Breeding grapevine rootstocks for resistance to soil-borne pests and diseases
We made more crosses to increase the number of Muscadinia rotundifolia-based progeny by crossing 101-14 Mgt, 161-49C (V. berlandieri x V. riparia) and 5BB with M. rotundifolia Trayshed pollen to create populations with broad pest resistance and the ability to induce fanleaf tolerance in scions. We have over 200 progeny in the 101-14 x Trayshed population and many are undergoing rooting and horticultural screening this Winter. We have screened subsets of the population for resistance to dagger, root-knot and ring nematodes; they segregate for dagger and root-knot resistance and all resist ring nematodes. To further our study of fanleaf tolerance, we also collected xylem sap from stronger progeny in the 101-14 x Trashed population. We will screen these saps with targeted metabolites from our fanleaf tolerance investigations. We also made crosses to produce PD resistant rootstocks with good nematode resistance and good rooting; better drought and salt tolerance; and crosses to make virus tolerant rootstocks. Cecilia Agüero successfully made constructs of two of the XiR1, Xiphinema index resistance genes we characterized from V. arizonica/girdiana b42-26 (Hwang et al. 2010. Theoretical and Applied Genetics 121:780-799). She has transformed them into St. George and Thompson Seedless, and into tomato (a host of X. index and very easy to transform and study). We should be able to inoculate these plants with X. index later this year to test the function of these gene candidates. This project is primarily funded by the American Vineyard Foundation, and it also supports our efforts to determine which metabolites are responsible for O39-16?s fanleaf tolerance. We will be testing for presence and levels of five metabolites and two cytokinins in saps from O39-16 and about 20 individuals from the 101-14 x Trayshed population. Kevin Fort?s excellent work on the mechanisms of, and screening for, salt tolerance are coming to fruition and four publications are ready for submission. He is now working as a post-doc on generous funding from E&J Gallo who funded a joint project between Andrew McElrone and myself. Kevin is studying interactions between drought and salinity, and working out experiments to accurately screen drought tolerance and to better understand root architecture. He is helping to supervise Claire Heinitz who is studying the eco-genetics of salt tolerance in southwestern Vitis, and Cecilia Osorio who is studying the anatomical basis of drought tolerance. Jean Dodson is also working on drought adaptation by studying the influence of rootstocks on phenological events such as root senescence, leaf drop and harvest dates, which will greatly impact vine water use. Karl Lund is analyzing the feeding behavior of eight phylloxera strains on the root tips of 11 rootstocks and Vitis species. He has also initiated the screening of a V. vinifera x V. berlandieri 9031 mapping population. This V. berlandieri accession has excellent phylloxera resistance and the progeny segregates for resistance, which allows the development of a genetic map for this source of resistance.