GENE ACTION AND HETEROSIS FOR QUANTITATIVE TRAITS IN Brassica rapa L

Abstract

The experiment was carried out to evaluate the seven parents and 21 F 1 hybrid that came from 7×7 half diallel cross of Brassica rapa, excluding reciprocals, for twelve yield and yield contributing attributes. The half diallel mating procedure was doneduring Rabi season 2021-2022 to develop 21 F 1 hybrids. A set of 7×7 half diallel cross (excluding reciprocals) of B. rapa along with their parents were evaluated to estimategenetic variability, correlation among the characters, path coefficient analysis, heteroticeffects and general and specific combining ability of parents and crosses respectivelyat Sher-e-Bangla Agricultural University research field during Rabi 2022-2023 atRandomized Complete Block Design with three replications. Results revealed that allthe observations exhibited high heritability in broad sense. Correlation revealed that at phenotypic level, plant height, number of primary branches per plant, number of secondary branches per plant and number of siliquae per plant showed positive and significant correlation with yield, while plant height and number of siliquae per plantshowed significant positive association at genotypic level. Path analysis revealed thatdays to first flowering (0.049), days to 50% flowering (0.745), number of primarybranches per plant (0.305), number of siliquae per plant (2.224), siliqua length (0.022),beak length (0.342), number of seeds per siliqua (1.734) and thousand seeds weight(0.821) has direct positive effects towards yield. Higher σ 2 sca than σ 2 gca was reportedfor all the characters, indicating non-additive gene action prevailing for the inheritanceof the traits. The parental lines P5 and P6 were reported best general combiner forearliness, where P2 act as for dwarfness and P5 for yield. Among the hybrids, V15 (P3×P7), V3 (P1×P4) and V13 (P3×P5) found as best specific combiner for earlymaturity where V10 (P2×P6), V11 (P2×P7), V21 (P6×P7) and V7 (P2×P3) found bestspecific combiner for dwarfness. The crosses V2 (P1×P3) and V18 (P4×P7) found as best specific combiner for yield. In heterosis analysis, the hybrids V15 (-16.49%), V13 (-24.77%) and V19 (-16.49%) showed higher magnitude of negative heterosis over mid-parent, better parent and check variety, respectively for days to first flowering. For days to maturity, V14 (P3×P6) exhibited highest negative heterosis over mid parent (7.98%),

better parent (-10.69%) and check variety (-5.46%). For plant height, V10 (P2×P6) showed highest negative heterosis over mid parent (-16.41%), better parent (17.91%)

and check variety (-14.38%), which can be used for development of dwarf variety. For number of primary branches per plant, V7 (P2×P3) and V17 (P4×P6) represented significant amount of positive heterosis over mid parent, better parent and check variety. V18 exhibited significant positive heterosis for number secondary branches per plant over mid parent and better parent. The highest heterotic advantage for number of seeds per siliqua over mid parent and better parent was observed by V10 (P2×P6). The most heterotic hybrids over check variety for seed yield per plant were V4 (28.14%) which was followed by V2 (27.20%) and V13 (25.33%). Vr-Wr graph showed over dominance for days to maturity, number of primary branches per plant, number of seeds per siliqua and thousand seed weight, and thus heterosis breeding is important to improve those traits.