| dc.description.abstract | Rising summer temperatures in Bangladesh severely constrain bottle gourd productivity,
necessitating the identification of heat-tolerant parents and the development of superior
hybrids. To address this challenge, a comprehensive research program was conducted from
2022 to 2025 at the BRAC Vegetable Research Center, Dinajpur, involving fifty-eight (58)
genetically diverse bottle gourd genotypes. The study aimed to assess genetic variability and
screen heat-tolerant genotypes, identify superior parents through combining ability, and
develop heterotic hybrids under heat stress. Initially, the 58 genotypes were evaluated under
both optimum (Rabi) and heat-stress (Kharif) environments for morphological, yield
contributing, and quality traits. Wide and significant genetic variability was observed for days
to first female flower appearance, node number at first female flower appearance, days to first
edible fruit harvest, fruit length, fruit diameter, number of fruits per plant, fruit weight, fruit
yield per plant, total soluble solids, dry matter content, and ascorbic acid content. High
heritability coupled with high genetic advance for most traits indicated the predominance of
additive gene action and substantial scope for genetic improvement through selection.
Correlation and path analyses identified number of fruits per plant, fruit weight, and fruit
diameter as primary yield determinants, with earliness contributing indirectly, establishing
these traits as key selection criteria under heat stress. Heat tolerance was assessed using
combined stress tolerance indices of major yield-contributing traits. Based on indices values,
ranking, and cluster analysis, genotypes were classified into 21 heat-tolerant, 18 mid-tolerant,
and 19 susceptible groups. From these, 20 tolerant and two mid-tolerant genotypes were
selected for further evaluation through line × tester analysis under heat stress conditions.
Combining ability analysis identified several parents with desirable general combining ability
(GCA) effects for earliness, fruit size, yield components, and yield per plant. Based on per se
performance and GCA ranking, six genotypes with BG-01, BG-16, and BG-21 as strong
general combiners and BG-42, BG-55, and BG-53 as moderate but trait-specific good
combiners were selected for a 6 × 6 full diallel mating design. Diallel analysis conducted
during Kharif 2025 under heat stress showed highly significant GCA, SCA, and reciprocal
effects for all studied traits, confirming the involvement of additive, dominance, and maternal
genetic components, as well as the importance of cross direction in hybrid performance.
Among the parents, BG-53 and BG-21 were identified as superior general combiners for fruit
yield and major yield determinants. Heterosis analysis revealed significant positive heterosis
over mid-parent, better-parent, and standard checks for yield and yield-contributing traits
under heat stress. The hybrid BG-53 × BG-16 exhibited maximum heterosis for number of
fruits per plant and fruit yield per plant. BG-53 × BG-01 recorded the highest heterosis for
average fruit weight along with substantial yield advantage. BG-55 × BG-42 showed
significant heterosis for fruit diameter along with favorable yield and quality traits. Crosses
BG-01 × BG-21 and BG-21 × BG-53 combined desirable earliness with high yield heterosis,
indicating strong dominance and over-dominance effects under heat-stress conditions.
Genotypes BG-53 (mid-tolerant, early, and prolific) and BG-21 (tolerant, with higher fruit
weight and yield) were identified as key parental lines for heat-stress breeding programs. The
hybrids BG-53 × BG-16, BG-53 × BG-01, BG-01 × BG-21, BG-21 × BG-53, and BG-55 ×
BG-42 were selected as promising for potential commercial hybrid development under heat
stress in Bangladesh. | en_US |
