Effect of Pathogen Virulence on Pathogenicity, Host Range, and Reproduction of Plasmodiophora brassicae, the Causal Agent of Clubroot Disease

A series of greenhouse experiments was conducted to evaluate the effect of Plasmodiophora brassicae virulence on clubroot development and propagation of resting spores in 86 plant species from 19 botanical families. Plants were artificially inoculated with two isolates of P. brassicae, which were virulent on clubroot-resistant oilseed rape cultivar Mendel [pathotype 1; P1 (+)] or avirulent on this cultivar (P1). Clubroot severity and the number of resting spores inside the roots were assessed 35 days post inoculation. Typical clubroot symptoms were observed only in the Brassicaceae family. P1 (+)-inoculated species exhibited more severe symptoms (two- to 10-fold more severe), bigger galls (1.1- to 5.8-fold heavier), and greater numbers of resting spores than the Pl-inoculated plants. Among all Brassica species, Bunias orientalis, Coronopus squamatus, and Raphanus sativus were fully resistant against both isolates, whereas Camelina sativa, Capsella bursa-pastoris, Coincya monensis, Descurainia sophia, Diplotaxis muralis, Erucastrum gallicum, Neslia paniculata, Sinapis alba, Sinapis arvensis, Sisymbrium altissimum, Sisymbrium loeselii, and Thlaspi arvense were highly susceptible. Colvingia orientalis, Diplotaxis tenuifolia, Hirschfeldia incana, Iberis amara, Lepidium campestre, and N. paniculata were completely or partially resistant to P1 isolate but highly susceptible to P1 (+). These results suggest that the basis for resistance in these species may be similar to that found in some commercial cultivars, and that these species could contribute to the buildup of inoculum of virulent pathotypes. Furthermore, the pathogen DNA was detected in Alopecurus myosuroides, Phacelio ionoccafolia, Papaver rhoeas, and Pisum sativum. It can be concluded that the number and diversity of hosts for P. brassicae are greater than previously reported.

Automated summary

The virulence of Plasmodiophora brassicae varies among different plant species, with severe impact on Brassicaceae family. Some Brassica species show complete resistance to the virus, while others are highly susceptible.