INFLUENCE OF POST-FRUIT SET PLANT EXPOSURE TO LOW LIGHT INTENSITY ON GROWTH AND YIELD OF ORIENTAL MELON

This study was conducted to examine the growth of oriental melon (Cucumis melo L.) in response to low light levels (100, 200, 400 µmol.m^-2.s^-1) by shading the natural light 10 d after fruit set. Plants exposed to low light intensity had significantly smaller leaf areas, shorter root, and lower fresh and dry weights as compared to those remained under natural light. However, plant height and stem diameter were unaffected by low light conditions. The photosynthetic rate and leaf chlorophyll index decreased with reducing light intensity. Root activity determined with formazan test was higher in plants grown under natural light than in those exposed to low light radiation. There was no significant difference in root activity among plants grown under the three different light levels. Leaves of the plants exposed to low light intensity had only 30 to 50% of trans-zeatin levels compared to those grown in natural light. Leaf chlorosis and fruit drop increased with reducing light intensity. Total fruit yield was severely reduced by light intensity reduction. Percent marketable fruits from total harvests were 0, 3, 10, and 81%, respectively, for plants grown under 100, 200, 400 µmol.m^-2.s^-1, and natural light. Marketable yield per plant was sharply decreased in low light intensity. Compared to natural light, the yield of low light intensity treatment ranges from 16 to 34%. The foliar fertilization treatment with 0.5% urea had 34% higher harvest index of marketable yield than other treatments. In conclusion, it is recommended that we should carry out fruit thinning and foliar fertilization with 0.5% urea when the long low light condition from 10th day after fruiting was forecasted.