Genetic and Environmental Factors that Influence Microgametophytic Variation

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9318224 Stephenson A large portion of the genome of the microgametophytes (pollen) is both transcribed and translated during development, germination and pollen tube growth. Consequently, the performance of pollen (speed and germination, pollen tube growth rate and the ability to penetrate ovules and achieve fertilization) can potentially be affected by its genetic composition, by its interactions with the pistil, by environmental conditions and by the resources provided to pollen by the pollen producing parent. This proposal seeks support to continue our detailed investigations of the factors that affect pollen performance, the relationship between pollen performance and non-random fertilization, and the effects of non-random fertilization on the progeny performance. The investigators will continue ongoing studies of pollen competition in Cucurbita texana, to determine if there is heritable variation for pollen performance and to determine if the effects of pollen competition on progeny vigor extend to subsequent generations. They will also determine the potential for pollen competition to occur and the effects of pollen competition on progeny vigor in natural populations of C. foetidissima growing in the Jornada Long-Term Ecological Research Site near Las Cruces, New Mexico. They will also determine if the growing conditions of the pollen producing parent affect the performance of the pollen. They will use C. texana and C. foetidissima to examine the effects of leaf herbivory by cucumber beetles (Diabrotica spp.) on pollen production, pollen grain size and the ability of the pollen to sire seeds when deposited into stigmas in mixture. This research will conclude studies of pollen competition and its effects on progeny performance and will result in the most carefully controlled and comprehensive set of experiments in this field of research. The herbivory studies will greatly extend the now very limited understanding of environmental factors that affect pollen performance.