Assessment of the response of Plasmodiophora brassicae in contaminated horticultural land, using lime‐based fertilizer concentrations

Robert Faggian,Mary Hanson,Geoff Petch,Alison Wakeham,Roy Kennedy

doi:10.1002/fes3.122

Abstract

AbstractInfection of brassica crops with the clubroot pathogen, Plasmodiophora brassicae, can result in stunted plant growth and wilting, which can severely affect crop yield. Determining P. brassicae infection within a field prior to crop planting has long posed a problem for choosing appropriate control treatments. The options for control of this pathogen are limited and in the UK and are based on adjusting pH with soil amendments. In this study quantitative polymerase chain reaction (qPCR) was investigated for measurement of this pathogen in different control treatments. The qPCR was capable of reliably quantifying P. brassicae at levels greater than and including 103 resting spores/g soil. The assay was used to study the effect of lime‐based products (LimeX) on the incidence of the clubroot pathogen in field trials with broccoli crops grown on contaminated land. The results showed that variation occurred in clubroot resting spore levels in treated and untreated plots during the crop growing period. In year one there was a 96% decrease in spore load during the growth of the crop. Treatment with LimeX resulted in a greater marketable head weight of broccoli in 2 years of the field trials, and significantly reduced gall numbers on the roots in 1 year. The rate of lime (calcium carbonate) application was not found to have a significant effect in this study, however a greater reduction in clubroot was observed at higher LimeX concentrations.

Highlights

Clubroot on brassica crops is caused by the soil-borne protist, Plasmodiophora brassicae
The molecular quantification of P. brassicae spores in soil is a relatively recent development (Jin-P ing et al, 2013; Lewis, 2011; Lewis, Wakeham, & Kennedy, 2013; Wallenhammar et al, 2012) but an important step forward in the study of this soil-borne organism
A detection level of 1000 spores/g soil was achieved in this study, and quantification of P. brassicae was performed that demonstrated the robustness of the assay with different operators with a good level of repeatability

Summary

| INTRODUCTION

Clubroot on brassica crops is caused by the soil-borne protist, Plasmodiophora brassicae. The steady accumulation of P. brassicae resting spores in the soil may occur over consecutive years of cropping resulting in severe yield losses. This was due to the effect of increasing pH rather than the presence of calcium They demonstrated that rhizosphere spore germination is inhibited when calcium carbonate (or calcium-rich organic matter) is used to neutralize the soil (Niwa, Nomura, Osaki, & Ezawa, 2008). Myers and Campbell (1985) studied the effects of pH and calcium, but took into account the effects of magnesium They found that high pH reduced clubroot incidence, and that calcium and magnesium concentration in the soil affected disease levels. The number of P. brassicae resting spores in soil was monitored in different control treatments and the subsequent effect on crop yield was ascertained

| MATERIALS AND METHODS

Findings

| DISCUSSION