Abstract

Clubroot, caused by Plasmodiophora brassicae Woronin, is an important soilborne disease of canola (oilseed rape; Brassica napus L.). In Canada, clubroot management relies heavily on the planting of resistant cultivars, but since 2013, resistance has been broken in an increasing number of fields. Prior to the introduction of resistance, P. brassicae pathotype 3H, as defined on the Canadian Clubroot Differential (CCD) set, was predominant in Alberta. In testing of pathogen collections from 2014 to 2016, however, pathotype 3A was most common, indicating rapid shifts in the pathogen population. Up-to-date knowledge of pathotype composition is important for effective resistance breeding and stewardship. Therefore, clubbed roots were collected from clubroot-resistant canola crops from 166 fields in Alberta, Saskatchewan, and Manitoba in 2017 and 2018, with one isolate per field evaluated for pathotype designation on the CCD set and the differentials of Somé et al. Seventeen pathotypes were detected on the CCD set, including the previously reported pathotypes 3A, 3D, 3H, 5 L, 5X, 8E, 8N and 8P, plus the novel pathotypes 2C, 6D, 8D, 9A, 9B, 9C, 11A, 13A and 13B. Five pathotypes were identified on the hosts of Somé et al. including P₁, P₂, P₃, P₄ and P₅, with P₄ and P₅ reported here from Canada for the first time. The majority of the isolates, representing 39 fields in 2017 and 92 fields in 2018, could overcome genetic resistance. The results suggest significant diversity in the virulence of P. brassicae populations and an increasing prevalence of resistance-breaking P. brassicae strains.

摘要

根茎由Plasmodiophora brasicae Woronin引起，是一种重要的油菜（油菜；Brassica napus L.）土传病害。在加拿大，根肿病管理严重依赖抗性品种的种植，但自 2013 年以来，越来越多的田间抗性被打破。在引入抗性之前，P. brasicae病理型 3H，根据加拿大 Clubroot 差异 (CCD) 集的定义，在艾伯塔省占主导地位。然而，在 2014 年至 2016 年的病原体收集测试中，致病型 3A 最为常见，表明病原体种群发生了快速变化。病原体组成的最新知识对于有效的抗性育种和管理很重要。因此，2017 年和 2018 年，从艾伯塔省、萨斯喀彻温省和马尼托巴省的 166 个农田的抗根肿油菜作物中收集了棒状根，每个农田对 CCD 集上的致病型指定和 Somé 等人的差异进行了评估。在 CCD 集上检测到 17 种病理型，包括先前报道的病理型 3A、3D、3H、5 L、5X、8E、8N 和 8P，以及新的病理型 2C、6D、8D、9A、9B、9C、11A、13A和 13B。在 Somé 等人的宿主上确定了五种病理类型。包括P₁、P ₂、P ₃、P ₄和P ₅，其中P ₄和P ₅首次来自加拿大。大多数分离株，2017 年代表 39 个领域，2018 年代表 92 个领域，可以克服遗传抗性。结果表明，芸苔藓种群的毒力存在显着差异，并且破坏抗性的芸苔藓菌株的流行率越来越高。