Author : Wirat Phuwiwat

Summary : The findings showed that the three sweet pepper cultivars have considerable morpho-anatomical and physiological adaptations to partial shade. Increasing shade levels had favorable effects on vegetative growth which subsequently contributed to growth and yield of the three cultivars. The morpho-anatomical adaptations of sweet pepper plants to low light intensity were: (a) increased total leaf area; (b) increased plant height; (c) longer internodes; (d) increased node number; (e) bigger canopy diameter; and (f) decreased leaf thickness. They were responsible for the plants' increased light interception and greater carbon dioxide assimilation which consequently increased overall photosynthesis and dry matter production. The decrease in leaf stomatal number on leaf area basis resulted to the reduction of the photosynthetic and transpiration rates on leaf area basis. Since total leaf area and total chlorophyll content increased, growth of the plants measured in terms of dry weight, leaf area index and crop growth rates, consequently increased. Moreover, analysis for sugar and starch contents of the various plant parts revealed that the fruit was the priority sink and that photosynthates (from the leaves) were efficiently translocated to this plant part. Fruit yield increased when shade level was increased up to 49% during the dry season and up to 43% during the rainy season. Fruit number, harvest index and to some extent fruit size were observed to be varietal characteristics and were not influenced by partial shade. 'Sinagtala' produced the most number of fruits but were significantly smaller than those produced by 'California Wonder' which were fewer but significantly bigger. The most suitable shade level for the production of these three sweet pepper cultivars was 49% for the dry season and 43% for the rainy season. Heavy shading (56% shade level) however, tended to have detrimental effects on growth, development and yield of the three sweet pepper cultivars.