Recently-released genotypes of naked oat (Avena nuda L.) out-yield early releases under water-limited conditions by greater reproductive allocation and desiccation tolerance

Naked oat (Avena nuda L.) is becoming increasingly popular because of its high nutritive value and increased yields. As naked oat is grown in marginal environments, one of the limitations to yield is drought stress. In this study conducted in the field and a rainout shelter, the yield, water relations, and physiological and biochemical responses to drought of six genotypes, three released since 2008 (recently-released, RR) and three genotypes released at least 60 years earlier (early-released, ER) were compared. The grain yield, harvest index (HI) and water use efficiency for grain were higher in the RR than ER genotypes under rainfed and irrigated conditions in the field and under drought and well-watered conditions in the rainout shelter. Aboveground biomass and HI had significant direct effects on grain yield, while leaf dry weight was negatively associated with grain yield in the rainout shelter. During a progressive soil drying experiment, the threshold soil water content (SWC) when stomatal conductance and photosynthesis began to decrease was lower in the RR [48–52% field capacity (FC)] than ER (54–58% FC) genotypes, but whole plant transpiration began to decrease when the leaf water potential and relative water content began to decrease at a threshold SWC of 31–44% FC in both the RR and ER genotypes. The beginning of the decrease in stomatal conductance and photosynthesis was associated with the increase in leaf abscisic acid concentration, but higher osmolyte accumulation, greater osmotic adjustment and less lipid peroxidation in the RR genotypes than the ER genotypes occurred at low SWC (below 30% FC) and are associated with greater desiccation tolerance in the RR genotypes. We conclude that the higher yields in the RR genotypes of naked oat are associated with selection for higher reproductive allocation and desiccation tolerance. The role of stomatal closure and osmotic adjustment on adaptation to drought are discussed.