Browsing by Author "Ernest, Emmalea Garver"
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Item Physiological effects of high temperatures and the genetic architecture of heat stress response in lima bean(University of Delaware, 2020) Ernest, Emmalea GarverHeat stress reduces yields of lima bean (Phaseolus lunatus) in the Mid-Atlantic Region of the US. High night temperatures during flowering reduce or delay pod set, resulting in delayed harvest, split pod sets and lower yield. Breeding heat tolerant small- and large-seeded lima beans is a high priority for the University of Delaware lima bean breeding program, but the physiological and genetic basis for lima bean’s heat stress response was poorly understood. The purpose of this project was to determine the physiological bases for heat stress induced yield loss in lima bean, identify tolerant genotypes and develop heat response screening methods to use in breeding. ☐ High nighttime temperatures reduce yield in some lima bean genotypes by reducing the number of pods set and the number of seeds per pod. High night temperatures do not reduce overall aboveground biomass, indicating that this type of temperature stress may have little effect on photosynthate availability. High night temperature has a significant effect on pollen release and viability, and in some genotypes results in changes to flower morphology that could interfere with pollination and fertilization. There is evidence that other aspects of reproduction, such as stigma receptivity or seed development are impaired by heat stress in some sensitive genotypes, but not others. The correlation of pollen quantity and yield under heat stress is present gene pool-wide. Heat sensitivity is not isolated to large-seeded Andean genotypes, but such genotypes exhibit heat sensitivity in the post pollination stage, which was not apparent in Mesoamerican types. ☐ Lanceolate leaflets are present in the lima bean gene pool and have been hypothesized to offer heat and drought stress tolerance advantages over the typical ovate leaflet shape. Shape descriptors, measured via image analysis, were used to characterize the leaflet shape for a diverse collection of lima bean germplasm. A few loci may be involved in determining leaflet shape, which is under strong genetic control. Lanceolate leaflet shape is conferred by one locus and could be incorporated into commercial germplasm if it is found to offer a stress tolerance advantage.