Primer pairs to identify physiological races of Plasmodiophora brassicae

Clubroot is a soil-borne disease caused by infection with Plasmodiophora brassicae, the causal agent of clubroot, and clubroot can directly cause enormous economic losses in cruciferous crops. The latent spores of P. brassicae are highly active, have a high rate of infection, and are transmitted over a wide range of channels. The manifestation of P. brassicae in fields is often caused by the mixed infection of multiple physiological races, and such mixed infections often pose a substantial challenge to the breeding of plants that are resistant to P. brassicae. In this study, a set of multiple molecular markers for the identification of the main physiological race of P. brassicae was established by utilizing a system to detect the clubroot microspecies-specific primers SCL14 (UP/LP), PBRA_000030-2 (F/R), PBRA_000303-1 (F/R), PBRA_009348-2 (F/R), and Novel342-1 (F/R). The molecular identification of clubroot physiological race resulted in identifying of five such races, including No. 1, 4, 7, 9, and 11. The primers used in this study were more specific, and some strains were not only identified as No. 4 but also as No. 7, such as strains P2, P3, and P4, or as No. 1, such as strain P60. The highest frequency and widest distribution of the small species No. 4 in the sampling site indicated that race No. 4 is the dominant race of P. brassicae. Based on the distribution of race in the sampling site, it was found that the isolated strains of P. brassicae were more differentiated and caused more types of disease. In this study, the primers obtained for the molecular identification of P. brassicae in previous studies were improved and combined to form a multi-molecular marker method to identify the physiological race isolates of P. brassicae, which will provide a theoretical basis to identify the isolates of P. brassicae using molecular markers.