RESISTANCE TO COLUMBIA ROOT-KNOT NEMATODE IN SOLANUM-SSP AND IN HYBRIDS OF S-HOUGASII WITH TETRAPOLOID CULTIVATED POTATO

Several tuber-bearing Solanum species were screened for resistance to races 1 and 2 of Columbia root-knot nematode, Meloidogyne chitwoodi. Reproductive factor (R(f) = P(f)/P(i)) was assessed and used to infer host resistance. Several clonal selections in one Plant Introduction accession of Solanum hougasii showed high levels of resistance to both races. Crosses of S. hougasii with tetraploid breeding clones yielded 14 vigorous F1 hybrids. Three of these interspecific hybrids expressed non-host (R(f) < 0.1) responses to race 1 and poor host (0.1 < R(f) < 1.0) responses to race 2. Six hybrids were non-hosts to race 1 but good hosts (R(f) > 1.0) to race 2. Three hybrids were good hosts to both races, and one was a poor host to race 1 and non-host to race 2. The occurrence of resistance to both races in the F1 hybrids indicates success in the first step of introducing resistance to races 1 and 2 of M. chitwoodi to the cultivated potato gene pool.