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 Plasm odiophora-resistant and two susceptible varieties of Chinese cabbage w ere used and three classes of glucosinolates, aliphatic (=alkenyl), ar omatic and indolic were analysed. Between the susceptible varieties 'G ranat' and 'Osiris' and the resistant varieties 'Parkin' and 'Yuki' th ere were significant differences in glucosinolate pattern. The total g lucosinolate content in roots of the two susceptible varieties was hig her throughout the experimental period than in roots of the two resist ant varieties. 'Osiris' showed the highest glucosinolate content of al l the varieties investigated (ca three-fold higher than 'Granat' and c a 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 dif ference between infected and control roots in 'Parkin' and 'Yuki'. The aliphatic glucosinolates were also enhanced in infected roots of 'Gra nat', whereas 'Osiris' showed a very high content of aliphatic glucosi nolates during the whole experimental period. Roots of 'Parkin' and 'Y uki' grown in the presence of Plasmodiophora spores showed an elevated concentration of aromatic glucosinolates after 14 and 30 days, respec tively, which was not found in 'Granat' and 'Osiris'. Total seed gluco sinolate content appeared to be correlated with the susceptibility of the Chinese cabbage varieties tested. Eight different susceptible vari eties showed higher total glucosinolate contents than the two resistan t 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 glucos inolates in the leaves, whereas salicylic acid induced indole glucosin olates also in the roots of both varieties. In the variety 'Parkin', w e also observed induction of aliphatic and aromatic, glucosinolates af ter jasmonate treatment. Although the variety 'Parkin' showed no clubr oot symptoms, we were able to detect fungal structures within the root s using scanning electron microscopy. We would, therefore, rather desc ribe this variety as tolerant not resistant to clubroot disease. The p otential role of different glucosinolates in plant-pathogen interactio ns is discussed. Copyright (C) 1997 Elsevier Science Ltd