Diversity of salt tolerance in Vigna riukiuensis

Vigna riukiuensis is one of the most salt-tolerant species within the genus Vigna, yet intraspecific variation in its salt tolerance remains uncharacterized. In this study, we evaluated 61 accessions of V. riukiuensis under 200 mM NaCl using effective quantum yield (Y(II)) as an indicator of salt tolerance. Accessions were classified into five clusters, showing substantial variation that accessions in the tolerant group maintained Y(II) for four weeks whereas those in the sensitive group lost Y(II) in a week. We repeated the Y(II)-based classification for a subset of accessions and the results generally reproduced that of the first evaluation. In addition, we measured Na⁺ and K⁺ allocation in roots, stems and leaves and found the pattern of Na⁺ allocation greatly varied even within the most tolerant accessions whereas the pattern of K⁺ allocation, not the Na⁺/K⁺ ratio, showed a minor correlation with salt tolerance. Interestingly, JP254554 restricted Na⁺ transport from roots to leaves, but it did not develop Casparian strips even under salt stress. This study provides the first comprehensive assessment of intraspecific variation in V. riukiuensis, identifying promising donor accessions for breeding, and highlighting various unknown mechanisms to be elucidated in the future.