Regarding plant responses to water stress, cultivars of Vigna unguiculata (yard-long bean), Cucumis sativus (cucumber) and Raphanus sativus (radish) in the tropical zone were compared with Japanese cultivars. Yard-long bean cultivars of Malaysia and Thailand showed good stomatal adjustment in response to water stress. The degree of wilting of Malaysian cultivars was much lower than other cultivars, and the recovery from leaf wilting after water stress was much faster than other cultivars from Thailand and Japan.
　Cucumber cultivars from Malaysia also showed less leaf wilting and quicker recovery from wilting than Japanese cultivars. The Malaysian cultivars, which had wilted under strong solar radiation, recovered from wilting in only 7 min after they were placed in the shade. Thus, the Malaysian cultivars of Vigna unguiculata and Cucumis sativus could avoid water stress efficiently.
　Radish cultivars from Malaysia and Taiwan showed no change in stomatal aperture and diffusion resistance, and no sign of any leaf drooping against water stress, while Japanese cultivar showed a significant increase of stomatal closure and diffusion resistance and severe leaf wilting. The same phenomenon was also observed with grown plants in the field. Furthermore, the radish cultivars from Malaysia and Taiwan had roots with large stele diameter and densely arranged vascular system compared to the Japanese cultivar.
　These results clearly indicate that Malaysian cultivars of yard-long bean, cucumber, and radish hold favorable properties to overcome water stress occurring frequently during a long period of summer in the humid-subtropical zone.