2002 · 34 citations · 6 references
AgricultureAgronomySoil SciencesPlant Disease ManagementSoil FertilitySoil ManagementComposting SystemsPlant Growth-promoting MicroorganismsPlant-pathogenic FungiRhizosphere InteractionsSoft Rot DiseasesSoil PathogensDamping-off DiseaseDisease SuppressivenessPlant Root DiseasesPythium Damping-offPythium Root RotSoil-borne Disease SuppressionSoil-borne Pathogen SuppressionVermicomposting
Vermicomposts are stabilized, non-thermophilic materials produced from organic wastes by interactions between earthworms and microorganisms. Suppression of Pythium by vermicomposts was tested by substituting 0, 10, 20 and 40% of vermicomposts (by volume) into 100, 90, 80 and 60% of a soil-less plant growth medium Metro Mix 360 (MM360), inoculated with Pythium at a rate of 1:4000 by volume. Disease severity was rated after 10 days, from 1 (symptomless) to 4 (heavy). The disease severity rating was 3.4 in 0% vermicompost substitution, compared with 1.1 in 10% substitution, 1.3 in 20% substitution, and 1.1 in 40% substitution. A similar range of substitutions of sterilized or non-sterilized MM360 and vermicompost was tested in three experiments with radish seeds inoculated with 1:2000 or 1:667 by volume of Rhizoctonia. Suppression of Rhizoctonia by vermicomposts was correlated progressively with increasing rates of substitution of vermicompost in three experiments. In field experiments planted with strawberries, the incidence of Verticillium wilt was suppressed significantly by the application of 5 t/ha and 10t/ha of commercial paper and food waste vermicomposts. INTRODUCTION The biological degradation and stabilization of organic wastes by earthworms and microorganisms is termed vermicomposting, and vermicomposts are excellent plant growth media or soil amendments (Edwards, 1998). Suppression of various soil-borne diseases by traditional thermophilic composts has been reported (Chung, et al., 1988). Certain types of composted pine bark suppressed Pythium damping-off diseases when incorporated into planting mixes (Boehm, et al., 1993). Only a few studies have investigated the suppression of soil-borne plant pathogens by vermicomposts (Szczech, et al., 1993), or disease suppression in the presence of earthworms (Stephens & Davoren, 1997; Stephens, et al., 1994). Disease suppression by composts has been attributed to the activities of competitive or antagonistic microorganisms. The main objective of our experiments was to determine the potential of vermicomposts to suppress the incidence of the plant diseases Pythium and Rhizoctonia in cucumbers and radishes in the laboratory, and Verticillium in strawberries in the field. MATERIALS AND METHODS Suppression of Pythium damping off in cucumber plants by substitution of vermicomposts into a greenhouse soil-less bedding plant medium (MM360) Pythium ultimum inocula were prepared by infesting an autoclaved (1h, 121 oC) light peat mix with Pythium. The potting mixtures were prepared by substituting 0, 10, 20 and 40% food waste vermicompost (Oregon Soil Corporation, Oregon City, OR) into a soil-less growth medium Metro Mix 360 (MM360) (Scotts Co., Marysville, OH), with half of all treatments sterilized by autoclaving. All treatments were inoculated with 0.5 g/litre (1:4000 dilution) Pythium inoculum. For all treatments, involving 0, 10, 20 and 40% vermicompost substituted into sterilized or unsterilized media, eight cucumber seeds were planted in each of 5 replicate, 15-cm diameter pots. The seedlings were kept in a growth chamber at 20 oC with 16-hour illumination, and watered daily. Ten days after germination, they were harvested and rated for disease severity, according to the following scale: 1, symptomless; 2, emerged but wilted; 3, post-emergent damping-off; and 4, pre-emergent damping-off. Completely randomized designs were used, and one way ANOVA was used with Minitab statistical software (Minitab Inc., State College, PA). Separations of means were based on the least significant differences (P<0.05). Suppression of Rhizoctonia root rot in radish seedlings by substitution of vermicomposts into a greenhouse soil-less bedding plant medium (MM360) Rhizoctonia solani inocula, prepared using the following method: 500 ml soil and 50 g finelychopped potatoes, in 35 ml water, were placed in a 500 ml flask. The mixtures were autoclaved twice over 2 days, for 1 hour. After cooling, the soil/potato mixture was inoculated with agar plugs of Rhizoctonia and incubated for 2 weeks. It was dried overnight at room temperature and sieved through 2-mm and 1-mm sieves; the inoculum collected in between the 2-mm and 1-mm sieves was saved and the rest discarded. The potting media were prepared by substituting 0, 10, 20 and 40% of either autoclaved or unsterilized cow manure-based vermicompost into sterilized or unsterilized MM360. All treatments, except the controls, were inoculated with 0.5 g/litre (1:2000 dilution) Rhizoctonia inoculum, and 35 g of slow release fertilizer (14-14-14) was added per 2.2 litre of planting medium. For all treatments, 32 radish seeds were planted in each of 5 replicate, 10-cm diameter pots. The seedlings were kept in a growth chamber at 25C under continuous light. After 7 days, the seedlings were harvested and rated for disease severity, according to the following scale: 1, symptomless; 2, small lesion on the stem; 3, large lesion on the stem; 4, post-emergent damping-off; and 5, pre-emergent damping-off. Incidence of pre-emergent damping off was calculated by subtracting the numbers of seedlings that emerged from the numbers that emerged in the non-inoculated controls (both sterilized and unsterilized MM360). Completely randomized designs were used, and one way ANOVA was performed using SAS software (SAS Institute, Cary, NC). Separations of means were based on least significant differences (P<0.05). In a second experiment, the same procedure was used, except that the concentrations of vermicompost used were: an uninoculated control, and 0, 20, 40, 60, 80 and 100% substitutions of vermicompost, which was not sterilized, into equivalent amounts of either sterilized or unsterilized MM360. For a third trial, the concentration of the inoculum added was increased to 1.5 g/litre (1:667 dilution), and the inoculum was incubated for 3 weeks. The vermicompost substitutions used in a third trial were 0, 10, 20, 40 and 70% of unsterilized cattle-based vermicompost substituted into 100, 90, 80 60 and 30% of unsterilized MM360. Suppression of Verticillium wilt in strawberry plants in vermicompost-amended field soils Six-week old strawberry seedlings var. ‘Chandler’ were grown in soils under high plastic tunnel hoop house structures measuring 9.14 x 14.6 x 3.6 m. Twenty-four plants were transplanted into each bed with 38 cm between plants with three rows spaced 38 cm between rows. Food and paper waste vermicomposts were surface-applied at 5.0 and 10.0 t/ha. Plastic mulch and drip irrigation systems were set-up over the raised beds after vermicompost and fertilizer applications. Disease severity was rated using the proportion of the total leaves and stems that showed Verticillium wilt symptoms. Treatments were replicated four times in a completely randomized design and differences between means were separated using least significant differences (P<0.05). RESULTS Suppression of Pythium damping off in cucumber plants by substitution of vermicomposts into a greenhouse soil-less bedding plant medium (MM360) Substitution of equal amounts of unsterilized vermicompost into sterilized MM360 increased Pythium suppression in cucumber seedlings significantly at all substitution rates (Figure 1). Substitution of sterilized vermicompost into sterilized MM360 also increased Pythium suppression in cucumber seedlings significantly, but to a lesser degree, and only at 20% and 40% substitutions. 1.0 1.5 2.0 2.5 3.0 3.5 4.0 SMM SMM + 10% SVC SMM + 20% SVC SMM + 40% SVC SMM + 10% VC SMM + 20% VC SMM + 40% VC D is ea se S up pr es si on R at in g a ab b b
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Michael J. Boehm, L. V. Madden, H. A. J. Hoitink · Applied and Environmental Microbiology · 1993 · 147 citations · Full text