Evaluation of Brassica oleracea accessions for resistance to Plasmodiophora brassicae and identification of genomic regions associated with resistance.

Clubroot disease caused by Plasmodiophora brassicae is a challenge to Brassica crop production. Breakdown of resistance controlled by major genes of the Brassica A genome has been reported. Therefore, identification of resistance in the Brassica C genome is needed to broaden the genetic base of resistance in Brassica napus canola. In this study, we evaluated 135 Brassica oleracea accessions, belonging to eight variants of this species to identify resistant accessions as well as to identify the genomic regions associated with resistance to two recently evolved P. brassicae pathotypes, F3-14 (3A) and F-359-13 (5X L-G2). Resistance to these pathotypes was observed more frequently in var. acephala (kale) followed by var. capitata (cabbage); few accessions also carried resistance to both pathotypes. Association mapping using single nucleotide polymorphism (SNP) markers developed through geno-typing by sequencing technique identified 10 quantitative trait loci (QTL) from six C-genome chromosomes to be associated with resistance to these pathotypes; among these, two QTL associated with resistance to 3A and one QTL associated with resistance to 5X L-G2 carried >= 3 SNP markers. The 10 QTL identified in this study individually accounted for 8%-18% of the total phenotypic variance. Thus, the results from this study can be used in molecular breeding of Brassica crops for resistance to this disease.