Clubroot-resistance in turnips (Brassica campestris L.)

A set of differential varieties of turnips was grown on three fields infested with Plasmodiophora brassicaeWoron. Gall tissue was collected from diseased roots of some of these varieties. Seedlings of the same varieties were inoculated in the green-house by the application of suspensions prepared from the separate groups of galls. Pathogenic differences between isolates from the same field were observed in some cases. However, when suspensions of the clubs produced in the glasshouse were used as inocula, the differences in pathogenicity between these isolates were much more pronounced. The results of the inoculation experiments indicated the presence of at least two races of the clubroot organism in the same soil and in roots of the same variety. They also showed the selective effect of some of the varieties on the racial mixtures.Some complications and consequences of the method applied to break up racial mixtures into their components were discussed.