Dissemination of Plasmodiophora brassicae in livestock manure detected by qPCR.
The present study was performed to investigate whether Plasmodiophora brassicae can be disseminated by livestock manure. A quantitative PCR (qPCR) assay was developed and used to detect and quantify P. brassicae in manure samples from naturally and artificially infested chickens and pigs. In naturally infested manure, quantifiable levels of infestation were observed in 7 out of the 28 samples, ranging from 103 to 107 resting spores per g of manure. The vast majority of the resting spores (76-91%) were viable, as determined by a dual fluorescence viability assay. Clubroot symptoms developed on plants inoculated with P. brassicae resting spores isolated from all seven qPCR-positive samples. Artificially infested manure samples were produced by feeding chickens and pigs on P. brassicae-contaminated feed. The levels of infestation were 103 resting spores per g of manure for both chicken and pig manure sampled 24 and 48 h after feeding, respectively. Spore viability was >80% for both samples, and the disease severity indices were both >40 as indicated by bioassay. This showed that resting spores can survive the digestive tracts of chickens and pigs, and retain strong pathogenicity. The findings indicate that manure dissemination is possible for P. brassicae. Farmers should avoid feeding livestock on P. brassicae-contaminated feed or applying infested manure as fertilizer on land intended for crucifer crops.