Effect of Plasmodiophora brassicae resting spore concentration and crop rotation on growth of clubroot-resistant crops
Clubroot caused by Plasmodiophora brassicae Woronin is an important threat to production of canola (Brassica napus L.) and Brassica vegetables in Canada and worldwide. To help understand the role of crop rotation in integrated clubroot management, this research examined the pattern of decline in resting spores and the influence of spore concentration on growth and development of clubroot-resistant crops. It was found that a portion of the resting spore population is long-lived, but most (>99%) spores survive for only 1–2 years. Higher concentrations of resting spores resulted in reduced plant growth and delayed development in resistant canola and napa cabbage. However, the growth response was inconsistent across studies and repetitions, and may be influenced by other factors such as soil type and crop species. For canola growers, a ≥ 2-year break from canola, in combination with a clubroot-resistant cultivar, is recommended as a clubroot management strategy wherever clubroot is found.