Identification and molecular characterisation of new Mexican isolates of Pochonia chlamydosporia for the management of Meloidogyne spp.

New Mexican isolates of the nematophagous fungus Pochonia chlamydosporia were obtained from nematode infested fields in the vegetable growing area of Tepeaca Valley, Puebla State, Mexico. Based on macro and microscopic morphology, seven ‘putative’ P. chlamydosporia isolates were selected and the DNA extracted for polymerase chain reaction (PCR). Three new isolates of P. chlamydosporia were identified: Pcp2, Pcp21 and Pcp31. The amplification reaction of the internal transcribed spacer (ITS) region revealed a 650 bp amplicon which was used in a maximum likelihood phylogenetic inference analysis. Three groups were recovered in the tree topology, supported by a > 90% bootstrap value. Nucleotide identity values were > 83.6% between the test sequences and the reference sequence. In addition, using specific primers for two existing varieties of P. chlamydosporia, restriction fragment length polymorphism on the ITS products in conjunction with the phylogenetic inferences and the molecular test for detection of P. chlamydosporia vcp1 gene, it was found that all three isolates belong to a new variety which we have named P. chlamydosporia var. mexicana. We compared the chlamydospore production rate, rhizosphere colonisation and egg parasitism percentages of the three native isolates in Meloidogyne spp. with a reference isolate (Pc10). Native isolates produced > 1×10⁶ chlamydospores/50 g of substrate (of which more than 80% were viable), colonised > 80% of the rhizosphere, and parasitised > 60% of Meloidogyne incognita and Meloidogyne arenaria eggs. Meloidogyne hapla egg parasitism was < 60%. Isolates Pcp2 and Pcp21 were identified as potential biological control agents of Meloidogyne spp. to be tested further in greenhouse and field tests.     

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.     

Interaction between Pseudomonas fluorescens and Meloidogyne incognita on tomato plant as influenced by the different levels of phosphorus

A pot experiment was conducted on tomato (Solanum lycopersicum cv. Pusa Ruby) to assess the effect of different phosphorus (P) levels (0, 125, 250 and 500 mg/pot) and the plant growth promoting rhizobacterium, Pseudomonas fluorescens, on the growth of tomato and on the reproduction of Meloidogyne incognita. Maximum growth of tomato occurred at P rates of 125 mg/kg soil, irrespective of whether plants were uninoculated or inoculated with P. fluorescens or M. incognita or inoculated with both the agents. Nematodes per gram of roots, egg masses per root, eggs per egg mass and galls per root significantly increased by increasing levels of P. P. fluorescens performed better than other treatments and different P levels in improving tomato growth and reducing galling and multiplication of M. incognita.     

Damage Functions for Three Meloidogyne Species on Arachis hypogaea in Texas

The yield response of Florunner peanut to different initial population (Pi) densities of Meloidogyne arenaria, M. javanica, and an undescribed Meloidogyne species (isolate 93-13a) was determined in microplots in 1995 and 1996. Seven Pi''s (0, 0.5, 1, 5, 10, 50, and 100 eggs and J2/500 cm³ soil) were used for each Meloidogyne species in both years. The three species reproduced abundantly on Florunner in both years. In 1995, mean reproduction differed among the three species; mean Rf values were 10,253 for isolate 93-13, 4,256 for M. arenaria, and 513 for M. javanica. In 1996, the reproduction of M. arenaria (mean Rf = 7,820) and isolate 93-13a (mean Rf = 7,506) were similar, and both had greater reproduction on peanut than did M. javanica (mean Rf = 2,325). All three nematode species caused root and pod galling, and a positive relationship was observed between Pi and the percentage of pods galled. Meloidogyne arenaria caused a higher percentage of pod galling than did M. javanica or isolate 93-13a. A negative linear relationship between log₁₀ (Pi + 1) and pod yield was observed for all three nematode species each year. The yield response slopes were similar except for that of M. javanica, which was less negative than that of isolate 93-13a in 1995, and less negative than that of M. arenaria and isolate 93-13a in 1996.     

Isolation and screening of fungi associated with eggs and females of root-knot nematodes and their biocontrol potential against Meloidogyne incognita in Bangladesh

A total of 297 fungal isolates belonging to 20 genera and 33 species were isolated and identified from eggs and females of Meloidogyne spp. in Bangladesh. The predominant genera were Fusarium, Aspergillus and Penicillium; and the significant ones were Purpureocillium, Trichoderma and Pochonia. The 24 well tissue culture plate screening technique was applied for pathogenicity tests against Meloidogyne incognita in vitro. The average percentages of egg parasitism, egg hatch inhibition and juvenile mortality varied significantly and were ranged from 8.2 to 64.9% (p = 0.05), 24.8 to 72.4% (p = 0.05), and 2.3 to 33.1% (p = 0.05), respectively. Two isolates of Purpureocillium lilacinum (PLSAU 1 and PLSAU 2) and one isolate of Pochonia chlamydosporia (PCSAU 1) reduced more than 60% average root galls of tomato, eggplant and cucumber in greenhouse experiments. This is the first investigation of fungi associated with nematodes in the country and their biological control potential against M. incognita.     

Interactions of arbuscular mycorrhizae,Meloidogyne arenaria,and phosphorus fertilization on peanut

 The individual and combined effects of two arbuscular mycorrhizal fungi (AMF), Meloidogyne arenaria, and phosphorus (P) fertilization, (0, 25, 75, and 125 μg/g soil) on peanut plant growth and pod yield were determined in greenhouse studies. Best growth and yield usually occurred at 75 or 125 μg P regardless of inoculation treatment. Peanut growth and yield were generally stimulated by AMF development, and growth alone was suppressed by M. arenaria at 0 and 25 μg P. In challenge inoculations, VAM increased peanut plant tolerance to the nematode and offset the growth reductions caused by M. arenaria at the two lower P levels. However, VAM and added P increased galling and M. arenaria egg production/g root, thereby increasing peanut susceptibility to nematode attack. M. arenaria had only a minimal effect on root colonization by AMF and sporulation by the fungi. Accepted: 9 June 1995     

Effect of plant growth promoting rhizobacteria,nematode parasitic fungi and root-nodule bacterium on root-knot nematodes Meloidogyne javanica and growth of chickpea

Effects of plant growth promoting rhizobacteria (Pseudomonas putida MTCC No. 3604 and Pseudomonas alcaligenes MTCC No. 493) and parasitic fungi (Pochonia chlamydosporia KIA and Paecilomyces lilacinus KIA) were studied, alone and together with Rhizobium sp. (charcoal commercial culture) on the growth of chickpea and multiplication of Meloidogyne javanica. Individually, P. putida 3604, P. alcaligenes 493 and Rhizobium caused a significant increase in the growth of chickpea in both nematode inoculated and uninoculated plants. Inoculation of Rhizobium with a parasitic fungus or with plant growth promoting rhizobaterium caused a greater increase in the growth of plants inoculated with nematodes than caused by either of them singly. Individually, P. lilacinus KIA caused a greater increase in the growth of nematode inoculated plants than caused by P. putida 3604 or P. alcaligenes 493. P. lilacinus KIA caused a greater reduction in galling and nematode multiplication followed by P. chlamydosporia KIA, P. putida 3604 and P. alcaligenes 493. Combined use of P. lilacinus KIA with Rhizobium was better in reducing galling and nematode multiplication than any other treatment. P. putida 3604 caused a greater colonization of root than P. alcaligenes 493 while P. lilacinus KIA was isolated from more nematodes than P. chlamydosporia KIA.     

Effect of concomitant application of Pseudomonas fluorescens and Purpureocillium lilacinum in carrot fields infested with Meloidogyne hapla

Root-knot nematode, Meloidogyne hapla remains a major limiting factor to obtain the estimated yield and quality of carrots in many countries. Effective use of nematode antagonistic bio-agents is a potentially important component of the eco-friendly agro-farming. The effect of seed treatment (ST) with liquid Pseudomonas fluorescens at 100 ml/kg seeds and soil drenching (SD) with Purpureocillium lilacinum at 5 l/ha, singly and jointly, was studied to minimise the damage caused by M. hapla in carrot plants under field conditions. The concomitant application of P. fluorescens ST + P. lilacinum SD reduced 70% of second stage juvenile (J2) population in soil, 71% of female population in root and 74% of egg numbers in roots. The carrot plants from P. fluorescens ST + P. lilacinum SD plots were 36% taller with 39% more leafs and 30% longer leaves than untreated plants. The yield was also 29% higher in concomitant application. There was no significant difference in the root colonisation of P. fluorescens and P. lilacinum in solo and combined treatments. It concludes that the concomitant application of P. fluorescens ST and P. lilacinum SD is more effective to suppress M. hapla infection and enhance the yield of carrot.     

Effects of crop plants on abundance of Pochonia chlamydosporia and other fungal parasites of root‐knot and potato cyst nematodes

The effects of a host plant on reproduction/abundance of fungal populations in relation to soil nutrients released by plants in the rhizosphere were studied. Abundance in the soil and potato rhizosphere of the fungi Paecilomyces lilacinus, Monographella cucumerina (CABI 380408) and Pochonia chlamydosporia var. chlamydosporia (Pc280, potato cyst nematode biotype) and P. chlamydosporia var. catenulata (Pc392, root‐knot nematode biotype) were assessed. The different ability of break crops (oilseed rape, sugarbeet and wheat) in the potato rotation to support Pa. lilacinus, Pochonia isolates Pc280 and Pc392 and abundance of the latter two isolates in soil and rhizosphere of potato plants infected with Meloidogyne incognita were also studied. Potato chits and crop seedlings were planted into boiling tubes containing 5000 chlamydospores or conidia g^?1 in acid washed sand (pH 6) and kept in a growth chamber at 20°C, and 16 h of light for up to 9 weeks. The abundance of the fungi in sand (fallow) differed significantly between fungal species, being in general less abundant in the absence than in the presence of the plant, although there was no interaction between plant species and fungal isolate. There was evidence of a different response to Me. incognita for Pc392 than for Pc280 but there was no significant effect of the presence of the nematode on the rate of increase of the fungus.     

关防风根腐病拮抗细菌筛选与鉴定

【背景】由木贼镰刀菌[Fusarium equiseti(Corda)Sacc.]引起的关防风根腐病,是近年来导致关防风产量及质量下降的主要土传病害之一。生物防治因其对环境安全及人畜无害等优势,成为目前植物病害防治的一种有效手段。【目的】挖掘关防风根际土壤中对木贼镰刀菌具有良好拮抗作用的生防菌株。【方法】采用稀释平板法分离根际土壤细菌;用滤纸片法和牛津杯法对拮抗细菌进行筛选和抑菌谱检测;用抗生素标记法标记拮抗细菌并测定其定殖能力;通过盆栽实验研究其对关防风根腐病的防效;通过形态学、生理生化特征及16S rRNA基因序列确定分类学地位。【结果】从健康关防风根际土壤中分离纯化了157株细菌,筛选获得对关防风根腐病菌具有显著抑菌作用的拮抗细菌SC-119,无菌滤液的抑菌率可达68.53%,而且兼具广谱抑菌能力和良好的定殖能力;盆栽实验表明,菌株SC-119对关防风根腐病的防治效果达到67.39%,其相对防效较接种哈茨木霉菌剂、枯草芽胞杆菌菌剂和代森锰锌分别提高了29.03%、32.26%和16.13%;对菌株SC-119进行分类学鉴定,确定其为萎缩芽胞杆菌(Bacillus atrophae...     

Effect of combination of bio-agents and mineral nutrients for the management of alfalfa wilt pathogen Fusarium oxysporum f. sp. medicaginis

Abstract

Biological and nutrient management of soil borne disease is increasingly gaining stature as a possible practical and safe approach. Inhibitory effects of fungal and bacterial antagonists were tested under in vitro conditions against the wilt pathogen of alfalfa Fusarium oxysporum f. sp. medicaginis. Trichoderma harzianum and Pseudomonas fluorescens (PI 5) were found to be effective against the alfalfa wilt pathogen. Manganese sulphate at 500 and 750 ppm inhibited the mycelial growth of F. oxysporumf. sp. medicaginis under in vitro conditions. In pot culture studies, manganese sulphate at 12.5 mg/kg reduced the wilt incidence (23.33%). Combined application of manganese sulphate 12.5 mg/kg + T. harzianum 1.25 mg/kg of soil significantly reduced the wilt incidence accompanied by improved plant growth and yield in pot culture. The mixture of manganese sulphate (25 kg/ha) + T. harzianum (2.5 kg/ha) significantly reduced the wilt incidence when applied as a basal dose in the field conditions. The average mean of disease reduction was 62.42% over control.     

Greenhouse Studies on the Effect of Marigolds (Tagetes spp.) on Four Meloidogyne Species

The effects of preplanted marigold on tomato root galling and multiplication of Meloidogyne incognita, M. javanica, M. arenaria, and M. hapla were studied. Marigold cultivars of Tagetes patula, T. erecta, T. signata, and a Tagetes hybrid all reduced galling and numbers of second-stage juveniles in subsequent tomato compared to the tomato-tomato control. All four Meloidogyne spp. reproduced on T. signata ''Tangerine Gem''. Several cultivars of T. patula and T. erecta suppressed galling and reproduction of Meloidogyne spp. on tomato to levels lower than or comparable to a fallow control. Phytotoxic effects of marigold on tomato were not observed. Several of the tested marigold cultivars are ready for full-scale field evaluation against Meloidogyne spp.     

The Potential of Five Winter-grown Crops to Reduce Root-knot Nematode Damage and Increase Yield of Tomato

Broccoli (Brassica oleracea), carrot (Daucus carota), marigold (Tagetes patula), nematode-resistant tomato (Solanum lycopersicum), and strawberry (Fragaria ananassa) were grown for three years during the winter in a root-knot nematode (Meloidogyne incognita) infested field in Southern California. Each year in the spring, the tops of all crops were shredded and incorporated in the soil. Amendment with poultry litter was included as a sub-treatment. The soil was then covered with clear plastic for six weeks and M. incognita-susceptible tomato was grown during the summer season. Plastic tarping raised the average soil temperature at 13 cm depth by 7°C.The different winter-grown crops or the poultry litter did not affect M. incognita soil population levels. However, root galling on summer tomato was reduced by 36%, and tomato yields increased by 19% after incorporating broccoli compared to the fallow control. This crop also produced the highest amount of biomass of the five winter-grown crops. Over the three-year trial period, poultry litter increased tomato yields, but did not affect root galling caused by M. incognita. We conclude that cultivation followed by soil incorporation of broccoli reduced M. incognita damage to tomato. This effect is possibly due to delaying or preventing a portion of the nematodes to reach the host roots. We also observed that M. incognita populations did not increase under a host crop during the cool season when soil temperatures remained low (< 18°C).     

Efficacy of dried seed powder of some plant species as soil amendment against Meloidogyne incognita (Tylenchida: Meloidogynidae) on tomato

The nematicidal activity of dried ground seeds of Ammi majus, Matricaria chamomilla, Ricinus communis, Brassica alba, B. oleracea, Peganum harmala, Solanum nigrum, Raphanus sativus and Eucalyptus sp. was assessed against the root-knot nematode, Meloidogyne incognita, infecting tomato in a glasshouse. The powdered seeds of the tested plants were incorporated into the soil at the rate of 5 g/kg and their nematicidal activity was compared with that of the synthetic nematicide carbofuran at the rate of 0.01 g a.i./kg. The effects of the treatments on the growth of tomato were also examined. The populations of M. incognita in the soil and root galling of tomato were significantly suppressed by the powdered seeds of all the plant species tested, with the greatest reduction occurring in soil amended with M. chamomilla, followed by soil treated with powdered seeds of A. majus, S. nigrum, R. communis and Eucalyptus sp. The efficacy of B. oleracea, B. alba, M. chamomilla and R. communis in reducing the number of J₂ in the soil was similar to that of carbofuran. All amendments, except powdered seeds of M. chamomilla and A. majus significantly increased shoot length compared to the untreated inoculated plants. Shoot weight was significantly increased in soil amended with powdered seeds of B. oleracea, B. alba, R. communis, P. harmala and S. nigrum, but not in soil amended with the other seed powders when compared with untreated inoculated soil. Significant increases in root length occurred in pots amended with seed powder of B. alba, R. communis and Eucalyptus and in root weight for P. harmala. None of the tested dried seeds was phytotoxic to tomato plants at the applied rate.     

Some isolates of the nematophagous fungus Pochonia chlamydosporia promote root growth and reduce flowering time of tomato

The fungal parasite of nematode eggs Pochonia chlamydosporia is also a root endophyte known to promote growth of some plants. In this study, we analysed the effect of nine P. chlamydosporia isolates from worldwide origin on tomato growth. Experiments were performed at different scales (Petri dish, growth chamber and greenhouse conditions) and developmental stages (seedlings, plantlets and plants). Seven P. chlamydosporia isolates significantly (P < 0.05) increased the number of secondary roots and six of those increased total weight of tomato seedlings. Six P. chlamydosporia isolates also increased root weight of tomato plantlets. Root colonisation varied between different isolates of this fungus. Again P. chlamydosporia significantly increased root growth of tomato plants under greenhouse conditions and reduced flowering and fruiting times (up to 5 and 12 days, respectively) versus uninoculated tomato plants. P. chlamydosporia increased mature fruit weight in tomato plants. The basis of the mechanisms for growth, flowering and yield promotion in tomato by the fungus are unknown. However, we found that P. chlamydosporia can produce Indole‐3‐acetic acid and solubilise mineral phosphate. These results suggest that plant hormones or nutrient ability could play an important role. Our results put forward the agronomic importance of P. chlamydosporia as biocontrol agent of plant parasitic nematodes with tomato growth promoting capabilities.     

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.     

Pathogenicity of root-knot nematode,Meloidogyne incognita on Lens culinaris (Medik.)

Effects of the root-knot nematode (Meloidogyne incognita) on lentil (Lens culinaris) were studied under greenhouse conditions. The plants were inoculated with 250, 500, 1000, 2000 and 4000 J₂ per plant. Plant growth, yield, nodulation, seed weight, chlorophyll, nitrogen, phosphorus and potassium, (NPK) contents, as compared to control, were found decreased in all the nematode infected plants. The extent of reduction increased with an increase in inoculum levels. The reductions were significant at 500 J₂ and at higher inoculum levels, i.e. 1000, 2000 and 4000 J₂ per pot over the control. An increase in inoculum level caused enhancement in galling, egg mass production and nematode population. At higher inoculum levels, the population of the nematode in the root as well as in the soil increased to a greater magnitude than at lower inoculum levels. On the contrary, reproduction factor (RF) and rate of population increase (RPI) decreased with increasing inoculum levels.     

Consequences of variation in species diversity in a community of root-feeding herbivores for nematode dynamics and host plant biomass

To date, no study has explicitly addressed effects of variation in species diversity of root‐feeding herbivores on host plant biomass. Root‐feeding nematodes typically occur in multi‐species communities. In a three‐year field experiment, we investigated how variation in species diversity of root‐feeding nematodes affected nematode dynamics and response of the dune grass Ammophila arenaria to root‐feeder activity. This plant species needs regular burial by fresh beach sand to remain vigorous, suggesting that A. arenaria benefits from a temporary escape from root‐feeding soil organisms and that root‐feeders are involved in plant degeneration in stabilized dunes. We created series of ceased and continued sand burial and added the endoparasitic nematodes Meloidogyne maritima, Heterodera arenaria and Pratylenchus penetrans alone or in combination to A. arenaria. We included treatments with and without the whole soil community, measured plant biomass and quantified numbers of nematodes. Addition of H. arenaria and P. penetrans decreased numbers of M. maritima juveniles and delayed the first appearance in time of both juveniles and females, while numbers of males only decreased when plants had been buried. Burial with sand and addition of the other two endoparasites affected numbers of H. arenaria juveniles, while numbers of P. penetrans were low and not affected. Shoot biomass of A. arenaria was lower when M. maritima had been added alone than when the three species had been added together. Addition of root zone soil decreased biomass of all plant parts. Burial with sand decreased aboveground shoot biomass, whereas it increased belowground shoot and root biomass. Our results point at idiosyncratic effects of nematode diversity on A. arenaria biomass. Heterodera arenaria and P. penetrans protected their host by reducing numbers and delaying activity of M. maritima to a later stage in the growth season, when root‐feeding activity was less harmful for plant biomass development.     

Effects of Cropping Sequences on Population Densities of Meloidogyne hapla and Carrot Yield in Organic Soil

The influence of various cropping sequences on population densities of Meloidogyne hapla and carrot yield was studied in organic soil under microplot-and field conditions. Spinach, radish, barley, oat, and wheat were poor or nonhosts for M. hapla. Population densities of M. hapla were maintained or increased on cabbage, celery, lettuce, leek, marigold, and potato. Marketable percent-age and root weight of carrots were greater following spinach, oat, radish, and fallow-onion than those following two crops of onion or carrot in microplots. Under field conditions, the carrot-onion-oat-carrot cropping sequence decreased M. hapla population densities and provided a 282% increase in marketable yield of carrot compared to a carrot monoculture. Two consecutive years of onion increased M. hapla population densities causing severe root galling and a 50% yield loss in the following crop of carrot. Based on root-gall indices, carrots could be grown economically for 2 years following radish, spinach, and oat, but not following onion and carrot without the use of nematicides.     

Evaluation of Argemone mexicana for Control of Root-Infecting Fungi in Tomato

Argemone mexicana L. (Papaveraceae), a tropical annual weed, is known to be phytotoxic to many crop species. This study was designed to examine the possible impact of A. mexicana on root‐infecting fungi, changes in fungal community structure and the growth of tomato. A. mexicana decaying shoots in soil provided a marked decrease in the infectivity of Fusarium solani and Rhizoctonia solani but Macrophomina phaseolina remained unaffected. Plant height and shoot growth of tomato plants increased markedly though high concentration of A. mexicana (5% w/w) was deleterious to tomato plants. General species diversity of soil fungal communities increased in the amended soils over the controls and greater increase in diversity occurred at higher concentrations of decaying A. mexicana. Likewise, equitability and richness components of diversity increased in treatments compared to controls but declined with increasing sampling period. Aspergillus nidulans, Cephaliophora irregularis, Drechslera halodes, Paecilomyces lilacinus and Trichoderma viride were isolated exclusively from the amended soils. Aqueous extract of A. mexicana when applied in soil greatly suppressed all three of the above root‐infecting fungi, and at lower concentration actually enhanced plant growth. The influence of different levels of N‐fertilization with NH₄NO₃ on the modification of the effect of decaying A. mexicana on root‐infecting fungi was also investigated. N‐fertilization to some extent alleviated the phytotoxicity to tomato plants while suppressing the root‐infecting fungi. A. mexicana in conjunction with Pseudomonas aeruginosa, a plant growth‐promoting rhizobacterium, significantly suppressed root‐infecting fungi with concomitant increase in plant growth. Whereas P. aeruginosa was reisolated from the rhizosphere and inner root tissues of tomato, its population slightly declined in the amended soil but not to an extent that could reduce the biocontrol and growth promoting potential of the bacterium.