ON RESISTANCE OF SPECIES OF SOLANUM (TUBERARIUM) AGAINST EUROPEAN RACES OF POTATO NEMATODE (HETERODERA ROSTOCHIENSIS WOLL)

63 tuber bearing Solanum species of 200 proveniencies were screened for cyst production with race A and 11 deviating (B-) races found in Scotland, Norway, The Netherlands, Germany, and Switzerland. The authors thankfully acknowledge the co-operation of A. Bumbulucz, J. M. Dunnett, H. Goffart, J. Münster, L. Roer, D. Rothacker, A. Savary, H. Stelter and B. Weischer. Each race could be characterized by a specific host range, which was different for every race. The races are distinguished by their aggressivity, expressed by the aggressivity number, i.e. the percentage of hosts among all the hosts tested that will form cysts. The race Chavornay has with 13,6% the lowest aggressivity number and the race ABC with 59,0% the highest. Solanum forms which are resistant to a race with high aggressivity number have the best chance to maintain this resistance against many races occurring in Europe. The following species are resistant to all 11 races: S. oplocense, S. spegazzinii (syn. S. famatinae) and S. vernei. The species S. sanctae-rosae EBS 1778 and P.H. 328, S. megistacrolobum EBS 1783, and S. tuberosum Chile EBS 2084 were tested with 6 races (the first two inclusive ABC) and found to be resistant to all. S. andreanum EBS 2183 and S. sparsipilum EBS 1801 and 1890 were resistant to 5-9 races but susceptible to one. Published and unpublished results showed the existence of major genes in resistant species responsible for resistance to one as well as to several races. It therefore seems possible to base breeding for resistance on a few major genes only. Some hybrids, wild species x S. tuberosum, are used in breeding work. The reaction of these hybrids with the different pathotypes is reproduced in table 4. © 1969 Springer-Verlag.