thermogradient bar from 24 to 36 °C under 12 h light/dark cycles. As germination temperature increased, the number of seeds that failed to germinate increased. Above 27 °C, seeds matured at 20/10 or 25/15 °C exhibited a lower percent germination than seeds that matured at 30/20 or 35/25 °C. Seeds of `Dark Green Boston' and `Everglades' that matured at 30/20 °C exhibited improved thermotolerance over those that matured at lower temperatures. Seeds of `Valmaine' produced at 20/10 °C exhibited 40% germination at 30 °C, but seeds that matured at higher temperatures exhibited over 95% germination. Germination of `Valmaine' at temperatures above 30 °C was not affected by seed maturation temperature. The upper temperature limit for germination of lettuce seed could thus be modified by manipulating the temperature during seed production. The potential thermotolerance of seed thereby increased, wherein thermosensitive genotypes became thermotolerant and thermotolerant genotypes (e.g., PI251245) germinated fully at 36 °C. This information is useful for improving lettuce seed germination during periods of high soil temperature, and can be used to study the biology of thermotolerance in lettuce.

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X.P. Zhang, B.B. Rhodes, W.V. Baird, H.T. Skorupska, and W.C. Bridges

Hybrid seed production can be facilitated by using male sterility coupled with a seedling marker. This research was initiated to combine the ms male sterility and dg delayed-green seedling marker into watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] lines. Male-sterile plants of the male-sterile line G17AB were crossed with plants of delayed-green breeding line Pale90, which has yellow cotyledons and pale-green, newly developed, true leaves. The double-recessive recombinants, male sterile and delayed green, from the F2 population were backcrossed to the male-fertile plants of G17AB. The pedigree method was used for selection in the progenies. The segregation ratios obtained from F2 and BC1F2 populations suggest that the male-sterile and delayed-green traits are inherited independently and that delayed green is inherited as a single recessive nuclear gene. Two male-sterile watermelon lines with delayed-green seedling marker have been developed. These lines will provide a convenient way to introduce male sterility and the delayed-green seedling marker into various genetic backgrounds. These two lines can be used for testing the efficiency of a new, hybrid, watermelon, seed production system.

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Donna J. Clevenger, James E. Barrett, Harry J. Klee, and David G. Clark

Pollen viability, in-vivo pollen tube growth, fruit ripening, seed germination, seed weight, whole plant vigor, and natural flower senescence were investigated in homozygous and heterozygous transgenic ethylene-insensitive CaMV35S::etr1-1 petunias (Petunia ×hybrida `Mitchell Diploid'). Homozygous or heterozygous plants were used to determine any maternal and/or paternal effects of the CaMV35S::etr1-1 transgene. All experiments except for those used to determine natural flower senescence characteristics were conducted in both high and low temperature greenhouses to determine the effect of temperature stress on transgenic plants when compared to wild-type. Results indicated that ethylene-insensitive plants had a decrease in pollen viability, root dry mass, seed weight, and seed germination. Fruit ripening, seed germination, and seed weight were maternally regulated. In contrast, the CaMV35S::etr1-1 transgene is completely dominant in its effect on natural flower senescence.

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Ellen K. Muchmor and Loverine P. Taylor

Seed set is affected by many factors. One of the most important is the number of pollen grains that germinate on the stigma. Our research has shown that kaempferol (a plant natural product) is required for pollen germination. Pollen lacking kaempferol does not germinate, but this defect can be reversed by adding powdered kaempferol to the stigma at pollination. Within 24 hours of wounding the corolla or stamens of V26, a Petunia inbred, high levels of kaempferol accumulate in the stigma. The requirement for kaempferol in pollen germination, and the high levels that can accumulate in the stigma, suggested that seed set might be enhanced by wounding 24 hours before pollination. We tested this hypothesis in two inbred lines of Petunia, a Petunia outcross, and another solanaceous plant Nicotiana tobacum cv. Samsum. The number of seeds per capsule were correlated with the levels of kaempferol in the stigma in wounded and non-wounded flowers.

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M.S. Stanghellini, J.T. Ambrose, and J.R. Schultheis

The number of honey bees (Apis mellifera L.) continues to decline due to parasitic mite pests and other factors. Honey bees and bumble bees (Bombus impatiens Cresson) were therefore compared for their effects on the seed set of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in a 2-year field experiment. The experiment was a 2 x 4 + 2 factorial, comparing bee type (honey bee or bumble bee) at four visitation levels (1, 6, 12, and 18 bee visits) to pistillate flowers, with two controls: a no-visit treatment and an open-pollinated treatment. Bee visitation level had a strong positive influence on seed set (P ≤ 0.0001). All flowers bagged to prevent insect visitation aborted, demonstrating the need for active pollen transfer between staminate and pistillate watermelon flowers. Flowers visited by B. impatiens consistently contained more seed than those visited by A. mellifera, when compared at equal bee visitation levels (P ≤ 0.0001). We conclude that bumble bees have great potential to serve as a supplemental pollinator for watermelon when honey bees available for rental are in limited supply.