Effectiveness of native West African arbuscular mycorrhizal fungi in protecting vegetable crops against root-knot nematodes

Twenty strains of arbuscular mycorrhizal fungi (AMF), native to West Africa, and three commercial AMF, were evaluated for their protective effect against root-knot nematodes, Meloidogyne spp., in pots and field experiments in Benin. In pots, these strains were assessed in sterilized soil following inoculation of nematodes and in non-sterilized soil naturally infested with nematodes using tomato. The four strains showing greatest potential in suppressing nematode development were further assessed in the field with a relatively high natural infestation level of nematodes (155 per 100 cm³ soil) over a tomato–carrot double cropping. In the pot experiments, most native strains provided significant suppression of nematode multiplication and root galling, but in most cases the level of nematode control depends on either sterilized or non-sterilized soils. In the field experiments, application of AMF mostly resulted in significant suppression of nematode multiplication and root galling damage on both crops indicating that the AMF persists and remains protective against root-knot nematodes over two crop cycles. Field application of AMF increased tomato yields by 26% and carrot yields by over 300% compared with the non-AMF control treatments. This study demonstrates for the first time, the protective effect of indigenous West African AMF against root-knot nematodes on vegetables. The potential benefits of developing non-pesticide AMF-based pest management options for the intensive urban vegetable systems are evident.     

连作番茄根区病土对番茄生长及土壤线虫与微生物的影响

探索连作番茄根区病土对番茄根结线虫病的诱导效果及引起连作障碍的微生态机制,可为深入了解番茄连作障碍发生机理及探究番茄连作障碍防治方法提供科学依据。本研究利用盆栽试验,测定了番茄在健康土壤及接种病土土壤中生物学特性变化及根结线虫侵染状况,并分析鉴定了土壤中微生物及线虫的种类与数量。结果表明,接种连作番茄根结线虫病株根区病土会对番茄生长及根结线虫侵染产生影响:1)番茄苗期根系根结数达9个?株~(-1),健康土壤无根结;土壤线虫数量较健康土壤增加390.4%;收获期番茄根结线虫侵染率达62.7%,病情指数为80.0%。2)番茄生长受到抑制,叶片防御酶活性降低,收获期茎叶及根系鲜质量较健康土壤分别减少50.2%及33.1%,苗期番茄叶片PPO活性较健康土壤降低15.8%,POD活性较健康土壤增加24.0%,差异均达显著水平(P0.05)。3)番茄根系更易感染有害菌,根系内病原菌甘蓝假单胞菌数量较健康土壤增加463倍,根区土壤细菌、真菌及放线菌总数分别增加46.3%、94.5%及134.0%。4)食细菌线虫、食真菌线虫及植物寄生性线虫数量分别为健康根区土壤的3.3倍、1.6倍及7.3倍,其中的植物寄生线虫95.6%为根结线虫。综上所述,接入连作番茄根结线虫病株根区病土不仅导致番茄遭受根结线虫侵染,而且会导致土壤线虫总量及植物寄生线虫所占比例大幅增加,并使番茄根系内有害细菌数量显著增加,对番茄生长造成显著抑制作用,同时影响番茄的生理生化特性,受线虫侵染番茄防御性酶活性降低,使其更易被根结线虫及病原菌侵染,番茄根区土壤线虫、微生物及根系内优势细菌的种类与数量及其之间的作用发生改变。     

Effects of Pseudomonas aeruginosa on the diversity of culturable microfungi and nematodes associated with tomato: impact on root-knot disease and plant growth

The available information on Pseudomonas biocontrol inoculants on the non-target fungal and nematode community is scant. The current paper addresses this issue and investigates the effects of biocontrol agents Pseudomonas aeruginosa IE-6 and IE-6S⁺ (previously shown to suppress several soil-borne plant pathogens) on soil microfungi and plant-parasitic nematodes as well as on the root-knot development and growth of tomato (Lycopersicon esculentum). Furadan, a granular nematicide was included as a treatment for comparative purposes. Treatments were applied to soil at the start of each 52-day-long tomato growth cycle, and their effects on the composition and diversity of rhizosphere and endophytic microfungi and plant-parasitic nematodes were examined at the end of first and fourth growth cycle. Several diversity indices were employed to assess community diversity. A total of 16 genera comprising 23 microfungal species were isolated from the tomato rhizosphere. The most abundant fungal species belonged to the genera Aspergillus, Fusarium, and Penicillium. With a few exceptions, fungi were neither exclusively inhibited nor specifically promoted by the application of treatments at any of the growth cycles studied. However, Paecilomyces lilacinus, an egg and female parasite of root-knot nematode, though exclusively absent in the controls was isolated from the treatments. Both general diversity and equitability of rhizosphere microfungi were greater at first compared to the fourth growth cycle while species richness remained uninfluenced across the growth cycles and treatments. However, Furadan and IE-6S⁺ treatments considerably abated general diversity and equitability. Of the microfungal species isolated from the rhizosphere seven were also recovered from surface-sterilized root tissue of tomato suggesting that all the endophytes are primarily rhizosphere organisms. Diversity of endophytic fungi was consistently lower compared with that of the rhizosphere. Both general diversity and equitability declined in all three treatments relative to controls in the root tissue but species richness remained unaltered. Diversity and equitability of plant-parasitic nematodes in soil were reduced by all three treatments over the controls at fourth growth cycle whilst species richness did not change at either growth cycle. The biocontrol agents significantly reduced root-knot development and enhanced shoot growth of tomato over the controls. The possible implications of fungal composition and abundance because of biocontrol by Pseudomonas application are discussed.     

Population dynamics of Trichoderma in fumigated and compost-amended soil and on strawberry roots

Effectiveness of Trichoderma strains for biocontrol of soilborne pathogens requires an improved understanding of soil and root ecology of this fungus. We compared the population dynamics of Trichoderma hamatum strain T382 (T382) and indigenous Trichoderma spp. in soil and on roots in different strawberry production systems. Strawberry transplants, either amended or not-amended with Trichoderma biocontrol strains, were planted in field soil left untreated or treated with soil fumigant, compost, and compost-amended with T382. Soil and root samples were taken between October and June of two production seasons (2002-03 and 2003-04), and Trichoderma populations were assessed by plating soil dilutions and root pieces onto selective medium. Identity of T382 was confirmed using strain-specific primers. T382 became established and maintained a stable population of 10³ cfu/g soil throughout the growing season when added to field soil in amended compost, but T382 was rarely isolated from strawberry roots. Populations of indigenous Trichoderma spp. were up to 60-fold greater in fumigated soil than in any other soil treatment. Indigenous Trichoderma spp. were isolated from a greater proportion (20–50%) of roots in fumigated soil than from roots in the other treatments (0–20%). Transplant treatments did not significantly affect Trichoderma populations on roots or in soil during field production. This study showed that compost may be used as a substrate to establish and promote survival of Trichoderma in field soil, and illustrates how soil manipulation can affect population dynamics of indigenous Trichoderma spp. on roots and in soil.     

Suppression of root-knot nematodes in natural and agricultural soils

The potential of the invertebrate communities in agricultural and natural soils to suppress Meloidogyne incognita on coleus (Coleus blumei) was evaluated in two greenhouse experiments. Soil from adjacent natural and agricultural habitats was collected from four locations that had very different soil types (loamy sand, muck, sand and rock). Soil of each type was placed into pots, planted with coleus seedlings, inoculated with 2000 eggs of M. incognita, and arranged in a 4 × 2 factorial design. Root-knot nematodes were suppressed in natural soil compared to agricultural soil for loamy sand, sand and rock soils, but not for muck soil. Plants grew larger and had less root galling in natural soils than in agricultural soils. Free-living nematodes (bacterivores, fungivores, omnivores and predators) were monitored but did not show population patterns consistent with the suppression of root-knot nematodes observed in natural soils. Reasons for the opposite result (higher root-knot levels in natural than in agricultural soil) on muck soil are unknown, but this soil type was very different from the other soils in its unusually high organic matter content and very low levels of omnivorous and predatory nematodes. The agricultural muck in particular was unusually low in fungivorous nematodes and extremely high in levels of sodium and macronutrients. Despite the exception on the muck soil, the relative suppression of root-knot nematodes in natural compared to agricultural soils of the other three soil types (loamy sand, sand and rock) support the idea that potential for nematode suppression may be greater in natural than in agricultural soils.     

Suppression of root-knot disease by Pseudomonas fluorescens CHA0 in tomato: importance of bacterial secondary metabolite, 2,4-diacetylpholoroglucinol

The antimicrobial metabolites 2,4-diacetylphloroglucinol (2,4-DAPG) and pyoluteorin contribute to the ability of Pseudomonas fluorescens strain CHA0 to control plant diseases caused by soil-borne pathogens. P. fluorescens strain CHA0 and its derivatives CHA89 (antibiotics-deficient) and CHA0/pME3424 (antibiotics overproducing) were investigated as potential biocontrol agents against Meloidogyne javanica the root-knot nematode. Exposure of root-knot nematode to culture filtrates of P. fluorescens under in vitro conditions significantly reduced egg hatch and caused substantial mortality of M. javanica juveniles. Nutrient broth yeast extract (NBY) medium amended with 2% (w/v) glucose or 1 mM EDTA markedly repressed hatch inhibition activity of the strain CHA0 but not that of CHA0/pME3424 or CHA89. On the other hand, NBY medium amended with glucose significantly enhanced nematicidal activity of the strain CHA0/pME3424. Neither glucose nor EDTA had an influence on the nematicidal activity of the strains CHA0 and CHA89. Under in vitro conditions, antibiotic overproducing strain CHA0/pME3424 and CHA0 expressed phl‘-’lacZ reporter gene but strain CHA89 did not. Expression of the reporter gene reflects actual production of DAPG. In general, CHA0/pME3424 expressed reporter gene to a greater extent compared to its wild type counterpart CHA0. Regardless of the bacterial strains, reporter gene expression was markedly enhanced when NBY medium was amended with glucose but EDTA had no such effect. A positive correlation between the degree of juvenile mortality and extent of phl‘-’lacZ reporter gene expression was also observed in vitro. Strain CHA0 produced zones of 4-6 mm on MM medium containing gelatin while strain CHA0/pME3424 and CHA89 did not. When MM medium containing gelatin was amended with 2% glucose of 1 mM EDTA size of haloes produced by the strain CHA0 reduced to 2 mm. Under glasshouse conditions aqueous cell suspension of the strains CHA0 or CHA0/pME3424 at various inoculum levels (10⁷, 10⁸ or 10⁹ cfu ml⁻¹) significantly reduced root-knot development. CHA89 caused significant reduction in galling when applied at 10⁹ cfu ml⁻¹. To better understand the mechanism of nematode suppression, split root bioassay was performed. Split-root experiments, that guarantee a spatial separation of inducing agent and a challenging pathogen, showed that soil treatment of one half of the root system with cell suspension of CHA0 or CHA0/pME3424 resulted in a significant systemic induced resistance leading to reduction of M. javanica infection of tomato roots in the non-baterized nematode treated half. The results clearly suggest that the antibiotic 2,4-DAPG from P. fluorescens CHA0 act as the inducing agents of systemic resistance in tomato roots. Populations of CHA0 and its derivatives declined progressively by 10-fold between first and fourth harvests (0-21 days after inoculation). However, bacterial populations increased at final harvest (28 days after application).     

Effect of the arbuscular mycorrhizal fungus <Emphasis Type="BoldItalic">Glomus intraradices</Emphasis> on the false root-knot nematode <Emphasis Type="BoldItalic">Nacobbus aberrans</Emphasis> in tomato plants

Information about the interaction between arbuscular mycorrhizal fungi (AMF) and the false root-knot nematode Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 is scarce. The effect of Glomus intraradices Schenk & Smith on tomato (Lycopersicon esculentum L.) cv. Platense inoculated with nematode juveniles from Lisandro Olmos (Argentina) was studied under greenhouse conditions. Six treatments with five replications were performed. After 80 days, nematode reproduction and percentage of AMF colonization in roots were estimated. Some plant growth parameters were also measured. In general, plants with AMF and AMF plus nematodes grew as well as the control without AMF and without nematodes. Furthermore, G. intraradices was beneficial in reducing nematode-induced damage in roots (lower number of galls) as well as in having a suppressive effect on parasite reproduction. This is the first study on the use of G. intraradices as a possible strategy in the control of N. aberrans in tomato.     

Effects of Pseudomonas fluorescens and fertilizers on the reproduction of Meloidogyne incognita and growth of tomato

A 60-day glasshouse experiment was conducted to assess the influence of two strains of Pseudomonas fluorescens (GRP3 and PRS9), organic manure, and inorganic fertilizers (urea, diammonium phosphate (DAP), muriate of potash and monocalcium phosphate) alone and in combination on the multiplication of Meloidogyne incognita and growth of tomato. Pseudomonas fluorescens GRP3 was better at improving tomato growth and reducing galling and nematode multiplication than PRS9. Organic manuring resulted in less galling and nematode multiplication than occurred with DAP. However, DAP was found better in reducing nematode multiplication and improving plant growth than urea. Muriate of potash was the inorganic fertilizer least effective in reducing galling and nematode multiplication. Pseudomonas fluorescens GRP3 with organic manure was the best combination for the management of M. incognita on tomato but improved management of M. incognita can also be obtained if DAP is used with the GRP3 strain of P. fluorescens.     

Response to root-knot nematodes of a germplasm collection of red clover and related species

A germplasm collection of red clover (Trifolium pratense L.) and seven related species was evaluated in greenhouse tests for resistance to Meloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood, and M. Javanica (Treub) Chitwood. Plants were rated for root galling severity and nematode egg production at eight weeks after inoculation with 1500 nematode eggs. A resistance index, RI = (gall₂; + egg₂;), was generated to assess the plants' reaction to nematode infection as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, or highly susceptible. More than 98% of red clover accessions were intermediately to highly susceptible to all four root-knot nematode species. Only one accession, PI 271627 introduced from India, had a moderate resistance level to the four nematodes tested. About one third of the T. medium accessions were resistant or highly resistant to M. arenaria, M. incognita, and M. javanica whereas more than 50% of the T. alpestre accessions were highly resistant or immune to all four nematodes species. Genetic factors for resistance to root-knot nematode could be introduced into T. pratense through interspecific hybridization with T. medium and/or T. alpestre     

Effects of the root-knot nematode Meloidogyne javanica on the symbiotic relationships between different strains of Rhizobia and Acacia holosericea (A Cunn. ex G. Don)

Several strains of Bradyrhizobium, Mesorhizobium and Sinorhizobium strains were tested for their compatibility with an Australian acacia: Acacia holosericea. All bacterial strains induced some nodule formation on roots. However, the rhizobia which greatly increased the development of seedlings belonged to the Bradyrhizobium genus. The root-knot nematode Meloidogyne javanica, strongly inhibited the symbiosis with most of the rhizobial strains. The rhizobia had no effect on nematode multiplication except for bacterial strain ORS 1020 where the final nematode population was higher than in the control treatment. The hypothesis concerning the interactions between nematodes and the nitrogen fixative process are discussed. Moreover, this investigation underlines the decreasing effect of nematodes on the potential benefits that may result from growing A. holosericea inoculated with selected rhizobial strains.     

Genetic diversity for root-knot nematode resistance in white clover and related species

A total of 237 Plant Introduction in eleven Trifolium species were evaluated for resistance to Meloidogyne arenaria (Neal) Chitwood race 1, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood race 3, and M. javanica (Treub) Chitwood. Plants were infected with 1500 nematode eggs collected from 'Rutgers' tomato (Lycoperiscon esculentum Mill.) roots with 0.5% NaOCl. Ratings of galling severity and egg mass production were assigned to each plant 8 wk after inoculation. Host plant reaction was classified as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, and highly susceptible according to the resistance index . More than 95% of 171 white clover accessions were moderately to highly susceptible to all four nematodes species. The best white clover accessions were only moderately resistant to either M. arenaria (PI 291843 and PI 306286) or M. hapla (PI 100250 and PI 204930). Accessions with moderate resistance or resistance to root-knot nematodes were found among relatives of white clover, with T. ambiguum M. Bieb. exhibiting the greatest resistance level. Among the other Trifolium species evaluated, T. carolinianum Michx. PI 516273 was immune or highly resistant to all four nematode species while accessions of T. hirtum All. showed a wide range of reaction to root-knot nematodes. Identified germplasm of white clover relatives with resistance to root knot nematodes should be useful for the selection of parents in white clover breeding programs.     

Inoculant rhizobia suppressed root-knot disease,and enhanced plant productivity and nutrient uptake of some field-grown food legumes

The potential effect of rhizobial inoculation on root knot nematodes in chickpea, mungbean and pigeonpea were studied under field condition. The seed treatment with respective rhizobium strains increased the nodulation, leghemoglobin content, bacteriod population, plant growth, yield and nitrogen uptake of three three food legumes compared to the plants without the rhizobium treatment. The nematode (1500?juveniles/kg soil) incited oval galls on the roots of the three legumes, and suppressed plant growth and yield. The galling, egg mass production and soil population of the nematode was greater on the plants without the rhizobium treatment. The pure culture and culture filtrate of the rhizobium strains suppressed the egg hatching and induced mortality to the juveniles of M. incognita over control. The nematode infection reduced the nodulation, bacteroid population and leghemoglobin contents of the nodules and NPK uptake by the plants. Hence, the rhizobia treatment shall be integrated to common agronomic practice of food legume cultivation so as to enhance crop productivity and to protect roots from nematode attack.     

蜡样芽孢杆菌菌株X5强化的生物有机肥能有效控制根结线虫(Meloidogyne sp.)

The efficacy of Bacillus cereus X5 as a potential biological control agent against root-knot nematodes was evaluated in vitro by examining second-stage juvenile mortality and egg hatching rate under addition of culture filtrate and in planta by application of bio-organic fertilizers enhanced with B. cereus X5, B. thuringiensis BTG, or Trichoderma harzianum SQR-T037 alone or together in greenhouse and field experiments. The biofumigation of the root-knot nematode-infested soil with organic materials (chicken manure, pig manure and rice straw) alone or in combination with B. cereus X5 was also conducted in greenhouse experiments. In laboratory, the filtrate of B. cereus X5 more effectively reduced egg hatching rates during the incubation period for 14 d and more effectively killed the second-stage juvenile during the incubation period of 24 h than that of B. thuringiensis BTG. The highest dry shoot weights for greenhouse tomatoes and field muskmelons were found in both the treatment consisting of the bio-organic fertilizer enhanced with the three biocontrol agents and the treatment consisting of the bio-organic fertilizer enhanced only with B. cereus X5. The two bio-organic fertilizers achieved better nematicidal effects than those enhanced only with B. thuringiensis BTG or T. harzianum SQR-T037. B. cereus X5 also enhanced effect of biofumigation, which resulted in increased plant biomass and reduced nematode counts in the roots and rhizosphere soil. Therefore, these results suggested that biological control of root-knot nematodes both in greenhouses and fields could be effectively achieved by using B. cereus X5 and agricultural wastes.     

The influence of the root-knot nematode Meloidogyne incognita, the nematicide aldicarb and the nematophagous fungus Pochonia chlamydosporia on heterotrophic bacteria in soil and the rhizosphere

Plant‐pathogenic nematodes are a major cause of crop damage worldwide, the current chemical nematicides cause environmental damage, but alternatives such as biological control are less effective, so further understanding of the relationship between nematodes, nematicides, biological control agents and soil and rhizosphere microorganisms is needed. Microbial populations from roots of cabbage and tomato plants infested with the root‐knot nematode Meloidogyne incognita were compared with those from plants where the nematode was controlled by the nematicide aldicarb, or a nematophagous fungus with biological control potential, Pochonia chlamydosporia. The total numbers of culturable bacteria and fungi in rhizosphere soil were similar in all three treatments for both plants, around 100‐fold more than in control soil in which there were no plants. However, there were clear differences in the catabolic diversity, assessed by Biolog EcoPlate? carbon substrate utilization assays, between microbial populations from unplanted soil and the rhizosphere. In cabbage, a poor host for M. incognita, the rhizosphere population from P. chlamydosporia‐treated plants was distinct from the population from untreated and aldicarb‐treated plants. In tomato, a host susceptible to the nematode, the catabolic diversity of populations from aldicarb‐ and P. chlamydosporia‐treated plants was similar and differed from the untreated, nematode‐infested plants. The genetic diversity of the fast‐growing heterotrophic bacteria in the tomato rhizosphere, indicated by PCR fingerprinting with ERIC primers, was very different in the infested roots, whereas the profiles of isolates from both aldicarb‐ and P. chlamydosporia‐treated roots were similar. Evidently, nematodes have a greater impact on the rhizosphere population of a susceptible host, tomato, than a poor one, cabbage, and nematode‐infested roots are colonized by a different subpopulation of soil microbes from that on plants where infection is controlled, illustrating differences in root morphology and physiology.     

Biological control of the root-knot nematode Meloidogyne javanica by Trichoderma harzianum

The filamentous fungi Trichoderma spp. is currently developed as biocontrol agents against many plant pathogens. Recent studies have shown that these fungi are able to infect nematode eggs and juveniles. In this research, biological control of root-knot nematode (Meloidogyne javanica) by Trichoderma harzianum BI was investigated in greenhouse and laboratory experiments. Results showed that different concentrations (10²–10⁸ spores/ml) of T. harzianum BI decreased nematode infection and other parameters significantly, compared to control. T. harzianum BI was able to penetrate nematode egg mass matrix and significantly decreased nematode egg hatching level. Specific activities of resistance-related enzymes, namely peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) increased significantly in T. harzianum BI inoculated plants. Maximum activities of POX, PPO and PAL were observed at the 5, 5 and 6 days after inoculation, respectively. Chitinase activity was also increased in culture filtrates of T. harzianum BI grown on wheat bran moistened with salt solution supplemented with colloidal chitin or nematode eggs. Maximum activity of chitinase was recorded at the 4 days after inoculation, in media supplemented with colloidal chitin (1.15 U/min per ml) and nematode eggs (0.85 U/min per ml). Results suggested that direct parasitism of eggs through the increase in extracellular chitinase activity, which would be indicator of eggs infection capability, and inducing plant defense mechanisms leading to systemic resistance are two main suppression mechanisms used by T. harzianum BI against nematode.     

定殖烟草根结线虫卵和雌虫机会真菌的多样性

机会真菌对根结线虫的生物防治具有巨大潜力。本研究于2010—2011年针对来源于中国7个省份的156份烟草根结线虫样本,分别分离根结线虫游离卵、卵块和雌虫上定殖的机会真菌。应用18S rDNA-ITS片段测序结果结合菌株的形态学观察和培养性状鉴定定殖游离卵、卵块和雌虫上的真菌。根据分离到菌株的培养性状、形态学和rDNA-ITS序列分析,对定殖于南方根结线虫或北方根结线虫的9 839个游离卵、408个卵块和284个雌虫的真菌菌株,明确鉴定出9属13个种,其中定殖根结线虫新记录种5个,即长梗木霉、芬芳镰刀菌、渐狭蜡蚧菌、虫草棒束孢和交枝顶孢。淡紫紫孢菌Purpureocillium lilacinum(原名:淡紫拟青霉)为优势种,分布广泛,在云南、安徽、湖北、贵州和山东省均被分离到。该菌在南方根结线虫和北方根结线虫的游离卵、卵块和雌虫平均分离率分别为0.49%、24.00%和16.90%,说明其地理和生态适应性广泛。不同地区来源的烟草根结线虫卵和雌虫上定殖的机会真菌种类存在明显差异。目前尚无渐狭蜡蚧菌和虫草棒束孢作为线虫病原物的报道,有待于进一步深入研究其对根结线虫的致病性。     

Control of tomato bacterial wilt and root-knot diseases by Bacillus thuringiensis CR-371 and Streptomyces avermectinius NBRC14893

Ralstonia solanacearum and Meloidogyne incognita are two soilborne pathogens that cause serious damage and great losses in the production of tomato. For this purpose, a bacterial isolate, Bacillus thuringiensis CR-371, and an actinomyces isolate, Streptomyces avermectinius NBRC14893, were examined for their ability to protect tomato from root-knot nematode and bacterial wilt diseases under glasshouse conditions. Treatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 followed by challenge inoculation with R. solanacearum and M. incognita significantly decreased disease severity of bacterial wilt alone, root-knot nematode alone, or mixed infection by both pathogens compared to the control. Furthermore, pretreatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 significantly reduced bacterial proliferation of R. solanacearum both in pathogen alone inoculated plants and in plants co-inoculated with R. solanacearum and M. incognita. In conclusion, our results suggest that the treatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 simultaneously suppresses bacterial wilt and root-knot nematode diseases. Therefore, B. thuringiensis CR-371 and S. avermectinius NBRC14893 could provide new options for integrated pest management strategies against plant diseases, especially against bacterial-nematode disease complexes that cause synergistic yield losses.     

Relationship between the biocontrol fungus Trichoderma harzianum and the phytopathogenic fungus Fusarium solani f.sp. pisi

Relationship between the biocontrol fungus Trichoderma harzianum ThzID1-M3 and the plant pathogen Fusarium solani f.sp. pisi (Fsp) was determined in this study. Dual culture assay indicated the competitive interaction between ThzID1-M3 and Fsp. Alginate pellets of ThzID1-M3 and Fsp conidia were added to non-sterile soil with pea seeds. The interaction between Trichoderma and Fsp adversely affected their establishment in soil. The addition of ThzID1-M3 significantly reduced the Fsp population, as well as the colonization of roots by Fsp. In contrast, the added Fsp significantly reduced the proliferation of ThzID1-M3 and Trichoderma spp. The results suggest that the competition may be the main mechanism of the antagonistic activity of Trichoderma against Fsp.     

Relationships between soil penetration resistance and soif nematode burden in barley on Prince Edward Island

Fifty sloping fields of barley with different short-term cropping histories across Prince Edward Island were examined for variations in root-zone depth and the severity of soil parasitic nematodes as part of a wider study of relationships between cropping sequence, topographic position, soil physical conditions and crop performance. Root lesion nematode (Pratylenchus penetrans) density in the roots was significantly greater (13%) at foot slopes than at top slopes, and stunt nematode (Tylenchorhynchus spp.) was significantly greater (8%) at top slopes where the soil was drier. The density of stunt nematodes and root lesion nematodes in the soil was significantly greater (>15%) under miscellaneous cereals-barley sequences than under potato-barley or hay-barley, attributable to level of carryover. Root lesion nematode density in the roots was significantly greater (12%) under hay-barley than either of the other two sequences. This nematode also showed a strong tendency to increase in number with increasing root-zone depth, and may be explained on the basis that increased root-zone depth provides increased host root mass (substrate). Stunt nematodes, on the other hand, increased with decreasing root-zone depth and may be explained by the known propensity of these organisms for drier, shallower soil conditions.     

Effect of entomopathogenic nematodes on the plant-parasitic nematode Nacobbus aberrans

Nacobbus aberrans is a sedentary endoparasite nematode that forms galls in the roots of infected plants and produces important economic losses in some countries of the American continent. It has a wide host range, attacking mainly potato, tomato, sugar beet, and pepper crops. A reduction in the plant-parasitic nematode populations in the presence of entomopathogenic nematodes (EPNs) has been frequently reported. In the present work, the effect of the application of two native EPN isolates (Steinernema rarum and Heterorhabditis bacteriophora) on a N. aberrans population was evaluated in tomato plants under greenhouse conditions. Sixty days after inoculation, the number of galls and egg masses and the reproduction factor (RF) of N. aberrans were calculated. Of the variables analyzed, only the RF was significantly lower in both EPN treatments than in control. N. aberrans reproduction decreased by 57 and 53 % in plants inoculated with S. rarum and H. bacteriophora, respectively. These results showed that EPNs and their bacterial symbionts affected the reproductive potential of the N. aberrans population. This is the first study addressing the use of EPNs in the control of this important plant-parasitic nematode.