Title: Promotion of growth and control of damping-off (Rhizoctonia solani) of greenhouse tomatoes amended with vermicompost
Abstract: The pathogen Rhizoctonia solani (teleomorph Tanatephorus cucumeris) can affect tomatoes germination and emergence and cause basal rot of seedlings. It is generally accepted that composts suppress plant diseases, improve soil nutrient availability and stimulate plant growth. However, no reports have been found on the simultaneous evaluation of vermicompost as plant growth promoter and suppressive to damping-off caused by R. solani on tomatoes. This research evaluated the suppressive effects of different concentrations of vermicompost against R. solani and the ability of vermicompost to promote tomato seedlings growth. The microbial composition of the substratum was explored. Thirty six microorganisms were isolated, 13 of which were antagonic to R. solani in vitro. The addition of 25 to 100% of vermicompost promoted seedlings growth and prevented damping-off caused by R. solani. Additional key words: antagonism, bacteria, biological control, disease incidence, fungi Tomatoes (Lycopersicon esculentum Mill.) are propagated by seeds. Six-week seedlings with 4 expanded leaves are transplanted into soil. This crop is susceptible to damping-off caused by Rhizoctonia solani Kuhn [teleomorph Tanatephorus cucumeris (Frank) Donk] (8). This fungus can affect seed germination or seedling emergence and cause basal rot of seedlings. If it is not prevented, the disease causes economic losses due to plant death, soil infestation with pathogens and delays in crop producFaculty of Agronomy. University of Buenos Aires, Av. San Martin 4453 (1417). Buenos Aires. Argentina. ACorresponding author: Marta C. Rivera, Catedra de Fitopatologia. Facultad de Agronomia. Universidad de Buenos Aires. Av. San Martin 4453 (1417). Buenos Aires. Argentina. Tel (005411)4524-8063; fax (005411)4514-8737/39 e-mail address: [email protected] Thanks are due to Mario Cuniolo, who provided the vermicompost and Dr. Laura Gasoni (IMYZA-INTA) from whom we obtained the isolate of R. solani Received 12.II.2004: accepted 18.III.2004 230 Rivera MC, et al, 2004 tion. The usual tools for the management of this pathogen include soil chemical disinfection or sterilization and seed treatments. Chemicals registered for the control of soilborne plant pathogens are toxic to humans and are environmental contaminants. Among these, methyl bromide was defined under The Montreal Protocol of 1991 as a chemical that contributes to depletion of the Earth’s ozone layer. Accordingly, its manufacture and importation will be phased out completely in 2005 in developed countries and in 2015 in developing countries (26). In a search for alternatives to soil chemical treatments, biological control may be a useful tool (5). Composts have the potential to control plant diseases biologically (11), as one of their beneficial propeties is the microbiologically induced suppression of soilborne pathogens (2, 6, 9, 10, 16, 27). Another important charactheristic is their role in increasing soil nutrient availability and in plant growth stimulation (4, 12, 13). Vermicomposts, that are produced through the action of earthworms on organic matter, also have a great potential as plant growing media (3). Their physical and chemical properties have been described (1, 19). Their biological properties include suppression of soilborne pathogens (23, 24). No reports were found on the simultaneous evaluation of vermicompost as plant growth promoter and suppressive to damping-off caused by R. solani in nurseries of tomato. In Argentina, one vermicompost’s ability to control damping-off caused by R. solani was confirmed on autumn squash (28), white pumpkin (22) and eggplant (21). The aims of this work were to evaluate the suppressive effect of different concentrations of vermicompost on tomato seedlings growth and health. The microbial composition of the substratum was explored. MATHERIALS & METHODS Inocula. Isolate R81 (R. solani AG-4) was mantained on 2% potato dextrose agar (PDA). To test its pathogenicity, it was inoculated by sowing tomato cv. UC 82 B (Neuman Seed Co., 92% germination) in soil artificially infested with the pathogen. Plants were kept in humidity chambers at 22 + 2 °C, under 12-h periods of fluorescent light. The pathogen was reisolated from symptomathic seedlings by superficial disinfection with 2% NaOCl and plating on PDA. Inocula for the pathogenicity test and for the bioassay was obtained by growing on PDA and multiplied on sterilized oat (Avena sativa L.) grains. The concentration of pathogen in the soil was estimated by the method of Ko & Hora (15), as number of colony forming units per gram of soil (cfu/g). For each of 5 replicates, 50 beet (Beta vulgaris L.) glomerules were distributed on the surface of 32 g of soil and covered with an additional 32 g of soil, in 10 cm O Petri dishes. Beet glomerules act as baits for the R. solani propagules. After 48 h incu231 Tomatoes growth and health by vermicompost bation at 26 °C, beet glomerules were recovered, washed for 5 min in tap water and placed in Petri dishes containing PDA pH: 4. After other 24 h incubation at 26 °C, Petri plates were scanned under a dissecting microscope (40 x). The number of glomerules colonized by R. solani were counted. Substrates. A one year old vermicompost produced from cow and horse manure and button mushroom [Agaricus bisporus Lange (Imbach)] crop substrate, was used. Treatments were 100 to 0% of mineral soil artificially infested with R. solani R81 with the amendment of 0 to 100% of vermicompost (by volume), respectively; 100% sterilized and 100% non sterilized soil. Compost and soil chemical properties are summarized in Table 1. The assay was designed in completely randomized blocks, with 7 replicates. Autoclavated soil was inoculated with grains colonized by R. solani (0.1% volume) and incubated in humidity chambers at 21-24 °C in darkness per ten days. After filling plastic trays (15 × 11 × 7 cm) with substrate mixtures, they were kept at 25 °C, in humidity chambers, for 10 days before and 10 days after sowing. Fifty tomato seeds were sown per tray. Disease evaluations were done 11, 14 and 39 days after sowing. Seedlings with damping-off or incipient crown rot, as well as those that did no emerge as expected from the germination control, were considered to be diseased. Data on seedling fresh and dry weight were obtained using Sartorius scales (precision: 0.1 mg). Statistical analysis. An analysis of variance (α: 5%) was used to compare means. A test described by Di Rienzo et al. (7) was employed as a multiple comparison procedure. The numbers of healthy seedlings were analysed following a repeated measures model. The assumption of sphericity of the covariance matrix was tested by the Maucly sphericity test. Univariate analysis was used when the interaction treatment-observation data were significant (7). Isolation of compost fungi and bacteria. Samples of vermicompost (3.5 cc) placed in Erlenmeyer flasks containing 250 ml of destilled sterile water were shaked in a shaker at 70 r.p.m. per 1 h. Dilutions of 0.5 ml of 10-1, 10-2, 10-3, 10-4 and 10-5 were incubated on plates with 10 ml of PDA, amended with 100 ppm streptomycin sulfate and nutrient Table 1.– Vermicompost and soil chemical properties
Publication Year: 2005
Publication Date: 2005-01-01
Language: en
Type: article
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