Association of Criconemella xenoplax and Fusarium spp. with Root Necrosis and Growth of Peach

Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens.     

Pathogenicity of Macroposthonia xenoplax to Walnut

Preplanting treatment of soil naturally infested with Macroposthonia xenoplax with 1,2-dibromoethane (ethylene dibromide) significantly increased the growth rate of Juglans hindsii seedlings. When seedlings of J. hindsii, J. regia CV "Serf" and J. regia CV Eureka were inoculated with M. xenoplax, their growth was signilicantly less than that of nematode-free controls. This retarded growth rate was accompanied hy feeder root necrosis, longitudinal cracks in the older roots, and distinct lesions in the secondary phloem.     

Dynamics of Concomitant Populations of Meloidogyne incognita and Criconemella xenoplax on Peach

The interaction between Meloidogyne incognita and Criconemella xenoplax on nematode reproduction and growth of Lovell peach was studied in field microlots and the greenhouse. Meloidogyne incognita suppressed reproduction of C. xenoplax in both field and greenhouse experiments. Tree growth, as measured by trunk diameter, was reduced (P ≤ 0.05) in the presence of M. incognita as compared with C. xenoplax of the uninoculated control trees 26 months following inoculation. A similar response regarding dry root weight was also detected in greenhouse-grown seedlings after 5 months. The presence of C. xenoplax did not affect Lovell tree growth. A synergistic effect causing a reduction (P ≤ 0.05) in tree growth was recorded 26 and 38 months following inoculation. The presence of M. incognita increased levels of malonyl-1-aminocyclopropane-1-carboxylic acid content in leaves of trees grown in field microplots 19 months after inoculaoon. Meloidogyne incognita appears to be a more dominant parasite than C. xenoplax on Lovell peach.     

Effects of Mesocriconema xenoplax on Vitis vinifera and Associated Mycorrhizal Fungi

Previous surveys of vineyards had indicated that Mesocriconema xenoplax was present in 85% of vineyards in western Oregon, but yields were not depressed in established vines. Microplot studies were initiated in 1997 in a Willamette Valley vineyard to determine the impact of M. xenoplax on vine establishment. Plots were infested with 0.03, 0.6, and 3.0 M. xenoplax g^-1 soil and planted with self-rooted Chardonnay and Pinot Noir vines. In November 2000, four growing seasons after planting, pruning weights, fine root weights, and fruit yield of vines planted in infested soil were reduced by 58%, 75%, and 33%, respectively, relative to control vines (planted in noninfested soil). In 1998 with ca 2000 degree-day base 9 °C accumulation, population densities increased 32-fold and 44-fold on 1-year-old Chardonnay and Pinot Noir vines, respectively. Nematode population dynamics and pruning data suggested that the carrying capacity of vines in microplots was 5 to 8 M. xenoplax g^-1 soil. In November 2000, more than 80% of the fine root length was colonized by arbuscular mycorrhizal fungi in all treatments. The frequency of fine roots containing arbuscules (the site of nutrient transfer between plant and fungus), however, was depressed from 5% to 65% in plants infested initially with M. xenoplax as compared to controls. Competition for photosynthate within the root system is proposed as a possible mechanism by which nematodes suppressed arbuscule frequency.     

Influence of Criconemella xenoplax and Pruning Time on Short Life of Peach Trees

Influences of Criconemella xenoplax and pruning dates were studied in field microplots with ''Nemaguard'' peach cuttings on a site not previously planted to peaches. Trees with or without C. xenoplax were pruned beginning in December 1984 or March 1985. Peach tree short life (PTSL) did not occur in the absence of C. xenoplax. PTSL occurred earlier in December-pruned than in March-pruned inoculated trees. Results confirm that "old" peach sites are not required for PTSL to occur. Pruning Nemaguard and ''Lovell'' greenhouse-grown seedlings reduced the root mass of both stocks and stimulated Nemaguard, but not Lovell, shoot regrowth. Numbers of C. xenoplax per gram of dry root were greater on pruned than on unpruned seedlings.     

Population Trends and Vertical Distribution of Plant-Parasitic Nematodes Associated with Vitis labrusca L. in Michigan

Nematode population trends and vertical distribution were monitored in a southwest Michigan vineyard (Vitis labrusca cv. Concord) from 1976 through 1983. Shallow (20 cm) and deep (90 cm) applications of 1,3-dichloropropene applied at 281 (shallow) plus 658 or 1,122 (deep) liters/ ha provided excellent control of Xiphinema americanum, Criconemella xenoplax, and Meloidogyne hapla. Populations of X. americanum remained below detectable levels for the entire 8-year experimental period where the fumigant was applied. X. americanum and C. xenoplax populations exhibited multiyear cycling in nonfumigated plots. M. hapla was first detected in 1978 and increased in prominence from 1980 through 1982. Criconemella spp. were commonly parasitized by an endoparasitic fungus. Parasitism was monitored and reported as an indication of nematode population quality.     

Pathogenicity of Criconemoides xenoplax to Prune and Plum Rootstocks

Elimination of Criconemoides xenoplax from a prune orchard soil by fumigation with ethylene dibromide at the rate of 42 μliter/liter of soil (equivalent to about 13 gal/acre) improved the growth of Myrobalan plum, Addition of this nematode to Myrobalan seedlings or young ''Marianna 2624'' plants propagated from cuttings resulted in destruction of cortical root tissue, darkening of roots, alteration of water stress, lowering of nutrient levels in leaves, and reduction in plant weight. C. xenoplax increased on all nine Prunus cerasifera varieties and hybrids tested, including those used commonly as rootstocks for prunes and plums. Rhizoctonia solani isolated from Myrobalan seedlings infected with C. xenoplax caused lesions on the hypocotyls of young Myrobalan seedlings in the laboratory, but had no effect on older seedlings in the greenhouse, and did not alter the effect of C. xenoplax.     

Competition Between Tylenchorhynchus annulatus and Mesocriconema xenoplax on Grain Sorghum as Influenced by Macrophomina phaseolina

Greenhouse experiments were conducted to examine competition between Tylenchorhynchus annulatus and Mesocriconema xenoplax on grain sorghum roots that were colonized by the fungus Macrophomina phaseolina or free from fungus colonization. An incomplete factorial treatment design consisted of two levels of M. phaseolina (0 or 10 colony-forming units/g soil) and 12 T. annulatus:M. xenoplax ratios: 1,000:0; 750:0; 500:0; 250:0; 0:0; 0:250; 0:500; 0:750; 0:1,000; 750:250; 500:500; and 250:750. Plants were harvested after 105 days. Despite similar feeding habits, competition between these ectoparasitic nematode species was limited. Tylenchorhynchus annulatus was more susceptible to antagonism by M. xenoplax than the reverse, but susceptibility depended on initial inoculum ratio. Root colonization by M. phaseolina reduced competitive effects of T. annulatus on M. xenoplax but not the reverse. Both nematode species reduced shoot dry weight but only T. annulatus reduced root dry weight. Both plant weight parameters were reduced by M. phaseolina.     

Reactions of Grape Rootstocks to Pratylenchus vulnus and Meloidogyne spp.

Five grape rootstocks were inoculated with 0, 100, 1,000, and 10,000 Pratylenchus vulnus. Dogridge and Saltcreek supported low average total numbers of P. vulnus, 136-705/pot, at 12 months after inoculation. Growth of both rootstocks was not affected. Harmony, Couderc 1613, and Ganzin 1 supported high average total numbers, 6-856 times the inoculum levels. Numbers in Harmony continued to increase at all levels but reduced root weight only at the 10,000 level after 12 months. Numbers in Couderc 1613 decreased by 15-30% after 12 months, and root weight was reduced at the 10,000 level. In Ganzin 1, total nematode numbers diminished after 12 months but were still at high levels; growth reduction was proportional to numbers of nematodes added. Meloidogyne incognita, M. javanica, and M. arenaria produced galls and egg masses in Harmony and Couderc 1613 only at 36 C. Galling in Ganzin 1 increased with increasing temperature. Galls in Ganzin 1 at 18 C supported mature females after 90 days. Harmony was resistant to M. incognita in single and concomitant inoculations of P. vulnus and M. incognita. At 250 days after inoculation, total numbers of P. vulnus increased above the inoculum level and the 150-day values; increase was greatest in P. vulnus added singly. Neither nematode species affected growth of Harmony.     

Variability in Reproduction of Four Races of Meloidogyne incognita on Two Cultivars of Soybean

Variability in the reproduction of the four races ofMeloidogyne incognita on the soybean cuhivars Pickett 71 and Centennial was studied in growth chamber experiments. Analysis of variance in the number of eggs produced by the races 6 weeks after the plants had been inoculated with 5,000 eggs of each race revealed that the nematode race by soybean cultivar interaction was highly significant (P = 0.001). Races 1, 3, and 4 produced from about 5,000 to 15,000 eggs per root system on Pickett 71 and only from about 300 to 600 eggs per root system on Centennial. In contrast, race 2 produced about 8,000 eggs per root system on Centennial and about 1,200 eggs per root system on Pickett 71. In a second experiment, in which the plants were inoculated with 2,000 second-stage juveniles, race 1 and race 2 produced about 13,000 and 3,000 eggs per root system, respectively, on Pickett 71 and about 600 and 10,000 eggs per root system, respectively, on Centennial. The results suggest that M. incognita resistance in soybean is race-specific.     

Behavior,Parasitism, Morphology,and Biochemistry of Criconemella xenoplax and C. ornata on Peach

Host-parasite relationships of Criconemella xenoplax and C. ornata on Nemaguard peach and common bermudagrass were determined in the greenhouse. Criconemella xenoplax reproduced on peach and reduced root volume, height, and dry stem weight after 6 months, compared with the noninfested check. Numbers of C. ornata did not increase on peach or influence peach growth, but they did reduce dry top weight and root volume of common bermudagrass, compared with C. xenoplax. Criconemella xenoplax and C. ornata produced the enzyme β-glucosidase and were capable of metabolizing prunasin, but only C. xenoplax produced β-cyanoalanine synthase to detoxify the cyanide released from prunasin. The apparent inability of C. ornata to detoxify cyanide is one explanation why numbers of this species did not increase on peach. Criconemella xenoplax and C. ornata can be distinguished by using stylet length, vaginal configuration, and shape of the anterior head region.     

Suppression of Meloidogyne arenaria Race 1 by Soil Application of Endospores of Pasteuria penetrans

The potential of Pasteuria penetrans for suppressing Meloidogyne arenaria race 1 on peanut (Arachis hypogaea) was tested over a 2-year period in a field microplot experiment. Endospores of P. penetrans were mass-produced on M. arenaria race 1 infecting tomato plants. Endospores were inoculated in the first year only at rates of 0, 1,000, 3,000, 10,000, and 100,000 endospores/g of soil, respectively, into the top 20 cm of microplots that were previously infested with M. arenaria race 1. One peanut seedling was planted in each microplot. In the first year, root gall indices and pod galls per microplot were significantly reduced by 60% and 95% for 100,000 endospores/g of soil, and 20% and 65% for 10,000 endospores/g of soil, respectively. Final densities of second-stage juveniles (J2) in soil were not significantly different among the treatments. The number of endospores attached to J2 and percentage of J2 with attached endospores significantly increased with increasing endospore inoculation levels. Pasteuria penetrans significantly reduced the densities of J2 that overwintered. In the second year, root and pod gall indices, respectively, were significantly reduced by 81% and 90% for 100,000 endospores/g of soil, and by 61% and 82% of 10,000 endospores/g of soil. Pod yields were significantly increased by 94% for 100,000 and by 57% for 10,000 endospores/g of soil, respectively. The effect of P. penetrans on final densities of J2 in soil was not significant. Regression analyses verified the role of P. penetrans in the suppression of M. arenaria. The minimum number of endospores required for significantly suppressing M. arenaria race 1 on peanut was 10,000 endospores/g of soil.     

Tests for Transmission of Prunus Necrotic Ringspot and Two Nepoviruses by Criconemella xenoplax

In two of three trials, detectable color reactions in ELISA for Prunus necrotic ringspot virus (PNRSV) were observed for Criconemella xenoplax handpicked from the root zone of infected peach trees. Criconemella xenoplax (500/pot) handpicked from root zones of peach trees infected with PNRSV failed to transmit the virus to cucumber or peach seedlings. The nematode also failed to transmit tomato ringspot (TomRSV) or tobacco ringspot viruses between cucumbers, although Xiphinema americanum transmitted TomRSV under the same conditions. Plants of peach, cucumber, Chenopodium quinoa, and Catharanthus roseus were not infected by PNRSV when grown in soil containing C. xenoplax collected from root zones of PNRSV-infected trees. Shirofugen cherry scions budded on Mazzard cherry seedling rootstocks remained symptomless when transplanted into root zones of PNRSV-infected trees. Virus transmission was not detected by ELISA when C. xenoplax individuals were observed to feed on cucumber root explants that were infected with PNRSV and subsequently fed on roots of Prunus besseyi in agar cultures. Even if virus transmission by C. xenoplax occurs via contamination rather than by a specific mechanism, it must be rare.     

Effect of Initial Population Density of Criconemella xenoplax on Reducing Sugars,Free Amino Acids,and Survival of Peach Seedlings over Time

Percentage of mortality, growth suppression, and changes in free amino acid and reducing sugar content in root and (or) stem tissue of Nemaguard peach seedlings were studied in the greenhouse in relation to time and eight different initial population densities (Pi) of Criconemella xenoplax. After 90 and 180 days, free amino acid content in root tissue significantly increased with increasing nematode numbers. Suppression of root volume, dry root and stem weight, height increase, plant survival, and content of reducing sugars in root tissue were detected at 180 and 270 days and following pruning. All criteria were negatively correlated with nematode Pi. Changes in growth, metabolic parameters, and survival percentage were attributed to Pi density of C. xenoplax, duration of the experiment, and nematode reproduction rate.     

Interrelationships Among Macrophomina phaseolina,Criconemella xenoplax,and Tylenchorhynchus annulatus on Grain Sorghum

Microplot experiments were established in 1992, 1993, and 1994 to investigate the relationships among Macrophomina phaseolina, Criconemella xenoplax, mad Tylenchorhynchus annulatus on grain sorghum in Louisiana. A factorial treatment arrangement of two grain sorghum hybrids (De Kalb DK 50 and Pioneer hybrid 8333), three levels of M. phaseolina (0, 10, and 100 colony-forming units (CFU)/g soil), and three nematode inoculum levels (0, 1x, and 2x) were used. Nematode inocula at 1x levels were 929, 1,139, and 1,445 C. xenoplax and T. annulatus/microplot in 1992, 1993, and 1994, respectively. Plants were harvested after 90-105 days. In all 3 years, grain sorghum root and head dry weights were suppressed as nematode inoculum level increased. These reductions were detected both in the absence and in the presence of M. phaseolina at 10 CFU/g. Reproduction of both nematode species was suppressed by M. phaseolina. Interactions between M. phaseolina and nematodes were antagonistic with regard to plant dry weights, yield, and nematode reproduction, so that combined effects were less than the sum of the effect of each pathogen alone.     

Influence of Pratylenchus penetrans on Plant Growth and Water Relations in Potato

Plants of potato (Solanum tuberosum) cultivars Katahdin and Superior were inoculated with 0, 1,500, or 15,000 Pratylenchus penetrans. Transpiration, measured in the greenhouse with a porometer after 56 days of growth, was not significantly different among nematode inoculum levels or between cultivars. The rate of xylem exudation from decapitated root systems of Katahdin plants inoculated with 1,500 or 15,000 P. penetrans and Superior plants inoculated with 15,000 P. penetrans was lower than from noninoculated plants. Root weight of Katahdin and Superior was not affected by P. penetrans inoculum level. Transpiration of plants inoculated with 0, 500, 5,000 or 50,000 P. penetrans was recorded weekly from 14 to 56 days after planting. No consistent effects of nematode inoculum density on transpiration rate were observed. Root hydraulic conductivity was lower in Katahdin plants inoculated with 266 P. penetrans per plant and in Chippewa with 5,081 per plant than in noninoculated plants. Nematodes reduced leaf area of Superior, Chippewa, and Katahdin and root dry weight of Chippewa but had no effect on growth of Hudson, Onaway, or Russet Burbank plants. Assessing nematode effects on root hydraulic conductivity may provide a measure of the tolerance of potato cultivars to nematodes.     

Effect of Entomopathogenic Nematodes on Mesocriconema xenoplax Populations in Peach and Pecan

The effect of Steinernema riobrave and Heterorhabditis bacteriophora on population density of Mesocriconema xenoplax in peach was studied in the greenhouse. Twenty-one days after adding 112 M. xenoplax adults and juveniles/1,500 cm³ soil to the soil surface of each pot, 50 infective juveniles/cm² soil surface of either S. riobrave or H. bacteriophora were applied. Another entomopathogenic nematode application of the same density was administered 3 months later. The experiment was repeated once. Mesocriconema xenoplax populations were not suppressed (P ≤ 0.05) in the presence of either S. riobrave or H. bacteriophora 180 days following ring nematode inoculation. On pecan, 200 S. riobrave infective-stage juveniles/cm² were applied to the soil surface of 2-year-old established M. xenoplax populations in field microplots. Additional applications of S. riobrave were administered 2 and 4 months later. This study was terminated 150 days following the initial application of S. riobrave. Populations of M. xenoplax were not suppressed in the presence of S. riobrave.     

Biological Control of the Phytoparasitic Nematode Mesocriconema xenoplax on Peach Trees

Seven fluorescent Pseudomonas spp. capable of inhibiting reproduction of Mesocriconema xenoplax have been isolated from soil sites that suppress both nematode multiplication and Peach Tree Short Life (PTSL). One of these seven strains, Pseudomonas sp. BG33R, inhibits M. xenoplax multiplication in vivo and egg hatch in vitro. Mesocriconema xenoplax populations on peach seedlings inoculated with BG33R and planted into soil-solarized field plots remained at or below the economic threshold for nematicide treatment in South Carolina for nearly 18 months. Soil solarization alone induced a shift toward a microbial community that was suppressive to nematode multiplication. Additionally, five Tn5 mutants of BG33R, lacking the ability to kill eggs, have been generated. The Tn5 insertion site in each mutant has been cloned and sequenced. DNA sequence analysis has revealed a high degree of homology to several genes of interest because of their potential involvement in the production of the egg-kill factor. These Tn5 egg-kill negative mutants also no longer produce protease or salicylic acid while producing nearly twice the amount of fluorescent siderophore as the wild type parent.     

Effects of Temperature,Plant Age,Soil Texture,and Meloidogyne incognita on Early Growth of Soybean

A digitizer-microcomputer combination was utilized to determine soybean seedling response to population densities of M. incognita (Mi) under varied environmental conditions. Plant age, temperature, soil texture, and initial Mi inoculum (Pi) influenced the pattern of shoot and root growth. Effects of Mi on plant top growth were evident on plants inoculated 2 days after seeding, but generally were not noticeable on those receiving Mi after 4, 6, or 8 days (observations limited to 6 days after inoculation). The greatest Pi of Mi (16,700 juveniles/plant) suppressed root growth on plants inoculated at 2 or 4 days after seeding. Mi had no impact on root growth at 22 C on plants inoculated 6 or 8 days after seeding at any temperature used (22, 26, 30 C). New root initiation was inhibited on soybeans inoculated 2 days after seeding at the highest Pi at all three temperatures, but only at 30 C for a Pi of 1,670 juveniles/plant. Growth of first order lateral roots and general root length were suppressed by Mi on the youngest (2-day) plants. However, a low Pi (167 juveniles/ plant) resulted in root proliferation on 4-day-old plants at 26 C. Mi was most damaging in a low clay-content soil mixture.     

Spatial Distribution of Plant-Parasitic Nematodes in Semi-Arid Vitis vinifera Vineyards in Washington

The most commonly encountered plant-parasitic nematodes in eastern Washington Vitis vinifera vineyards are Meloidogyne hapla, Mesocriconema xenoplax, Pratylenchus spp., Xiphinema americanum, and Paratylenchus sp.; however, little is known about their distribution in the soil profile. The vertical and horizontal spatial distribution of plant-parasitic nematodes was determined in two Washington V. vinifera vineyards. Others variables measured in these vineyards included soil moisture content, fine root biomass, and root colonization by arbuscular mycorhizal fungi (AMF). Meloidogyne hapla and M. xenoplax were aggregated under irrigation emitters within the vine row and decreased with soil depth. Conversely, Pratylenchus spp. populations were primarily concentrated in vineyard alleyways and decreased with depth. Paratylenchus sp. and X. americanum were randomly distributed within the vineyards. Soil water content played a dominant role in the distribution of fine roots and plant-parasitic nematodes. Colonization of fine roots by AMF decreased directly under irrigation emitters; in addition, galled roots had lower levels of AMF colonization compared with healthy roots. These findings will help facilitate sampling and management decisions for plant-parasitic nematodes in Washington semi-arid vineyards.