Varietal variations in rice seedling growth under low oxidation-reduction potentials

In direct seeding of rice (Oryza saliva L.), rice seedlings are exposed to low oxidation-reduction (redox) potential soil, and to low temperatures in cold areas. In order to trace the genealogy of tolerance to low redox potential among Japanese rice cultivars, we selected 12 Japanese rice cultivars that had been released over the past century and determined the ability of their seedlings to tolerate immersion in low redox culture solution of Eh = -150 to -180 mv. Seedlings with coleoptiles and radicles of about 1 to 2 cm were incubated in low redox potential culture solution for 2 days at 18 and 30degreesC, and then in distilled water for 3 days at the same temperatures to examine the recovery abilities. The lengths of shoots and roots were measured after pre-germination, after low redox treatment, and after recovery from damage that occurred in the de-oxidized solution. At 30degreesC, the tolerance of low redox potentials was positively and significantly correlated with recovery from damage that occurred in the de-oxidized solution. The high tolerance of recent cultivars to these low redox potentials at 30degreesC appeared to originate from Fujisaka 5. However, at 18degreesC, the differences among the cultivars in their tolerance of low redox potentials and in their ability to recovery became small.