A breeding program to develop rootstocks with resistance to Xiphinema index, the dagger nematode vector of grapevine fanleaf virus (GFLV), has been underway for many years at UC Davis. A mapping ...population (0705) derived from 161-49C x R8916-22 was created in 2007 to develop an SSR-based linkage map for X. index resistance. 161-49C is a commercial rootstock susceptible to X. index feeding and R8916-22 is a heterozygous resistant cross originating from b40-14, a form of Vitis arizonica. Preliminary results suggest a 1:1 resistant:susceptible segregation ratio for X. index under greenhouse conditions. Previous studies showed that X. index resistance was controlled by a single homozygous locus. To date, 190 of 400 SSR markers were polymorphic, with coverage on all 19 linkage groups. These markers and others are being applied to the entire 0705 population to complete a genetic map of this excellent source of X. index resistance.
Over a 5-year period a total of 108 uprooted virus-diseased vineyard plots were sampled for the presence of Xiphinema index and X. diversicaudatum nematodes, respective vectors of Grapevine fanleaf ...virus (GFLV) and Arabis mosaic virus (ArMV) in viticulture. A total of 711 trenches (approx. 10/ha) were sampled for nematode extraction. Xiphinema index was the most frequent, being detected in 310 samples (43%) whereas X. diversicaudatum was present in 81 samples (11%). Nematode numbers were very variable among plots and among samples of the same plot. We never found high numbers of both species on the same plot. No link was found with any management factor, except for high levels of living roots in the absence of devitalisation, that were often associated with higher nematode numbers. We propose to use the maximum number of nematodes found in any sample on a plot to adapt the fallow period using 4 classes: 0 ('absent', no Xiphinema found, no need for fallow); 1 ('few' ≤5 nematodes per sample: 2 years); 2 ('medium: >5 to 20: 3 years) and 3 ('high' >20; >4 years). Combining this rule for the two species would result in 22% of plots that can be replanted immediately, 28% after 2.5 years, 21% after 3.5 years, and only 29% requiring 4 or more years of fallow period. Monitoring nematodes to adapt fallow periods can be useful both to reduce unnecessary long fallow periods in the absence of nematodes and to avoid costly mistakes when replanting too early in the presence of high nematode numbers.
The dagger nematode, Xiphinema index, feeds aggressively on grape roots and in the process vectors grapevine fanleaf virus (GFLV) leading to the severe viral disease known as fanleaf degeneration. ...Disease symptoms consist of disrupted fruit set caused by GFLV and depressed plant growth caused by root damage from X. index. The use of fumigants to control X. index in vineyards is no longer recommended because of their high cost, detrimental environmental effects and lack of effective soil penetration to control nematodes on a deep perennial root system. Therefore, resistance to X. index has been an important objective in grape rootstock breeding programs. We previously demonstrated that resistance to X. index derived from a Vitis arizonica/girdiana hybrid b42-26 was largely controlled by a major quantitative trait locus, XiR1 (X. index Resistance 1) located on chromosome 19. Genetic studies leading to the isolation and characterization of the genes conferring resistance to X. index would further our understanding of resistance and assist molecular and classical breeding efforts to control X. index. In this report, we present the development of high resolution genetic and physical maps in the XiR1 region as well as the isolation of the XiR1 locus by a positional cloning approach. This study has identified the first locus responsible for ectoparasitic nematode resistance. The markers developed from this study are being used to expedite the breeding of resistant grape rootstocks.
Grapevine fanleaf virus (GFLV) is vectored specifically from grapevine to grapevine by the ectoparasitic nematode Xiphinema index. Limited information is available on the vector competency of X. ...index populations from diverse geographical origins. We determined the transmissibility of two GFLV strains showing 4.6% amino acid divergence within their coat protein (e.g., strains F13 and GHu) by seven clonal lines of X. index developed from seven distinct populations from the Mediterranean basin (Cyprus, southern France, Israel, Italy, and Spain), northern France, and California. X. index lines derived from single adult females were produced on fig (Ficus carica) plants to obtain genetically homogenous aviruliferous clones. A comparative reproductive rate analysis on Vitis rupestris du Lot and V. vinifera cv. Cabernet Sauvignon showed significant differences among clones, with the single-female Cyprus line showing the highest rate (30-fold the initial population) and the Spain and California lines showing the lowest rate (10-fold increase), regardless of the grapevine genotype. However, there was no differential vector competency among the seven X. index lines for GFLV strains F13 and GHu. The implications of our findings for the dynamic of GFLV transmission in vineyards and screening of Vitis spp. for resistance to GFLV are discussed.
The ectoparasitic dagger nematode, Xiphinema index, transmits Grapevine fanleaf virus (GFLV), which is responsible for a progressive degeneration of grapevines occurring across the world's vineyards. ...Since 2000, new data on the biology and ecology of the vector nematode and on the virus-nematode and plant-nematode interactions have contributed to elicit new alternatives to chemicals for nematode control. Molecular tools have allowed reliable nematode identification and new insights have been acquired into its genetic diversity at both the world and local scales and into its mode of reproduction. The long virus retention by the nematode in the bare soil combined with the location of the nematode in deep soil layers have highlighted the interest of both the development of nematode-resistant rootstocks as priority control alternative and the fundamental studies on molecular mechanisms of this specific virus retention. Some Muscadine accessions are currently the most efficient resistance sources. An optimization of their use through the characterization of Vitis × Muscadinia F1 and BC1 material for spectrum, histological mechanisms, genetics and durability is in progress. In the perspective of an integrated control, the resistance strategy could be completed by fallow crops showing an antagonistic (direct or indirect) effect on nematode numbers between two successive grapevine plantings.
Classical breeding methods that were developed to enable indirect selection have rarely been applied to grape breeding. These methods involve evaluating genetic diversity for a broad array of traits ...to determine whether there are strong associations that might allow indirect selection for traits that are difficult or expensive to measure. In order to evaluate these methods and determine which traits were strongly associated, 113 progeny from a cross between D8909-15 (Vitis rupestris x V. arizonica/girdiana) x B90-116 (V. vinifera) were assayed for 13 traits: number of clusters, leaf morphology, cluster length, peduncle length, number of berries per cluster, weight of 10 berries, seed number, nature of seeds, berry color, Brix, pH, titratable acidity, and anthocyanin content. D8909-15 is a wild source of resistance to Pierce’s disease and the dagger nematode, Xiphinema index, and B90-116 is a large-berried seedless table-grape selection. Multivariate procedures were applied to estimate the genetic divergence among the genotypes. Genetic variability was observed for all traits. The Ward grouping method was able to divide the progeny into 10 separate clusters, some with good yield and high-quality characteristics as well as resistance to dagger nematode and Pierce’s disease. The estimated correlations between the characteristics suggest that selection of genotypes with good productivity (number of clusters), high Brix values, moderate pH and acidity, and few seeds is possible. Principal component analysis found that the nature of the seeds proved to be invariant in the population, and the leaf scores had the lowest relative importance for the characterization and discrimination of the genotypes tested.
The control of grapevine pathogens is a rising concern in
Vitis vinifera
culture. The current international trend is toward banning chemicals that are highly toxic to the environment and human ...workers, and adopting tighter regulations. We evaluated the impact of saponins on three kinds of organisms found in grapevine culture. The ectoparasitic nematode
Xiphinema index
, the parasitic fungus
Botrytis cinerea
and various yeast strains representative of the must fermentation population were incubated on synthetic media supplemented with variable concentrations of
Quillaja saponaria
saponins. Saponins induced reduction in the growth of
B. cinerea
and showed nematicide effects on
X. index
. The control of
X. index
and
Botrytis cinerea
is discussed in the context of the potential use of these chemicals as environmentally-friendly grapevine treatments. With
Saccharomyces cerevisiae
and other yeasts, saponins showed higher toxicity against
S. cerevisiae
strains isolated from wine or palm wine whereas laboratory strains or strains isolated from oak exhibited better resistance. This indicates that
Q. saponaria
saponins effects against yeast microflora should be assessed in the field before they can be considered an environmentally-safe new molecule against
B. cinerea
and
X. index
.
The application of Trichoderma spp. for the suppression of plant-parasitic nematode populations is a promising tool in biological control. Sixteen strains of six Trichoderma species (T. atroviride, ...T. harzianum, T. rossicum, T. tomentosum, T. virens and T. asperellum) were tested in vitro in order to identify the most appropriate strains to control the dagger nematode Xiphinema index. Mortality assays revealed that the strains of the widely investigated T. harzianum species have caused significant reduction of X. index populations, although T. harzianum strains were not the most efficient among all the tested fungi. Certain T. virens and T. atroviride strains and T. rossicum have triggered faster and higher mortality. Generally, our data indicate that Trichoderma species have innate ability to decrease X. index population. Furthermore, as we had difficulties with maintaining X. index in vitro, we successfully used a newly developed method to keep X. index specimens viable during the experiments.
The efficacy of cross-protection at mitigating the impact of Grapevine fanleaf virus (GFLV) on grapevines (Vitis vinifera) was assessed in two naturally infected vineyard sites. Test vines consisted ...of scions grafted onto rootstocks that were healthy or infected by mild protective strains GFLV-GHu or Arabis mosaic virus (ArMV)-Ta. Challenge GFLV infection via the nematode Xiphinema index was monitored over nine consecutive years in control and ArMV-Ta cross-protected vines by double-antibody sandwich-enzyme-linked immunosorbent assay using GFLV-specific antibodies, and in GFLV-GHu cross-protected vines by characterizing the coat protein gene of superinfecting isolates by immunocapture-reverse transcription-polymerase chain reaction-restriction fragment length polymorphism. Results were consistent with a significantly reduced challenge infection rate in cross-protected vines compared with control vines, more so in those protected with GFLV-GHu (19 versus 90%) than with ArMV-Ta (40 versus 65% in field A and 63 versus 90% in field B). However, the two mild strains significantly reduced fruit yield by 9% (ArMV-Ta) and 17% (GFLV-GHu) over 8 years and had a limited effect on fruit quality. Therefore, in spite of a great potential at reducing the incidence of challenge field isolates, cross-protection with natural mild protective strains GFLV-GHu and ArMV-Ta is not attractive to control GFLV because the negative impact on yield is a limiting factor for its deployment.
A sample of clay loam vineyard soil, containing the nematode Xiphinema index, was divided into equal portions and stored in plastic bags. Nematodes were extracted immediately or remained in fridge ...for a short time or at room temperature for longer periods. The number of extracted nematodes did not differ significantly between treatments, indicating that X. index in soil samples collected for diagnostic purposes could remain viable for a period up to six months. Four other samples, of similar soil type, were collected from different vineyards and kept stored in plastic bags at room temperature. Variable periods of nematode survival recorded, ranging from less than two years in one sample, up to five years in another one. It is concluded that a long fallow period of at least five years may be required between successive grapevine crops to eliminate the nematode from clay loam soils.
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