Genetic analysis of downy mildew resistance and identification of molecular markers linked to resistance gene Ppa207 on chromosome 2 in cauliflower

Abstract

Downy mildew is one of the most damaging fungal diseases of cauliflower. The present study was undertaken to identify molecular markers linked to the downy mildew resistance gene using 84 recombinant inbred lines (RILs) from a cross of Pusa Sharad (susceptible [S] to downy mildew) and DMR-2-0-7 (resistant [R] to downy mildew). The resistant and susceptible lines in the 84 RILs segregated in 1:1 (R:S) ratio, indicating that resistance for downy mildew disease is monogenic and the gene was named as Ppa207. During polymorphism survey between the parents using 105 simple sequence repeat (SSR) markers, 43 were polymorphic (27.55%). Bulked segregant analysis revealed that two of these markers that showed polymorphism, namely BoGMS0486 and BoGMS0900, could distinguish resistant and susceptible bulks and segregated in 1:1 (R:S) ratio. The recombination frequencies between BoGMS0486 and BoGMS0900, BoGMS0486 and Ppa207 and BoGMS0900 and Ppa207 were 4.8, 3.6 and 1.2%, respectively. The resistant gene Ppa207 was mapped in 4.8 cM linkage interval on linkage group 2 (C02) of cauliflower, flanked by the markers BoGMS0486 and BoGMS0900 at 3.6 and 1.2 cM, respectively, from Ppa207. Markers BoGMS0486 and BoGMS0900 were located 2.9 and 23.2 Mb positions, respectively, on chromosome 2 and the 4.8 cM marker interval corresponds to a physical distance of 20.3 Mb. The identified SSR markers linked to the new resistance gene Ppa207 will be very useful in marker assisted selection in cauliflower for developing varieties and/or hybrids resistant to downy mildew.