Thermotolerance at the cost of reproduction: contrasting adaptive strategies of lima bean genotypes under heat stress conditions

In Northeast Brazil, lima bean ( Phaseolus lunatus L.) production is subject to severe thermal constraints, limiting cultivation to periods of milder temperatures and increased rainfall. Heat stress impairs crop productivity by disrupting photoassimilate translocation and compromising grain filling. To assess the remobilization of these resources under heat stress and elucidate the mechanisms underlying thermotolerance in this crop, five contrasting lima bean genotypes were evaluated throughout their developmental cycle under two representative thermal regimes: natural conditions (44–46 °C) and severe stress (50–52 °C) in the semiarid region of Northeast Brazil. Analyses included vegetative development, gas exchange, pigment content, and oxidative stress indicators such as hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), as well as antioxidant enzyme activities (SOD, APX, and GPOD) and male gametophyte viability. Data were subjected to analysis of variance, Tukey’s test ( p < 0.05), and multivariate analyses using canonical variables and GGE biplot. The results revealed a metabolic compensation system among the genotypes, prioritizing individual survival over pod formation. This strategy was evidenced by a trade-off between reproductive success and the production of defense proteins, consistent with a metabolic compensation strategy, and accompanied by reduced concentrations of reactive oxygen species (ROS). The findings suggest that the main limitation to production during periods of high temperature may not be gametophyte sensitivity alone, but may also be associated with a possible preferential allocation of photoassimilates toward vegetative maintenance structures and osmolyte accumulation.