EFFECTS OF SUPPLEMENTAL LIGHTING AND FRUIT THINNING ON FRUIT YIELD AND SOURCE-SINK RELATIONS OF GREENHOUSE TOMATO PLANTS

The purpose of this study is to determine an optimal source sink relat ionship by pruning clusters to an appropriate size to maximize fruit y ield of tomato plants grown under supplemental lighting (SL). An incre ase in SL from 50 to 150 mu mol .(-2). s(-1) resulted in an increase i n total fruit yield and percentage of marketable fruit. Large cluster size decreased percentage of marketable fruit. A SL of 150 mu mol . m( -2). s(-1) with fruit thinning prevented the reduction in marketable f ruit yield. Using a SL of 150 mu mol . m(-2). s(-1) increased photosyn thesis and sugars and starch centent in leaf. Fruit thinning caused an increase in glucose, fructose, and starch content in leaf but a reduc tion in photosynthetic rate. A large cluster size, representing a high photosynthate demand, decreased sugars and starch content and increas ed photosynthetic rate. The combination of a SL of 150 mu mol . m(-2). s(-1) with 3 fruit/cluster appears to be a better source sink equilib rium during periods of low natural light.