Location: Vegetable Crops Research2013 Annual Report
1a. Objectives (from AD-416):
1) Identification of sources of PVYNO resistance genes and determination of whether taxonomic or biogeographic data predict the distribution of resistance genes in wild Solanum species. 2) Determination of whether wild Solanum species that exhibit resistance to PVYO also express resistance to PVYNO. 3) Initiation of genetic studies that will elucidate the inheritance pattern of PVYNO resistance in selected wild Solanum species. 4) Characterization of the mechanisms of PVYNO and PVYO resistance (e.g. extreme resistance, hypersensitive response, inhibition of phloem transport) in new germplasm sources. 5) Determination of whether existing molecular markers for PVY resistance co-segregate with resistance in new germplasm sources. 6) Characterization of in-plant distribution of PVY throughout the growing season in selected resistant germplasm. 7) Initiation of efforts to introgress new PVYNO and PVYO resistance genes into the cultivated potato.
1b. Approach (from AD-416):
A set of true potato seeds of 160 accessions of 40 wild Solanum species (4 accessions per species) has been obtained from the NRSP-6 Potato Gene Bank. Seeds will be sown in a greenhouse and transplanted to individual pots 3 weeks later. One week after transplanting, the seedlings will be mechanically inoculated with the PVYO strain. Leaves from each asymptomatic plant will be evaluated for PVY titer using ELISA. Beginning 4 weeks after inoculation, individual plants will be scored weekly for symptom expression. Tubers will be collected from each plant and evaluated for PVY titer using ELISA. The proposed research project will repeat this study using PVYNO instead of PVYO. Diploid wild species clones selected for resistance to PVYNO will be crossed with susceptible diploid clones of the cultivated potato to initiate genetic and introgression studies. F1 hybrids will be created in the first year of the study. We will compare responses of each interaction type (susceptible, extreme res., local hypersensitive and systemic hypersensitive) using non-inoculated individuals (from cuttings of Solanum species taken before PVY inoculations). Plants from two different accessions (from two different species, if possible) from each interaction category will be grown to 6 weeks of age and inoculated with PVY on a lower leaf. One cm2 leaf samples will be taken from the inoculated leaf and a non-inoculated upper leaf 0 hours, 1 day, 5 days, and 7 days after inoculation. These samples will be used for RNA extraction. Real-time reverse transcription PCR will be used to assay the transcription of known pathogenesis-related genes (e.g. PR1a, PDF1, PR3, and PR5). Results will give us a better understanding of the temporal responses of the host during different resistance responses.
3. Progress Report:
This project was renumbered from 3655-21000-049-11S to 3655-21220-002-01S. This is the final report, project terminated 06/29/2013. Identification of sources of Potato Virus Y (PVY) NO recombinant genes and determination of whether taxonomic or biogeographic data predict the distribution of resistance genes in wild Solanum species. Determination of whether wild Solanum species that exhibit resistance to PVYO also express resistance to PVYNO. Clones that were resistant to PVYo were inoculated with PVYNO and found to retain their resistance. Clones are in 2013 field trials to confirm these results. Initiation of genetic studies that will elucidate the inheritance pattern of PVYNO resistance in selected wild Solanum species. A major gene for resistance has been identified. Five single-nucleotide polymorphism (SNP) markers co-segregate with resistance. Characterization of the mechanisms of PVYNO and PVYO resistance (e.g. extreme resistance, hypersensitive response, inhibition of phloem transport) in new germplasm sources. Extreme resistance with heat stability has been identified. Determination of whether existing molecular markers for PVY resistance co-segregate with resistance in new germplasm sources. Existing markers do not co-segregate. However, single-nucleotide polymorphism (SNP) markers have localized the gene. Candidate markers are being evaluated in segregating populations. Trials are underway for the characterization of in-plant distribution of PVY throughout the growing season in selected resistant germplasm. To investigate how the timing of PVY infection within the growing season affected the efficiency of tuber infection or distribution of infection within developing daughter tubers, replicated field experiments have been carried out in commercial potato production regions in Wisconsin. The potato varieties Russet Norkotah, Silverton Russet, Dark Red Norland, and Goldrush were inoculated twice monthly throughout the growing season. A double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was used to measure PVY infection. At the end of the season the virus in a subset of the infected plants in replicated plots was examined using ELISA. To examine rates of tuber infection and within tuber distribution of PVY from plants infected at different intervals during the growing season in field experiments, tubers were green sprouted, transplanted into soil mix, and developing shoots serologically tested for PVY infection. To comparatively determine how periods of cold storage might affect PVY distribution within tubers, longitudinal half-sections were removed from storage after 98 days and allowed to complete dormancy break through bench-top, green-sprouting. Half sections were then sub-sectioned into rose end, middle and stem-end regions and meristems were excised, transplanted, and tested serologically for PVY infection on 20 cm tall plants. Infection of developing tubers under plants naturally infected with PVY in the field generally did not change, but became infected during later developmental stages. As plant age at the time of infection increased, a reduction in the mean proportion of PVY-infected shoots only in Russet Norkotah and Silverton Russet. The proportion of infected tubers was variable in Dark Red Norland and Goldrush. PVY infection frequencies among shoots produced on complementary tuber half sections did not appear to be influenced by post-harvest storage compared to chemical dormancy break. Initiation of efforts to introgress new PVYNO and PVYO resistance genes into the cultivated potato. New sources of PVY resistance have been crossed to diploid and tetraploid clones. Clonal and seedling families are in the field for evaluation of adaptation and agronomic quality.