ABSTRACTACCESSING CROP WILD RELATIVES OF POTATO WITH A FOCUS ON SOLANUM VERRUCOSUM AND THE 1EBN WILD SPECIES IN THE TERTIARY GENEPOOLByWilliam Behling Potato, Solanum tuberosum L. group Tuberosum (2n=4x=48), remains one of the most important crops worldwide and plays an integral role in global food security. Due to challenges with tetraploid breeding, the past century of potato breeding has struggled to make significant genetic gains or utilize valuable crop wild relatives effectively. A recent movement towards diploid breeding methods to develop commercial potato varieties aims to address these issues. Diploid breeding methods also offer new opportunities to leverage the immense potential of untapped genetic diversity in wild potato. However, the lack of broad self- and interspecific compatibility in diploid potato remains a substantial barrier to this effort. We characterized interspecific reproductive barriers which breeders are likely to encounter when using wild species in the genetic improvement of potato. The wild potato species S. verrucosum was selected for these experiments as it exhibits a desirable high level of self-compatibility and broad interspecific compatibility. We first examined the validity and consistency of the Endosperm Balance Number (EBN) hypothesis. Two experiments were used to examine the accuracy of the EBN hypothesis to predict normal seed development in interspecific crosses. Eleven 1EBN species and three S. verrucosum clones were used to elucidate significant inter- and intraspecific variation for effective ploidy and regular seed development. The variation observed could not be predicted or characterized by the EBN hypothesis, thus questioning the value and application of this classification system. Second, we sought to understand the genetic basis and heritability of the broad interspecific compatibility phenotype present in S. verrucosum, using an F2 population derived from a cross between the S. tuberosum doubled monoploid DM1s1 and the S. verrucosum clone MSII1813-02. The population was phenotyped using self-pollinations, pollen viability assays, and interspecific pollinations with S. pinnatisectum and S. tarnii. Biparental linkage mapping identified two major QTLs on chromosomes 1 and 11 together explaining 56.6% of the phenotypic variance in interspecific compatibility. We also identified three QTL associated with male fertility on chromosomes 3, 8, and 9 explaining, respectively: 27.1%, 26.5% and 16.2% of the phenotypic variance in male fertility. Third, breaking from the S. verrucosum focus, we evaluated a novel germplasm pool of advanced breeding clones of hybrids between the wild species S. ehrenbergii, S. jamesii, and S. stenophyllidium for their potential in 1EBN germplasm characterization and development. In a modest yield trial, advanced clones exhibited desirable cultivated traits and outperformed their wild species sources. These results, along with crossing experiments, evince the suitability of this material as a prebreeding resource and alternative germplasm worthy of further research. This work explores pathways to harness underutilized genetic resources of wild potato species, expanding the armamentarium available to breeders for the genetic improvement of diploid S. tuberosum for commercial variety development. The availability of diploid S. tuberosum germplasm with broad interspecific compatibility and high self-compatibility derived from S. verrucosum will facilitate further utilization and characterization of wild germplasm.
Read
