NEW PATHOTYPES OF THE BEET CYST-NEMATODE (HETERODERA-SCHACHTII) DIFFERENTIATED ON ALIEN GENES FOR RESISTANCE IN BEET (BETA-VULGARIS)

Two populations (Schach 0 and Schach 1) of the beet cyst nematode, Het erodera schachtii, were used to select for new virulences to resistanc e genes transferred from Beta section Procumbentes into B. vulgaris (H s1(web-7) and additional resistance information on chromosome 7). Both nematode populations were able to produce a few cysts which were mult iplied for six successive generations on resistant plants. The two res ulting populations, selected from either Schach 0 or Schach 1, were hi ghly virulent on four monosomic additions with chromosome (web-7) or ( pro-7). However, the population selected from Schach 0 was unable to b reak the resistance of translocation lines carrying resistance gene Hs 1 from chromosome (pro-1), (pro-7) or (web-7), whereas the population selected from Schach 1 was still virulent on these translocation lines . A resistance gene Hs2(web-7) is postulated to exist on chromosome 7, having an epistatic effect on Hs1(web-7). The two new virulent pathot ypes are named Schach 2 and Schach 1,2. (C) Orstom/Elsevier, Paris.