Glucosinolate content in susceptible and resistant Chinese cabbage varieties during development of clubroot disease

The glucosinolate content in Chinese cabbage (Brassica campestris ssp. pekinensis) during the development of clubroot disease caused by the obligate biotroph Plasmodiophora brassicae was investigated. Two Plasmodiophora-resistant and two susceptible varieties of Chinese cabbage were used and three classes of glucosinolates, aliphatic (=alkenyl), aromatic and indolic were analysed. Between the susceptible varieties 'Granat' and 'Osiris' and the resistant varieties 'Parkin' and 'Yuki' there were significant differences in glucosinolate pattern. The total glucosinolate content in roots of the two susceptible varieties was higher throughout the experimental period than in roots of the two resistant varieties. 'Osiris' showed the highest glucosinolate content of all the varieties investigated (ca three-fold higher than 'Granat' and ca five-fold higher than 'Parkin' and 'Yuki'). After infection with P. brassicae the indole glucosinolates increased after 14 and 20 days in roots of 'Granat' and 'Osiris', respectively, whereas there was no difference between infected and control roots in 'Parkin' and 'Yuki'. The aliphatic glucosinolates were also enhanced in infected roots of 'Granat', whereas 'Osiris' showed a very high content of aliphatic glucosinolates during the whole experimental period. Roots of 'Parkin' and 'Yuki' grown in the presence of Plasmodiophora spores showed an elevated concentration of aromatic glucosinolates after 14 and 30 days, respectively, which was not found in 'Granat' and 'Osiris'. Total seed glucosinolate content appeared to be correlated with the susceptibility of the Chinese cabbage varieties tested. Eight different susceptible varieties showed higher total glucosinolate contents than the two resistant varieties. Treatment of plants of the varieties 'Parkin' and 'Granat' with salicylic acid and jasmonic acid resulted in increased amounts of glucosinolates, although differences in the response were observed between the two treatments. Jasmonic acid induced mainly indole glucosinolates in the leaves, whereas salicylic acid induced indole glucosinolates also in the roots of both varieties. In the variety 'Parkin', we also observed induction of aliphatic and aromatic glucosinolates after jasmonate treatment. Although the variety 'Parkin' showed no clubroot symptoms, we were able to detect fungal structures within the roots using scanning electron microscopy. We would, therefore, rather describe this variety as tolerant not resistant to clubroot disease. The potential role of different glucosinolates in plant-pathogen interactions is discussed.