Reevaluation ofSolanum species accessions showing resistance to bacterial ring rot

One hundred and fifty-six plant accessions, including susceptible checks, from the IR-1 collection were evaluated for resistance/immunity to bacterial ring rot (BRR). Each accession selected had been previously rated as highly resistant to BRR based on symptom expression but, in our tests, 57 of them yielded no plants which failed to produce symptoms. However, the remaining 99, represented by a total of 2589 inoculated plants, yielded 1000 plants which failed to produce BRR symptoms after eight weeks. Immunofluorescent antibody stain testing showed that 679 of the symptomless plants supported detectable numbers ofCorynebacterium sepedonicum cells. Comparison of root-inoculated and tuber-inoculated accessions showed that root-inoculations yielded significantly fewer symptomless and bacterial cell-free plants. No significant differences were found in BRR reactions of fiveSolanum spp. when inoculated with two different strains ofC. sepedonicum. Appreciable numbers of symptomless plants were obtained from inoculated progeny of crosses with resistant cultivars but none of those retested proved to be immune.