Abstract
Surveys were conducted in eastern Washington and Idaho to determine the plant-parasitic nematodes associated with winegrape (Vitis vinifera) vineyards. The most commonly encountered plant-parasitic nematodes in eastern Washington and Idaho winegrape vineyards were Meloidogyne hapla, Paratylenchus spp., and Xiphinema spp. (detected in >50% of sampled vineyards) with Pratylenchus spp. and Helicotylenchus spp. also commonly detected in Idaho. The frequency of occurrence of these plant-parasitic nematodes was consistently greater in Idaho compared to eastern Washington, except for M. hapla, which had a similar frequency of occurrence in both states. The types of groundcover or irrigation method used in vineyards and estimates of previous crop yields did not influence nematodes present in soil, but differences in plant-parasitic nematode communities were found among geographical areas (American Viticultural Areas, AVAs). Xiphinema spp. was more commonly associated with vineyards in the Horse Heaven Hills and Snake River Valley AVAs than in the Yakima Valley and Columbia Valley AVAs. Twenty-seven juice grape (Vitis labruscana) vineyards were sampled to enable a comparison of plant-parasitic nematode communities among red and white winegrapes (V. vinifera) and juice grape varieties. Meloidogyne hapla and Xiphinema spp. were more commonly found in red and white winegrape vineyards than in juice grape vineyards, while Mesocriconema xenoplax and Paratylenchus spp. were more commonly associated with white wine and juice grape vineyards than with red winegrape vineyards. While plant-parasitic nematodes were commonly found in eastern Washington and Idaho vineyards, the impact of these plant-parasitic nematodes on winegrape productivity in this region remains to be determined.
Winegrapes (Vitis vinifera) produced in semiarid regions of the Pacific Northwest (PNW; Idaho and eastern Washington) are grown in desert-like conditions. In eastern Washington, the environment is characterized by warm summers and cool winters, with average maximum and minimum temperatures of 31°C and 13°C in July and 5°C and −4°C in January, respectively (Prosser, WA). Average annual precipitation for this area is 210 mm. In Idaho, the average maximum and minimum temperatures are 33°C and 14°C in July and 4°C and −5°C in January, respectively; average annual precipitation is 288 mm (Nampa, ID). Most vineyards in this region are grown on sandy soils and receive regulated deficit irrigation (Schreiner et al. 2007). Both states have growing winegrape industries. Washington is the second largest wine producer in the United States, with more than 16,592 ha planted to V. vinifera grapes as of 2011 (USDA 2012). The first commercial-scale plantings in eastern Washington began in the 1960s, and the industry rapidly expanded in the mid-1970s. There are 10 recognized American Viticulture Areas (AVAs) in eastern Washington. The Idaho wine industry started in the 1970s and in 2007 there were 602 ha under production (USDA 2007). A single AVA, Snake River Valley, is found in Idaho. In both of these states the majority of the V. vinifera grape acreage is grown as self-rooted vines. Washington also has a large juice grape (Vitis labruscana) industry, with 10,521 ha in production (USDA 2012).
Little is known about the plant-parasitic nematodes associated with winegrapes grown in the semiarid PNW. Plant-parasitic nematodes are significant parasites and reduce productivity of potatoes, alfalfa, wheat, and mint grown in the region (Hafez et al. 1992, Smiley et al. 2004). Many new vineyards are planted in areas which were previously under nematode-susceptible row crop production such as those stated above. Winegrapes are an excellent host for many plant-parasitic nematodes. Meloidogyne spp. (M. incognita, M. arenaria, M. javanica, and M. hapla) have a cosmopolitan distribution and are a major production constraint (Arredondo 1992, Jenser et al. 1991, Nicol et al. 1999, Raski et al. 1973). The root-lesion nematode, Pratylenchus vulnus, causes economic loss in California (Raski et al. 1973) and Australia (Walker and Morey 2000). Dagger nematodes, Xiphinema spp., are pathogenic on grape (Raski and Radewald 1958) and also vector viruses that can severely affect grapevines (Ramsdell and Meyers 1974). In western Oregon, the ring nematode, Mesocriconema xenoplax, was present in 85% of surveyed vineyards (Pinkerton et al. 1999) and was shown to significantly reduce pruning weights, fine root weights, and fruit yield (Pinkerton et al. 2004).
The objective of this study was to determine the occurrence and distribution of plant-parasitic nematodes in winegrape vineyards in eastern Washington and Idaho. To a lesser extent, relationships among plant-parasitic nematode genera and vineyard management practices, site characteristics, and grape type, including juice grapes, were examined. Results of the surveys reported here are important preliminary steps to determine the role of plant-parasitic nematodes to Washington and Idaho winegrape production and to direct future management and research needs.
Materials and Methods
Soil samples were collected in August from established vineyards during 2000 and 2003 in eastern Washington and during 2007 in Idaho. Eighty vineyards were sampled in 2000, and an additional 77 vineyards were sampled in 2003 in the Columbia Valley, Horse Heaven Hills, and Yakima Valley AVAs in eastern Washington. Forty vineyards in the Snake River Valley AVA were sampled in Idaho in 2007. In both states, vineyards to be sampled were selected because a grower cooperator was identified. Regardless of location or collection date, a sample from a vineyard was a composite of 30 to 40 randomly located soil cores (1.8 cm diam × 45 cm deep) collected from a 1- to 2-ha block. The cores were collected in the generally weed-free vine row, ~30 to 45 cm from the base of the vine in a “W” pattern across the sampled area. Soil cores from each vineyard were combined into a composite sample, placed in a labeled plastic bag, and kept cool during transport to the laboratory.
At the laboratory the composite sample was placed in a bucket, mixed, and a 250 g subsample removed. Nematodes were extracted from this 250 g wet soil subsample by elutriation and then sucrose flotation and centrifugation in 2003, or by wet sieving through nested 250- and 25-μm sieves, sucrose flotation, and centrifugation in 2000 and 2007, using established protocols (Ayoub 1980). Plant-parasitic nematodes in each sample were identified to genus and counted. Subsamples of individual nematodes of Meloidogyne and Mesocriconema were mounted on slides and identified to species level morphologically when possible. A subsample of soil from each sample was dried in a 70°C oven for 1 week prior to determining dry weight; nematode population densities are expressed as number of nematodes per 250 g dry soil.
Additional vineyard management and site information was collected in the eastern Washington surveys only in 2000 and 2003. The grower cooperator was asked to provide information on vineyard variety, age, history of nematodes, vine vigor, vine spacing, cropping history, soil type, groundcover, and irrigation type. After compiling the information submitted by the grower cooperators, a consistent management and site information data set was compiled. Information on variety, age, and groundcover was obtained for both years, while information on previous year’s yield and irrigation type was also obtained for 2003 sampling sites. Vineyard management and site information were categorized as follows: AVA (Yakima Valley, Horse Heaven Hills, Columbia Valley, Snake River Valley), vineyard age (<5 years, 5–10 years, >10 years), yield of winegrape vines >5 years old (0–15,000 kg/ha, >15,000 kg/ha), groundcover (native, nonnative), and irrigation type (drip, overhead).
To allow for comparison of plant-parasitic nematode communities between red and white winegrapes and juice grape (Vitis labruscana) in eastern Washington, seven juice grape vineyards were included in the 2000 survey and 20 juice grape vineyards were included in 2003. Soil samples were collected and nematodes extracted from soil samples as described above. Grape type was categorized as red, white, or juice to allow for statistical comparisons. The plant-parasitic nematode data from juice grape vineyards were only included with the data from winegrape vineyards for this statistical analysis.
In the eastern Washington survey in 2000, separate soil core samples were collected from the same area where nematode samples were collected from 32 of the winegrape vineyards to determine root density and colonization of fine roots by arbuscular mycorrhizal fungi (AMF). Four replicate samples, comprised of five soil cores (3.1 cm diam, 0–50 cm depth) pooled from 10 continuous vines in a row, were collected along a diagonal transect across each vineyard. Roots were washed from soil samples, separated into woody and fine root fractions, and fine root length and colonization by AMF were determined as described by Schreiner and Linderman (2005). The proportion of fine root length colonized by any AMF structures inside roots, and specifically by arbuscules, was measured.
Plant-parasitic nematode population frequency of occurrence, average, and range of population densities in eastern Washington and Idaho winegrape vineyards were calculated. Effects of location on frequency of occurrence and average population densities of each plant-parasitic nematode genus were determined by one-way ANOVA or non-parametric Mann-Whitney test. Relationships among categorical data (AVA, grape type, vineyard age, previous year’s yield, irrigation type, and groundcover) and plant-parasitic nematode genera were examined by Pearson’s chi-square test (X2). The relationship between plant-parasitic nematodes and root density or AMF colonization was determined using linear correlation. All analyses were considered significant at p ≤ 0.05. Analyses were performed using JMP software (SAS Institute, Cary, NC).
Results
Eight genera of plant-parasitic nematodes were encountered in soil samples collected in eastern Washington and Idaho winegrape vineyards (Table 1). Commonly encountered plant-parasitic nematodes (≥50% detection) in both Idaho and eastern Washington were M. hapla, Paratylenchus, and Xiphinema. For M. hapla, the detection frequency was similar between the two states, while Xiphinema and Paratylenchus were found more frequently (p < 0.001) in Idaho vineyards. The plant-parasitic nematodes Pratylenchus and Helicotylenchus were also commonly encountered in Idaho (>50% detection), and their percentages of occurrence were significantly higher (p < 0.001) than in eastern Washington (Table 1). Mesocriconema xenoplax was less commonly detected in the sampled vineyards in both states, but was more frequently (p = 0.002) detected in Idaho. Other ectoparasitic nematodes found during this survey were Tylenchorynchus and Trichodorus. Mean population densities of M. hapla, Pratylenchus, and M. xenoplax were not significantly different between the two states (p > 0.05). Paratylenchus population densities were significantly higher (p < 0.001) in eastern Washington than in Idaho vineyards, while mean population densities of Xiphinema (p = 0.012) and Helicotylenchus (p < 0.001) were higher in Idaho than in eastern Washington vineyards. For the other plant-parasitic nematodes encountered, mean population densities were similar (p > 0.05) between the two states and relatively low.
Mean and range of plant-parasitic nematode population densities and frequencies of detection in soil samples collected from vineyards (Vitis vinifera) in eastern Washington (WA) and Idaho (ID).
Few of the recorded vineyard management and site differences were related to plant-parasitic nematode occurrence (data not shown). P values for X2 analyses ranged from 0.09 to 0.88 across plant-parasitic nematode genera and vineyard age, groundcover, previous year’s yield, and irrigation. The only exception was AVA, which was related to the presence of the plant-parasitic nematodes Paratylenchus, Pratylenchus, and Xiphinema (p < 0.001) (Table 2). Paratylenchus was more common in winegrape vineyards in the Yakima Valley and Snake River Valley AVAs compared to the other two AVAs. This was more evident when Paratylenchus population density distributions were considered, with >56% of winegrape vineyards in the Columbia Valley and Horse Heaven Hills AVAs having no Paratylenchus (Figure 1). Population densities of Pratylenchus tended to be low across AVAs, with only 0 to 3% of vineyards in the AVAs with population densities >100 Pratylenchus/250 g soil. Pratylenchus was more common in vineyards in Snake River Valley, Yakima Valley, and Horse Heaven Hills AVAs than in Columbia Valley AVA. Xiphinema was more common in vineyards in Horse Heaven Hills and Snake River Valley AVAs than in Yakima and Columbia Valley AVAs. When Xiphinema were detected, population densities were relative consistent across density classes (Figure 1).
Detection frequencies of plant-parasitic nematodes in winegrapes (Vitis vinifera) across the American Viticulture Areas (AVA) in Washington (WA) and Idaho (ID).
Frequencies of population densities of three genera of plant-parasitic nematodes observed in four AVAs in eastern Washington and in Idaho. The frequency represents the percentage of vineyards in each AVA in which plant-parasitic nematode populations were within the specified density classes.
Grape type (red, white, juice) was related to the presence of M. hapla, Paratylenchus, Xiphinema, and M. xenoplax (p < 0.002) (Table 3). Higher population densities of M. hapla and Xiphinema were found in red and white winegrapes than in juice grapes. For Paratylenchus and M. xenoplax, similar higher population densities were found in juice grapes and white winegrapes compared to red winegrapes. In general, mean population densities of Pratylenchus were low and not significantly different among the grape types. Population distributions are shown for those plant-parasitic nematodes that differed (p ≤ 0.002) between grape types (Figure 2). Almost 80% of juice grape vineyards had no detectable M. hapla. Meloidogyne hapla population densities in red and white winegrapes were similarly distributed, with 25% of winegrape vineyards having population densities >100 M. hapla/250 g soil. A similar trend was observed for Xiphinema: >80% of juice grape vineyards had no Xiphinema, while in red and white winegrape vineyards, 22 and 26% of surveyed vineyards had Xiphinema population densities >25 nematodes/250 g soil, respectively. Mesocriconema xenoplax was not commonly encountered in any grape type, with >55% surveyed vineyards having no M. xenoplax. While M. xenoplax was found at a range of densities in the different grape types (Figure 2), these densities rarely exceeded 100 M. xenoplax/250 g soil. Paratylenchus was only found in 41% of surveyed red winegrape vineyards compared to 78% and 56% of juice grape and white winegrape vineyards, respectively. The distribution of Paratylenchus across density classes was similar across grape types.
Mean population densities of plant-parasitic nematodes detected in juice grapes (Vitis labruscana) and red and white winegrapes (V. vinifera) in eastern Washington.
Frequencies of population densities of four genera of plant-parasitic nematodes observed in juice grapes (Vitis labruscana) and red and white winegrapes (V. vinifera) in eastern Washington. The frequency represents the percentage of vineyards of each grape type in which plant-parasitic nematode populations were within the specified density classes.
Colonization of winegrape roots by AMF was generally high across vineyards in eastern Washington in 2000, and red varieties had significantly (p < 0.05) higher colonization (78.2%) than white varieties (72.0%). Red varieties had also a higher (p < 0.05) proportion of roots with arbuscules (the site of nutrient transfer between plant and fungus) (21.6%) compared to white varieties (15.6%). There was a significant (p = 0.004) but weak inverse relationship between the proportion of roots with arbuscules and M. hapla population densities. There were no other correlations between M. hapla or any other plant-parasitic nematode genera and root or AMF colonization (data not shown).
Discussion
Many of the plant-parasitic nematode genera commonly encountered in winegrape vineyards worldwide were found in eastern Washington and Idaho; however, only some have been reported to cause economic damage. Meloidogyne hapla appears to have the greatest potential to impact winegrape production in eastern Washington and Idaho because it is commonly found in both states and because it was above the proposed threshold for this nematode (100 M. hapla/250 g soil; G. Santo, unpublished data, 2000) in 26% of the eastern Washington vineyards. It is important to emphasize that thresholds are not absolute and that the ability of a nematode to cause damage will depend upon many factors, including variety and edaphic factors. Threshold levels for Meloidogyne spp. have been reported to vary from 1.5 M. incognita/L soil in Australia (Quader et al. 2002) to 35 Meloidgyne spp./250 g soil in California (McKenry 1992). Meloidogyne hapla is a sedentary endoparasite, and root galling can occur on vines, limiting the ability of the plant to acquire water and nutrients. This nematode was the most virulent plant-parasitic nematode to French-American hybrid grapevines in a microplot study where M. xenoplax, P. penetrans, X. americanum, and M. hapla were applied individually to plots (Ramsdell et al. 1996).
Xiphinema spp. were also commonly encountered in eastern Washington and Idaho winegrape vineyards. In eastern Washington and Idaho, 30% and 54% of surveyed winegrape vineyards, respectively, had population densities in excess of proposed threshold levels (>25 Xiphinema/250 g soil; McKenry 1992). The Xiphinema spp. detected in these surveys belong to the taxonomically confusing Xiphinema americanum group (Robbins 1993). Xiphinema americanum is not a serious pest to grape; however, if the nematode transmits tomato ringspot virus to vines, then productivity can decline (Uyemoto 1970). Because of the virus-vectoring ability of this nematode, the theoretical damage threshold is often assumed to be lower than for other plant-parasitic nematodes. However, the actual risk of X. americanum to grapevines is likely minimal because tomato ringspot virus has not been detected in vineyards in Washington (Martin et al. 2005).
Mesocriconema xenoplax is the most commonly encountered plant-parasitic nematode in western Oregon winegrapes (Pinkerton et al. 1999). This was not the case in eastern Washington and Idaho, with the nematode detected in fewer than 40% of the surveyed vineyards in both states. In addition, none of the vineyards surveyed in either state had population densities of M. xenoplax in excess of the proposed threshold for this nematode (>300 M. xenoplax/250 g soil; G. Santo, unpublished data, 2000). This result was surprising because the soils upon which winegrapes are grown in this region tend to be sandy. It appears there may be other edaphic factors that limit population densities of this nematode east of the Cascade Mountains, the most likely being high soil pH. Mesocriconema xenoplax is known to be a problem in western Oregon vineyards and in peach orchards in the southeast United States where soil pH is typically acidic (Pinkerton et al. 2004, Reilly et al. 1986). In eastern Washington and Idaho, soil pH tends to be alkaline; when pH measurements were taken on soil samples collected during the 2000 survey, the majority of the measurements were between 8.5 and 9.5 (P. Schreiner, data not shown).
Of the other plant-parasitic nematodes detected in eastern Washington and Idaho winegrape vineyards, Pratylenchus spp. is of potential concern. It is important to note that only Pratylenchus spp. population densities in soil were considered and a more accurate estimate of population densities of this nematode would be achieved by also collecting root samples. Both P. neglectus and P. penetrans are commonly found in the PNW (Hafez et al. 1992, Smiley et al. 2004). The pathogenicity of P. neglectus to grapevines is unknown. However, there is information on the pathogenicity of other Pratylenchus species on grape. Pratylenchus penetrans did not reduce yields of any winegrape cultivar evaluated in a Michigan microplot study (Ramsdell et al. 1996). Pratylenchus vulnus can limit vine productivity of grapevines in California (Raski et al. 1973), but this species of Pratylenchus is rarely encountered in the PNW. Information on the pathogenicity of the other plant-parasitic nematodes (Paratylenchus and Helicotylenchus) found on grapevines is limited or unknown.
The occurrence of Xiphinema, Pratylenchus, and Paratylenchus was related to AVA. Of particular interest was the frequent occurrence of Xiphinema in the Horse Heaven Hills and Snake River Valley AVAs. It is difficult to link the occurrence of Xiphinema to any specific AVA attribute. It is unlikely that the occurrence of Xiphinema in these two AVAs was related to previous row crops grown on the sites because Xiphinema was not frequently encountered in previous surveys of these crops in the semiarid PNW (Hafez et al. 1992, Smiley et al. 2004). It is possible that Xiphinema entered these vineyards on infested planting material. It is also unlikely that this occurrence is related to soil type because Xiphinema spp. have been found in a diversity of soils. Xiphinema americanum were found equally in silt loam and silty clay loam soils (Ferris and Bernard 1971), while X. rivesi was associated with a wide variety of soil types from fine sandy loam to a clay loam soils (Allen et al. 1988).
None of the other management or vineyard site characteristics that were identified in the eastern Washington surveys of 2000 or 2003 (vine age, previous year’s yield, groundcover, and irrigation type) were related to the occurrence of plant-parasitic nematodes in a consistent manner. That is not surprising, considering the myriad of biotic and abiotic factors that may interact and influence nematodes in vineyard soils. Similar findings have been reported elsewhere; in a Chilean survey, grape type and soil type only explained 19.7% of the variation in nematodes, indicating that other environmental or management factors may influence plant-parasitic nematode communities in vineyards (Aballay et al. 2009). In Switzerland, the abundance of plant-parasitic nematodes was independent of geographic location, but was correlated to soil type and moisture (Güntzel et al. 1987).
Plant-parasitic nematode communities in eastern Washington grapevines were influenced by grape type. Meloidogyne hapla and X. americanum were not commonly found in juice grape vineyards (found in <20% of surveyed vineyards), while M. xenoplax was more common in juice grapes (found in 45% of samples) than in red winegrape varieties. Our results are both contradictory to and in concurrence with those of Santo and Hackney (1980). They found infestations of M. hapla associated with poor growth of juice grapevines but also demonstrated that field populations of M. hapla race A with different chromosome numbers varied in ability to parasitize juice grapevines. Neither the race nor the chromosome number of the M. hapla populations found in eastern Washington was determined in these surveys. In Michigan, M. xenoplax and X. americanum were found in >72% of surveyed juice grape vineyards, with M. hapla found in 60%. Mean population densities of these nematodes in Concord grape were 488, 118, and 48 nematodes/250 g soil for M. xenoplax, X. americanum, and M. hapla, respectively (Bird and Ramsdell 1985), population densities much higher than those observed on juice grapes in this survey.
We thought that there might be an interaction between plant-parasitic nematodes and AMF colonization of roots in eastern Washington vineyards. Mesocriconema xenoplax depressed the frequency of fine roots containing arbuscules in infested grapevines compared to noninfested grapevines (Pinkerton et al. 2004). Conversely, infection of tamarillo (Cyphomandra betacea) by M. hapla was reduced in plants that were inoculated previously with AMF compared to non-AMF plants (Cooper and Grandison 1987). The inverse relationship between M. hapla population densities and arbuscules in roots observed here supports the work with M. xenoplax, suggesting that competition for root carbohydrates may also occur with M. hapla. However, no other significant correlations among the measured variables were found. Given the sparse occurrence of M. xenoplax in eastern Washington winegrape vineyards (found in only 14% of surveyed vineyards), it was not possible to examine the relationship of this nematode to AMF colonization or measured root parameters. AMF are believed to play an important role in grapevines in eastern Washington, as available soil P levels in the region are low and deficit irrigation may further limit root access to P (Schreiner et al. 2007).
Conclusion
The most common plant-parasitic nematodes occurring in eastern Washington and Idaho winegrape vineyards were M. hapla, Xiphinema, Pratylenchus, and Paratylenchus. The population densities of M. hapla and Xiphinema found in vineyards indicates that these nematodes are first priorities for further study. Several questions remain regarding plant-parasitic nematodes in arid PNW vineyards, including: (1) what is the impact of plant-parasitic nematodes on grape establishment and productivity; (2) does M. hapla impact AMF root colonization and functionality; (3) what species of Pratylenchus are present in eastern Washington and Idaho vineyards and are they pathogenic; (4) how does regulated deficit irrigation impact the distribution of plant-parasitic nematodes in vineyards; and (5) are populations of X. americanum in eastern Washington and Idaho able to transmit tomato ringspot virus to grape, and if so, what is the significance of these virus infections. These questions will need to be answered to give growers in this region the tools they need to better manage plant-parasitic nematodes.
Acknowledgments
Acknowledgments: The authors thank Charles Hand and Timothy Lair for assistance in the field.
- Received April 2012.
- Revision received June 2012.
- Accepted June 2012.
- Published online December 1969
- ©2012 by the American Society for Enology and Viticulture
Vol 63 Issue 4
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