Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 1998
Publication Date: N/A
Interpretive Summary: Due to the general susceptibility of potato cultivars to Phytophthora infestans, the cause of late blight of potatoes, this disease is a major world-wide problem for potato production. It is not surprising, then, that a source of genetic resistance to this devastating disease that caused the Irish potato famine has been long sought by plant breeders. One Mexican species, Solanum bulbocastanum, is highly resistant to late blight but extremely difficult to cross directly with potato. We have used somatic hybridization, a procedure for fusing leaf cells of different species, to generate somatic hybrids of potato and S. bulbocastanum that can be backcrossed to common cultivars. These hybrids retain the resistance of the wild species and yield resistant progeny when crossed with susceptible potatoes. These results indicate that effective resistance to the late blight fungus in this sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and this resistance can be further transmitted into potato breeding lines. As costs of fungicides to farmers are often $100 to $200/ year to control this disease, and over 80,000 acres were planted in Wisconsin alone last year, the savings to Wisconsin farmers in future years could exceed 16M if suitable cultivars carrying this resistance can be produced.
Solanum bulbocastanum, a wild diploid (2n=2x=24) Mexican species is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato but virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum and the tetraploid potato line, PI 203900, yielded hexaploid somatic hybrids that retained the high resistance of the S. bulbocastanum parent. The BC1 progeny segregated for resistance to US8 genotype (A-2 mating type) of P. Infestans. Resistant BC1 lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field plot in Wisconsin, to which no fungicide was applied, two of the BC1 lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late blight epidemic. In contrast, under those conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. At the end of the season (August 26) the high yielding S. bulbocastanum- derived lines shown only 3.5 and 4.7% leaf infection, respectively, whereas the cultivar controls were completely defoliated by August 12. These results indicated that highly effective resistance to late blight can be transferred into potato by somatic hybridization.