RESISTANCE TO ERWINIA-CAROTOVORA SUBSP ATROSEPTICA IN 2ND BACKCROSS POPULATIONS OF SOMATIC HYBRIDS BETWEEN SOLANUM-TUBEROSUM AND SOLANUM-BREVIDENS

Eleven clones obtained from a cross between cv. Katahdin and fusion pr oducts between Solnum tuberosum and the non tuber-bearing species S. b revidens, were backcrossed again with S. tuberosum (clone AR80-127-5). Small tubers harvested from 583 seedlings of these second backcross ( BC2) populations were screened for tuber tissue resistance to Erwinia carotovora subsp. atroseptica under aerobic conditions. After multipli cation in the field, BC2 clones again were screened for soft rot resis tance under aerobic as well as anaerobic conditions. In general, the r esistance of the BC2 populations was reduced in comparison with the BC 1. Variation for resistance was found within the BC2 populations, but there was no correlation between the results of the three tests perfor med. Four BC2 populations were also screened for resistance to blackle g in the field. Significant differences were found between populations for mean percentage of diseased plants, but these differences could n ot be explained by the resistance of the parental clones.