Imran Ali Siddiqui

Suppression of the root rot–root knot disease complex by Pseudomonas aeruginosa in tomato: The influence of inoculum density, nematode populations, moisture and other plant-associated bacteria

The influence of different application rates of the plant growth-promoting rhizobacterium, Pseudomonas aeruginosa, population densities of the root-knot nematode, Meloidogyne javanica, moisture and other plant-associated bacteria in the suppression of root rot–root knot disease complex of tomato are described. The impact of these factors on bacterial rhizosphere and inner root and shoot establishment are also presented. The highest inoculum level of P. aeruginosa (7.4 × 108 cfu ml−1) in the presence of the lowest population density of M. javanica (500 J2/plant) caused the greatest reduction in gall formation due to M. javanica. The number of root–knot nematodes recovered from soil and roots treated with P. aeruginosa were also significantly reduced. Root infection caused by the soilborne root-infecting fungi Fusarium oxysporum, F. solani and Rhizoctonia solani was also effectively suppressed following application of P. aeruginosa. A P. aeruginosa-Bacillus subtilis treatment was the most effective in the suppression of root-rot disease complex with enhancement of plant growth. Biocontrol and growth promoting potential of the bacterium was enhanced when soil was kept at 50% or 75% moisture holding capacity, whereas a 25% MHC reduced bacterial efficacy. Rhizosphere population of P. aeruginosa declined drastically in P. aeruginosa-Bradyrhizobium japonicum treatments. Rhizosphere colonisation by P. aeruginosa seems to be governed by two factors: Initial inoculum size of the bacterium and severity of the root-knot disease. Endoroot and endoshoot colonisation of the bacterium was dependent on degree of root-colonisation by Fusarium oxysporum. An inoculum level 2.5 × 108 cfu/ml of P. aeruginosa was optimal for the enhancement of plant growth, whereas inoculum below this level reduced plant growth.

Trichoderma harzianum enhances the production of nematicidal compounds in vitro and improves biocontrol of Meloidogyne javanica by Pseudomonas fluorescens in tomato

Aims:  To determine the influence of soil‐borne fungus Trichoderma harzianum on the biocontrol performance of Pseudomonas fluorescens strain CHA0 and its 2,4‐diacetylphloroglucinol (DAPG) overproducing derivative CHA0/pME3424 against Meloidogyne javanica.

Improvement of Pseudomonas fluorescens CHA0 biocontrol activity against root-knot nematode by the addition of ammonium molybdate.

Aims: To improve the efficacy of Pseudomonas fluorescens CHA0 and its genetically modified (GM) derivatives by adding ammonium molybdate to control Meloidogyne javanica, the root‐knot nematode in mungbean.

The influence of mineral and carbon sources on biological control of charcoal rot fungus, Macrophomina phaseolina by fluorescent pseudomonads in tomato

Aims: To determine the influence of various trace minerals and carbon source on the biocontrol performance of Pseudomonas aeruginosa strain IE‐6S+ and P. fluorescens strain CHA0 against Macrophomina phaseolina.

Differential impact of some Aspergillus species on Meloidogyne javanica biocontrol by Pseudomonas fluorescens strain CHA0

Aims:  The aim was to determine the influence of some Aspergillus species on the production of nematicidal agent(s) in vitro and biocontrol of Meloidogyne javanica in tomato by Pseudomonas fluorescens strains CHA0 and CHA0/pME3424.

Liquid culture carbon, nitrogen and inorganic phosphate source regulate nematicidal activity by fluorescent pseudomonads in vitro

Aims:  The aim of the present investigation was to determine the influence of nutrients on the nematicidal activity by Pseudomonas aeruginosa strain IE‐6S+ and Ps. fluorescens strain CHA0 in vitro.

Non-pathogenic Fusarium solani represses the biosynthesis of nematicidal compounds in vitro and reduces the biocontrol of Meloidogyne javanica by Pseudomonas fluorescens in tomato.

Aims: The aim of the present investigation was to determine the influence of various Fusarium solani strains on the production of nematicidal agent(s) in vitro and biocontrol of Meloidogyne javanica in tomato by Pseudomonas fluorescens strains CHA0 and CHA0/pME3424.

Nematicidal and allelopathic responses of Lantana camara root extract

The impact of root leachates of Lantana camara L., a tropical weed, against Meloidogyne javanica, the root-knot nematode, was tested under laboratory and pot conditions. Concentrated and diluted root leachate caused substantial mortality of M. javanica juveniles. Significant suppression of the nematode was achieved when soil was treated with a full-strength concentration of the leachate. Whilst this high concentration retarded plant height and shoot fresh weight, more diluted concentrations actually enhanced plant growth. To establish whether this inhibition of plant growth from the leachate was the result of depleted nitrogen levels in the soil due to the leachate, soil treated with such leachates was given urea as an additional nitrogen source. Urea not only enhanced nematode suppression activity of the root leachates but also increased seedling emergence and growth of mungbean. Application of the L. camara root leachates in combination with Pseudomonas aeruginosa, a plant growth-promoting rhizobacterium, significantly reduced nematode population densities in roots and subsequent root-knot infection, and enhanced plant growth. While a high concentration of root leachate slightly reduced P. aeruginosa colonization in the rhizosphere and inner root tissues, the nematicidal efficacy of the bacterium was unaffected. The root leachate of L. camara was found to contain phenolic compounds, including p-hydroxybenzoic acid, vanillic acid, caffeic acid, ferulic acid and a quercetin glycoside, 7-glucoside. It also contained weak enzymic hydrogen cyanide.

Survival of Pseudomonas aeruginosa in various carriers for the inhibition of root rot-root knot disease complex of mungbean

The survival of Pseudomonas aeruginosa strain 78 was tested on mungbean seeds coated with a variety of substrates/carriers and was found best on talc amended with carboxymethyl cellulose or on gum arabic. Albizia saman- and Cordia myxa-gum gave poor survival. On all substrates the antagonist populations declined dramatically at 120 days after coating. In the repeating experiments, a seed coating with talc-based inoculum of the antagonist caused marked reduction in nematode population densities in the soil and roots and also reduced subsequent root-knot development due to Meloidogyne javanica, the root-knot nematode. However, the incidence of the rootinfecting fungi Macrophomina phaseolina and Rhizoctonia solani did not differ significantly from the controls. Strain 78 significantly promoted growth with increased Bradyrhizobium-nodules in mungbean.

Avicennia marina (mangrove) soil amendment changes the fungal community in the rhizosphere and root tissue of mungbean and contributes to control of root-knot nematodes

The effect of soil amendment with Avicennia marina (mangrove) on mungbean growth and mungbean infestation with Meloidogyne javanica was determined in greenhouse pot experiments. Galling and final nematode population densities were reduced by all soil amendments with mangrove. To better understand whether nematode suppression by A. marina was caused directly by the release of nematicidal factor(s) into the soil, or was due indirectly to changes in the fungal community, the diversity of the rhizosphere populations of culturable fungi was assessed before organic amendment (day 0), after decomposition but before seed sowing (day 15) and at harvest (day 73). Thirteen out of 20 fungal species were isolated from both A. marina-amended and unamended soils, the most frequent genera being Alternaria, Aspergillus, Fusarium, Penicillium, Trichoderma, Mucor, Myrothecium and Rhizoctonia. The other seven were found only in amended soils. At different times in the course of the experiment amended and unamended soils differed significantly in the fungi isolated from the rhizosphere and/or in the concentrations of A. marina. Trichoderma viride was isolated only from surface-sterilized mungbean roots grown in amended soils, whereas Chaetomium sp. was isolated only from unamended soils.