M1-M5 (GRIN ID BS 223-227). These are tetraploid potato clones with resistance to cold-induced sweetening. This trait is important for the potato processing industry, as it allows the production of light-colored chips and fries after the storage of tubers at cold temperatures. All five clones contain the Solanum tuberosum haploid-wild species hybrid clone US-W973 x S. chacoense. They were developed by unilateral sexual polyploidization, in which the diploid female parent produced 2n eggs and the tetraploid male parent produced n pollen. After sexual polyploidization, clones M4 and M5 underwent additional crosses to the tetraploid clones W870 (M4) and W1005 (M4 and M5) from the University of Wisconsin potato breeding program. Germplasm release Tetraploid clones with resistance to cold induced sweetening
M6 (GRIN ID BS 228). This is a diploid potato clone generated by seven generations of self-pollination. This trait is important for inbred line development and utilization in potato breeding and genetics research. This clone is a member of the wild diploid potato species Solanum chacoense. Diploid forms of the cultivated potato (S. tuberosum) and most wild diploid Solanum relatives are self-incompatible due to a gametophytic self-incompatibility system. The object of this release, clone M6, is homozygous for the dominant self-incompatibility inhibitor gene, Sli. Cultivar development in potato is carried out at the tetraploid level, where clones are self-compatible, but the approach to homozygosity is too slow for inbred line development to be used as a breeding strategy. Inbred line development has thus far not been considered a viable strategy in potato breeding due to self-incompatibility. When self-pollination has been carried out at the diploid level, inbreeding depression has been too severe to allow the production of inbred lines. Presumably, the genetic load due to deleterious recessive alleles is high in diploid potato. M6 A diploid potato inbred line
M7 (GRIN ID BS 229). This is a long, russet potato clone generated from an interspecific cross between a cultivated and a wild species. This novel source of russet germplasm has been identified as a parent for processing and fresh market breeding programs. It was derived via bilateral sexual polyploidization following a cross between a diploid cultivated potato and the diploid wild species Solanum infundibuliforme. This clone, designated M7, is tetraploid, highly fertile and crosses readily to germplasm in breeding programs. It produces large tubers with long shape and russet skin. A high proportion of its offspring exhibits desirable tuber appearance. In addition, M7 expresses resistance to common scab and cold sweetening. It will be useful to potato breeders interested in expanding the genetic base of russet germplasm. M7 germplasm release
Clones with resistance to early blight and late blight. Three clones in a segregating population derived from a cross between the disease resistant parents +297 and K41 are being released as germplasm with resistance to both early blight, caused by Alternaria solani, and late blight, caused by Phytophthora infestans. The source of resistance to early blight in +297 is the wild species S. palustre and late blight resistance in K41 is conferred by the RB gene from S. bulbocastanum. These clones, named BR3, BR5, and BR85 (BR for Blight Resistant), yield well at a temperate zone latitude. In addition to containing heritable resistance to both early and late blights, these clones possess multiple other desirable agronomic traits, are fertile, and readily cross to cultivars.