Date Published: August 19, 2019
Publisher: Public Library of Science
Author(s): Saurabh Singh, S. S. Dey, Reeta Bhatia, Raj Kumar, Kanika Sharma, T. K. Behera, Harsh Raman.
In Brassica oleracea, heterosis is the most efficient tool providing impetus to hybrid vegetable industry. In this context, we presented the first report on identifying superior heterotic crosses for yield and commercial traits in cauliflower involving cytoplasmic male sterile (CMS) and doubled haploid (DH) lines as parents. We studied the suitability of genomic-SSRs and EST-SSRs based genetic distance (GD) and agronomic trait based phenotypic distance (PD) for predicting heterosis in F1 hybrids using CMS and DH based parents. 120 F1 hybrids derived from 20Ogura based CMS lines and 6 DH based testers were evaluated for 16 agronomic traits along with the 26 parental lines and 4 commercial standard checks. The genomic-SSRs and EST-SSRs based genetic structure analysis grouped the 26 parental lines into 4 distinct clusters. The CMS lines Ogu118-6A, Ogu33A, Ogu34-1A were good general combiner for developing early maturity hybrids. The SCA effects were significantly associated with heterosis suggesting non-additive gene effects for the heterotic response of hybrids. Less than unity value of σ2A/D coupled with σ2gca/σ2sca indicated the predominance of non-additive gene action in the expression of studied traits. The correlation analysis of genetic distance with heterosis for commercial traits suggested that microsatellites based genetic distance estimates can be helpful in heterosis prediction to some extent.
In the plant kingdom, the family Brassicaceae holds a great agronomic, scientific and economic significance and comprises of more than 372 genera and 4060 species . Brassica oleracea (CC, 2n = 18) constitutes a diverse group of economically and nutritionally important morphotypes known as cole vegetables (kale, kohlrabi, cabbage, cauliflower, broccoli, brussels sprout) . The Brassica vegetables are also termed as ‘super-food’ as they are vital source of secondary metabolites, antioxidants, vitamins and minerals [3, 4, 5, 6]. Among the cultivated B. oleracea morphotypes, cauliflower (B. oleracea var. botrytis L.) is an important vegetable crop grown worldwide. Great efforts have been made to improve the productivity and quality of this crop because of its huge economic value and quality attributes . The replacement of open-pollinated varieties with F1 hybrids become more pronounced in cole vegetables because of their high uniformity, better quality, tolerance to various biotic and abiotic stresses [5, 8]. The genetic mechanisms namely, sporophytic self-incompatibility (SI) and cytoplasmic male-sterility (CMS) have been used widely in hybrid breeding programme of B. oleracea [5, 8, 9, 10, 11, 12]. However, frequent breakdown of self-incompatibility has been reported in Brassica vegetables due to the high temperature sensitivity of S-alleles. Thus, SI lines are not always stable and result in ‘sibbed’ seed in hybrid population . Moreover, maintenance of S-allele lines is time-consuming and expensive. In snowball cauliflower, SI system is very poor or not present at all [11, 13]. Under these circumstances, the CMS provides a better alternative for the heterosis breeding in cole crops [5, 8, 14].
The current study is first of its kind in determining the heterotic groups based on combining ability for morphological, yield and commercial traits using Ogura cytoplasm-based CMS lines and DH based testers. We also presented the first comprehensive report on predicting the association of genomic SSRs and EST-SSRs based GD and morphological traits-based PD with heterosis involving CMS and DH parental lines in snowball cauliflower. Analysis of variance of parents and their testcross progenies revealed the presence of significant genetic variability. Present investigation also emphasizes the relevance of both GCA and SCA in the selection of elite parents for the improvement of yield and commercial traits and predicting appropriate breeding strategies for the crop genetic improvement, developing high yielding hybrids, synthetics and composites in cauliflower. High and significant correlation among SCA with heterosis suggested the role of non-additive gene effects in heterosis. It was also evident that development of DH lines could broaden the genetic base of any crop through creating more diversity in the existing population. The findings of our study further suggested that genetic distances based on genomic and EST-SSRs can be used as a predictor of heterosis for commercial traits in CMS and DH based F1cauliflower. Contrasting results obtained in different earlier studies regarding the efficacy of genetic distances in the prediction of heterosis, invites further investigation with different sets of large number of molecular markers covering entire genome, and a different set of parental germplasm, in multiple standard environments.