This is the second installment of a two-part report that includes abstracts of recent articles that deal with the part of the grapevine we don’t see—the root system and its immediate environment. The first installment included articles related primarily to rootstock effects on vine performance: yield, berry composition, scion physiology, etc. (See “Rootstocks and Vine Performance” in the July 2012 issue of Wines & Vines.) The second group of abstracts deals with pest problems that may be reduced by rootstock choice, including viruses and nematodes.

Consequences of ring nematodes for Pinot Noir grafted on various rootstocks
Researchers in Oregon studied Pinot Noir grapevines (Wädenswil clone) to evaluate their resistance to ring nematode and better understand how ring nematode parasitism affects below- and above-ground vine growth and physiology. The vines were either own-rooted or grafted to one of five rootstocks (3309C, 1103P, 110R, 101-14, 420A) known to vary in resistance to ring nematode (Mesocriconema xenoplax.)

Ring nematode populations in infested plots of all three susceptible treatments (self-rooted, 3309C, 17 1103P) increased rapidly during the second year and remained high throughout the study, while nematodes increased in two of the previously resistant rootstocks (110R, 101-14) during the third year.

Only 420A remained resistant during the entire four-year period. The impact of ring nematode parasitism on vines was most apparent in the susceptible rootstocks and self-rooted vines with reductions in fine root growth and colonization by arbuscular mycorrhizal fungi (AMF) occurring as early as the second year. Reductions in both fine-root production and AMF colonization due to ring nematode were greater during subsequent years in the susceptible vines. The frequency of fine roots containing vesicles of AMF was reduced in all five rootstocks that supported a population increase of ring nematode (only 420A was unaffected.)

Ring nematode did not alter above-ground vine performance until the third or fourth growing season, when shoot lengths and pruning weights were reduced in the three susceptible vines. By year four, however, ring nematode reduced fruit yield across all rootstock treatments.

R.P. Schreiner, I.A. Zasada and J.N. Pinkerton. Amer. J. Enol. Vitic. published ahead of print Feb. 14, 2012, doi: 10.5344/ajev.2012.11104. Contact the senior author through the Department of Horticulture at Oregon State University: (541) 738-4084, (541) 738-4087 or schreinr@mail.oregonstate.edu.

Effects of viruses associated with rugose wood complex on rootstocks
Four rootstocks (Vitis rupestris St. George, Kober 5BB, LN33 and Freedom) were graft-inoculated with viruses associated with the rugose wood complex (RW) to study their growth response and symptom expression. The virus sources used in this study were isolates LR127, CB111, CB105 and PA94-142 (grapevine virus A, or GVA); CB120 (grapevine virus B, or GVB); LV92-07 and a field selection of Chardonnay (grapevine virus D, or GVD), and a field selection of Cabernet Sauvignon (grapevine rupestris stem pitting-associated virus, or GRSPaV.) Each rootstock plant was graft-inoculated with one, two or three virus sources using bud chips from virus-infected grapevines.

After two years, plant diameter was measured, bark was removed and the woody cylinders were observed for the presence of RW symptoms and rated based on symptom severity. The greatest reduction in trunk diameter was in plants inoculated with the virus source combination of GVB+GVD+GRSPaV, regardless of the rootstock. Furthermore, GVB+GVD, GVA+GVB+GVD and GVB+GVD+GRSPaV had the highest effect on LN33 growth, and GVA+GVB+GRSPaV, GVB+GVD+GRSPaV and GVA+GVB had the greatest effects on 5BB. In general, GVB source material had more adverse effects on growth in multiple infections, particularly in triple combinations.

C. Rosa, J.F. Jimenez, P. Margaria and A. Rowhani. Amer. J. Enol. Vitic. 62:207-213 (2011). Contact the senior author through the Department of Plant Pathology at UC Davis: akrowhani@ucdavis.edu.

Effect of methyl bromide alternatives on nematodes under replant conditions
Preplant fumigants and nematode-resistant rootstocks were evaluated as alternatives to methyl bromide in a vineyard replant situation near Parlier, Calif., in the San Joaquin Valley. Two months after fumigation, Thompson seedless (own-rooted or on Freedom rootstock) and Merlot on 1103 Paulsen were planted. The treatments—1,3-dichloropropene + chloropicrin (578 kg/ha shank injected), iodomethane + chloropicrin (515 kg/ha shank injected or 448 kg/ha drip applied) and propargyl bromide (221 kg/ha shank injected or 207 kg/ha drip applied)—controlled root-knot and citrus nematodes equal to methyl bromide (507 kg/ha shank injected) during an eight-year evaluation period. Sodium azide (336 kg/ha drip applied followed with either a water cap or tarp), metam sodium (124 kg/ha applied with microspray sprinklers) and chloropicrin alone (448 kg/ha drip applied) were less effective.

The effects of fumigants on nematode control were very evident in the own-rooted Thompson seedless. The 1103P rootstock was partially tolerant to root-knot and citrus nematodes for the first three to four years, respectively, before nematode populations began to rebuild. Freedom rootstock proved to be highly resistant and kept root-knot nematode populations low during the eight-year evaluation. Authors indicated that preplant fumigation is still likely to be required in fields where citrus nematodes are present. Application of propargyl bromide and replanting with Merlot on 1103P was the only fumigant-rootstock combination that resulted in grape yield similar to the standard methyl bromide treatment. However, this effect was observed onl y during the first four years of fruit production.

J.A. Cabrera, D. Wang, S.M. Schneider and B.D. Hanson. Amer. J. Enol. Vitic. 62:42-48 (2011). Contact the senior author through UC Riverside at (559) 596-2851 or alfonsoc@ucr.edu.

Grapevine necrotic union, a new disease in grapevines grafted on 110 Richter rootstock
In Northern California, surveys of several Pinot Noir vineyards [(PN); clones 02A, 667, 777, and UCD 04] grafted to V. berlandieri x V. rupestris 110 Richter (110R), revealed that 2%-45% of vines had solid red leaf canopies and two distinct disease stages—i.e., full canopied plants with normal grape clusters (designated as acute) or stunted shoots and straggly bunches (designated as chronic.) In addition, the scion-rootstock junction of symptomatic grapevines had developed a necrotic union, hence the name “grapevine necrotic union” (GNU). Additionally, Chardonnay (clone 04, Yolo County) and Pinot Gris (clone 152, Monterey County) exhibited GNU-associated symptoms, with the exception of pale yellowed leaves. A detailed survey from 2004-09 was made in a sub-block (PN 02A Sonoma County, planted 1997) containing 664 grapevines in which initial incidence of GNU was 2.1% in 2004 and rose to 21.9% by 2009, suggesting secondary spread.

Assays for grapevine viruses phytoplasmas and Xylella fastidiosa failed to detect a causal agent. Likewise, bud-chip inoculations of test plants of Cabernet Sauvignon scions on different rootstocks including 110R were inconclusive. Based on the results obtained so far, GNU is being regarded as an emerging disease of unknown etiology in California vineyards.

M. Al Rwahnih, A. Rowhani, R.J. Smith, J.K. Uyemoto and M.R. Sudarshana. J. Plant Pathology 94:149 (2012). Contact the senior author through the University of California, Davis, Department of Plant Pathology: (530) 752-0300 or malrwahnih@ucdavis.edu.

Soil properties influencing phytoparasitic nematode populations in Chilean vineyards
Lifecycles of parasitic nematodes take place in the rhizosphere, therefore their breeding, parasitism and mobility dynamics are inevitably influenced by the soil-root interaction. A study was performed to evaluate the influence of rootstocks to some plant parasitic nematodes under different soil conditions. Nematode populations were assessed for Chardonnay vines either ungrafted or grafted on two rootstocks (5BB, SO4) in three different alluvial soils in the central zone of Chile. Soils were two Inceptisols of the Casablanca Valley (Valparaíso region), the first one with minimal soil structure and with a densification zone in lower horizons (S1); the second was a Mollisol (S2) more structured than the others, situated at Melipilla (Metropolitan region); the third one was a sandy textural class (S3.) The soils were characterized physically and morphologically, and nematode genera were identified and counted using a dissecting microscope. Ungrafted Chardonnay had the highest populations of Meloidogyne spp. (root knot nematodes) in all three soils but only significant in S2 soil.

P.M. Fajardo, E.E. Aballay and P.M. Casanova. Chilean J. Agricultural Research 71(2):240-248 (2011).

Andrew G. Reynolds is professor of biological sciences/viticulture at the Cool Climate Oenology and Viticulture Institute at Brock University in St. Catharines, Ontario. He has written the Wine East column “What’s New in Research: Summaries of Current Literature on Grapes and Wine” for Wine East since 1997.