qPCR as a decision-making tool for Plasmodiophora brassicae forecast in the field

Abstract

Abstract Clubroot caused by Plasmodiophora brassicae is a very destructive soilborne disease of brassica plants worldwide. The pathogen survives in soil with resting spores, that are produced in large numbers inside infected roots and can persist in the soil for up to 17 years. These resting spores can build up in the soil when brassicas are repeatedly grown, increasing the inoculum potential, leading to increased disease incidence and severity in subsequent crops. Infection by this pathogen can result in considerable yield and quality losses in susceptible crops, accounting for a 20–90% yield loss of broccoli, cauliflower, and cabbage crops in Colombia. A national survey to determine the extent of clubroot in Colombia was done in 2017, and it was found that 53.7% of the visited fields had clubroot disease on the crops, but the pathogen DNA was detected by PCR methods on 91.3% of the surveyed fields in all the departments where crucifers are grown. At the time of the survey, no symptoms of clubroot disease were observed in Nariño department, despite finding the pathogen DNA at concentrations varying from 2x103 to 2x104 resting spores per gram of soil. However, during the year 2020, Nariño farmers reported the presence of a disease, causing wilting and plant death of their cruciferous crops. Here we report that P. brassicae is the causal agent of the newly appeared disease in brassica crops in Nariño. The aims of this study were to determine the inoculum threshold needed to cause disease and the inoculum concentration that can be detected in both artificially and naturally infected soils to use them as tools for P. brassicae management and control. We propose the use of qPCR as a decision-making tool for cruciferous growers.