Physiological studies on the sudden wilting of Japonica/Indica crossed rice varieties in Korea, 2; artificial induction of sudden wilting in Korea and the effect of nutrio-physiological status

The results of the investigation on the effects of plant nutrio-physiological status and reemergence of sudden wilting in rice on the occurrence of sudden wilting were summarized. The occurrence of sudden wilting, degree of damage and occurring time in the investigated variety showed to concur with the results of the previous experiment. Nitrogen and potassium contents in leaves related to an occurrence of sudden wilting at heading stage have a very high negative correlation (the value is -0.9224 at Yushin and -0.8243 at Milyang 23). Regarding the relation between occurrence of sudden wilting and root activity capacity at the late growth stage, the root activity capacity at productive growth stage showed higher than at reproductive growth stage, which is the same in the two varieties but Milyang 23 is higher than Yushin. It is confirmed that root activity capacity in the two varieties has become very low at reproductive growth stage. The root activity capacity in the field with potassium showed a small occurrence of sudden wilting and the root activity capacity in the field with no potassium showed a very high correlation value (the value is 0.8947 at Yushin and 0.7301 at Milyang 23). Regarding the relation between the occurrence of sudden wilting and water evaporation quantity, water evaporation quantity after the heading date has a more direct relation to sudden wilting than that which occurs prior to the heading date. Water evaporation quantity is higher in the field with no potassium, low leaves and Yushin, than in the field with potassium high leaves and Milyang 23. The starch content in culm of Yushin and Milyang 23 at ripening stage showed high value in proportion to potassium quantity, and the starch content is lower as internode is lower. However, in fourth internode, the starch content is greatly increased in the field with potassium contrasted to the field with no potassium