Snake gourd (Trichosanthes anguina l.) belongs to the family cucurbitaceae having a chromosome number 2n=22, which primarily originated in Indo-Malayan region. It is a common annual creeper and cultivated in various parts of Bangladesh. Winter vegetables are usually grown in 62.05% of the total land area, while 37.95% areas are covered by summer vegetables (BBS, 2003). Snake gourd is a day neutral type vegetable which usually grows well from March to October both in the field and homestead garden. As a result, it can meet the vegetable demand during early kharif when there exists an acute shortage of vegetables in Bangladesh. In addition, it has got tremendous export potentiality because of its excellent keeping quality. Again from the nutritional point of view, snake gourd can be considered as a nutritious fruit vegetable. It contains a considerable amount of protein (0.5%), fat (0.3%), minerals (0.5%), fiber (0.5%) and carbohydrates (3.3%) (Gopalan et al., 1982). Ripe fruits are rich in vitamin A. Snake gourd 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 for the development of the Open Pollinated (OP) variety utilizing the existing variability. Other countries like India and Thailand have developed some OP and hybrid varieties. Hybrid and mutant varieties having high yield potentiality have also been developed in India (Natarajon et al., 1984). Recently, Thailand has also developed a high-yielding hybrid variety of snake gourd.
Genetic information, such as gene action and contribution of genetic components to the inheritance of the quantitative characters, is necessary for the planning of effective breeding program in snake gourd. Very limited information is available for determining the nature of gene effects and inheritance of yield and yield-contributing characters in snake gourd. Banik (2003) reported that the number of fruits per plant, nodes on the main vine and number of seeds per fruit were controlled by over-dominant gene actions. Branches per plant, days to first male flower opening, node number of the first female flower, weight of fruits per plant, fruit length, fruit girth and 100-seed weight were controlled by partial dominant gene actions. Diallel cross analysis leads to a fruitful result for identification of genetic parameters regarding the combining ability as well as dominance relationship of the parents by studying the F1 hybrids. Thus the main objective of the present study of 5 ´ 5 half diallel cross was to estimate the nature and extent of gene action of yield-contributing characters. |