Salt tolerance in wild relatives of adzuki bean, Vigna angularis (Willd.) Ohwi et Ohashi

Salt stress is becoming a serious problem in food production field. To find sources of salt tolerance, we screened 74 accessions of adzuki bean (Vigna angularis) and 145 accessions of cross-compatible wild relatives (seven species). We performed the primary screening in soil culture and the secondary screening in hydroponic culture, and identified JP205833 of V. riukiuensis (strain ‘Tojinbaka’) and JP107879 of V. nakashimae (strain ‘Ukushima’) as the valuable source of salt tolerance. We found these two strains had different salt tolerance mechanism, where ‘Ukushima’ prevented Na⁺ accumulation in leaves by filtering Na⁺ in roots and stems, while ‘Tojinbaka’ accumulated Na⁺ throughout the whole plant body. We also found ‘Tojinbaka’ and ‘Ukushima’ could retain photosynthesis even under salt stress. In addition, ‘Ukushima’ and especially ‘Tojinbaka’ showed even better growth in a salt-damaged field in Fukushima, Japan where soybean cultivar ‘Tachinagaha’ could not survive. Since both salt tolerant strains are cross-compatible with adzuki bean, our results will facilitate developing salt tolerant cultivar by introducing two different mechanisms of salt tolerance.