Anticipatory breeding: molecular markers as a tool in developing donors of potato (Solanum tuberosum L.) late blight resistance from complex interspecific hybrids

Potato late blight caused by oomycete Phytophthora infestans Mont de Bary remains the most significant agronomic and economic problem of potato husbandry. The unique rate of evolution of this pathogen as well as its migration are a major obstacle to producing varieties with durable late blight resistance. The best way to counter this threat is the anticipatory breeding based on donors that carry genes of resistance to a wide range of pathogen races. Combining multiple genes for late blight resistance in the same plant (pyramiding of genes) makes such resistance durable. The most promising way of obtaining such donors is introgression breeding of interspecific potato hybrids with resistance genes transferred from potato wild relatives - the tuber-bearing species of Solanum L. Molecular markers allowing to reliably distinguish between resistance genes of diverse specificity and successfully control their transfer in the process of crossing and selecting, dramatically increase the efficiency of introgression breeding for late blight resistance. We examined about 40 complex hybrids bred in the A.G. Lorkh All-Russian Research Institute of Potato Husbandry, the N.I. Vavilov All-Russian Institute of Plant Genetic Resources and the All-Russian Research Institute of Plant Protection using the germplasm of 16 species of tuber-bearing Solanum, and further maintained as clones. Each of these clones carries the genetic material introgressed from two to eight wild species established as the sources of resistance to late blight. Most of these clones have manifested, from year to year, high late blight resistance in field trials under natural infection and in vitro studies when detached leaves were infected with a highly virulent and aggressive isolate of P. infestans. SCAR (sequence-characterized amplified region) markers, the fragments of R genes of race-specific (vertical) resistance to late blight discerned in various Solanum species, were employed to screen the clones of interspecific hybrids. The information on the presence of SCAR markers for six R genes, i.e. R1 (chromosome 5), R2 / Rpi-blb3 (chromosome 4), R3a and R3b (chromosome 11), RB / Rpi-blb1 = Rpi-sto1 (chromosome 8), and Rpi-vnt1.3 (chromosome 9), was juxtaposed against the indices of late blight resistance. Comparison of the resistance of the clones of interspecific hybrids and potato varieties devoid of R gene marker presumes a significant contribution of these genes to general late blight resistance of potato plants. The higher number of R gene markers per plant corresponded to superior late blight resistance. Presumably, future use of these clones for pyramiding resistance genes under the control of molecular markers will enable target introgression breeding. Such approach will streamline developing new potato varieties with durable late blight resistance to maintain high productivity even after significant changes in the populations of P. infestans.