Abstract
Rice plants accumulate iodine and display a physiological disorder due to the toxicity of iodine. The disorder is called "Akagare" disease. The relationship between soluble iodine in soil and "Akagare" disease of rice plants was examined. Seedlings of rice plants 20 d after germination were grown in soils rich in iodine for 29 d. In addition, the difference in response to "Akagare" disease among varieties of rice plants was compared. 1. Soluble iodine was evaluated by incubating a mixture of 2 g of soil and 10mL of 2.8×10^<-2>mol L^<-1> glucose solution for 10 to 20 d at 30℃. The concentration of iodine absorbed by rice plants correlated positively with the concentration of soluble iodine in soil. 2. Height and dry weight of shoots of rice plants decreased with the increase in the concentration of iodine in rice plants due to the toxicity of iodine. 3. The symptom of "Akagare" disease became remarkable when the concentration of iodine in rice plants (shoots) was over 300 mg kg^<-1> (dry weight basis). Iodine concentration in rice plants exceeded 300 mg kg^<-1> when the concentration of soluble iodine in soil surpassed 6-8 mg kg^<-1>. From these results, it was indicated that the possibility of incidence of "Akagare" disease was predicted on the basis of the concentration of soluble iodine in soil. 4. A remarkable difference in response to "Akagare" disease among varieties of rice plants was recognized.
