Late blight of potato, caused by the fungal pathogen Phytophthora infestans, is of great economic significance and no important U.S. potato cultivars are reliably resistant. The diploid species Solanum bulbocastanum is highly resistant to late blight, even under extreme conditions, but is sexually incompatible with potato. We have generated potato + S. bulbocastanum somatic hybrids. These hexaploid hybrids are highly resistant to late blight and progeny from two successive backcrosses to cultivated potato are either fully resistant or susceptible. The advanced generations are morphologically similar to potato. We have initiated mapping efforts to identify bulbocastanum chromosomal regions responsible for late blight resistance. Using RFLPs, RAPDs, and AFLPs, we identified a single chromosomal region (i.e., single gene or group of linked genes) on chromosome 8 that accounts for 62.2% of the observed resistance. The tomato cDNA clone CT88 cosegregates with late blight resistance in our material and was used to isolate a homeologous BAC clone from a S. bulbocastanum library. Our current efforts include mapping resistance in both fusion-derived and diploid S. bulbocastanum materials via map merging. As markers linked to late blight resistance are identified, we will attempt to convert them to marker forms useful for large-scale breeding efforts. To date, we have successfully converted RAPD and RFLP markers to SCAR and CAPS marker forms. Finally, continued fine mapping and BAC clone characterization will enable future map-based cloning efforts.
Development of somatic hybrids Solanum × michoacanum Bitter. (Rydb.) (+) S. tuberosum L. and autofused 4x S. × michoacanum plants as potential sources of late blight resistance for potato breeding
