二十世紀ナシのユズ肌病に関する研究 (第4報)

Abstract

In order to investigate the relationship of mineral nutrition of trees to the incidence of Yuzuhada, a physiological disorder of fruit of Japanese pear, cv. Nijisseiki, effects of the rate of K fertilization, soluble K, Ca, and Mg contents of fruit, and nutritional balance among these elements were compared between healthy and unhealthy trees. The results obtained are summarized as follows:1) In a sand culture experiment with 5-year-old Nijisseiki trees, it was revealed that the incidence of Yuzuhada fruit was more pronounced both in number and in severity as the K level of culture solution was increased from 40 to 320ppm.2) Soluble K, Ca and Mg contents of the fruit pulp of healthy and unhealthy trees located in the orchard where numerous numbers of fruit are suffering from Yuzuhada disorder were compared to those of healthy trees located in the orchard that usually produces almost no Yuzuhada disorder. Fruit of unhealthy trees showed a tendency to contain more K and Mg and less amount of Ca as compared to those of healthy trees. The Ca/K ratios of fruit, therefore, were lower in unhealthy trees than in healthy ones, especially during the periods from early to mid-May and from late June through late July. The Ca/Mg ratios of fruit also remained lower in unhealthy trees than in healthy trees throughout the growing period. No consistent differences, however, were observed between the Mg/K ratios of healthy and unhealthy trees.3) In mid-June, the content of ethanol-soluble K, Ca, and Mg was determined to ascertain the effects of these elements on the number and severity of Yuzuhada fruit produced. Fruit of unhealthy trees contained more ethanol-soluble K and less amount of ethanol-soluble Ca as compared to those of healthy trees. The correlation coefficient (r) between the content of ethanol-soluble Ca and the degree of Yuzuhada disorder produced was -0.56, though every correlation of the other combinations between each of the ethanol-soluble elements all remained insignificant. On the other hand, the ratios of each ethanol-soluble element to the other had considerably close correlations with the degree of Yuzuhada disorder i. e., r=-0.76 in the case of ethanol-soluble Ca/K ratio and r=-0.67 in the case of ethanol-soluble Ca/Mg ratio. However, the correlation coefficient between the ethanol-soluble Mg/K ratio and the degree of Yuzuhada disorder showed only a slight value, -0.26.4) These results imply that nutritional imbalance of fruit, especially narrow ratios of ethanol-soluble Ca content to the ethanol-soluble K and/or Mg content during the earlier stages of fruit development, is closely related to the incidence of Yuzuhada disorder.