Screening for Heat Tolerance in Phaseolus spp. Using Multiple Methods

Common bean (Phaseolus vulgaris L.) is a nutritious crop grown around the world, a staple that provides high levels of protein and iron in the diets of Central and South Americans and East Africans. Heat stress negatively affects common bean seed yields and prevents cultivation in certain areas. Furthermore, under field conditions, heat stress often coincides with and exacerbates drought stress effects. Breeding more heat-tolerant cultivars would stabilize seed yield and open new regions to field production. To support these efforts, we examined a variety of methods for screening large numbers of bean germplasm exposed to heat stress at the vegetative growth stage as opposed to the reproductive stage, which would prolong the screening process. Tepary bean (P. acutifolius A. Gray), a closely related species to common bean, was used as a heatstress-tolerant check. Plants exposed to day/ night temperatures of 45/36 degrees C for 2 d showed measurable signs of heat stress, but tepary bean outperformed the common beans on all stress tolerance measures. Gas exchange, chlorophyll fluorescence, and oxidative stress were only affected by this high temperature and not by temperatures below 45/36 degrees C. Heat stress measurements also correlated well with visual signs of leaf tissue damage. Gradually raising temperatures was useful for screening large number of entries for heat tolerance, but this heat tolerance was only partially related to drought tolerance in the field. Plant breeders can use some of these methods to supplement field data and to further characterize the stress tolerance of bean lines.