EFFECTS OF OVERHEAD SHADING ON YIELD AND FRUIT QUALITY OF KIWIFRUIT IN REGIONS WITH HIGH TEMPERATURES IN SUMMER

In most kiwifruit production areas of China, hot summer conditions frequently result in severe premature fruit drop and leaf fall. This has become a major technical restriction for kiwifruit development in China. In this study, we examined the effectiveness of overhead shading as a means to overcome the harmful effects of high summer temperatures. Field-grown vines of two Actinidia chinensis cultivars 'Cuiyu' and 'Fengyue' and one A. deliciosa cultivar, 'Miliang-1' were subjected to treatment of 70% overhead shading from early July to early September, with un-shaded vines as controls. Rates of premature fruit drop and leaf fall, fruit quality and storability, canopy microclimate conditions, and flower number the following year were subsequently investigated. In all three cultivars, shading dramatically reduced fruit drop and leaf fall, and improved fruit external appearance. Shading also improved fruit storage quality of 'Miliang-1'. Fruit soluble solids concentration was not affected by shading in 'Miliang-1' and 'Cuiyu', but was markedly decreased in 'Fengyue'. Shading did not affect flower production the following year in 'Miliang-1', but dramatically decreased flower number in 'Fengyue' and 'Cuiyu'. There was a marked increase in canopy humidity and a decrease in canopy temperature, and more strikingly, a decrease in temperatures of fruit surface and leaf surface in shaded vines. Results indicated that overhead shading in summer could effectively overcome the harm caused to kiwifruit by high temperatures. However, the level of shading should be tested carefully for individual cultivars to avoid the adverse effects of excessive shading.