The evolution of genetic diversity of broccoli cultivars in China since 1980

Abstract

Broccoli is a worldwide vegetable famous for good nutrition that is particularly rich in sulforaphane. The evolution of 95 broccoli cultivars that were widely collected and cultivated in China since 1980 was evaluated using 35 pairs of SSR markers. Thirty-five markers were selected from 960 pairs of SSR markers designed from Brassica oleracea, rapa and napus by two resources with different maturity periods. The results revealed that all 35 pairs of SSR markers were polymorphic, and 167 alleles were amplified with an average of 4.8 per marker. The mean content was 0.79 for polymorphism information, with a range from 0.48 to 0.99. The genetic diversity indexes ranged from 0.6909 to 0.8969, with an average of 0.7809. Genetic diversity analysis indicated the 95 genotypes could be separated into five primary sub-groups at a 0.72 distance. Sub-group A included more than 70% of genotypes with early and mid-early maturating cultivars, and the cultivars covered more than 87% of the genotypes of the 95 materials, including the primary cultivars widely planted that directed the domestication of broccoli in China in the past 37 years. Sub-groups B and C contained one inbred line with high generation and one DH line, respectively, suggesting both were innovative resources in cultivation. Sub-groups D and E were all inbred lines, and sub-group D had six members with similar characteristics: small florets, high-domed head, tall plants with nearly no lateral branches and good heat tolerance. Sub-group E had five members that presented similar wrinkle leaf morphology, and most matured at an intermediate rate, except IVF-B18. In this study, the evolution of broccoli cultivars in China was first summarized overall, together with their characteristics and distributions in China. Our study provides important information on genetic diversity and for cultivar replacement of broccoli in China, in addition to two new germplasms and polymorphism markers for research and molecular breeding.