Additional Hosts for the Ring Nematode,Criconemella xenoplax

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.     

Influence of Temperature and Soybean Phenology on Dormancy Induction of Heterodera glycines

Growth room and field experiments were conducted to determine the influence of soil temperature and soybean phenology on dormancy induction of a North Carolina population of Heterodera glycines race 1. Three temperature regimes and two photoperiods to regulate plant phenology were investigated in growth rooms. H. glycines hatch was greatest from the 26 and 22 C (day and night) temperature treatment, intermediate at 22 and 18 C, and least from the decreasing regime (26 and 22 C, 22 and 18 C, and 18 and 14 C). More eggs hatched and greater nematode reproduction occurred on pod-producing soybeans than on those that remained vegetative. In the field study, hatching patterns were not different between depodded and naturally senescing soybeans nor between the different maturity groups of soybean cultivars (groups V through VIII). Egg hatch (9-16%) was greatest in August and September when mean soil temperatures were between 25 and 29 C. Hatch declined to 1% in vitro and was not detectable in the bioassay in November. Greatest nematode numbers were observed on the latest maturing cultivar (group VIII) and fewest on the cultivar which matured earliest (group V). Decreasing temperature appears to be more important than soybean phenology in dormancy induction of H. glycines.     

Differential plant response to inoculation with two VA mycorrhizal fungi isolated from a low-pH soil

Sericea lespedaza and ladino clover were inoculated withAcaulospora laevis andGigaspora margarita VA mycorrhizal fungi, both isolated from a local soil having a pH of 4.4. Plants were grown in a greenhouse in fumigated (methyl bromide) soil with four rates of applied P. This soil had a pH of 5.1 for theG. margarita experiment and a 5.8 for theA. laevis experiment. Neither plant species responded to theG. margarita isolate in terms of mycorrhizal infection of roots, top growth, or elemental uptake. TheA. laevis isolate caused increased growth of Ladino clover at the lowest rate of P application and increased growth of sericea lespedeza at the two lowest P application rates. Shoot tissue concentrations of P for both plant species were greater at the two lowest rates of P application when inoculated withA. laevis. Inoculation withA. laevis also resulted in different VAM fungal root colonization patterns between the two plant species as a function of P application rate. Roots of both plants had high infection rates (near 70%) for the two lowest P application rates but sericea lespedeza declined to 40 and 6% at the next two P application rates, respectively, whereas infection in Ladino clover was 74 and 41% at the next two P application rates, respectively. The results of this study support the concept that plant host-VAM fungal endophyte interactions are extremely variable and that characterization of individual combinations must be done if types and magnitudes of responses are to be defined.     

Variations in Host Preference among and within Populations of Heterodera trifolii and Related Species

Seven populations of Heterodera trifolii from Arkansas, Kentucky, Pennsylvania, and Australia plus 3 or 4 single-cyst isolates (SCI) from each population were tested for reproduction on seven species of plants to compare the host preferences among and within populations. Common lespedeza, Kummerowia striata cv. Kobe, was a good host for all populations and isolates. Therefore, a plant was considered to be a host if the number of females produced on it was 10% or more of the number on Kobe. All seven populations reproduced on Trifolium repens and T. pratense. None reproduced on Beta vulgaris or Glycine max. One single-cyst isolate from the Australian population produced a few females on T. pratense. The Australian population maintained on carnation, Dianthus caryophyllus, produced females on carnation but not on curly dock, Rumex crispus. However, its subpopulation maintained on T. repens produced females on R. crispus but not on carnation. Four of the other six populations produced females on R. crispus, and four produced females on carnation. Differences in host range were observed among seven of the mother populations and their SCI, and among isolates within each population. Five host range patterns were found in populations and SCI of H. trifolii. Significant quantitative differences occurred among populations in the numbers of females on most hosts, between isolates and their original populations, and among isolates from the same population. SCI selected from white clover produced fewer females on a series of test hosts and had host ranges the same as or narrower than those of the original populations. However, SCI selected from Kobe lespedeza had more females on some hosts and had host ranges the same as or wider than those of the original populations. The host ranges of all populations and SCI of H. trifolii were different from those of populations and SCI of race 3 of H. glycines and H. lespedezae.     

Importance of Temperature in the Pathology of Meloidogyne hapla and M. chitwoodi on Legumes

Effects of temperatures on the host-parasite relationships were studied for three legume species and four populations of root-knot nematodes from the western United States. The nematode populations were Meloidogyne hapla from California (MHCA), Utah (MHUT), and Wyoming (MHWY), and a population of M. chitwoodi from Utah (MCUT). The legumes were milkvetch (Astragalus cicer), alfalfa (Medicago sativa), and yellow sweet clover (Melilotus officinalis). All milkvetch plants survived inoculation with all nematode populations, while alfalfa and yellow sweet clover were more susceptible. On yellow sweet clover, MHCA was most pathogenic at 30 °C based on suppression of shoot growth while MHUT, MHWY, and MCUT were most pathogenic at 25 °C. All nematode populations suppressed growth of yellow sweet clover more than growth of milkvetch and alfalfa. The reproductive factor (Rf = final nematode population/initial nematode population) of MHCA was positively correlated (r = 0.83) with temperature between 15 °C and 30 °C. The greatest Rf occurred on alfalfa inoculated with MHCA at 30 °C. The Rf of MHUT, MHWY, and MCUT were positively correlated (r= 0.76, r= 0.78, and r= 0.73, respectively) with temperature between 15 °C and 25 °C. The Rf values of MHUT and MHWY were similar on all species and exceeded the Rf of MCUT at all temperatures (P < 0.05).     

The Influence of Temperature on Meloidogyne incognita on Soybean

The effects of temperature and initial inoculum density of Meloidogyne incognita on soybean growth and nematode reproduction were investigated in greenhouse temperature tanks and in controlled-growth chambers. The interactions of initial inoculum density (P_i) and soil temperature in effects on shoot growth were adequately described by multiple-regression models. At the highest temperatures (30 or 32/28 C), moderate to high inoculum killed many plants. A P_i of 27,000 eggs/15-cm-diam pot retarded shoot growth at 26 C. Only the greatest P_i (81,000 eggs/15-cm pot) suppressed shoot growth at 18, 22, or 20/16 C. Inoculation with 3,000 or 9,000 eggs/plant resulted in heavier root systems at all temperatures except 30 C. At that temperature, 9,000 eggs suppressed root growth. At 18 and 26 C, a Pi of 81,000 eggs was required to retard root growth. Nematode reproduction was related directly to temperature and P_i except at a density of 81,000 eggs/15-cm pot.     

Effects of the Mi-1, N and Tabasco Genes on Infection and Reproduction of Meloidogyne mayaguensis on Tomato and Pepper Genotypes

Meloidogyne mayaguensis is a damaging root-knot nematode able to reproduce on root-knot nematode-resistant tomato and other economically important crops. In a growth chamber experiment conducted at 22 and 33°C, isolate 1 of M. mayaguensis reproduced at both temperatures on the Mi-1-carrying tomato lines BHN 543 and BHN 585, whereas M. incognita race 4 failed to reproduce at 22°C, but reproduced well at 33°C. These results were confirmed in another experiment at 26 ± 1.8°C, where minimal or no reproduction of M. incognita race 4 was observed on the Mi-1-carrying tomato genotypes BHN 543, BHN 585, BHN 586 and ‘Sanibel’, whereas heavy infection and reproduction of M. mayaguensis isolate 1 occurred on these four genotypes. Seven additional Florida M. mayaguensis isolates also reproduced on resistant ‘Sanibel’ tomato at 26 ± 1.8°C. Isolate 3 was the most virulent, with reproduction factor (Rf) equal to 8.4, and isolate 8 was the least virulent (Rf = 2.1). At 24°C, isolate 1 of M. mayaguensis also reproduced well (Rf ≥ 1) and induced numerous small galls and large egg masses on the roots of root-knot nematode-resistant bell pepper ‘Charleston Belle’ carrying the N gene and on three root-knot nematode-resistant sweet pepper lines (9913/2, SAIS 97.9001 and SAIS 97.9008) carrying the Tabasco gene. In contrast, M. incognita race 4 failed to reproduce or reproduced poorly on these resistant pepper genotypes. The ability of M. mayaguensis isolates to overcome the resistance of tomato and pepper genotypes carrying the Mi-1, N and Tabasco genes limits the use of resistant cultivars to manage this nematode species in infested tomato and pepper fields in Florida.     

Embryogenesis and Postinfection Development of Meloidogyne konaensis

The effects of temperature on embryogenesis and postinfection development in Meloidogyne konaensis were examined. Embryogenesis was evaluated at 5, 8, 10, 13, 16, 20, 22, 24, 26, 28, 30, 35, and 40 C. No embryonic development occurred at 5 C. Some development, although incomplete, occurred at 8 and 10 C. The rate of embryogenesis was linear from 13 to 30 C, but decreased at 35 C. The lowest egg mortality occurred at 24 C, whereas all eggs died within 24 hours at 40 C. Postinfection development was determined on coffee and tomato in a greenhouse at an average temperature of 30 C and in a growth chamber with a constant temperature of 26 C. Development of M. konaensis J2 to mature female required 38 and 48 days on coffee at 30 and 26 C, respectively. This process took 20 and 26 days, respectively, on tomato.     

Post-Infection Development of Heterodera lespedezae

Morphological changes occurring during post-infection development and the influence of temperature on the life cycle of Heterodera lespedezae are reported. Morphological development was similar to that of H. schachtii. Each post-infection stage had a distinct styler, and fed actively. Detailed observations were made of cuticle formation and markings, esophageal glands, and reproductive system. Certain developmental phases, such as matrix deposition and oviposition, appeared to be correlated with color changes of the adult female body. The effect of temperature on nematode development was observed in a phytotron at day/night temperatures of 18/14, 18/18, 22/18, 26/22, 26/26, and 30/26 C; the optimum was 26/26 C. More time was required to complete the life cycle at the three lower temperatures than at the three higher temperatures.     

The Internal Transcribed Spacer Region of Belonolaimus (Nemata: Belonolaimidae)

Belonolaimus isolates from six U.S. states were compared by restriction endonuclease digestion of amplified first internal transcribed spacer region (ITS1) of the nuclear ribosomal genes. Seven restriction enzymes were selected for evaluation based on restriction sites inferred from the nucleotide sequence of a South Carolina Belonolaimus isolate. Amplified product size from individuals of each isolate was approximately 700 bp. All Midwestern isolates gave distinct restriction digestion patterns. Isolates identified morphologically as Belonolaimus longicaudatus from Florida, South Carolina, and Palm Springs, California, were identical for ITS1 restriction patterns. The correlation between ITS1 restriction patterns and the distribution of B. longicaudatus isolates suggest that the California isolate is a relatively recent introduction into the state.     

Growth of Isolates of Paecilomyces lilacinus and Their Efficacy in Biocontrol of Meloidogyne incognita on Tomato

The potential of 13 Paecilomyces lilacinus isolates from various geographic regions as biocontrol agents against Meloidogyne incognita, the effects of temperature on their growth, and the characterization of the impact of soil temperature on their efficacy for controlling this nematode were investigated. Maximum fungal growth, as determined by dry weight of the mycelium, occurred from 24 to 30 C; least growth was at 12 and 36 C. The best control of M. incognita was provided by an isolate from Peru or a mixture of isolates of P. lilacinus. As soil temperatures increased from 16 to 28 C, both root-knot damage caused by M. incognita and percentage of egg masses infected by P. lilacinus increased. The greatest residual P. lilacinus activity on M. incognita was attained with a mixture of fungal isolates. These isolates effected lower root-galling and necrosis, egg development, and enhanced shoot growth compared with plants inoculated with M. incognita alone.     

Interaction of Ditylenchus dipsaci and Meloidogyne hapla on Resistant and Susceptible Plant Species

Numbers ofDitylenchus dipsaci or Meloidogyne hapla invading Ranger alfalfa, Tender crop bean, Stone Improved tomato, AH-14 sugarbeet, Yellow sweet clover, and Wasatch wheat from single inoculations were not significantly different from numbers by invasion of combined inoculations. D. dipsaci was recovered only from shoot and M. hapla only from root tissue. Combined inoculations did not affect reproduction of either D. dipsaci or M. hapla. D. dipsaci suppressed shoot growth of all species at 15-30 C, and M. hapla suppressed shoot growth of tomato, sugarbeet, and sweet clover at 20, 25, and 30 C. There was a positive correlation (P < 0.05) between shoot and root growth suppression by D. dipsaci on all cultivars except wheat at 20 C and tomato at 30 C. M. hapla suppressed (P < 0.05) root growth of sugarbeet at 20-50 C and wheat at 30 C. Growth suppression was synergistic in combined inoculations of sweet clover shoot growth at 15 C and root growth at 20-30 C, wheat root growth at 15 and 20 C, and tomato root growth at 15-30 C (P < 0.05) D. dipsaci invasions caused mortality of alfalfa and sweet clover at 15-30 C and sugarbeet at 20-30 C. Mortality rates of alfalfa and sweet clover increased synergistically (P < 0.05) from combined inoculations.     

In vitro antagonism of cotton seedlings fungi and characterization of chitinase isozyme activities in Trichoderma harzianum

The antagonistic fungus Trichoderma harzianum is widely recognized as a potential biocontrol agent against several soil-borne plant pathogens. T. harzinum is rich source of chitinoltic enzymes. In vitro screening of 5 isolates of T. harzinum, one isolate of Chaetomium globosum and one isolate of Conetherium mentance, revealed that all of them had reduced growth area of Macrophomina phaseolina, Fusarium solaniand Rhizoctonia solani on PDA medium, significantly. The inhibition percentage ranged from 77.9 % to 55.9% for M. phaseolina and 59.2% to 40.4% for R. solani by T. harzinum and C. mentance, respectively. Inhibition for F. solani ranged from 76.5% to 55.7% by T. harzinum and C. globosum, respectively. Isozyme gel electrophoresis was used to assess chitinase activity secreted by selected isolates of T. harzinum under different pH degrees and temperatures. Obtained results indicated that activity of chitinase isozyme produced at 30 °C was higher than 15–20 °C for all tested isolates and activity of chitinase produced by isolates No. 4 and 5 of T. harzinum at pH (7–7.5) was higher than at pH 6, respectively.     

Effect of Temperature on Pratylenchus penetrans Development

Reproduction and development of Pratylenchus penetrans were studied on genetically transformed ladino clover roots. Solitary females developing on transformed roots in nutrient gellan gum medium (pH 5.5) deposited 1.2, 1.5, 1.6, 1.8, and 2.0 eggs per day at the respective temperatures of 17, 20, 25, 27, and 30 °C. The number of eggs deposited was highly correlated with temperature. A reduction in egg-laying rates at the start of hatching was observed at all temperatures. Juvenile mortality was higher at 17 °C (50.4%), 20 °C (50.3%), and 30 °C (58.4%) than at 25 °C (34.6%) and 27 °C (37.6%). Life-cycle (egg deposition to egg deposition) duration was 46, 38, 28, 26, and 22 days at the respective temperatures. The developmental zero degrees (°C) and the effective accumulative temperatures (degree-days) required for hatching, female emergence, and onset of oviposition (completion of one generation) of P. penetrans were estimated to be 2.7 and 200, 4.2 and 548, and 5.1 and 564, respectively. Pratylenchus penetrans reproduces over a wide range of temperatures.     

Host Suitability of Twelve Leguminosae Species to Populations of Meloidogyne hapla and M. chitwoodi

Legumes of the genera Astragalus (milkvetch), Coronilla (crownvetch), Lathyrus (pea vine), Lotus (birdsfoot trefoil), Medicago (alfalfa), Melilotus (clover), Trifolium (clover), and Vicia (common vetch) were inoculated with a population of Melaidogyne chitwoodi from Utah or with one of three M. hapla populations from California, Utah, and Wyoming.Thirty-nine percent to 86% of alfalfa (M. scutellata) and 10% to 55% of red clover (T. pratense) plants survived inoculation with the nematode populations at a greenhouse temperature of 24 ± 3°C. All plants of the other legume species survived all nematode populations, except 4% of the white clover (T. repens) plants inoculated with the California M. hapla population. Entries were usually more susceptible to the M. hapla populations than to M. chitwoodi. Galling of host roots differed between nematode populations and species. Root-galling indices (1 = none, 6 = severely galled) ranged from 1 on pea vine inoculated with the California population of M. hapla to 6 on yellow sweet clover inoculated with the Wyoming population of M. hapla. The nematode reproductive factor (Rf = final nematode population/initial nematode population) ranged from 0 for all nematode populations on pea vine to 35 for the Wyoming population of M. hapla on alfalfa (M. sativa).     

Management of Heterodera glycines by Cropping and Cultural Practices

Heterodera glycines was identified in North Carolina in 1954, although symptoms of the disease were noted in the state at least 8 years earlier. Crop rotation experiments designed to develop management systems were initiated in 1956. Two or more years in production of a nonhost crop resulted in decreases of the nematode to low or undetectable levels with acceptable subsequent yields of soybean (Glycine max). Because of almost complete dependence on resistant cultivars and (or) nematicides for nematode control, crop rotation experiments were not conducted from 1962 to 1980. Research on control of H. glycines, beginning in 1981, emphasized biological and ecological aspects of the nematode in order to determine cropping systems that restrict the nematode to nondamaging levels. Mortality during embryogenesis was high at temperatures above 30 C. Hatching of eggs occurs readily in May and June. Postinfection development takes 2-3 weeks at weekly mean temperatures of 22-29 C and is slow above and below those temperatures. Egg production is high during the late growing season. Some cultural practices such as planting early maturing cultivars in mid-to-late June and rotation with a nonhost effectively keeps populations at low levels.     

Development of Selected Tobacco Cyst Nematode Isolates on Resistant and Susceptible Cultivars of Flue-cured Tobacco

Tobacco cyst nematode (Globodera tabacum solanacearum) isolates were collected from 11 locations in Virginia, 3 in North Carolina, and 1 in Maryland. Isolates from each location were maintained and increased on flue-cured tobacco, Nicotiana tabacum cv K326. Plants of flue-cured tobacco cultivars K326 (susceptible) and NC567 (resistant) were each inoculated with 6,000 G. t. solanacearum eggs/plant. Tests were conducted over one (6 weeks) or two (14 weeks) generations of the nematode. Shoot and root weights and the number of nematodes present within a 1-g subsample of feeder roots were recorded at completion of the tests. Nematode counts were categorized by nematode life stage (vermiform, swollen, pyriform, and adult). Although significant differences in nematode development were detected among isolates, differences were not consistent across experiments. Results indicate similar virulence among G. t. solanacearum isolates on resistant and susceptible flue-cured tobacco cultivars. Therefore, plant breeders may effectively use a single G. t. solanacearum isolate when screening tobacco germplasm for resistance.     

Incidence and Pathogenicity of Plant-Parasitic Nematodes Associated with Blueberry (Vaccinium spp.) Replant Disease in Georgia and North Carolina

Blueberry replant disease (BRD) is an emerging threat to continued blueberry (Vaccinium spp.) production in Georgia and North Carolina. Since high populations of ring nematode Mesocriconema ornatum were found to be associated with commercially grown blueberries in Georgia, we hypothesized that M. ornatum may be responsible for predisposing blueberry to BRD. We therefore tested the pathogenicity of M. ornatum on 10-wk-old Rabbiteye blueberries (Vaccinium virgatum) by inoculating with initial populations (Pi) of 0 (water control), 10, 100, 1,000. and 10,000 mixed stages of M. ornatum/pot under both greenhouse (25 ± 2°C) and field microplot conditions. Nematode soil population densities and reproduction rates were assessed 75, 150, 225, and 255, and 75, 150, 225, and 375 d after inoculation (DAI) in both the greenhouse and field experiments, respectively. Plant growth parameters were recorded in the greenhouse and field microplot experiments at 255 and 375 DAI, respectively. The highest M. ornatum population density occurred with the highest Pi level, at 75 and 150 DAI under both greenhouse (P < 0.01) and field (P < 0.01) conditions. However, M. ornatum rate of reproduction increased significantly in pots receiving the lowest Pi level of 10 nematodes/plant compared with the pots receiving Pi levels of 100, 1,000, and 10,000 nematodes 75 DAI. Plant-parasitic nematode populations were determined in commercial blueberry replant sites in Georgia and North Carolina during the 2010 growing season. Mesocriconema ornatum and Dolichodorus spp. were the predominant plant-parasitic nematodes in Georgia and North Carolina, respectively, with M. ornatum occurring in nearly half the blueberry fields sampled in Georgia. Other nematode genera detected in both states included Tylenchorhynchus spp., Hoplolaimus spp., Hemicycliophora spp., and Xiphinema spp. Paratrichodorus spp. was also found only in Georgia. In Georgia, our results indicate that blueberry is a host for M. ornatum and its relationship to BRD warrants further investigation.     

Variation among Populations of Belonolaimus longicaudatus

Three North Carolina populations of Belonolairnus longicaudatus differed significantly from three Georgia populations in stylet measurements, the c ratio, the distance of the excretory pore from the anterior end for both sexes; the a ratio for females only; and the total body length, tail length, and spicule length for males only. The Georgia nematodes were stouter, and the females possessed sclerotized vaginal pieces. The distal portion of the spicules of North Carolina males had an indentation and hump lacking in those of the Georgia males. The haploid number of chromosomes was eight for males from all populations of B. longicaudatus and a North Carolina population of B. maritimus. Interpopulation matings of the Tarboro, N.C. and Tifton, Ga. populations indicated that the offspring produced were infertile. Morphological differences and reproductive isolation suggest that the North Carolina and the Georgia populations belong to different species.