Resistance and susceptibility to powdery mildew, root-knot nematode, and western flower thrips in two types of winter cress (Brassicaceae)

Two types of Barbarea vulgaris R. Br. (Brassicaceae) were tested to compare their resistance and susceptibility to powdery mildew, Erysiphe cruciferarum Opiz ex L. Junell (Erysiphales: Erysiphaceae), root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwoodi (Tylenchida: Heteroderidae), and western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). In experiments conducted in the greenhouse, the percentage of plants showing powdery mildew symptoms ranged from 54.2 to 83.3% in P-type B. vulgaris plants and from 0 to 20.8% in G-type B. vulgaris plants. In plants infected by powdery mildew, the percentage of leaves affected was higher in P-type than in G-type plants, ranging from 11.8 to 21.1% in P-type plants, and from 0 to 0.36% in G type plants. Infection by powdery mildew was more likely to occur on the leaves of largest diameter. Root galling showed that G- and P-type plants were equally attacked by root-knot nematode, but the multiplication rate of the nematode was 4.1-7.6 times higher in P-type than in G-type plants. Significantly more leaves per plant were damaged by western flower thrips in P-type (73.1-88.3% of leaves affected) than in G-type plants (2.1-2.9% of leaves affected). The total numbers of adult and immature thrips found per plant on P-type plants were, respectively, 29.9 and 2.5, while on G-type plants less than 0.3 adult and immature thrips were found per plant. This study indicates that G-type B. vulgaris could be a source of resistance to powdery mildew and western flower thrips.