THE RESISTANCE OF 6 POTATO CULTIVARS TO ENGLISH POPULATIONS OF POTATO CYST-NEMATODES, GLOBODERA-PALLIDA AND G-ROSTOCHIENSIS

Six cultivars of potato (Sante, Morag, Paladin, Glenna and Fingal bred for resistance to both potato cyst-nematodes (Globodera rostochiensis and G. pallida) and Valiant bred for resistance to G. pallida alone) were exposed to 28 English populations of G. pallida and eight English populations of G. rostochiensis in pots. Susceptible cv. Desiree potatoes served as controls for all 36 populations. Inoculum (Pi) was 12 000 eggs in cysts per 400 ml pot of soil. Average increase of G. rostochiensis (Pf/Pi) on cv. Desiree was 23.5 but on cvs Sante, Glenna and Fingal it was < 1.0 and on cv. Morag it was 2.2. In contrast, cvs Paladin and Valiant were susceptible (average Pf/Pi = 17.4 and 26.5, respectively). Against G. pallida populations, average Pf/Pi for cv. Desiree was 21.7; on cvs Paladin, Sante and Glenna it was 2.9, 2.6 and 2.4, respectively; cvs Morag and Fingal were less resistant (7.4 and 5.6, respectively) and cv. Valiant was quite susceptible (11.0). Resistance to the different populations of G. pallida and G. rostochiensis varied but for the most resistant cultivars (Sante, Glenna and Paladin) the variation was usually small. The value of the six resistant cultivars studied to the integrated control of potato cyst-nematodes in England and the genetic diversity of the nematode populations to which they were exposed are discussed.