Reduced Root Galling Research Articles

Isolation of nematophagous fungi from eggs and females of Meloidogyne spp. and evaluation of their biological control potential

Fungi were isolated from Meloidogyne spp. eggs and females on 102 field-collected root samples in China. Of the 235 fungi isolated (representing 18 genera and 26 species), the predominant fungi were Fusarium spp. (42.1% of the isolates collected), Fusarium oxysporum (13.2%), Paecilomyces lilacinus (12.8%), and Pochonia chlamydosporia (8.5%). The isolates were screened for their ability to parasitise Meloidogyne incognita eggs in 24-well tissue culture plates in two different tests. The percentage of eggs parasitised by the fungi, the numbers of unhatched eggs and alive and dead juveniles were counted at 4 and 7 days after inoculation. The most promising fungi included five Paecilomyces isolates, 10 Fusarium isolates, 10 Pochonia isolates and one Acremonium isolate in test 1 or test 2. Paecilomyces lilacinus YES-2 and P. chlamydosporia HDZ-9 selected from the in vitro tests were formulated in alginate pellets and evaluated for M. incognita control on tomato in a greenhouse by adding them into a soil with sand mixture at rates of 0.2, 0.4, 0.8 and 1.6% (w/w). P. lilacinus pellets at the highest rate (1.6%) reduced root galling by 66.7%. P. chlamydosporia pellets at the highest rate reduced the final nematode density by 90%. The results indicate that P. lilacinus and P. chlamydosporia as pellet formulation can effectively control root-knot nematodes.

Protective effect of Dryopteris crassirhizoma extracts in the control of the root-knot nematode Meloidogyne incognita

Root-knot nematodes (Meloidogyne spp.) are among the most damaging soilborne plant parasites and are responsible for large economic losses in a wide variety of crops worldwide. More recently attention has increased on the use of phytochemicals as natural and biodegradable control agents to control plant-parasitic nematodes. In this study the nemat-icidal activity of extracts from 13 cryptogamic species was tested against the root-knot nematode Meloidogyne incognita. Ten extracts caused more then 50% mortality of second-stage juveniles after 48 h in an in vitro assay at 1 mg·ml-1. The extract from Dryopteris crassirhizoma displayed the highest activity, resulting in 100% mortality after 72 h at 1 mg·ml-1. The extract of D. crassirhizoma was then separated into five fractions by sequential extractions with water, petroleum ether, chloroform, ethyl acetate, and n-butyl alcohol. The chloroform fraction contained the highest level of total phloroglucinols (64.4%) and also was the most bioactive, with the lowest LC50 value of 0.4 mg·ml-1. In pot experiments, D. crassirhizoma was tested against M. incognita on tomato and applied in three ways: as a liquid extract for soil drenching and root-dip treatments, or as a powder applied as a soil additive. All of these treatments reduced root galling and the final population density of M. incognita and increased plant growth compared with the control. Of the three types of treatments, soil amendment with pulverized rhizomes from D. crassirhizoma was the most effective treatment against M. incognita.

Evaluation of Achook (Azadirachtin 1500ppm) against root knot nematode (Meloidogyne incognita) infecting okra

Evaluation of different doses of Achook (1500 ppm azadirachtin EC) against Meloidogyne incognita (RKN‐Mi) infecting okra (Abelmoschus esculentus Moench.) was undertaken under net house and open‐field conditions. Results of pot (10cm dia) experiment showed that soil drenching of Achook and Achook A1 (contains sesame oil) at higher dosage (≥10litre/ha) showed reduced root galling, greater suppression of final soil nematode (J2) population and increased shoot height of okra. The single drenching of Achook andAchook A1 at 5 litre/ha at 15 days after sowing (DAS) immediately after appearance of first gall was also quite effective for managing the RKN‐Mi on okra. Results from open‐field testing of Achook EC showed efficacy to control RKN‐Mi. The Achook and Achook A1 formulations at 5 litre/ha as single application after with the appearance of first gall was found to be most effective for reduction of root galling, soil nematode population (63 to 67%), increasing shoot height and improving (20 to 23%) fruit yield of okra. Further, at all dosages both formulations showed nematode control efficacy and enhancement of crop yield. The Achook A1 was found to be more effective (38%more yield) than soil application of carbofuran 2kg a.i./ha and neem cake at 1000kg/ha. Considering incremental cost benefit ratio (ICBR), the Achook (ICBR~4.23) and Achook1 (ICBR~4.03) at 5 litre/ha as a single soil drench with the appearance of root galling in okra was found to be the most economical. This was followed by Achook1 at 2.5 litre /ha as soil drench twice (7 DAS and 30 days after first drench) and Achook A1 5litre and 10litre/ha. The Achook A1 was found to be relatively more effective than that of carbofuran at 2kg a.i./ha and neem cake at 1000kg/ha.

Grafting for Root-knot Nematode Control and Yield Improvement in Organic Heirloom Tomato Production

Organic heirloom tomatoes (Solanum lycopersicum L.) are difficult to grow in Florida as a result of root-knot nematodes (Meloidogyne spp.) (RKN) and hot, humid growing conditions. Although grafting with resistant rootstocks has been shown effective for RKN management in tomato production, little research has been conducted on grafted heirloom tomatoes under Florida conditions. In this 2-year study, two susceptible heirloom tomato scions, ‘Brandywine’ and ‘Flamme’, were grafted onto two hybrid rootstocks, i.e., interspecific tomato hybrid rootstock ‘Multifort’ (S. lycopersicum × S. habrochaites) and tomato hybrid rootstock ‘Survivor’ (S. lycopersicum). Non-grafted and self-grafted scions were used as controls. Three field trials were conducted including the 2010 and 2011 organic field trials as well as a transitional organic field trial in 2011. There was a lack of RKN pressure in the organic field in 2010. In 2011, the RKN population was higher in the transitional field than the organic field, whereas grafting with hybrid rootstocks significantly reduced root galling (P ≤ 0.0001) in both fields. In the organic field, the hybrid rootstocks performed similarly and significantly reduced root galling compared with the non-grafted and self-grafted scions by ≈80.8%. In the transitional field, compared with non-grafted scions, the root galling reduction by ‘Survivor’ (97.1%) was significantly greater than that by ‘Multifort’ (57.6%). In general, tomato plants grafted onto ‘Multifort’ tended to be more vigorous than all other treatments. There was no clear relationship between root galling and tomato yields. Grafting did not significantly affect the total marketable yield for the scion ‘Flamme’ in both years. Total marketable yield was similar among treatments in 2010 but varied in 2011 for the scion ‘Brandywine’. In 2011, the non-grafted ‘Brandywine’ and ‘Brandywine’ grafted to ‘Survivor’ produced significantly higher (P < 0.05) yields than other treatments in the organic field. However, in the transitional field, ‘Brandywine’ grafted to ‘Multifort’ resulted in significantly higher (P < 0.05) yields than the non- and self-grafted ‘Brandywine’ treatments. Grafting with appropriate rootstocks may play an effective role in RKN management during the transition to organic production when high populations of nematodes are present.

Evaluation of organic materials for ingibition of nematode reproduction in soybean

Synthetic pesticides have been found to increase the yield of agricultural products over tenfold. However, the effects of pesticide misuse around the world include costly environmental pollution and disruption of the balance of nature in addition to their high cost and non-availability. Hence the need for search for alternative pesticideformulations to avert these undesirable effects. A study was conducted to evaluate the efficacy of Neem (Azadirachta indica A. Juss) leaf powder and organic fertiliser for management of M. incognita in soybean(Glycine max) production. A screenhouse experiment was conducted to test the efficacy of neem leaf powder (NLP) and organic based fertiliser (OBF), alone and a combination of 50% each of the NLP and OBF against root galling and Meloidogyne incognita multiplication on soybean and their potency in grain yield improvement. Theexperiment was laid out in completely randomised design with three replications. Although all treatments were effective in reducing root galling and nematode reproduction, NLP applied alone gave the highest reduction (92.59 %) in gall formation and nematode multiplication (82.07 %), followed by NLP + OBF and then OBF alone. Increases in grain yield ranged from 103.08 to 108.46% in response to organic soil amendment. Integration of the two organic substances is a better and more promising strategy since it reduced the quantity of organicfertiliser that had to be transported to farmer’s field by 50%.

Nematicidal Effects of Five Plant Essential Oils on the Southern Root-Knot Nematode, Meloidogyne incognita Race 2

This research was conducted to evaluate the nematicidal activity of five plant essential oils (rosemary, thyme, mint, garlic and sesame) against Southern root-knot nematode, Meloidogyne incognita race 2. Trial was designed as randomized complete block design with three nematode inoculums densities (0, 1000 and 2000 J2 plant(-1)) and three essential oil volumes (0, 50 and 150 plant mu L(-1)) replicated six times. There were no significant differences between nematode inoculums density and essential oil volumes used. However, all oil treatments suppressed nematode populations and resulted an increase in root mass tissue. Compared with control groups, among the essential oils, thyme (2.82+/-0.47%) and garlic (5.53+/-1.68%) treatments reduced root galling significantly and produced the lowest percent of galls on the plants whereas, rosemary, mint and sesame treatments were less effective in reducing root-galling. Compared with control groups thyme (2.46+/-0.17) and garlic (2.50+/-0.22) yielded also the lowest egg masses. Among five plant essential oils, application of a rate of 50 mu L plant(-1) of thyme or garlic in tomato production areas could give the best results in root nematode control and be an alternative to the current control methods. However, more studies need to be conducted in the field and greenhouse conditions to see the possible differences because nematodes and essential oils could be influenced by different experimental conditions.

Plant growth-promoting rhizobacteria,Paenibacillus polymyxaandPaenibacillus lentimorbussuppress disease complex caused by root-knot nematode and fusarium wilt fungus

To screen and evaluate the biocontrol potential of Paenibacillus strains against disease complex caused by Meloidogyne incognita and Fusarium oxysporum f. sp. lycopersici interactions. Paenibacillus strains were collected from rotten ginseng roots. The strains were tested under in vitro and pots for their inhibitory activities, and biocontrol potential against disease complex caused by M. incognita and F. oxysporum f. sp. lycopersici on tomato. In in vitro experiments, among 40 tested strains of Paenibacillus spp., 11 strains showed antifungal and nematicidal activities against F. oxysporum f. sp. lycopersici and M. incognita, respectively. Paenibacillus polymyxa GBR-462; GBR-508 and P. lentimorbus GBR-158 showed the strongest antifungal and nematicidal activities. These three strains used in pot experiment reduced the symptom development of the disease complex (wilting and plant death), and increased plant growth. The control effects were estimated to be 90-98%, and also reduced root gall formation by 64-88% compared to the untreated control. The protective properties of selected Paenibacillus strains make them as potential tool to reduce deleterious impact of disease complex plants. The study highlights biocontrol potential of Paenibacillus strains in management of disease complex caused by nematode-fungus interaction.

Gastrodia anti-fungal protein from the orchid Gastrodia elata confers disease resistance to root pathogens in transgenic tobacco

Diseases of agricultural crops are caused by pathogens from several higher-order phylogenetic lineages including fungi, straminipila, eubacteria, and metazoa. These pathogens are commonly managed with pesticides due to the lack of broad-spectrum host resistance. Gastrodia anti-fungal protein (GAFP; gastrodianin) may provide a level of broad-spectrum resistance due to its documented anti-fungal activity in vitro and structural similarity to insecticidal lectins. We transformed tobacco (Nicotiana tabacum cv. Wisconsin 38) with GAFP-1 and challenged transformants with agriculturally important plant pathogens from several higher-order lineages including Rhizoctonia solani (fungus), Phytophthora nicotianae (straminipile), Ralstonia solanacearum (eubacterium), and Meloidogyne incognita (metazoan). Quantitative real-time PCR and western blotting analysis indicated that GAFP-1 was transcribed and translated in transgenic lines. When challenged by R. solani and P. nicotianae, GAFP-1 expressing lines had reduced symptom development and improved plant vigor compared to non-transformed and empty vector control lines. These lines also exhibited reduced root galling when challenged by M. incognita. Against R. solanacearum expression of GAFP-1 neither conferred resistance, nor exacerbated disease development. These results indicate that heterologous expression of GAFP-1 can confer enhanced resistance to a diverse set of plant pathogens and may be a good candidate gene for the development of transgenic, root-disease-resistant crops.

Observations on the suppression of root-knot nematode ( Meloidogyne arenaria) on tomato by incorporation of cyanobacterial powder ( Oscillatoria chlorina) into potting field soil

Experiments were carried out to investigate the nematicidal potential of a cyanobacterium, Oscillatoria chlorina, against the root-knot nematode, Meloidogyne arenaria on tomato plants grown in pots filled with 500 cm 3 of field soil infested with 12-s stage juveniles (J 2)/cm 3 soil. Incorporation of freeze-dried cyanobacterial powder into potted field soil at the rate of 0.2%, 0.4%, 0.6%, 0.8% and 1.0% (w/w) 5 days prior to tomato planting, reduced root galling, final population of M. arenaria and increased vegetative growth of tomato plants and root-mass production, compared with untreated control ( P ⩾ 0.05). The beneficial effect of adding cyanobacterial powder into infested potted field soil increased exponentially with concentration up to 0.8%. Root galling and nematode population decreased by 68.9% and 97.6%, respectively at the highest dose (1%) of cyanobacterial powder compared with the untreated control. Addition of cyanobacterial powder into infested potted field soil at 5 days before planting was the most effective followed by 2 days before and at the time of tomato planting. We conclude that application rate and timing are important factors in the control of root-knot nematodes with O. chlorina.

Biological control of the root-knot nematode Meloidogyne incognita by Paecilomyces lilacinus strain 251

Abstract The fungal biocontrol agent, Paecilomyces lilacinus strain 251 (PL251), was evaluated for its potential to control the root-knot nematode Meloidogyne incognita on tomato. In growth chamber experiments, a pre-planting soil treatment reduced root galling by 66%, number of egg masses by 74% and the final nematode population in the roots by 71% compared to the inoculated control. Significant dose–response relationships were established when conidia were applied to soil either with or without the glucose-based formulation. The effective concentration 50 (EC 50 ) values for the commercially formulated product ranged between 0.097 g and 0.08 g/500 cm 3 soil, equivalent to an EC 50 of 1.29 × 10 6 and 9.88 × 10 5 colony forming units (CFU)/g soil for the parameters gall index and final population per root, respectively. For the number of egg masses per root the EC 50 was 0.007 g product or 2.64 × 10 5 CFU/g soil. Similarly, EC 50 values for conidia applied without formulation were 0.068 g or 0.103 g/500 cm 3 soil (EC 50 of 8.10 × 10 5 –1.40 × 10 6 CFU/g soil) for gall index and final population per root. In contrast, the EC 50 was 0.096 g (EC 50 of 1.28 × 10 6 CFU/g soil) for the number of egg masses per root. We demonstrated that a single pre-plant application at a concentration of 1 × 10 6 CFU/g soil is needed for sufficient biocontrol of M. incognita by PL251.

The predatory nematode, Mononchoides fortidens (Nematoda: Diplogasterida), suppresses the root-knot nematode, Meloidogyne arenaria, in potted field soil

Experiments were conducted to evaluate the effect of inoculum density and application time of the predatory nematode, Mononchoides fortidens, against the root-knot nematode, Meloidogyne arenaria, on tomato plants (Lycopersicon esculentum) cv. Pusa Ruby grown in pots containing 500 g field soil infested with 10 s stage juveniles (J2)/g soil. Addition of M. fortidens to pots at different concentrations (0, 50, 100, 150, 200, and 250 per pot) 7 days prior to tomato planting reduced root galling and the final population of M. arenaria and increased vegetative growth of tomato plants and root-mass production, compared with zero predators. The beneficial effect of adding predatory nematodes to infested potted field soil increased exponentially with concentration up to 200 nematodes per pot. Application of predatory nematodes 2 days after tomato planting was ineffective. Efficacy of predatory nematodes applied at the time of planting was intermediate between the treatments where predatory nematodes were added before and after tomato planting. At the end of the experiments, higher numbers of predators were recovered than were inoculated.

Bioactivity of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii filtrates on egg hatching, survival and infectivity of juveniles of Meloidogyne incognita race 2

The effects of culture filtrates of Fusarium oxysporum and Sclerotium rolfsii on egg hatching and juvenile survival of Meloidogyne incognita in vitro and impact of these filtrates on infectivity of M. incognita were investigated on soybean seedlings. Five- and 10-day-old filtrates of F. oxysporum caused 65 and 54% egg-hatching inhibition, while that of S. rolfsii caused 61 and 49% inhibition, respectively. Juveniles of M. incognita died within 6 days when incubated in 5-day-old filtrate of F. oxysporum, while the similar filtrate of S. rolfsii caused 100% juvenile mortality on the fifth day. Filtrates reduced root galling, egg population, number of adult females in soybean plants at harvest and also soil population. Culture filtrates could be used as source of biological nematicides.

Management of Root-knot Nematode, Meloidogyne incognita (kofoid & White) Chitwood in Chrysanthemum Using Paecilomyces lilacinus (Thom) Samson in Combination with Neem Cake

Talc and pesta granule formulations of P. lilacinus spores, obtained from solid and liquid media, at 12, 10, 8 and 6 per cent moisture levels were evaluated for their spore viability and tbeir field efficacy, singly and in combination with neem cake against root-knot nematode, Meloidogyne incognita in the farmer's field. The preparation of P. lilacinus used in the field consisted mainly of spores. The fungus was cultured under two sets of defined conditions to produce aerial spores, i. e ., cultured on sorghum grains, and submerged spores, grown in a liquid medium. Aerial spores were more robust (96, 87, 80 and 60% viability at 6, 8, 10 and 12% moisture levels, respectively, in talc formulation from sorghum grains), compared to submerged spores (83, 72,64 and 54% viability at 6, 8, 10 and 12% moisture levels, respectively, in talc formulation from liquid broth), over a period of 60 days after formulation. Talc and pesta granules of P. lilacinus , applied at 2 doses, 10 and 15 kg/ha to the root-knot nematode infested chrysanthemum field correspondingly reduced root gall index to 1.4-2.7, nematode multiplication rate to 1.4-2.12, and enhanced floral yield by 12 per cent depending on the dose of formulation. Further, combined use of these formulations with neem cake enhanced fungal propagules in rhizosphere to 700-1070, fungal infectivity to 32- 52 per cent and chrysanthemum flower yield (by 23-28 %) depending on the dose of formulation.

Influence of particle size and application method on the efficacy of calcium cyanamide for control of clubroot of vegetable brassicas

The ability of calcium cyanamide to control clubroot caused by Plasmodiophora brassicae was evaluated in field trials conducted over a 6-year period (1996–2001). During this time a decrease in efficacy was recorded and the cost of the product increased. These factors were addressed in a subsequent glasshouse trial, in which the cause of the observed decrease in efficacy was investigated, and field trials, designed to develop and evaluate improved methods of application to reduce the cost of treatment. Broadcast application of a ‘standard’ formulation of calcium cyanamide (containing particles 68% w/w>850 μm and 31% w/w 300–850 μm) at 1 t/ha consistently reduced root galling due to clubroot and increased the marketable yield of broccoli by between 1.1 and 4.7 t/ha in a series of five field trials. The efficacy of calcium cyanamide decreased in subsequent field trials when the commercial formulation changed to a macrogranule from which the fine particle component had been removed. Three formulations, calcium cyanamide ‘powder’, ‘standard’ and ‘macrogran’, were subsequently evaluated in a glasshouse experiment. The ‘powder’ containing small particles (98% w/w<300 μm) was the most effective formulation virtually eliminating root galling due to clubroot when used at the high rate (1000 kg/ha). The ‘standard’ formulation used by growers until 1998 was more effective than the ‘macrogran’ product (98% w/w >850 μm) currently used, indicating that the small particle fraction is responsible for the reduction in root galling due to clubroot . A new method of application was developed to incorporate the product into two bands approximately 15 cm deep. This method of application reduced the amount of calcium cyanamide required for control of clubroot by approximately two thirds. This has reduced the cost of treatment from A$1400/ha to A$467/ha (US$896 to US$299). Use of this method together with the anticipated reintroduction of the ‘standard’ formulation of calcium cyanamide will provide an efficacious and cost-effective treatment for Australian growers to manage clubroot in vegetable brassicas.

Investigation of alternatives to methyl bromide for management of Meloidogyne javanica on greenhouse grown tomato.

The root galling index and the densities of eggs in roots and juveniles in soil of the root-knot nematode Meloidogyne javanica (Treub) Chitwood on tomato, and the effect of these on crop yield were assessed in greenhouse experiments applying various treatments at two different sites in Crete, Greece. Tomato crops were grown for four cycles by rotating nematode-resistant (first and third spring crops) with susceptible (second and fourth autumn crops) cultivars and receiving the following treatments: (a) untreated control; (b) methyl bromide application before the first and third crops; (c) application of the fungus Pochonia chlamydosporia (Goddard) Zare, Gams & Evans before planting the first, third and fourth crops with a supplementary application three weeks after the beginning of the fourth crop; (d) application of oxamyl in both sites and fenamiphos in site 1 only at the second and fourth crops; (e) combination of treatments (c) and (d). The fungus density in soil was monitored three weeks after application and at the end of each crop, when roots were lifted. Pochonia chlamydosporia had a variable establishment and did not control the nematode. Its pathogenicity on eggs was not demonstrated, as in all cases galls were big, with all egg masses inside and protected from infection. The methyl bromide treatment significantly reduced root galling and egg production compared to other treatments in all crop cycles and the yield of the fourth crop was significantly greater. Nematicides reduced nematode densities compared with untreated controls and the fungus treatment, but they were less effective than methyl bromide and resulted in increased yield in one site only.

Evaluating Pochonia chlamydosporia in a double‐cropping system of lettuce and tomato in plastic houses infested with Meloidogyne javanica

The effect of Pochonia chlamydosporia, a facultative fungal parasite of nematode eggs, alone or in combination with oxamyl was evaluated in a double‐cropping system of lettuce and tomato in unheated plastic houses infested with Meloidogyne javanica at two sites for two consecutive growing seasons. An additional treatment of methyl bromide fumigation was included to compare crop yield in nematode‐free vs. nematode‐infested soil. Final population densities, reproductive rate, root gall rating, and egg production were determined after each crop. Pochonia chlamydosporia was isolated from nematode eggs up to nine months after application to soil. The fungus survived in the rhizosphere for the entire growing season at one site, but only at low densities. Final population densities of M. javanica decreased after cultivation of lettuce and increased after tomato, and this pattern of population fluctuation was unaffected by treatment, experiment or site. The reproductive rate on lettuce was equal to or below 1, and it was similar among treatments in both experiments at both sites. Eggs were not found on lettuce roots. On tomato, the reproductive rate in the fungus + oxamyl treatment was significantly lower (P &lt; 0·05) than other treatments in experiment 1 at both sites. Fungus + oxamyl consistently reduced root gall ratings on tomato in all cases, but numbers of eggs per g root varied depending on treatment. Methyl bromide‐treated plots remained free of M. javanica at the end of the 2‐year study.

Dry mycelium ofPenicillium chrysogenum protects cucumber and tomato plants against the root-knot nematodeMeloidogyne javanica

Incorporation into soil of dry mycelium ofPenicillium chrysogenum, a waste product of the pharmacological industry, enhanced plant growth and reduced root galling caused by the root-knot nematodeMeloidogyne javanica in cucumber and tomato plants. Incorporation into sandy loam soil in pots of dry mycelium at a concentration of 0.25% (w/w) resulted in complete protection of cucumber plants from the nematode. The number of juveniles recovered from soils containing dry mycelium was greatly reduced even at a concentration of 0.1% (w/w). In microplot studies conducted at two sites in two seasons, with three or four doses, dry mycelium caused a dose-dependent reduction in root galling index (GI) and promotion of plant growth of cucumber and tomato plants. Inin vitro studies, the water extract of dry mycelium immobilized nematode juveniles and reduced the egg hatching rate, but these effects were partly reversible after a rinse in water. Soil-drenching of cucumber and tomato seedlings with water extract of dry mycelium did not reduce GI or number of root-invading juveniles. The results show that dry mycelium promotes plant growth and protects plants against nematode infection. Protection, however, does not operatevia induced resistance.

Nematicidal Activity of Essential Oils and Their Components Against the Root-Knot Nematode

ABSTRACT Nematicidal activity of essential oils extracted from 27 spices and aromatic plants were evaluated in vitro and in pot experiments. Twelve of the twenty-seven essential oils immobilized more than 80% of juveniles of the root-knot nematode Meloidogyne javanica at a concentration of 1,000 mul/liter. At this concentration, most of these oils also inhibited nematode hatching. Essential oils of Carum carvi, Foeniculum vulgare, Mentha rotundifolia, and Mentha spicata showed the highest nematicidal activity among the in vitro tested oils. These oils and those from Origanum vulgare, O. syriacum, and Coridothymus capitatus mixed in sandy soil at concentrations of 100 and 200 mg/kg reduced the root galling of cucumber seedlings in pot experiments. The main components of these essential oils were tested for their nematicidal activity. Carvacrol, t-anethole, thymol, and (+)-carvone immobilized the juveniles and inhibited hatching at >125 mul/liter in vitro. Most of these components mixed in sandy soil at concentrations of 75 and 150 mg/kg reduced root galling of cucumber seedlings. In 3-liter pot experiments, nematicidal activity of the essential oils and their components was confirmed at 200 and 150 mg/kg, respectively. The results suggest that the essential oils and their main components may serve as nematicides.

Effect of Temperature on and Histopathology of the Interaction Between Meloidogyne incognita and Thielaviopsis basicola on Cotton

ABSTRACT Controlled environments were used to study the relationship between the root-knot nematode (Meloidogyne incognita) and Thielaviopsis basicola on cotton. Temperature treatments were continuous 20, 24, and 28 degrees C or two cyclic linear regimes with ranges of 14 to 32 or 18 to 28 degrees C over 24 h. Cotton seeds were planted in fumigated soil infested with T. basicola, M. incognita, or both. After 42 days, pathogen effects on plant growth and pathogen development were evaluated. Histology was conducted on roots collected 14, 28, and 42 days after planting in the continuous 24 degrees C treatment. Reductions in plant height-to-node ratio and total fresh weight were observed for soils infested with both pathogens compared with the control or with soils infested with either pathogen, except for M. incognita-infested soil at 28 degrees C. T. basicola reduced root galling and reproduction of the nematode at all temperatures. Vascular discoloration caused by T. basicola was greater in the presence of M. incognita compared with that by T. basicola alone. At 2 and 4 weeks, histological studies showed that plants grown in all T. basicola-infested soils contained chlamydospore chains on the root surface and in cortical cells. The fungus was not observed inside the vascular cylinder. Roots from 4-week-old plants from soils infested with T. basicola and M. incognita showed fungal sporulation in vascular tissue and localized necrosis of vascular tissue adjacent to the nematodes. At 6 weeks, plants grown in soil infested with T. basicola alone exhibited no remaining cortical tissue and no evidence of vascular colonization by the fungus. Six-week-old plants grown in T. basicola + M. incognita-infested soils exhibited extensive vascular necrosis and sporulation within vascular tissue. These studies suggest that coinfection expands the temperature ranges at which the pathogens are able to cause plant damage. Further, M. incognita greatly increases the access of T. basicola to vascular tissue.

Control of root-knot nematode (Meloidogyne javanica) on tomato with molasses and other organic amendments

In two pot experiments in which molasses (10 g molasses/L water) was drenched regularly onto field soils infested with root-knot nematodes (Meloidogyne javanica), both root galling and nematode reproduction were reduced. Results of in vitro experiments suggested that this suppressiveness of molasses to nematodes was not an osmotic effect, but was probably due to antagonism of nematodes by microorganisms that utilise it as a substrate. In a field grown tomato crop, the suppressive effects of sawdust (150 m3/ha) plus urea (600 kg/ha), filter press (400 m3/ha), molasses (375 L/ha/week for 14 weeks), a velvet bean green manure crop and the nematicide fenamiphos (10 kg a.i./ha) were compared. Untreated plants were heavily galled but all organic treatments except the green manure crop reduced root galling and all except the green manure crop and molasses reduced root-knot nematode populations in soil. Sawdust-amended soil was almost free of galls and had the lowest populations of root-knot nematode.