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Studies on the Necrosis in Grapevine Beds(III) : The Time of the Occurrence of Bud Necrosis in 'Kyoho' and the Relation between its Occurrence and the Amounts of Nutritional Elements in Buds
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The time when necrosis was first detected in the central buds of lateral buds in 'Kyoho' grapevines was a little different depending on their position on shoot ; it was 28 days after full bloom between the 5th and 8th nodes at which the percentage of necrotic buds was highest and was 34 days after full bloom between the 13th and 16th nodes. Necrotic buds increased rapidly thereafter and the percentage of them reached the highest value in about 20 days. Only few buds developed necrosis after the period. The time when necrosis was first detected was almost the same in the axillary buds of lateral buds as in the central ones although the occurrence percentage in the axillary buds was much lower than that in the central ones. Further, the percentage of necrotic buds was higher in both the central and axillary buds of strong shoots than those of weak ones, and strong shoots elongated vigorously during the time when the suspective lateral buds at lower position on them developed in size.
Among the contents of starch, reducing sugar, non reducing sugar, N, P, K, Ca, Mg, Mn and B in the lateral buds of lower position on shoots, only those of starch, total sugar and reducing sugar exhibited close relation with the occurrence of necrosis. In 'Kyoho', starch was higher and on the contrary total and reducing sugars were lower in weak shoots than in strong ones. Furthermore, starch was higher than total sugar in weak shoots and an oposit tendency between them was detected in strong ones during the period when necrotic buds increased rapidly. Almost the same quantitative relation of both elements was found between the strong shoots of 'Kyoho' which was suspective to necrosis and those of 'Delaware' and 'Muscat Bailey A' which were resistant.
Shimane University, Faculty of Agriculture