Abstract
The average yield of bottle gourd in Bangladesh is very low as compared to that in other tropical countries. This low yield may be due to lack of high yielding varieties. Therefore, the present study was undertaken with three separate experiments during July, 2012 to March, 2015 to study the diversity among 30 bottle gourd genotypes considering eight morpho-physiological traits for developing high yielding heterotic varieties suited to cultivate in different seasons. The field experiments were conducted at the experimental farm of the Dept. of GPB, BAU, Mymensingh and ACI R&D Farm, Rural Development Academy (RDA), Bogra. In the mean square performance, significant variations were observed among the genotypes for all the characters. The highest fruits/plant and the highest yield/plant were obtained from the genotype Hajari with minimum days for 50% female flower opening and for first edible harvest. This was followed by the genotypes BG-498, BG-582, BG-522, BG-581, BG-489 and BG-657. From the study of genetic parameters, high heritability coupled with high genetic advance in percent of mean suggested the presence of major role of additive gene action in the inheritance of these characters and improvement through selection may be effective. The correlation analysis indicates that different yield and yield contributing characters were inter correlated and they had positive association with fruit yield/plant. The results of path analysis revealed fruits/plant and fruit weight were the major contributors to yield/plant. On the basis of cluster analysis, 30 bottle gourd genotypes were grouped into three clusters. Based on higher yield and diversity, 7 genotypes viz., BG-498 and BG-582 from cluster-I, Hajari, BG-489 and BG-522 from cluster-II and BG-581, BG-657 from cluster-III were selected for 7 × 7 half-diallel crosses for heterotic breeding. Genetic diversity analyzed by RAPD markers using five random decamer primers. The primer OPL 03 showed the highest level of polymorphism. Pair wise comparisons of Nei's genetic distance (GD) among bottle gourd genotypes were estimated and the highest genetic distance was found in BG-657 Vs BG-506 followed by Hajari Vs BG-581, Hajari Vs BG-522, BG-657 Vs BG-522, BG-582 Vs BG-522 and Hajari Vs BG-657. The genotypes BG-522, BG-581, BG-498, Hajari, BG-657, BG-489 and BG-582 showed high yield performance in morphological study and most of them were genetically diverse and selected as parents in 7 × 7 half-diallel crosses. The mean squares due to GCA and SCA were significant for most of the characters indicated both additive and non-additive gene actions had greater role in the inheritance of these characters. Out of the seven parents, Hajari was found the best general combiner as it depicted high GCA effect in desirable direction for most of the traits and this was followed by BG-522, BG-657 and BG-581. Regarding SCA and heterosis effects (both mid-parent and better parent), the crosses F₁ (Hajari × BG-581), F₁ (BG-657×BG-522), F₁ (Hajari × BG-657) and F₁ (Hajari × BG-522) showed better result in respect of yield/plant revealed a great scope of obtaining higher yield in bottle gourd through heterosis breeding. The estimates of pooled variance and mean results over two distant locations and two seasons showed significant effect of seasons for all the characters and non-significant effects in location for most of the characters and the combined (genotype × location × season) effects were found to be non-significant for all the traits. Based on environmental effect, pooled mean and selection score rank, the crosses F₁ (Hajari × BG-581), F₁ (Hajari × BG-657), F₁ (Hajari × BG-522) and F₁ (BG-657 × BG-522) were showed better yield performance. On the basis of selection index score the best hybrid was F₁ (Hajari × BG-657) followed by F₁ (Hajari × BG-581), F₁ (BG-657 × BG-522) and F₁ (Hajari × BG-522). From the study in respect of all analyses and results, two crosses F₁ (Hajari × BG-657) and F₁ (Hajari × BG-581) found promising and might be recommended for farmers' cultivation for higher yield in both winter and summer seasons across the country.