Adaptation strategy of Setaria viridis var. pachystachys to coastal environments based on morphological, anatomical, and mechanical analyses using wild and cultivated populations

Abstract Coastal areas are unique environments, and plants have undergone various changes to adapt to them. Morphological, anatomical, and mechanical analyses of wild and cultivated populations of Setaria viridis var. pachystachys (Franch et Savat.) Makino and Nemoto (Poaceae) were used to elucidate their adaptation patterns in coastal environments. In addition, comparisons were made with the closely related species S. viridis (L.) P.Beauv. var. minor (Thunb.) Ohwi. Morphological analyses revealed that S. viridis var. pachystachys has maintained its maximum fitness by increasing the number of tillers, even though this species has a short culm length and a small panicle that tolerates strong coastal winds. Anatomical analyses indicated that this species shows a decrease in stomatal number and size, which increased under cultivation conditions, revealing plastic changes in the stomata to adapt to coastal environments. Mechanical analyses showed no significant differences in culm strength between S. viridis var. pachystachys and S. viridis var. minor. In addition, cultivation experiments showed that the cultivated populations of S. viridis var. pachystachys had fewer tillers, longer culms, and larger panicles than those of the wild population. However, panicle mass per individual was not significantly different between these populations, suggesting that S. viridis var. pachystachys plastically changed its morphology to adapt to wind stress without affecting total yield. Our study showed that artificial alteration of coastal areas may exceed the phenotypic plasticity of S. viridis var. pachystachys, making it unable to adapt.