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Differences in microbial activity and microbial populations of peat associated with suppression of damping-off disease caused by Pythium sylvaticum.

ABSTRACT: The microbiological characteristics associated with disease-suppressive peats are unclear. We used a bioassay for Pythium sylvaticum-induced damping-off of cress seedlings to identify conducive and suppressive peats. Microbial activity in unconditioned peats was negatively correlated with the counts of P. sylvaticum at the end of the bioassay. Denaturing gradient gel electrophoresis (DGGE) profiling and clone library analyses of small-subunit rRNA gene sequences from two suppressive and two conducive peats differed in the bacterial profiles generated and the diversity of sequence populations. There were also significant differences between bacterial sequence populations from suppressive and conducive peats. The frequencies of a number of microbial groups, including the Rhizobium-Agrobacterium group (specifically sequences similar to those for the genera Ochrobactrum and Zoogloea) and the Acidobacteria, increased specifically in the suppressive peats, although no single bacterial group was associated with disease suppression. Fungal DGGE profiles varied little over the course of the bioassay; however, two bands associated specifically with suppressive samples were detected. Sequences from these bands corresponded to Basidiomycete yeast genera. Although the DGGE profiles were similar, fungal sequence diversity also increased during the bioassay. Sequences highly similar to those of Cryptococcus increased in relative abundance during the bioassay, particularly in the suppressive samples. This study highlights the importance of using complementary approaches to molecular profiling of complex populations and provides the first report that basidiomycetous yeasts may be associated with the suppression of Pythium-induced diseases in peats.

SUBMITTER: Hunter PJ

PROVIDER: S-EPMC1610304 | biostudies-literature | 2006 Oct

REPOSITORIES: biostudies-literature

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Differences in microbial activity and microbial populations of peat associated with suppression of damping-off disease caused by Pythium sylvaticum.

Hunter Paul J PJ Petch Geoff M GM Calvo-Bado Leo A LA Pettitt Tim R TR Parsons Nick R NR Morgan J Alun W JA Whipps John M JM

Applied and environmental microbiology 20061001 10

The microbiological characteristics associated with disease-suppressive peats are unclear. We used a bioassay for Pythium sylvaticum-induced damping-off of cress seedlings to identify conducive and suppressive peats. Microbial activity in unconditioned peats was negatively correlated with the counts of P. sylvaticum at the end of the bioassay. Denaturing gradient gel electrophoresis (DGGE) profiling and clone library analyses of small-subunit rRNA gene sequences from two suppressive and two cond ...[more]

PMID: 17021192

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Project description:Pythium myriotylum is a notorious soil-borne oomycete that causes post-emergence damping-off in chili pepper. Of various disease management strategies, utilization of plant growth promoting rhizobacteria (PGPR) in disease suppression and plant growth promotion is an interesting strategy. The present study was performed to isolate and characterize PGPR indigenous to the chili rhizosphere in Pakistan, and to test the potential to suppress the damping-off and plant growth promotion in chili. Out of a total of 28 antagonists, eight bacterial isolates (4a2, JHL-8, JHL-12, 1C2, RH-24, 1D, 5C, and RH-87) significantly suppressed the colony growth of P. myriotylum in a dual culture experiment. All the tested bacterial isolates were characterized for biochemical attributes, and 16S rRNA sequence based phylogenetic analysis identified these isolates as Flavobacterium spp., Bacillus megaterium, Pseudomonas putida, Bacillus cereus, and Pseudomonas libanensis. All the tested bacterial isolates showed positive test results for ammonia production, starch hydrolase (except 4a2), and hydrogen cyanide production (except 4a2 and 1D). All the tested antagonists produced indole-3-acetic acid (13.4-39.0 μg mL-1), solubilized inorganic phosphate (75-103 μg mL-1), and produced siderophores (17.1-23.7%) in vitro. All the tested bacterial isolates showed varying levels of susceptibility and resistance response against different antibiotics and all these bacterial isolates were found to be non-pathogenic to chili seeds and notably enhanced percentage seed germination, plumule, redical length, and vigor index over un-inoculated control. Additionally, under pathogen pressure, bacterization increased the defense related enzymes such as Peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activates. Moreover, the treatment of chili seeds with these bacterial isolates significantly suppressed the damping-off caused by P. myriotylum and improved PGP traits compared to the control. In addition, a positive correlation was noticed between shoot, root length, and dry shoot and root weight, and there was a negative correlation between dry shoot, root weight, and seedling percentage mortality. These results showed that native PGPR possesses multiple traits beneficial to the chili plants and can be used to develop eco-friendly and effective seed treatment formulation as an alternative to synthetic chemical fungicides.

Project description:BackgroundVolatilomes from natural plants and microbes imparts diverse antifungal properties to suppress the growth of plant pathogens and therefore can be a suitable alternative of chemical fungicides. The present experiment was to study effect of volatiles produced by natural plants and microbes on the fungal growth of Pythium aphanidermatum, which is a tomato seedling pathogen.ResultsIsolate of P. aphanidermatum, causing damping off in tomato were isolated and incubated at 25 ± 2 °C. The isolate was tested for the anti-oomycetes activities of volatiles in vitro. The volatiles produced by the leaves of Mentha spicata and Cymbopogon citratus showed the maximum inhibitory effect of 45.56 and 24.70 percent, respectively on the mycelial growth of P. aphanidermatum, whereas, the pathogen was not inhibited on exposure to the volatiles of macro-basidiomycetes fungi. The volatiles of T. asperellum showed the maximum inhibitory effect of 69.26 percent against P. aphanidermatum. The study also included the identification of Volatile Organic Compounds (VOCs) involved in the suppression of pathogens by Headspace Gas Chromatography Mass Spectrometry (HS GCMS). The results revealed the production of carvone by the leaves of M. spicata; citronellol and geraniol by C. citratus; isopentyl alcohol and limonene by T. asperellum with increased peak area percentage and these compounds possessed antifungal properties. The vaporous action of isopentyl alcohol completely suppressed the mycelial growth of P. aphanidermatum, which is highly correlated to the T. asperellum extract on pathogenic growth. While the compounds, carvone, and citronellol showed the maximum inhibitory effect of 89.02 and 85.49 percent, respectively when used at 500 ppm and also altered the sporulation behavior of P. aphanidermatum.ConclusionResults showed that volatiles of M. spicata and T. asperellum have anti-oomycetes action on pathogenic growth leading to a distortion of sporulation of P. aphanidermatum. High antifungal properties make VOCs suitable for incorporation as a new integrated plant disease management programs.

Dataset Information

Differences in microbial activity and microbial populations of peat associated with suppression of damping-off disease caused by Pythium sylvaticum.

Publications

Differences in microbial activity and microbial populations of peat associated with suppression of damping-off disease caused by Pythium sylvaticum.

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