Genetic diversity of Canadian elite summer rape (Brassica napus L.) cultivars from the pre- to post-canola quality era

Abstract

The development of canola quality Brassica napus oilseed cultivars was a major achievement of Canadian public oilseed breeding programs. Simple sequence repeat (SSR) markers were applied to assess the genetic diversity of 300 plants representing one landrace introduced from Argentina in 1943, seven Canadian elite cultivars developed and released by Agriculture and Agri-Food Canada since 1954, and two European cultivars that were the source of the low erucic acid and low glucosinolate traits that define canola quality. Application of 22 SSR primer pairs from eight linkage groups detected 88 polymorphic alleles from 33 likely loci. The allelic frequencies in 300 samples ranged from 0.003 to 0.993 and averaged 0.388. The estimates of mean heterozygosity for these cultivars ranged from 0.055 to 0.203 and averaged 0.139. The most SSR variation was detected in the cultivars Argentine, Golden and Oro. A trend of decline in SSR variation was observed over the years of breeding effort. The proportion of total SSR variation residing among the cultivars was 51.4%; between high vs. low erucic acid cultivars 15% and between high vs. low glucosinolate cultivars 21.2%. Pairwise genetic differentiations among these cultivars ranged from 0.140 to 0.819 and averaged 0.500. Cluster analysis revealed that the genetic relationships of these cultivars were consistent with their known pedigrees. These findings are useful for broadening the genetic base of improved B. napus gene pools, selecting genetically diverse genotypes for hybrid combinations, and conserving summer rape germplasm.Key words: Simple sequence repeat, summer rape, Brassica napus, genetic diversity, genetic relationship, genetic structure