Fysiologische specialisatie bijPlasmodiophora brassicae Woron.

Summary

In testing cruciferous crops for varietal resistance indications were obtained of the existence of two races ofP. brassicae (verbal communication from Dr. J.C. s'Jacob, I.P.O., Wageningen). Further evidence was obtained in an inoculation experiment. This experiment was done in eight open, concrete containers, which were set into the soil. Four of these containers were filled with clay and four with sand. In the autumn of 1954 clubs from cabbage, grown in a field in Koedijk, were placed on the soil in two of the clay filled containers and two of the sand filled containers. Clubs from turnip, grown in a field in Nijbroek, were placed on the soil in the remaining four containers. In the spring of 1955 the residue of the clubs was pulverized and mixed with the upper layer of the soil. On June 15 one row of cauliflower and one row of turnip were sown in each container. The plants were lifted and examined August 23 (1st sowing). The experiment was repeated immediately and the plants of this second crop were lifted November 20 (2nd sowing). Turnip was heavily clubbed byP. brassicae originating from turnip and only slightly by the fungus originating from cabbage. Cauliflower was heavily affected by both sources; slightly less by the source „turnip” than by the source „cabbage”. Thus the results of the experiment confirmed the existence of two races ofP. brassicae. Where it is not known whether other races do occur, it is advised in breeding for resistence to use inocula ofP. brassicae from as many sources as possible.