MORPHO-PHYSIOLOGICAL AND VINE DEVELOPMENT, FLOWERING AND SEX EXPRESSION OF WATERMELON PLANTS GROWN IN WINTER SEASON UNDER LOW-TECH GREENHOUSE

Although a few works have been conducted on low-tech greenhouse (LTG) for growing horticultural crops in Bangladesh but the cultivation of watermelon in winter season is unexplored. Therefore a study was conducted from late autumn to winter season of 2015/2016 to evaluate the production potentials of four varieties of watermelon viz. Sonya, Black Dorin, Badsha and Dragon. Three LTGs each represents a replication were erected where four pits were prepared under each LTG and four watermelon varieties were separately grown in separate pits. The variation in temperature between the LTG and those at outside was observed larger at around middle of the day and maximum variations were noticed in air and soil temperatures as much as 9 and 2oC, respectively around the noon time. Phenological development like days to first leaf, first vine and first male flower appearance was hastened due to high temperature by 2, 9 and 8 days, respectively. Vine growth in terms of number and length of vine, vine diameter, node number and internode length, leaf size etc. was found significantly greater in the plants grown with LTG than that found in the plants grown outside. Low-tech plants produced thinner leaves (i.e. higher specific leaf area) than that at outside indicate that leaf lamina expanded rapidly under high temperature. The higher vine growth under LTG can be ascribed due to the higher photosynthetic and transpiration rates as much as 3.5-fold (than that at outside) as favoured by high temperature. However, such excessive vine growth under LTG seriously hampered the development of female flower although a plenty of male flower production was observed. Thus it is concluded that watermelon fruit cannot be produced in winter (off-season) by using low-tech greenhouse without taking the other scientific measures for blooming the female flowers.