Successful hybrid development work in cotton involves unearthing information of combining ability, heterosis and per se performance of the genetic material. This study involved multi‐environment estimation of combining ability and heterosis along with the stability of per se performance using Bt cotton genetic materials for seed cotton (Gossypium hirsutum L.) yield. Combining ability analysis across environments showed significant effects on the performance of genotypes, general combining ability (gca), specific combining ability (sca), genotype × environment, GCA × environment, and SCA × environment interactions. Combining ability variance revealed the predominance of nonadditive gene actions for seed cotton yield. The mean performance combining ability estimates were varied with the locations for parents as well as for hybrids. In a low yielding environment, the transgenic BGI parents, as well as hybrids, showed superior seed cotton yield levels compared with BGII or non‐Bt versions. There was a significant increase in heterosis noticed in BGII hybrids compared with BGI hybrids in a low yielding environment. The stability parameters showed significant genotype × environment variation and indicated that the stability of the genotype was mainly affected by the genetic background of the material. A positive association was noticed between per se performance and gca effects, heterobeltiosis and sca, and heterobeltiosis and mean of hybrids as the environment`s yield potential increased. The majority of the Bt hybrids showed positive heterosis over a better parent. Among the two versions of Bt transgenic cotton, BGI excelled in per se performance and gca and sca effects for seed cotton yield either in the homozygous form or hemizygous hybrids.
A study was conducted to understand the stability of seed cotton yield of 105 Bt cotton hybrids (BGI and BGII) using Additive Main effects and Multiplicative Interactions (AMMI) analysis across three diverse locations in India during rainy season 2018. This study holds importance as the hybrids were resistant to Helicoverpa bollworms due to Bt events (MON531 and MON15985) in them which were expected to nullify variation arising out of differential bollworm pressure in different location, unlike in non Bt hybrids where this variation also played role in the stability of the hybrids. The main effect differences among hybrids (41.23 %), environments (39.56 %) and the interaction effects (19.21%) were highly significant of the total variance of seed cotton yield indicating a large difference between the testing location causing different hybrids to perform differently across the testing environments. The first two principal components axes (IPCA I and IPCA II) were highly significant and contributed 52.12 % and 47.88% of total interaction respectively. The distance from the origin and the placement of locations in different quadrants of biplot reflected that the locations were substantially discriminatory as Aurangabad and Dharwad, which were high yielding and Raichur was low yielding. Results showed that hybrids IAHH-8096 BGII, IAHH-8103 BGI, IAHH-8061 BGII and IAHH-8007 BGII were having lowest interaction and stable across the location, whereas hybrids IAHH-8080 BGI, IAHH-8084 BGI, IAHH-8004 BGII and IAHH-8105 BGI were having more interaction and unstable genotypes. Large frequency of hybrids (57) were stable with IPCA scores nearing zero and low ASV values which is attributed resistance to bollworm due to Bt events.
A study was conducted at Dharwad, Raichur and Aurangabad in India during the rainy season of 2018 to investigate the environmental impact on combining ability and heterosis estimates in cotton. Combining ability analysis across locations showed significant effects on the performance of genotypes, GCA, SCA, genotype×environment, GCA×environment and SCA×environment interactions for most of the characters. Combining ability variance revealed the predominance of non-additive gene actions for characters under study. The parents and crosses varied with locations for combining ability and better parent heterosis estimates. Out of 22 parents, ten parents recorded high overall gca and among them, two BGII, six BGI and two non-Bt parents were under study. Similarly, 55 hybrids were exhibited high overall sca and better parent heterosis from the study and most of the crosses were derived from lines crossed with high overall gca (H) with low overall gca (L) or vice versa. This study indicated the requirement of parents with contrasting gca effects to realize a higher frequency of heterotic hybrids. The predominance of H×L type of crosses indicated the presence of non-additive gene action suggesting exploitation of good heterotic hybrids from the study. The frequency of hybrids with high overall sca and heterobeltiosis was more in BG II hemizygous hybrids compared to BG II homozygous condition with H×L type. Similar were the results with BGI hemizygous hybrids.
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