Evaluation of Paecilomyces lilacinus as a Biocontrol Agent of Meloidogyne javanica on Tobacco

The efficacy of the nematode parasite Paecilomyces lilacinus, alone and in combination with phenamiphos and ethoprop, for controlling the root-knot nematode Meloidogyne javanica on tobacco and the ability of this fungus to colonize in soil under field conditions were evaluated for 2 years in microplots. Combinations and individual treatments of the fungus grown on autoclaved wheat seed, M. javanica eggs (76,000 per plot), and nematicides were applied to specified microplots at the time of transplanting tobacco the first year. Vetch was planted as a winter cover crop, and the fungus and nematicides were applied again the second year to specified plots at transplanting time. The fungus did not control the nematode in either year of these experiments. The average root-gall index (0 = no visible galls and 5 = > 100 galls per root system) ranged from 2.7 to 3.9 the first year and from 4.3 to 5.0 the second in nematode-infested plots treated with nematicides. Plants with M. javanica alone or in combination with P. lilacinus had galling indices of 5.0 both years; the latter produced lower yields than all other treatments during both years of the study. Nevertheless, the average soil population densities of P. lilacinus remained high, ranging from 1.2 to 1.3 × 106 propagules/g soil 1 week after the initial inoculation and from 1.6 to 2.3 × 104 propagules/g soil at harvest the second year. At harvest the second year the density of fungal propagules was greatest at the depth of inoculation, 15 cm, and rapidly decreased below this level.     

Parasitism of Heterodera schachtii and Meloidogyne javanica by Hirsutella rhossiliensis in Microplots over Two Growing Seasons

Numbers of cyst and root-knot nematodes and percentage parasitism by the nematophagous fungus Hirsutella rhossiliensis were quantified in microplots over 2 years. The microplots contained either sugarbeets in loam infested with Heterodera schachtii or tomatoes in sand infested with Meloidogyne javanica. The fungus was added to half of the microplots for each crop. Although H. rhossiliensis established in both microplot soils, the percentage of nematodes parasitized did not increase with nematode density and nematode numbers were not affected by the fungus. The results indicate that long-term interactions between populations of the fungus and cyst or root-knot nematodes will not result in biological control.     

Effects of Pratylenchus penetrans and Rhizoctonia fragariae on Vigor and Yield of Strawberry

Microplot and small field-plot experiments were conducted to determine the effects of Pratylenchus penetrans on strawberry yield over several seasons and to evaluate the effects of nematode control on strawberry vigor and yield. Pratylenchus penetrans alone or in combination with the black root rot pathogen, Rhizoctonia fragariae, reduced strawberry yield in microplots over time. There were no differences in effects on yield among R. fragariae anastomosis groups A, G, or I. The interaction of the two pathogens appeared to be additive rather than synergistic. In field plots infested with P. penetrans alone, plant vigor and yield were increased by the application of carbofuran and fenamiphos nematicides. Nematode control was transitory, as P. penetrans populations were initially suppressed but were not different in samples taken 10 months after treatment. These data highlight the error in associating causality between plant damage and nematode populations based on a correlation of root disease with nematode diagnostic assays from severely diseased plants. These findings may help to explain how nematode numbers can sometimes be higher in healthy plants than in severely diseased plants that lack sufficient roots to maintain nematode populations. Because nematode populations from up to a year before harvest are better correlated with berry yield, preplant nematode diagnostic assays taken a year in advance of harvest may be superior in predicting damage to perennial strawberry yield.     

Relationship between Meloidogyne incognita and Rotylenchulus reniformis as Influenced by Soybean Genotype

The effect of soybean genotype on competition between Meloidogyne incognita race 2 (Mi) and Rotylenchulus reniformis (Rr) was evaluated in greenhouse and microplot replacement series experiments. Soil in pots containing seedlings of ''Davis'' (susceptible to Mi) or ''Buckshot 66'' (resistant to Mi) was infested with 1,000 vermiform individuals in the following Mi:Rr ratios: 0:0, 100:0, 75:25, 50:50, 25:75, or 0:100. After 91 days, the relative nematode yields (number of nematodes in mixed culture divided by the number in nonmixed culture) of each species were calculated based on soil and root nematode populations expressed as nematodes per gram of dry root tissue. To define the relationship between the two species, calculated relative nematode yields were compared with a theoretical noncompetition model using lack-of-fit regression. In the greenhouse, Mi populations on ''Davis'' were stimulated in the presence of Rr. In microplots, low Mi and Rr population densities likely resulted from severe galling and destruction of feeder roots that probably occurred early in the season. Enhanced susceptibility to Mi was not observed on ''Buckshot 66'', which remained resistant to Mi even when colonized by Rr. Host resistance is a key factor in determining the nature of the relationship between Mi and Rr.     

Field Efficacy of Verticillium lecanii,Sex Pheromone,and Pheromone Analogs as Potential Management Agents for Soybean Cyst Nematode

A soybean cyst nematode sex pheromone (vanillic acid), chemical analogs of the pheromone, and the fungus Verticillium lecanii were applied in alginate prills (340 kg/ha) to microplots and small-scale field plots as potential management agents for Heterodera glycines on soybean. In 1991 microplot tests, treatment with V. lecanii, vanillic acid, syringic acid plus V. lecanii, or vanillic acid plus V. lecanii lowered midseason cyst numbers compared with the untreated susceptible cultivar control, autoclaved V. lecanii treatment, or aldicarb treatment, At-harvest cyst numbers were lowest with V. lecanii and with vanillic acid treatments. Aldicarb treatment reduced midseason cyst numbers in 1992. There were no differences among seed yields either year. In the field trials, numbers of cysts were reduced one or both years with aldicarb, ferulic acid, syringic acid, vanillic acid, or 4-hydroxy-3-methoxybenzonitfile treatments, or with a resistant cultivar, compared to an untreated susceptible cultivar. Highest yields were recorded after treatment with 4-hydroxy-3-methoxybenzonitrile (1991), methyl vanillate (1992), and aldicarb (1992). These studies indicate that some chemical analogs of vanillic acid have potential for use in soybean cyst nematode management schemes.     

Influence of Selected Cultural Practices on Winter Survival of Pratylenchus brachyurus and Subsequent Effects on Soybean Yield

Planting date of soybean, Glycine max, influenced winter survival of Pratylenchus brachyurus in microplots at two locations in North Carolina. Delayed planting resulted in a linear decrease (P = 0.05) in the numbers of P. brachyurus at soybean harvest. Effects of planting date on nematode numbers persisted over winter, indicating that survival in the absence of a host is density independent. Compared with winter fallow, winter wheat, Triticum aestivum, reduced winter survival of P. brachyurus. Subsequent soybean yields were suppressed by the overwintering population of this nematode at one location but not at another.     

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.     

Effects of Fluctuating Temperatures and Different Host Plants on Development of Pasteuria penetrans in Meloidogyne javanica

Greenhouse and growth room experiments were conducted to investigate the effect of host plant in relation to different nematode inoculum levels, and temperature fluctuations on the development of Pasteuria penetrans. Host plant affected the development of P. penetrans indirectly through its effect on nematode development. Endospores collected from Meloidogyne javanica females reared on different hosts did not show any differences in subsequent attachment and infectivity. The numbers of endospores produced per infected female were reduced with increasing numbers of females parasitizing okra and tomato roots. Fluctuating temperatures retarded the development of P. penetrans. The life cycle of the parasite was completed faster at approximately constant temperatures close to 30 °C than when the temperature fluctuated away from 30 °C. The temperature of irrigation water did not affect the duration of life cycle of P. penetrans.     

Pasteuria penetrans for Control of Meloidogyne incognita on Tomato and Cucumber,and M. arenaria on Snapdragon

Meloidogyne incognita and Meloidogyne arenaria are important parasitic nematodes of vegetable and ornamental crops. Microplot and greenhouse experiments were conducted to test commercial formulations of the biocontrol agent Pasteuria penetrans for control of M. incognita on tomato and cucumber and M. arenaria on snapdragon. Three methods of application for P. penetrans were assessed including seed, transplant, and post-plant treatments. Efficacy in controlling galling and reproduction of the two root-knot nematode species was evaluated. Seed treatment application was assessed only for M. incognita on cucumber. Pasteuria treatment rates of a granular transplant formulation ranged from 1.5 × 10⁵ endospores/cm³ to 3 × 10⁵ endospores/cm³ of transplant mix applied at seeding. Additional applications of 1.5 × 10⁵ endospores/cm³ of soil were applied as a liquid formulation to soil post-transplant for both greenhouse and microplot trials. In greenhouse cucumber trials, all Pasteuria treatments were equivalent to steamed soil for reducing M. incognita populations in roots and soil, and reducing nematode reproduction and galling. In cucumber microplot trials there were no differences among treatments for M. incognita populations in roots or soil, eggs/g root, or root condition ratings. Nematode reproduction on cucumber was low with Telone II and with the seed treatment plus post-plant application of Pasteuria, which had the lowest nematode reproduction. However, galling for all Pasteuria treatments was higher than galling with Telone II. Root-knot nematode control with Pasteuria in greenhouse and microplot trials varied on tomato and snapdragon. Positive results were achieved for control of M. incognita with the seed treatment application on cucumber.     

Interaction of Endomycorrhizal Fungi,Superphosphate, and Meloidogyne incognita on Cotton in Microplot and Field Studies

Microplot and field experiments were conducted to determine the effects of two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices (Gi) and Gigaspora margarita (Gm), and dicalcium phosphate (P) on Meloidogyne incognita (Mi) reproduction and seed cotton yield of the Mi-susceptible cotton cultivar, Stoneville 213. In 1983 population densities of Mi juveniles were significantly lower 60 and 90 days after planting in microplots receiving Gi. Mycorrhizal fungi reduced the severity of yield losses to Mi, whereas P fertilization increased yield losses to Mi. In 1984 microplot yields were reduced linearly as nematode inoculum densities increased in treatments of Mi alone, Gm, or P, but the response was curvilinear with Gi. Yield suppressions in the 1984 field experiment occurred only in plots infested with Mi alone. In the 1984 microplots, numbers of Mi juveniles penetrating seedling roots increased Iinearly with increasing nematode inoculum densities and was favored when mycorrhizal fungi or superphosphate were added. Juvenile penetration of roots was negatively correlated with yields in all treatments (r = -0.54 to -0.81) except Gm and with number of bolls in Mi alone (r = -0.85) and P (r = -0.81) treatments. Mycorrhizal fungi can increase host tolerance to M. incognita in field conditions and may function as important biological control agents in soils infested with high population densities of efficient VAM species.     

Antagonistic Interaction of Heterodera schachtii Schmidt and Fusarium oxysporum (Woll.) on Sugarbeets

In a field experiment, nematicides controlled the disease of sugarbeets caused by Heterodera schachtii and Fusarium oxysporum. Biocides that were both fungicidal and nematicidal also controlled the disease, but sugar yields were no higher than those obtained with the plain nematicides. In greenhouse experiments, the interaction between H. schachtii and F. oxysporam was disadvantageous to the nematode. Damage to sugarbeets was less when the fungus and the nematode were present than when only the nematode was present. The fungus inhibited nematode invasion and development in sugarbeet seedlings, thereby decreasing the number of nematodes that matured about 3-fold.     

Peach Leaf Senescence Delayed by Criconemella xenoplax

Fall annual leaf senescence of peach was delayed in the field and in microplots in the presence of Criconemella xenoplax. Soil from the rhizosphere of orchard trees with greener leaves had ca. 2.5 × more nematodes than soil around trees in a more advanced state of fall senescence. In microplots, monoclonal antibody enzyme immunoassay (EIA) of leaf cytokinins indicated that concentration of zeatin riboside-like substances and chlorophyll content were greater in leaves of trees growing in nematode-infested soil than in trees in uninfested soil. EIA also indicated the presence of substances resembling trans-zeatin, zeatin riboside, dihydrozeatin, and dihydrozeatin riboside-like substances in whole body homogenates of C. xenoplax. Levels of zeatin-like substances were present in the nematode in greater levels than the other related substances.     

Additive Effects of Meloidogyne arenaria and Sclerotinin rolfsii on Peanut

Field observations have suggested that infection of peanut by Meloidogyne arenaria increases the incidence of southern blight caused by Sclerotium rolfsii. Three factorial experiments in microplots were conducted to determine if interactions between M. arenaria and S. rolfsii influenced final nematode population densities, incidence of southern blight, or pod yield. Treatments included four or five initial population densities of M. arenaria and three inoculum rates of S. rolfsii. Final nematode population densities were affected by initial nematode densities in all experiments (P = 0.01) and by S. rolfsii in one of three experiments (P = 0.01). Incidence of southern blight increased with increasing inoculum rates of S. rolfsii in all experiments and by the presence of the nematodes in one experiment (P = 0.01). Pod yield decreased with inoculation with S. rolfsii in all experiments (P = 0.05) and by M. arenaria in two of three experiments (P = 0.05). In no experiment was the interaction among treatments significant with respect to final nematode population densities, incidence of southern blight, or pod yield (P = 0.05). The apparent disease complex between M. arenaria and S. rolfsii on peanut is due to additive effects of the two pathogens.     

Effects of Potassium Fertilization and Pratylenchus penetrans on Yield and Potassium Content of Red Clover and Alfalfa

Red clover and alfalfa were inoculated with Pratylenchus penetrans and grown in an Alberry sandy loam soil to which potassium (K⁺) was added at seeding at 0, 41.5, 83, and 166 μg/g. In one experiment with alfalfa, additional K⁺ was added after each forage cut to replace that which was removed. Nematode populations were not consistently affected by K⁺ fertilization. Nematode infection stunted red clover and alfalfa and resulted in lower yields at all K⁺ levels, except for alfalfa at the lowest K⁺ level. Nematode infection had no effect on taproot yields. However, it resulted in lower rootlet yields from red clover at all K⁺ levels, lower rootlet yields from alfalfa only at the highest K⁺ level in one experiment, and lower rootlet yields at all but the lowest K⁺ level in a second experiment, potassium fertilization enhanced yield of red clover and alfalfa. Yield increases were smaller from increased K⁺ fertilization in nematode-infested soil than in noninfested soil. Pralylenchus penetrans had little effect on the K⁺ content of red clover or alfalfa. The stunting of plants from nematode infection resulted in less K⁺ being removed from the soil.     

Effect of Crop Rotation on Meloidogyne spp. and Pratylenchus spp. Populations in Strawberry Fields in Taiwan

Changes in population levels of Meloidogyne hapla, M. incognita, Pratylenchus coffeae, and P. penetrans were studied in 12 strawberry fields in the Dahu region of Taiwan. Ten potential rotation crops and two cultural practices were evaluated for their effect on nematode populations and influence on strawberry yield. Rotation with rice or taro and the cultural practice of flooding and bare fallowing for four months were found to reduce nematode soil populations to two or fewer nematodes per 100 ml soil. Average strawberry yields increased between 2.4% to 6.3% following taro compared to the bare fallow treatment. Corn suppressed M. incognita and M. hapla populations and resulted in an increased in strawberry yield compared to bare fallow. Other phytopathogens also present in these fields limited taro as the rotation choice for nematode management. Results of this research and economic analysis of the input requirements for various rotation crops, corn and bare fallow were recommended as the most appropriate rotation strategies for nematode management in strawberry in this region.     

Cyperus Tubers Protect Meloidogyne incognita from 1,3-Dichloropropene

Meloidogyne incognita-infected and noninfected tubers of yellow nutsedge (Cyperus esculentus) and purple nutsedge (Cyperus rotundus) were treated with 56 L/ha 1,3-dichloropropene (1,3-D) in microplots and subsequently examined for tuber and nematode viability in the greenhouse using a chile pepper (Capsicum annuum) bioassay system. The study was conducted three times. Nutsedge tuber viability and M. incognita harbored in both yellow and purple nutsedge tubers were unaffected by 1,3-D treatment. Nematode reproduction on nutsedges and associated chile pepper plants varied among years, possibly due to differing levels of tuber infection or soil temperature, but was not affected by fumigation. The presence of M. incognita resulted in greater yellow nutsedge tuber germination and reproduction. The efficacy of 1,3-D for management of M. incognita in chile pepper production is likely to be reduced when nutsedges are present in high numbers, reinforcing the importance of managing these weeds and nematodes simultaneously.     

A Method for Isolation of Pasteuria penetrans Endospores for Bioassay and Genomic Studies

A rapid method for collection of Pasteuria penetrans endospores was developed. Roots containing P. penetrans-infected root-knot nematode females were softened by pectinase digestion, mechanically processed, and filtered to collect large numbers of viable endospores. This method obviates laborious handpicking of Pasteuria-infected females and yields endospores competent to attach to and infect nematodes. Endospores are suitable for morphology studies and DNA preparations.     

Role of Nematodes,Nematicides, and Crop Rotation on the Productivity and Quality of Potato,Sweet Potato,Peanut, and Grain Sorghum

The objective of this experiment was to determine the effects of fenamiphos 15G and short-cycle potato (PO)-sweet potato (SP) grown continuously and in rotation with peanut (PE)-grain sorghum (GS) on yield, crop quality, and mixed nematode population densities of Meloidogyne arenaria, M. hapla, M. incognita, and Mesocriconema ornatum. Greater root-gall indices and damage by M. hapla and M. incognita occurred on potato than other crops. Most crop yields were higher and root-gall indices lower from fenamiphos-treated plots than untreated plots. The total yield of potato in the PO-SP and PO-SP-PE-GS sequences increased from 1983 to 1985 in plots infested with M. hapla or M. arenaria and M. incognita in combination and decreased in 1986 to 1987 when root-knot nematode populations shifted to M. incognita. The total yields of sweet potato in the PO-SP-PE-GS sequence were similar in 1983 and 1985, and declined each year in the PO-SP sequence as a consequence of M. incognita population density increase in the soil. Yield of peanut from soil infested with M. hapla increased 82% in fenamiphos-treated plots compared to untreated plots. Fenamiphos treatment increased yield of grain sorghum from 5% to 45% over untreated controls. The declining yields of potato and sweet potato observed with both the PO-SP and PO-SP-PE-GS sequences indicate that these crop systems should not be used longer than 3 years in soil infested with M. incognita, M. arenaria, or M. hapla. Under these conditions, these two cropping systems promote a population shift in favor of M. incognita, which is more damaging to potato and sweet potato than M. arenaria and M. hapla.     

Yield-loss Models for Tobacco Infected with Meloidogyne incognita as Affected by Soil Moisture

Yield-loss models were developed for tobacco infected with Meloidogyne incognita grown in microplots under various irrigation regimes. The rate of relative yield loss per initial nematode density (Pi), where relative yield is a proportion of the value of the harvested leaves in uninfected plants with the same irrigation treatment, was greater under conditions of water stress or with high irrigation than at an intermediate level of soil moisture. The maximum rate of plant growth per degree-day (base 10 C) was reduced as nematode Pi increased when plots contained adequate water. When plants were under water stress, increasing Pi did not luther reduce the maximum rate of plant growth (water stress was the limiting factor). Cumulative soil matric potential values were calculated to describe the relationship between available water in the soil (matric potential) due to the irrigation treatments and subsequent plant growth.     

Host Range and Ecology of Isolates of Pasteuria spp. from the Southeastern United States

Isolates of Pasteuria penetrans were evaluated for ecological characteristics that are important in determining their potential as biological control agents. Isolate P-20 survived without loss of its ability to attach to its host nematode in dry, moist, and wet soil and in soil wetted and dried repeatedly for 6 weeks. Some spores moved 6.4 cm (the maximum distance tested) downward in soil within 3 days with percolating water. The isolates varied greatly in their attachment to different nematode species and genera. Of five isolates tested in spore-infested soil, three (P-104, P-122, B-3) attached to two or more nematode species, whereas B-8 attached only to Meloidogyne hapla and B-I did not attach to any of the nematodes tested. In water suspensions, spores of isolate P-20 attached readily to M. arenaria but only a few spores attached to other Meloidogyne spp. Isolate P-104 attached to all Meloidogyne spp. tested but not to Pratylenchus scribneri. Isolate B-4 attached to all species of Meloidogyne and Pratylenchus tested, but the rate of attachment was relatively low. Isolate P-Z00 attached in high numbers to M. arenaria when spores were extracted from females of this nematode; when extracted from M. javanica females, fewer spores attached to M. arenaria than to M. javanica or M. incognita.