Selection By Resistant Potato Cultivars in Populations of Globodera Rostochiensis, Pathotypes Ro 1 and Ro 3

Potato cv. Alcmaria (resistance ex andigena CPC 1673-20 against pathotype Ro 1 of Globodera rostochiensis) selected a population similar to pathotype Ro 3 of this species from one of pathotype Ro 1 in three years. The rate of selection was consistent with the assumption that females produced on cv. Alcmaria were all homozygous for the virulence gene of the selected population and that the proportion of pathotype Ro 1 and heterozygous males that matured was about a quarter of that of males homozygous for the virulence gene of the selected population. A contamination of the Ro 1 population used with 8.7% Ro 3 genes was deduced from the susceptibility of cv. Alcmaria to this population of 0.3% of that of cv. Irene. The relative susceptibilities <0.05% relative to cv. Irene at initially 5 eggs/g soil of cvs Cardinal, Saturna and Ehud (resistance ex andigena) to the same Ro 1 population (relative susceptibility to the selected population and to pathotype Ro 3 about 30% of that of cv. Irene, cv. Alcmaria 50%) is, most probably, due to a negative effect of the presence of Ro 1 juveniles on the development of Ro 3 juveniles in the latter cultivars which did not operate in cv. Alcmaria. A range of potato cultivars resistant to pathotypes Ro 1 and Ro 3 did not select more virulent populations from one of pathotype Ro 3 in three or four generations. These cultivars are, therefore, only partially resistant against pathotype Ro 3.

Affiliations: 1: Middelberglaan 6, Ede, the Netherlands