Location: Vegetable Crops Research2010 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
Potato virus Y (PVY) resistance was evaluated in 135 accessions of wild Solanum species. New germplasm with resistance to PVY includes S. albornozii, S. andreanum, S. bukasovii, S. bulbocastanum, S. cardiophyllum, S. hjertingii, S. iopetalum, S. jamesii, S. kurtzianum, S. paucijugum, S. pinnatisectum, and S. schenckii. There was no consistent association between PVY resistance and taxonomic series, clade, ploidy or breeding system. However, the correlation between resistance and the collection site elevation was high and significant. This relationship may be related to the distribution of aphids, which act as vectors for PVY. Out of a total of 22 PVYO resistant accessions tested, 20 were also resistant to PVYNO. Consequently, genes that confer resistance to PVYO almost always confer resistance to PVYNO. Interspecific and intraspecific crosses have been made between PVY resistant and PVY susceptible clones. Two populations of approximately 200 clones each are being evaluated for PVY resistance. Two out of three replications have been completed. Crosses have been made between diploid PVY resistant wild species clones and diploid cultivated potato. Hybrids are being evaluated for PVY resistance. In addition, new sources of resistance have been identified in diploid cultivated clones. All the reported markers associated with PVY resistance genes (Rysto, Rychc, Ryadg,, Ny1 and Nytbr) have been screened, but they did not consistently identify resistance in new resistant germplasm. New molecular markers are being developed and screened in segregating populations. The project is monitored through in person discussions, phone calls, and e-mail exchanges.