VIRULENCE IN THE BEET CYST-NEMATODE (HETERODERA-SCHACHTII) VERSUS SOME ALIEN GENES FOR RESISTANCE IN BEET

Three populations of the beet cyst nematode (BCN), Heterodera schachti i, were used in resistance tests with various plant materials of the g enus Beta. Population 129-SB had been selected for virulence to gene(s ) for resistance obtained from chromosome pro- 1 of B. procumbens and is considered to be a new pathotype of this nematode species. In addit ion, an unselected sib population (129-FR) and the wild-type populatio n BCN-WA were used. The wild species B. procumbens and B. patellaris s howed nearly complete resistance to all three nematode populations. Po pulation 129-SB was able to produce cysts on the two breeding stocks o f sugar beet (B. vulgaris subsp. vulgaris), with resistance from chrom osome pro-1. However, the mean number of cysts per plant was significa ntly less than on the susceptible control cv. Regina. Nematode populat ion 129-SB also was able to break the resistance from chromosome pat-1 of B. patellaris, when present as a monotelosomic addition. The monos omic addition carrying chromosome pro-7 of B. procumbens and the parti ally resistant accession BMH of the wild sea beet (B. vulgaris subsp. maritima) showed resistance in tests with all three nematode populatio ns, but population BCN-WA produced significantly more cysts on the sus ceptible plants and on BMH than the other two populations. These diffe rences indicate variation in the nematode populations for fitness and perhaps also for virulence. It is proposed to modify the nomenclatural system for the naming of the postulated genes for resistance to H. sc hachtii on the chromosomes pro-1, pat-1 and pro-7, and to name them Hs 1 pro-1, Hs(pat-1), and Hs2 pro-7, respectively.