Male gametophyte is a powerful screening tool for drought and heat tolerance in garden bean

Common bean (Phaseolus vulgaris L.) is the most important grain legume for human consumption, and drought stress affects over 73% of dry bean production worldwide. The effect of drought can vary depending on different stages of plant development, soil fertility, root health, temperature, etc. In general, drought has the greatest impact on bean pods and grain yield when it occurs during reproductive development. In addition, studies on the effects of heat stress on cultivated plants suggested that pollen development and pollination are the most sensitive stages of reproductive development. The objective of this study was to investigate the genotypic differences in reproductive stress tolerance between advanced garden bean lines using pollen germination and pollen tube length as stress tolerance indices. Data on reproduction and yield were collected during two growing seasons in a field experiment using advanced garden bean lines under controlled (NS) and drought-stressed (DS) conditions and an average high temperature of 30°C during the reproductive stages of plants. Stressed plants from all genotypes exhibited a more severe reduction in seed set and grain/pod yield, correlated with a decrease in pollen tube growth potential and pollen germination with an average of 37.5 µm and 21.1%, respectively. The bean genotypes were divided into four distinct groups based on the male gametophyte viability under DS and NS conditions. Line 952-70 was identified as a relatively stress-tolerant one together with the standard cultivar. BiPlot analyses of yield components revealed good correlations between mean productivity (MP), geometric mean productivity (GMP), harmonic mean of productivity (HARM), stress tolerance index (STI), and male gametophyte. Our results showed that gamete selection could be a powerful tool for breeders. Pollen germination and pollen tube length indices performed best results when used in combination for identifying drought and heat tolerant genotypes in common bean.