| Solanum is a diverse genus with over 200 species. Plant breeders have transferred various traits, such as disease resistance, storage quality, and potato chip color from wild Solanum species to the cultivated tetraploid potato, Solanum tuberosum. Mexican diploid Solanum species with an Endosperm Balance Number (EBN) of one have received less attention because of crossing difficulties due to ploidy and EBN.; Late blight of potato, caused by the fungus Phytophthora infestans , is a devastating disease that attacks leaves, stems, and tubers. Recent changes in P. infestans populations have increased the need for sources of genetic resistance. We have characterized resistance to P. infestans in the Mexican 2x(1EBN) species S. pinnatisectum. An interspecific cross between resistant S. pinnatisectum and susceptible S. cardiophyllum plants was used to generate a backcross family segregating for late blight resistance. A single dominant resistance locus (Rpi1) was mapped to chromosome 7, a region previously unassociated with late blight resistance. Characterization of the P. infestans isolate used in disease evaluations suggests that Rpi1 conditions a similar compatibility as the R9 resistance locus from S. demissum.; Many angiosperms have developed mechanisms to prevent self pollination and inbreeding. The most wide spread self incompatibility (SI) system is gametophytic SI, where pollen tube growth is inhibited in the style by a self recognition mechanism at a single locus (S-locus). Similar inhibition of pollen tube growth is also seen in interspecific crosses, where successful pollinations occur in only one direction, termed unilateral incompatibility.; In crosses between S. pinnatisectum and S. cardiophyllum , we have observed unilateral incompatibility. Progenies were generated only with S. pinnatisectum was used as the pistillate parent. Generation of two backcross families, one to each parent, revealed segregation for unilateral incompatibility. Segregations in the BC1 family backcrossed to S. cardiophyllum revealed two independent putative loci controlling this incompatibility, both inherited independent of the S-locus. However, segregation ratios in the second backcross family did not agree with those observed in the first family. Segregation disparity between the two families may be due to distorted transfer of specific alleles or the presence of different mechanisms controlling pistil and pollen recognition systems. |
