Molecular Genetic Support to Optimize the Breeding of Fanleaf Resistant Rootstocks

AVF Proj. ID: 513 / /Cat.: ,
Primary Investigator(s): Andrew Walkerby

This report presents results of 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 (XiR1) from Vitis arizonica to the dagger nematode, Xiphinema index, which vectors grapevine fanleaf virus (GFLV) from vine-to-vine by root feeding. We have genetically and physically mapped XiR1 and we have transformed two candidate genes, XiR1.1 and XiR1.2 into V. rupestris St. George, V. vinifera Thompson Seedless, and tomato (all susceptible to X. index feeding) and have produced plantlets that are approaching the size needed to transfer to the greenhouse for X. index inoculation. These studies will determine which of and if these gene candidates controls resistance to X. index. We are also working on ways to rapidly evaluate fanleaf resistance and tolerance through in vitro grafting. We are also preparing to test saps from progeny of the 101-14 x M. rotundifolia population as a means of screening for the ability to induce tolerance to fanleaf disease. We worked with the UC Davis Metabolomics Center director and Doug Adams to identify a group of 5 metabolites and several cytokinin precursors that might be involved in this response based on their levels in infected and healthy O39-16 and St. George. These compounds will be pre-screened in the rotundifolia-based population and about 10 other Vitis species x M. rotundifolia hybrids I have produced. The saps are harvested and are preparing processing at the Metabolomics Center and more will be collected this year.

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

Development of Grape Rootstocks with Multiple Nematode Resistance

AVF Proj. ID: 136 / /Cat.: ,
Primary Investigator(s): Howard Ferris, Andrew Walkerby

Rootstocks currently available for nematode resistance have either inappropriate horticultural characteristics (such as the inducement of excessive vigor in scions leading to poor production and quality) or they have insufficient resistance against aggressive nematode strains and species. Several species of plant-feeding nematodes are present in most vineyards, however few rootstocks have resistance to more than one species.

Sources of resistance to root-knot and dagger nematodes have been detected in several Vitis species. Crosses made among these species in 1989, 1993 and 1994 were screened first for rooting characteristics and then sequentially against three nematode species: the root knot nematode (Meloidogyne incognita race 3), a strain of root-knot nematode that overcomes the resistance of Harmony rootstock (Meloidogyne arenaria), and the dagger nematode (Xiphinema index).

We have selected several candidate rootstocks with strong resistance to the individual nematode species, and some with broad resistance to two or more of the nematode species. Candidate selections will progress to field trials for testing of resistance durability and horticultural characteristics in the coming year. Screening of candidate selections against other nematode species, and against combinations of nematode species, will proceed in greenhouse trials.

Rootstock candidates evaluated in these studies are selected from Dr. Walker’s rootstock breeding program. This report addresses the nematode screening, not the breeding and horticultural components of that program.

PDF: Development of Grape Rootstocks with Multiple Nematode Resistance

A Search for More Durable Resistance

AVF Proj. ID: 9803 / /Cat.: ,
Primary Investigator(s): Michael McKenryby

This report concludes a three-year study. The location and quantity of resistance mechanisms within Harmony, Freedom, Teleki 5C, 10-17A, 10-23B, 6-19B, RS-3 and RS-9 have now been microscopically observed as various root knot nematodes infected them. A resistance mechanism common to many plants is referred to as a host hypersensitive response (HHR). This is observable as the plant kills its own cells just ahead of an invading pest. The new rootstocks listed above exhibit five- to ten-times more HHR than Harmony or Freedom rootstock. All the new rootstocks listed above are also able to exclude our aggressive pathotypes of root knot nematodes which can devastate roots of Harmony and Freedom. The biochemical method each rootstock utilizes to kill these cells has not been studied and should be considered to be dissimilar among the rootstocks. All the new rootstocks listed above are known to possess broader nematode resistance than Harmony or Freedom. This study indicates that HHR in the new rootstocks can occur in abundance all along the surface, cortex and vascular bundles of the extending root system. We believe HHR to be the main source of “Broad Nematode Resistance.” It is also clear that HHR only occurs as a response to infective J2 of root knot nematode. Once the J2 have developed a feeding site and developed to J3, the HHR was never observed. Freedom and Harmony possess HHR but in limited amounts and locations. Invasion by seven or eight J2 at one time is adequate to overwhelm the mechanism, the juvenile feeds and a new and distinct pathotype eventually results for that rootstock. Teleki 5C exhibits minimal HHR but is able to starve some of the J4 and adult stages by limiting feeding site development (also results in none or smaller galls). This mechanism may not be too effective on the younger roots but can have value on older roots where offspring J2 attempt to take over feeding sites from their mother. 10-23B exhibits HHR as well as a mechanism that limits feeding site development. Of all the rootstocks we have studied we believe 10-23B to have the broadest and potentially most durable mechanisms for nematode resistance. 10-17A and RS-9 exhibit such an abundance of HHR that if other mechanisms also occur we were unable to detect them. Our two-year nematode rootstock profiles revealed that Boerner, 110R, 101-14, and 5BB do have resistance to specific nematode pests but do not possess the breadth of resistance like the new rootstocks listed above. An improved nematode susceptibility chart has been developed. Additionally, five and 10 year old rootstock trials that we have monitored have indicated weaknesses and strengths of the original two-year studies.

A Search for More Durable Resistance

AVF Proj. ID: 9702 / /Cat.: ,
Primary Investigator(s): Michael McKenryby

In this second year our experiments to meet each of our objectives are well underway. The split-root experiments are set to determine if Meloidogyne arenaria pt. Harmony can physiologically alter Harmony rootstock thereby permitting normal root knot populations to enter Harmony roots. Our two-year evaluation of ectoparasitic nematodes feeding on 110R, 101-14, 5BB, Boerner, and Ramsey x Schwarzmann hybrids will complete this winter. We can already state that R x S-2 is too good a host for X. index but another R x S-9, which has low to medium vigor, continues to be a poor host for X index. We also continue to move these rootstocks and the USDA rootstocks into field trials. To determine resistance durability we have been observing and quantifying the resistance mechanisms of Freedom in the presence of different root knot nematode populations. A hypersensitive response (HR) is the browning of cells and tissues that often occur when a resistance mechanism is activated. Essentially the plant kills its own cells to defend itself from an invading pest. An HR can activate within 30 minutes of plant invasion. Infection by root knot nematodes does result in an HR in Freedom at site of penetration, during female development and during egg laying. It also occurs when nematodes attempt to enter some places other than just behind the root tip. The HR is also visible when the aggressive M. arenaria pt. Freedom is the infection nematode. The HR in Freedom involves only a few cells but can occur behind the root tip, along the differentiating vascular area and other locations along the root surface. The HR for 6-19B, 10-17A, R x S-2, and R x S-3 also occurs at all these locations but at each location involves 10 to 100 times the amount of plant tissue. We have not adequately studied 10-23B at this point in time and its mechanisms appear different. The new roots of the resistant stocks can actually become quite browned internally as compared to Freedom roots when under nematode attack. One of our concerns with HR has been that killing of plant cells could certainly result in slow plant growth until the pest population is depleted. However, the grape rootstock that promotes the greatest HR is 10-17A and to date we have never seen it with a lack of vigor. The 6-19B rootstock is slow to get started in sandy soils and it also exhibits extensive HR.

A Search for More Durable Resistance

AVF Proj. ID: 9601 / /Cat.: ,
Primary Investigator(s): M.V. McKenryby

During 1996 soil samples were collected and analyzed from existing rootstock trials in Kern County (500), Mendocino County (50), Gilroy (30), Kearney Ag Center (150), Fresno area (60), Merced County (20), and Monterey County (20). These results are still being tabulated and compared to previous findings from the same vineyards. We have focused more in this area this year because there is value to such work, but also because after eight months into this project I have still not found a post-doctorate or other scientist to conduct the microscopic studies we proposed. That search is still underway. We do have young vines of the five rootstocks (10-17A, 10-23B, 6-19B, RS-2, and RS-3) inoculated into microplots with 10 reps each in the presence of root knot populations that break resistance of Ramsey, Freedom, and Harmony. We are also initiating this winter the microplot evaluations of ectoparasites against 110R, 101-14, and 5BB. In spring 1997 we will plant conventional rootstocks in the presence of aggressive root knot populations using a split-root technique with half of each root system growing in the presence of pin nematode or ring nematode only. This project is being funded equally by the American Vineyard Foundation, the California Table Grape Commission and the Grape Rootstock Commission. Our support is ample and the work we still expect to complete within our three-year goal. On a side note, we are initiating a large field trial using these five rootstocks after various soil treatments with Thompson Seedless as the scion.

Soil Pest Profile for Grape Rootstocks

AVF Proj. ID: 9130 / /Cat.: ,
Primary Investigator(s): M.V. McKenryby

At this time we can present a ranking of sixteen rootstocks and indicate their deficiencies and attributes as a tool of nematode management. FREEDOM — {V. champini X 1613C by Weinberger/Harmon 1967). This is one of the best rootstocks for broad resistance to nematode species. It has excessive vigor and will perform best in sandy or loamy sand soils. Its single major nematode problem is a particular root knot nematode, M. arenaria pv. Harmony, which is rare in occurrence but may eventually build up on it and become a problem in the subsequent vineyard. Freedom performs as well as any rootstock against ring nematode and citrus nematode. It is reported to provide protection against Type A and Type B phylloxera. It does tolerate nematode feeding, though not as well as Ramsey. Sandy soils having ring nematode present should be fumigated before planting. RAMSEY — {V. champini formerly called Salt Creek). This stock imparts even greater scion vigor than Freedom. It should be considered for use in the sandiest soils where no pre-plant fumigation is planned (this needs testing). This stock is damaged most by M. arenaria pv. Harmony and is more susceptible to ring nematode than is Freedom. Propagation is somewhat difficult. Ramsey is one of the best sources of broad nematode resistance and has untapped utility as breeding stock. Ramsey generally grows better in the presence of nematodes than it does in their absence. TELEKI 5C — {V. berlandieri X V. riparia selected from Teleki 5A, 1924). Presumably, this stock does not impart as much vigor as Freedom or Ramsey. It has broad resistance to root knot nematodes, except H. arenaria pv. Harmony. It is susceptible to root lesion nematode and citrus nematode. It provides some protection against X. index build-up but not against the ring nematode or X. americanum. Observers have reported it to do best in the best soils but we find it to grow as well in sand or sandy loam. This rootstock should not follow plantings that host root lesion nematode or M. arenaria pv. Harmony. It provides