2011 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.
Selected accessions which vary in their response to infection with Potato Virus Y (PVY) were analyzed using the Climex software database in an attempt to spatially identify locations anticipated to possess species which may contain resistance (R) or susceptibility (S) to PVY infection. Infectivity data from greenhouse bioassays were used for selected accessions and the Climex software suggests that resistant plants are found in warmer, drier climates when compared to susceptible plants. Specifically, weather stations were mapped in three main primary areas of Central and South America: Mexico, Peru/Bolivia, and Argentina/Chile/Uruguay. Available coordinates (n=124) from the database were then mapped according to R or S. In addition to coordinate proximity of sample sites to weather stations, altitudes were also determined. By completion of this objective, we were better able to determine which weather stations were most appropriate to use to represent sampling locations. Representative weather stations for both R and S samples were, in turn, selected and using a Climex template, temperature and moisture constraints were manipulated until the R-representative weather stations were “favorable” and the S-representative weather stations were “unfavorable” to determine what climate was better represented by R. Moisture and temperature parameter data (the limits for favorable growth) for R and S data were then graphed representing climates that were better approximations for R which were much drier and a bit warmer, than those better represented by S. Among accessions of interest, three tables were generated representing: Resistance, Susceptibility, and Both. These correspond to what the CLIMEX models predicted at these locations. For each weather station listed in each table there are often several accessions from that location. Locations where resistance is suggested (city, country, lat, long, alt): Arequipa, Peru (-16.400, -17.500, 2330); Lima, Peru (-12,100, 77.000, 120); Mendoza, Argentina (-32.800, -68.00, 800); Oploca, Bolivia (-21.300, -65.800, 3120); Vasques co. (airport); Peru (-4.200, -69.900, 84); and San Luis Potosi, MX (22.100, -101.000, 1877). Locations where susceptibility is suggested include: San Miguel Tucum, Argentina (-26.800, -65.200, 480); Corrientes, Arg (-27.500, -58.800, 54); Huancabamba, Peru (-5.200, -79.400, 1952); Quito, Ecuador (-.200, -78.500, 3345); and Morelia, MX (19.700, -101.200, 1941). Finally, locations where both R and S are suggested include: Abancay, Peru (-13.600, -72.900, 2398); Cordoba, Argentina (-31.500, -64.300, 423); and La Oroya, Peru (-11.600, -75.900, 3750). The project is monitored through in person discussions, phone calls, and e-mail exchanges.