SOMATIC HYBRIDS BETWEEN SOLANUM-BULBOCASTANUM AND POTATO - A NEW SOURCE OF RESISTANCE TO LATE BLIGHT

Solanum bulbocastanum, a wild, diploid (2n = 2x = 24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually imposs ible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tubero sum PI 203900 (2n = 4x = 48) yielded hexaploid (2n = 6x = 72) somatic hybrids that retained the high resistance of the S. bulbocastanum pare nt. RFLP and RAPD analyses confirmed the hybridity of the materials. F our of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC1 progeny segregated for resistance to the US8 gen otype (A-2 mating type) of P. Infestans. Resistant BC1 lines crossed w ith susceptible cultivars again yielded populations that segregated fo r resistance to the fungus. In a 1996 field-plot in Wisconsin, to whic h no fungicide was applied? two of the BC1 lines, from two different s omatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-bli ght epidemic. In contrast, under these same conditions the cultivar Ru sset Burbank yielded only 0.86 kg/plant. These results indicate that e ffective resistance to the late-blight fungus in a sexually incompatib le Solanum species can be transferred into potato breeding lines by so matic hybridization and that this resistance can then be further trans mitted into potato breeding lines by sexual crossing.