Bangladesh J. Pl. Breed. Genet., 23(2): 01-06, 2010 COMBINING ABILITY AND HETEROSIS IN SNAKEGOURD (Tricosanthes cucurminata L) R. Podder, M. G. Rasul, A. K. M. A. Islam, M. A. K. Mian and J. U. Ahmed 1 Department of Genetics and Plant Breeding Bangabandhu Sheikh Mujibur Rahman Agricultural University Gazipur 1706, Bangladesh ABSTRACT A half diallel set of five parents and their 10 F 1 ’s were studied to determine the combining ability and magnitude of heterosis for eight important characters in snakegourd at the experimental field of Bangabandhu Sheikh Mujibur Rahman Agricultural University during April to July, 2004. Combining ability analysis revealed that both general and specific combining ability variances were significant for all the characters except fruit diameter and fruit yield per plant. Predominance of additive gene action was noted for all the characters except days to first female flower where non-additive gene action was predominant. Parent P 1 was the best general combiner for fruit yield and some yield contributing characters. Among the crosses P 2  P 3 , P 1  P 2 and P 1  P 4 were the best specific combiner for fruit yield and some of yield contributing characters. Both positive and negative heterosis was obtained of which few hybrids showed desirable and significant values. P 2  P 5 showed the highest significant mid parental heterotic value for earliness and high yield whereas, P 1  P 2 , P 2  P 3 , P 2  P 5 and P 3  P 4 showed the highest significant better parent heterotic effect for earliness and high yield. Key words: Snakegourd (Trichosanthes cucurminata L.), combining ability, heterosis, fruit yield INTRODUCTION Snakegourd is an annual, climbing type day neutral herbaceous vegetable crop and belongs to the family cucurbitaceae. It is cultivated all over the Bangladesh and an important summer vegetable in this country. There are lean period at the end of winter and beginning of summer seasons when there is always a scarcity of vegetables in this country. Vegetable scarcity during that gap period can be ameliorated to same extent through improvement of cucurbitaceous crops like snakegourd. In addition it has got tremendous export potentiality because of its excellent keeping quality. There are a number of cultivars with wide range of variability in size, shape and color of fruits available in this country (Rashid, 1993). Snakegourd is monoecious and highly cross- pollinated in nature. Such pollination mechanism can be exploited for the production of hybrid variety. Moreover, there is a bright scope of development of open pollinated variety utilizing the existing variability. Combining ability is one of the powerful tools in identifying the best combiners that may be used to exploit heterosis or to accumulate fixable genes (Srivastaba and Bajpai, 1977). Diallel cross analysis leads to a fruitful result for identification of genetic parameters related to combining ability as well as 1 Department of Crop Botany, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh