1985 Volume 54 Issue 3 Pages 293-300
The aim of this study was to determine the optimum leaf area index(LAI) for fruit production of grapes when using a structure of extending arms and horizontal canes on a complete overhead pergola, as is popular in Japan. From 21 days after full bloom to harvest time, net assimilation rate(NAR) was measured in 3-year-old ‘Delaware’ vines grown in pots, half of which were kept non-shaded and half under the pergola(foliage) of 5-year-old ‘Delaware’ vines. All vines used were grown in a plastic film house. Fruit quality, NAR and crop growth rate(CGR) were measured in 4-year-old ‘Delaware’ vines grown in pots in a glasshouse with different LAIs and fruit loads.
1. A close relation was found between the NAR(Y) of the shaded vines and the LAI(X) of the shading vines (Y=0.126X2-1.33X+3.10). Growth analysis showed that the optimum LAI of ‘Delaware’ was about 3, since the LAI of the shading vines was calculated to be 3.2 when the NAR of the shaded vines was 0.
2. Little difference was observed in NAR between the vines whose LAIs were 2.08 and 2.82 but CGR increased with an increase in LAI and crop load. Bunches of vines whose LAI was 2.08 did not color well when the crop load was higher than 2kg/m2. However, in the vines whose LAI was 2.82, nearly all bunches matured normally, even when the crop load was as high as 2.8kg/m2.
3. From these results, the optimum LAI for both quantitative and qualitative fruit production in ‘Delaware’ vines grown with a complete overhead pergola in a plastic house in thought to be at least 2, and preferably 3.