S5-1: Disease reaction of different plant species against virulent isolates of Plasmodiophora brassicae

Abstract: Clubroot disease, caused by Plasmodiophora brassicae, is an important disease of
oilseed rape worldwide. In the current study, 86 plant species from 19 botanical families
were evaluated for their potential as hosts of P. brassicae. Plants were artificially
inoculated with two isolates of P. brassicae, which were either virulent on P. brassicaeresistant OSR cv. Mentor [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 clubbed root symptoms were produced only in the Brassicaceae family; none of the other species showed external disease symptoms. Plant species infected with P1 (+) had more severe symptoms, larger galls, and more resting spores than the plants infected
with P1. Among all Brassica species, Bunias orientalis, Coronopus squamatus and
Raphanus sativus were fully resistant to both isolates. Camelina sativa, Coincya monensis,
Descurainia sophia, Diplotaxis muralis, Erucastrum gallicum, Neslia paniculata, Sinapis
alba, S. arvensis, Sisymbrium altissimum, S. loeselii and Thlaspi arvense were infected
severely by both isolates. In contrast, Conringia orientalis, Diplotaxis tenuifolia,
Hirschfeldia incana, Iberis amara, Lepidium campestre and Neslia paniculata were
entirely or partially resistant to P1 but very susceptible to P1 (+). Furthermore, the
pathogen DNA was detected not only in all Brassica species but also in Alopecurus
myosuroides, Phacelia tanacetifolia, Papaver rhoeas and Pisum sativum. These results
suggest that the number and diversity of hosts for P. brassicae are more significant than
previously reported.