ブドウの早期落葉に及ぼす低照度の影響

Abstract

In many vineyards of horizontal trellis, defoliation due to leaf-yellowing often occurs at the basal portion of shoots in early summer. This disorder seems to be partially caused by low light intensity on this portion.1. In the Delaware vineyards, light intensity at the apical portion of shoots is higher than the basal portion. The leaves on the basal nodes receive a light intensity of 10% of full sun-light during mid June to late August. Defoliation was therefore greater in the basal portion of shoots.2. When a whole shoot of a youngDelawarevine was darkened or shaded, defoliation due to browning appeared at the apical portion of the shoot. In contrast, if only the basal portion was shaded, defoliation due to leaf-yellowing was observed at the basal portion of the shoot as seen in the commercial vineyards. There was no difference in the degree of defoliation of the apical or basal portion between bearing and non-bearing shoots.3. In youngDelawarevines, if the basal portion of the shoot was shaded, defoliation of the basal portion was promoted by basal application of GA3 50ppm and NAA 100ppm, but inhibited by BA 50ppm. In the Campbell Early vineyards, pinching and cutting back of lateral shoots were effective to prevent such defoliation.4. In theDelawarevines shading of the basal portion of the shoot sharply decreased photosynthetic activity of the leaves in this portion, and increased respiration of the leaves in the apical portion. Carbohydrate content of the leaves was less in the shaded portion. Furthermore, the translocation of 14C was greater in the leaves of the apical portion receiving high light intensity than in the leaves of the shaded basal portion. From these results, early defoliation of grapevines caused by low light intensity seemed to be attributed to the competition for carbohydrates between the leaves of these two portions.