Virulence Spectrum of Single-Spore and Field Isolates of Plasmodiophora brassicae Able to Overcome Resistance in Canola ( Brassica napus ).

Abstract

Clubroot, caused by Plasmodiophora brassicae Woronin, is an important disease of canola ( Brassica napus L.) that is managed mainly by planting clubroot-resistant (CR) cultivars. Field isolates of P. brassicae can be heterogeneous mixtures of various pathotypes, making assessments of the genetics of host-pathogen interactions challenging. Thirty-four single-spore isolates were obtained from nine field isolates of the pathogen collected from CR canola cultivars. The virulence patterns of the single-spore and field isolates were assessed on the 13 host genotypes of the Canadian Clubroot Differential (CCD) set, which includes the differentials of Williams and Somé et al. Indices of disease (IDs) severity of 25, 33, and 50% (±95% confidence interval) were compared as potential thresholds to distinguish between resistant and susceptible reactions, with an ID of 50% giving the most consistent responses for pathotype classification purposes. With this threshold, 13 pathotypes could be distinguished based on the CCD system, 7 on the differentials of Williams, and 3 on the hosts of Somé et al. The highest correlations were observed among virulence matrices generated using the three threshold IDs on the CCD set. Genetically homogeneous single-spore isolates gave a clearer profile of the P. brassicae pathotype structure. Novel pathotypes, not reported in Canada previously, were identified among the isolates. This large collection of single-spore isolates can serve as a reference in screening and breeding for clubroot resistance.

Plant phenotyping relevance

植物の病徴重症度を用いた病害表現型の閾値比較と病原型分類を中心に、測定・分類法を技術的に評価しているため、植物フェノタイピング手法の検証・適用として含める。

Code and data availability

The article describes greenhouse virulence phenotyping of Plasmodiophora brassicae isolates on differential hosts and UPGMA/Mantel analyses in NTSys-pc, but no public phenotype dataset, image/sensor data, author code, or model deposit is mentioned. Supplementary figures are referenced without any repository or access语言

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