Maintaining good leaf water status, but not intrinsic biological nitrogen fixation, is a key factor for drought tolerance in US peanut cultivars

Abstract Peanut ( Arachis hypogaea L.) is an important oil crop for its nutritional benefits and its ability for biological nitrogen fixation (BNF). However, peanut faces significant challenges from drought, which reduces BNF efficiency and leads to yield loss. Understanding the relationship between BNF‐related physiological traits and yield in peanut under drought is crucial for breeding drought‐tolerant peanut genotypes. In this study, we examined multiple peanut genotypes for yield, δ 15 N (a BNF indicator), N concentration, photosynthesis, stomatal conductance, and leaf water status‐related traits with drought and well‐water treatments in rainout shelters. There were significant correlations between yield and photosynthesis, leaf relative water content (RWC), seed δ 15 N, and plant nitrogen (N) uptake. Genotypic variations were observed in yield, seed δ 15 N, seed and shoot N%, seed and shoot N uptake, and specific leaf area in both 2019 and 2020, with RWC observed only in 2019. Drought‐tolerant genotypes having higher yield showed BNF was included in this group (as indicated by its lower δ 15 N). This suggests that maintaining effective BNF contributes to higher yields under drought. Interestingly, plants characterized as “water spenders” (having high stomatal conductance) also had high BNF levels, thus corresponding to contrasting characteristics of being “water savers.” This observation can be attributed to the maintenance of favorable leaf water status in drought‐tolerant genotypes, regardless of their stomatal conductance. Overall, sustaining adequate leaf water status during drought is foundational for efficient BNF, thereby contributing to improved yields, particularly in drought‐tolerant peanut genotypes. In this study we did not find cultivars with intrinsic BNF that are tolerant to drought even though the plant has a bad leaf water status. This could be an opportunity to find such types of cultivars that exist in other collection and introgress them in US lines to provide another layer of protection against drought.