Physiological and genetic components of black rot resistance in double haploid lines of Brassica rapa L

In some vegetation seasons black rot may damage up to 80 % of cabbage, turnip, rapeseed, mustard crop all over the world including Russia. To prevent the spread of black rot is difficult, and it is almost impossible to fight a pathogen penetrating into a susceptible plant. Among Brassica rapa L., the disease is most dangerous for root crops and leaf crops. Data on loci which determine the plant-specific resistance of B. rapa plants to black rot is still extremely limited. This study is the first to estimate resistance to four races of Xanthomonas campestris pv. campestris (Pam.) Dow., the causative agent of black rot in Brassicaceae, in the lines of doubled haploids of two B. rapa mapping populations, DH38 (♀Р175 x ♂P143) and DH30 (♀P115 x ♂Р143). Here, we report data on identification and mapping the linkage groups and QTLs associated with physiological resistance to strains PHW231 (race 1), HRI5212 (race 3), HRI1279а (race 4), and В-32 (race 6). For three of these races, OTLs have not been mapped so far. The study revealed lines which were resistant or hypersensitive to the four races of black rot agent. Monogenic non-linked inheritance of resistance to these races prevailed. Significant correlation was found between response to an individual strain and general infection in plants. A total of 13 QTLs which control resistance to four races of the black rot pathogen were identified for DH30 population and 19 QTLs were found for DH38 population. All detected loci did not change their localization during two years of investigation. The most important loci responsible for manifestation of physiology resistance to different races of black rot pathogen in DH30 were mapped in the linage groups A01, A03 and A07, whereas in DH38 these were in A03, A06 and A08. SSR analysis of the lines contrast in resistance to individual races of the pathogen revealed the microsatellite markers linked to the loci which control resistance to several races of black rot agent. So we have found effective molecular descriptors of B. rapa black rot resistance to each race separately and to the pathogen as such. The obtained data are of interest in elucidation of basic physiological and genetic mechanisms of gene-to-gene interaction and B. rapa resistance to different races of X. campestris pv. campestris.