COMBINATION OF RESISTANCE TO POTATO LATE BLIGHT IN FOLIAGE AND TUBERSBY INTRASPECIFIC DIHAPLOID PROTOPLAST FUSION

Five dihaploid Solanum tuberosum genotypes, encompassing different lev els of polygenically inherited resistance to potato late blight diseas e (Phytophthora infestans (Mont.) de Bary) in foliage and tubers, were used in four intraspecific protoplast fusion combinations. Vigorous g rowing putative hybrid calli were selected four weeks after electrofus ion. Intact plants were regenerated from 6% of the selected calli. Ver ification of hybridity was accomplished by use of RAPD analysis which revealed that 53% of the regenerated plants were true somatic hybrids. The score of true somatic hybrids in the different fusion combination s ranged within 21% - 100%. The hybrid plants were analysed for resist ance to foliage blight in a field trial and assessed for tuber blight resistance by use of a laboratory test. Resistance to late blight in f oliage and tubers varied between the hybrids. Very high levels of resi stance to both foliage and tuber blight were obtained in some hybrids. However, loss of resistance in some hybrids as compared to the parent al plants were also observed. Possible reasons for the phenotypic disa ppearance of resistance to either foliage or tuber blight are suggeste d.