日本ナシ果実の硬化障害に関する研究 (第2報)

Abstract

This paper deals with the effects of application of CaO2 and CaO and soil moisture regimes, pF 1.3, 2.2 and 2.6, on the incidence of ‘Yuzuhada’ disorder. The effects were examined during the period from 1973 to 1977, using potted eight-year-old Nijisseiki pear trees that so far had developed the symptoms of ‘Yuzuhada’ disorder more or less every year. Besides the pot tests, multivariate analysis was applied to the data obtained by chemical analysis of soils, fruits, and leaves to detect major contributing factors. This information is necessary for devising an effective control measure of the ‘Yuzuhada’ disorder. The results obtained are summarized as follows:1. In the treatment of pF 2.2, the incidence of ‘Yuzuhada’ disorder was decreased markedly by CaO2 and CaO applications even in the first year after the application and thereafter decreased further to as low as 13 percent in the fourth year. Fruits of these treatments had grown fully and showed considerably high marketable quality with slight symptoms of the disorder. Under both pF 2.6 and 1.3, however, CaO2 application increased the percentage of ‘Yuzuhada’ fruit up to 60 percent, and CaO up to 80 percent, though the calcium applications decreased it to less than 50 percent in the first year only.2. When expressed as percentages of dry weight basis or as total quantity per fruit, N, P, and K contents of fruits of pF 1.3 treatment were lower than those of pF 2.2 and 2.6, and Ca and Mg contents of pF 1.3 treatment were lower than those of pF 2.2. K and Ca contents of fruits were lower, while N content was higher, under pF 2.6 than under pF 2.2 and 1.3.3. P, K, and Ca contents of leaves expressed on a dry weight basis were lower under pF 1.3, and K and Ca contents were lower under pF 2.6 than under pF 2.2. Exchangeable Ca and Mg contents of soils were decreased in the pF 1.3 treatment, while exchangeable K and Ca were decreased in the pF 2.6 treatment. Besides, total calcium content of the soil was lower under pF 1.3 and 2.6 than under pF 2.2. These facts imply that the fixation and leaching of basic elements occurred in the soil by drying and moistening treatments, respectively.4. Fructose and sucrose contents in the fruit were increased, while glucose and sorbitol contents were decreased, by the calcium applications under pF 2.2. Under pF 1.3 and 2.6, however, neither fructose nor sucrose was increased and glucose or sorbitol was not decreased by calcium application. On the other hand, titratable acidity of fruit juice was somewhat increased under pF 2.6 and conversely decreased under pF 1.3.5. Respiration rate and ethylene production in the fruit were more increased under pF 1.3 and 2.6 than under pF 2.2. In other words, fruit maturity was markedly progressed by both drying and moistening of pot soils.6. Principal component analysis was applied to the data obtained by chemical analysis of soil and plant materials. Ca contents of both fruit and leaves significantly contributed to the first principal component, while various factors, such as the content of exchangeable Ca and Mg, percentage calcium saturation, and pH values of soils, contributed to the second principal component. Additionally, amounts of CO2, ethylene, and starch production also seemed to be significant factors pertaining to the incidence of ‘Yuzuhada’ disorder. The results of multiple regression analysis showed a tendency similar to those obtained by principal component analysis. It is suggested that factors which significantly contribute to the first and second components may influence the incidence of ‘Yuzuhada’ disorder developed on the Nijisseiki pear tree.