Search for, and Development of, Nematode Resistance in Grape Rootstocks

AVF Proj. ID: 396 / /Cat.: ,
Primary Investigator(s): Howard Ferris, Andrew Walkerby

We released, to the grape industry, five rootstocks with broad and durable resistance toIhe root-knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenariastrain A and Meloidogyne incognita strain C), and the dagger nematode (Xiphinemaindex), with resistance to Grape Phylloxera, and with a range of rooting characteristics.We continue our search in Vitis and Muscadinia spp. for sources of resistance to nematode species that are important in California vineyards. This year we have focused our attention on the ring nematode. Criconemoides xenoplax; we have evaluated accessions of wild species and many crosses among Muscadinia and various Vitis species.

Molecular genetic support to optimize the breeding of fanleaf resistant

AVF Proj. ID: 410 / /Cat.: ,
Primary Investigator(s): Andrew Walkerby

This report presents results on Walker lab efforts to optimize the breeding of fanleaf degeneration (fanleaf) resistant rootstocks through molecular genetic methods. These efforts are two-fold: 1) to understand and utilize O39-16’s (a Muscadinia rotundifolia based rootstock) ability to induce tolerance to fanleaf virus infection in scions; and 2) to understand and utilize resistance from Vitis arizonica to the dagger nematode, Xiphinema index, which vectors grapevine fanleaf virus (GFLV) from vine to vine. We are in the process of repeating and clarifying past mapping and xylem sap analysis. We hope to have the previous work verified and corrected by Summer. The field trials we established to study xylem borne compounds with an influence on fanleaf infection will fruit well for the first time this Summer and we have renewed our efforts to determine the basis of induced tolerance. We alsosuccessfully completed a reworking of our fine-scale mapping efforts and that publication is submitted. This work will generate gene candidates for XiR1, the locus we have identified as responsible for X. index, resistance as derived from V. arizonica. This discovery will be followed with transformation experiments to confirm the resistance function of these candidate genes and allow us to use traditional breeding methods more carefully to avoid the breakdown of resistance and might lead to grape rootstocks genetically engineered with grape resistance genes.

Breeding Rootstocks Resistant to Aggressive Root-Knot Nematodes

AVF Proj. ID: 362 / /Cat.: ,
Primary Investigator(s): Peter Cousins, Ph.Dby

The USDA grape rootstock improvement program, based at the Grape Genetics Research Unit, is breeding grape rootstocks resistant to aggressive root-knot nematodes. We define aggressive root-knot nematodes as those which feed on and damage the rootstocks Freedom and Harmony. In 2007 we screened 2669 candidate grape rootstock seedlings for resistance to aggressive rootknot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. These selected seedlings are propagated and then planted into the vineyard. In 2007 we planted 70 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2006 and 2005. We tested the propagation ability of 105 nematode resistant selections and inoculated the 20 easiest rooting selections with aggressive root-knot nematodes to confirm the resistance of these selections. In 2007 we pollinated 1193 clusters of crosses in 87 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes. An additional 305 clusters in 16 cross combinations were pollinated specifically for genetic study. We identified nematode resistant germplasm that may be parents for rootstock breeding. We sent nine nematode resistant elite selections to Foundation Plant Services (FPS) for virus testing; only virus tested plant material of our rootstocks will be released. Virus testing by FPS anticipates the release of some or all of these selections as rootstocks within several years.

Development, Testing and Introduction of Grape Rootstocks with Broad & Durable Nematode Resistance

AVF Proj. ID: 341 / /Cat.: ,
Primary Investigator(s): Howard Ferrisby

We continue toward our goal of developing and releasing grape rootstocks with broad and durable resistance to nematode species that are important in California vineyards. In previous years, we have screened rootstock candidates against the root-knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne incognitastrain C), and the dagger nematode (Xiphinema index). Fourteen rootstock candidates exhibit broad resistance to those nematodes. Those fourteen have been narrowed to a group of six with desirable horticultural characteristics and broad resistance across all the nematodes tested. During 2006, we continued to test the breadth of that resistance beyond the range of the primary screen species by evaluating the resistance of the 14 candidates to the ring nematode, Mesocriconema xenoplax, in the presence of other nematode species. We also evaluated ring nematode resistance in the parents of the current rootstock candidates and in some other Vitissources. Only two of the rootstock candidates exhibit any resistance to the ring nematode and that may not be durable when other nematodes are present. We continue to seek new sources of resistance. Field testing of the rootstock candidates continues in fields that were heavily infested with root-knot nematodes. Nematode population levels are declining in the root-zones of all rootstock candidates, indicating that reproduction of root-knot nematodes is not occurring. However, population levels of ring nematodes at the field site are high on most of the selections, underscoring the need for obtaining new sources of resistance to that nematode. Rootstock candidates have also been tested in soils from three vineyards with populations of root-knot and ring nematodes. We initiated a new series of tests to screen for sources of resistance to ring nematode. Those tests will continue in 2007.

Grapevine Canker Diseases

AVF Proj. ID: 344 / /Cat.: ,
Primary Investigator(s): Douglas Gublerby

Until recently, grapevine dieback in California grapevines was attributed mainly to the fungus Eutypa lata in the family Diatrypaceae. This fungus has been known as the causal agent for Eutypa dieback. However, we have shown that dieback of grapevines in California is also caused by other fungi in the family Diatrypaceae (Eutypa leptoplaca, Eutypella and Diatrypella) as well as by several Botryosphaeria spp. To date, we have identified at least nine species of Diatrypaceous fungi associated with grapevine cankers as well as nine different species of Botryosphaeria, which appeared to constitute the main pathogens isolated from grapevine cankers statewide (Úrbez-Torres, et al., 2006; Úrbez-Torres, et al., 2007). Isolation from cankers and spore trapping studies in the table grape areas of the Coachella Valley have revealed the high incidence of Eutypella vitis (Diatrypaceae). This is a new pathogen in Coachella Valley table grape area. In addition, isolations from cankers have shown Phomopsis viticola to be the most common pathogen isolated from grapevine cankers in table and raisin cultivars in Fresno and Tulare Cos (Úrbez-Torres, et al., 2006). Results of spore trapping studies have shown that Botryosphaeria spores were mainly trapped following rainfall events in Napa Valley, Arbuckle, Lodi and San Luis Obispo, and following overhead irrigation in the Coachella Valley. Botryosphaeria spores were trapped from September 2006 to Jan., 2007. Interestingly, Botryosphaeria spores were also trapped without rainfall or irrigation in Arbuckle, suggesting that other environmental factors may contribute to spore release. Temperature studies for mycelial growth and pycnidial formation have shown different optimum temperature regimes among Botryosphaeria spp found in California, which agree with the actual differences in terms of geographical distribution of Botryosphaeria spp in California. We have developed new assays to evaluate the pathogenicity or virulence of the various fungi associated with grapevine dieback. Indeed, pathogenicity testing using green shoots in the laboratory as well as in the field appeared as a reliable method to rapidly assess fungal pathogenicity. Surveys for the host range as well as perithecia of Botryosphaeria spp in California have revealed additional host plants and sources of inoculum for these pathogens. These findings are providing a better understanding of the disease cycle of Botryosphaeria canker disease. Also, our work has stressed the importance of riparian and forest systems adjacent to vineyards in understanding the epidemiology, disease cycle and development of canker diseases in grapevines. Double pruning was shown to be an effective cultural practice which completely eliminates canker formation by Eutypa spp (Weber, E. et al., 2007) and we are now testing this practice against the more rapidly moving Botryosphaeria spp. Finally, our research has offered alternative control methods for E. lata using boron based chemicals. The use of 3-5% boron mixed with a commercial tree wound paste gave excellent disease control (91%). Interestingly, 1%boric acid also gave excellent disease control (82%).

Physiological Role of Rootstocks in Determining Grapevine Vigor

AVF Proj. ID: 187 / /Cat.: ,
Primary Investigator(s): David Smartby

We have made substantial progress in understanding at least one mechanism involved in determining why grapevines achieve such high vigor in deep fertile soils, even when irrigation water is withheld. This mechanism can be generally defined as hydraulic redistribution and involves the passive movement of water from roots in moist soil zones, under the drip irrigation emitter or from groundwater, to roots in dry surface or subsurface soils outside the emitter zone. We achieved this result by labeling water with 2%deuterium oxide, D2O. We then applied the labeled water through a drip emitter on one side of each of three 5-7 yr-old 420A rootstocks (Vitis berlandieri X V. riparia). We extracted roots and soil from both the labeled side and the dry side of the vine. Using the quantity of isotope found in roots we estimated that nearly 6 to 8%of the water in roots on the dry side of the vine came from the labeled water in the emitter zone. This water was conducted through the grapevine trunk and into roots on the dry side almost immediately (36 h). These observations suggest that the establishment of an extensive root system may contribute to over vigorous vines more than any single physiological trait like nutrient absorption because total root system size probably has more to do with total capacity for nutrient and water absorption than any other single factor. Hydraulic redistribution probably allows vines to sustain roots even during adverse conditions for growth. We are proposing further experiments in this area.

Development of Grape Rootstocks with Multiple Nematode Resistance

AVF Proj. ID: 198 / /Cat.: ,
Primary Investigator(s): Howard Ferris, Andrew Walkerby

Several species of plant-feeding nematodes are present in most vineyards, however few rootstocks have resistance to more than one species. Our goal is to develop grape rootstocks with broad and durable resistance to important nematode species. We have screened rootstock candidates against: the root knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenaria strains A and C), and the dagger nematode (Xiphinema index). From these selections, several candidate rootstocks with strong resistance to the individual nematode species, and some with broad resistance to two or more of the nematode species, were selected.
Of the thousands of seedlings produced from these crosses, only 14 have graduated through the rooting trial and individual nematode screening trials. These are extremely valuable plants. We know of no other examples of rootstocks for perennial crops selected for broad (multi-species) nematode resistance.

To test the durability of the resistance, some of the rootstock selections resistant to all four nematodes when inoculated individually were exposed to all of the species at the same time. Preliminary results are puzzling and need to be repeated. When inoculated together there appeared to be some galling. However, there were some logistical problems in conducting these preliminary experiments. We also need to test durability of resistance to root-knot and dagger nematodes when the plants are inoculated with other nematode species, including ring, citrus, pin and lesion nematodes.

PDF: Development of Grape Rootstocks with Multiple Nematode Resistance

Rootstock Interaction with Cultural Practices

AVF Proj. ID: 207 / /Cat.: ,
Primary Investigator(s): Jim Wolpertby

of rootstock affected total vegetative growth and higher pruning formulae resulted in reduced shoot vigor on all rootstocks. Total leaf area per vine averaged 28.1, 16.7, 14.6, 11.0, 9.6, and 4.2 m2 on 1103P, 110R, 3309C, S04, 101-14, and 420A respectively. Shoot lengths averaged 150, 120, 98, and 84 cm at the 4, 8, 12, and 16 bud formulae. Under the extreme pruning formulae and rootstock capacities used in this study, rootstock/pruning interactions were noted for all aspects of vegetative growth except final pruning weight. At low pruning formulae, higher capacity rootstocks produced larger shoots (176cm on 1103P and 110R compared to 118 cm on 420A). Differences in vigor diminished at higher pruning formulae. Total vegetative growth responded curvilinearly to pruning. Leaf area per vine was reduced by 40%at the lowest pruning formula on all rootstocks except 110R. For all rootstocks, it reached a maximum between the 8 and 12 bud/lb formulae and declined slightly thereafter. Rootstock affected yields both through effects on initial vine size and through effects on bud fruitfulness. Yields averaged 13.7, 9.0, 7.2, 4.4, 5.5, and 1.9 per vine for 1103P, 110R, 3309c, SO4, 101-14, and 420A respectively. Larger vines also produced larger clusters with more and larger berries. Cluster weights averaged 105, 101, 93, 88, 94, and 72 gm for 1103P, 110R, 3309c, SO4, 101-14, and 420A, respectively. The number of clusters per shoot varied by rootstock but was less dependent on vine size, averaging 1.79, 1.86, 1.68, 1.68, 1.86, and 1.60 clusters per shoot for 110R, 101-14, 1103P, 3309C, SO4, and 420A. Significant pruning/rootstock interactions existed due to very low fruitfulness on lowest capacity rootstock at the lowest pruning formula. Rootstock and pruning formula affected crop to pruning weight ratio without significant interaction. Crop to prunings ratios were lower on SO4 and 420A than on other rootstocks (3.5, 3.6, 4.8, 5.1, 5.4, and 5.5 on SO4, 420A, 3309C, 101.14, 110R, and 1103P). Crop to pruning weight ratios increased from 2.5 at the 4bud/lb pruning treatment to 6.3 at 16 bud/lb. Significant effects of rootstock, pruning formula, and their interaction were noted for rate of maturation. °Brix on 1103P was delayed at all pruning levels. Fruit from vines on 420A and SO4 was riper than that of vines on 110R, 309C or 101-14. Rootstock, pruning, and their interaction affected maturity solely through differences in crop and vegetative growth.

The independence of rootstock and pruning on vigor was found to break down at extreme capacities and pruning formulae. Further, the response of total vegetative growth to pruning was found to be curvilinear across the broader range of pruning formulae.

Total vegetative growth was dependent on pruning level and vine spacing. Pruning weights declined slightly from 0.9 kg/vine at 3 and 6 bud/m2 to 0.7 kg/vine at 9 bud/m2. Pruning weights increased from 0.65 kg/vine on 1M spacing to 1.2 kg/vine at 2.2m. Vigor was dependent on rootstock, pruning level and vine space. In all cases shoot growth fell to inadequate levels (below 30 gm/shoot) at the highest pruning level of 9 bud/m2. Yields were dependent on rootstock, pruning level, and vine space. With fewer clusters per shoot and setting fewer berries per cluster, 101-14 was less fruitful than 110R. Yields averaged 4.3 and 5.4 kg/vine on 101-14 and 110R respectively. Yields on 5-C were comparable to those of 110R. Yields were dependent on vine space and pruning level through number of shoots retained but reached a maximum at the 6 bud/m2 pruning level due to reductions in clusters per shoot and berry weight. At pruning levels of 3, 6, and 9 bud/m, yields were 1.5, 3.5, and 3.4 kg/vine on 1M vine spacing and 4.6, 7.5, and 7.4 kg/vine on 2m spacing. The balance of crop to vegetative growth depended solely on pruning level. Crop to pruning weight ratios were 3.9, 6.6, and 9.2 for the 3, 6, and 9 bud/m2 treatments. Rootstock and vine spacing had no effect on fruit composition at harvest. Maturities depended on pruning level without significant interaction. Soluble solids were adequate up to pruning levels of 6 buds per square meters but fell below 23° Brix at higher bud numbers.

PDF: Rootstock Interaction with Cultural Practices

Field Evaluation of Wine Grape Rootstocks

AVF Proj. ID: 209 / /Cat.: ,
Primary Investigator(s): Jim Wolpertby

As growers are aware, rootstock performance is highly dependent on site, with the most significant component appearing to be soil type, followed by vineyard spacing, and farming practice. When sites have few limitations rootstocks tend to perform more uniformly than when sites or farming practices are marginal. Rooting depth and water availability also seem to play a significant role.

Rootstocks such as 110R and 1103P have performed better than other rootstocks in sites where soil types are coarse-textured and/or where irrigation is sparingly applied. 1103P generally yields about the same as 110R but responds with more growth. Growth of both can be excessive in deep, well drained soils. 110R responds poorly to water-logged soils. The rootstocks 3309C and 101-14Mgt are clearly more moderate in vigor, often about 60 to 70%of 110R. In side-by-side comparisons, 101-14 is generally slightly more vigorous than 3309 but not in all conditions. Both are recommended for moderate to moderately high vigor sites. The rootstock 420A was generally low in vigor. Although it has comparable yield to other rootstocks if pruned to similar bud numbers per vine, the resultant growth is 20 to 50%of the more vigorous rootstocks. It could only be recommended for sites where vigor potential is high or where the vine spacing is very close. The Teleki hybrids 5C and 5BB are moderately vigorous in most sites except where water stress is present. Both tolerate heavy, poorly drained soils better than other rootstocks, provided there is no threat of Phytophthora.

Other rootstocks included in the trials were Freedom, Harmony, St George, 1616C and O39-16. Readers are encouraged to consult the full report for in-depth details about the trial sites and the individual rootstock recommendations.

PDF: Field Evaluation of Wine Grape Rootstocks