2018 ASHS Annual Conference

Heat stress reduces yields of May and early June-planted lima bean (Phaseolus lunatus) in the Mid-Atlantic Region of the US. High night temperatures during flowering and seed development can reduce or delay pod set, resulting in delayed harvest, lower yield and split pod sets. Breeding heat tolerant baby and Fordhook type lima beans is one goal of the University of Delaware lima bean breeding program. Greenhouse experiments were used to characterize the response of several lima bean genotypes to high versus ideal nighttime temperatures in order to better understand the mechanism by which high night temperatures reduce yield.

Higher amounts of pollen shed onto the stigma and style under heat stress are correlated with higher yield under heat stress, and that there is genotypic variation for this trait. Additionally, some heat sensitive genotypes exhibited a number of physiological changes to reproductive structures while under heat stress, some of which may interfere with reproduction and affect yield: lower in vitro germination of pollen collected from the pistil, extrusion of the stigmatic pad from the keel and anther indehiscence. Other aspects of reproduction, such as stigma receptivity, are affected in some heat sensitive genotypes, but not others.

Vegetative growth was not reduced by high night temperatures. Plants grown under stressed and unstressed conditions produced similar shoot dry weights. Heat sensitive plants produce more leaves and stems under high temperature conditions, compensating for the reduction in seed weight.

In the University of Delaware lima breeding program, characterization of some of the physiological changes to reproductive structures that are associated with heat sensitivity is being used to screen diverse germplasm and breeding lines in order to select for heat tolerance.