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.

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Wild relatives of crops have the potential to improve food crops, especially in terms of improving abiotic stress tolerance. Two closely related wild species of the traditional East Asian legume crops, Azuki bean (Vigna angularis), V. riukiuensis “Tojinbaka” and V. nakashimae “Ukushima” were shown to have much higher levels of salt tolerance than azuki beans. To identify the genomic regions responsible for salt tolerance in “Tojinbaka” and “Ukushima”, three interspecific hybrids were developed: (A) azuki bean cultivar “Kyoto Dainagon” × “Tojinbaka”, (B) “Kyoto Dainagon” × “Ukushima” and (C) “Ukushima” × “Tojinbaka”. Linkage maps were developed using SSR or restriction-site-associated DNA markers. There were three QTLs for “percentage of wilt leaves” in populations A, B and C, while populations A and B had three QTLs and population C had two QTLs for “days to wilt”. In population C, four QTLs were detected for Na+ concentration in the primary leaf. Among the F2 individuals in population C, 24% showed higher salt tolerance than both wild parents, suggesting that the salt tolerance of azuki beans can be further improved by combining the QTL alleles of the two wild relatives. The marker information would facilitate the transfer of salt tolerance alleles from “Tojinbaka” and “Ukushima” to azuki beans.

A Straight Twisted Polymeric Fiber Actuator (STPFA) has attracted attention as a new rotational actuator because it is soft, lightweight, silent, and inexpensive. It can rotate when heating, and be back when cooling. However, it is difficult to improve the response, especially in the cooling phase when using natural cooling. In order to improve the response in natural cooling, antagonistical actuation is one of the effective methods. However, the diactivated-side actuator generates a disturbance-like torque when the other-side actuator is activated due to its passive torsional spring-like characteristics. In order to realize the antagonistical actuating module using a pair of rotational-type STPFA, in this paper, the models are constructed that can estimate the torque generated at both ends of an antagonistically arranged rotational STPFA from the change in heater resistance. A sensorless output torque control method is proposed for the total torque obtained as the difference between the torques at the two ends using the proposed STPFA models. The effectiveness of the proposed method is demonstrated through fundamental experiments using a prototype module.