|HEWAVITHARANA, SHASHIKA - Washington State University|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2016
Publication Date: 5/4/2016
Citation: Hewavitharana, S.S., Mazzola, M. 2016. Carbon source-dependent effects of anaerobic soil disinfestation on soil microbiome and suppression of rhizoctonia solani AG-5 and pratylenchus penetrans. Phytopathology. doi: 10.1094/PHYTO-12-15-0329-R.
Interpretive Summary: Soil-borne disease management without chemical fumigants remains a major challenge in tree fruit production systems when planting orchards on sites previously planted to the same or closely related crop species. In apple, the disease problem has been termed apple replant disease and it caused by a diverse group of fungal plant pathogens acting in concert with the parasitic lesion nematode. Modifications to existing regulations are likely to intensify this challenge by further limiting availability of fumigants, increasing the cost of application, and limiting total orchard use due to buffer zone restrictions. Anaerobic soil disinfestation (ASD) was developed in Japan and the Netherlands as an alternative to soil fumigation and involves the generation of an anaerobic environment through a combination of flooding and addition of a carbon source to the soil system. Results from this study demonstrate that the effectiveness of ASD in the control of fungal and nematode pathogens of apple will be determined, in part, by the type of carbon amendment that is used in application of the ASD process. Previous studies demonstrated that different carbon inputs resulted in production of different fungicidal and nematicidal compounds. This study demonstrated that there was an association between changes in composition of the soil microbial community in response to different carbon inputs, and the efficacy of ASD in controlling plant parasitic nematodes and fungal plant pathogens. Use of grass, but not compost, as the ASD carbon input dramatically changed the soil microbial community. Similarly, ASD conducted with grass, but not compost, provided effect disease control. ASD with grass significantly reduced diversity of the soil fungal and bacterial communities, but specific groups know to function in suppression of plant pathogens were amplified. These data indicated that enhanced “biodiversity” was not instrumental in achieving system resistance and/or pathogen suppression.
Technical Abstract: The effect of carbon source on efficacy of anaerobic soil disinfestation (ASD) toward suppression of apple root infection by Rhizoctonia solani AG-5 and Pratylenchus penetrans was examined. Orchard grass (GR), rice bran (RB), ethanol (ET), composted steer manure (CM) and Brassica juncea seed meal (SM) were used as ASD carbon inputs, with plant assays conducted in natural and pasteurized orchard soils. Subsequent studies investigated differential rates of the effective carbon input GR for use in ASD for control of these pathogens. In general, apple root infection by R. solani AG-5 was significantly lower in ET, GR, RB and SM-ASD treatments compared to the control. Among different ASD treatments, apple seedling growth was significantly greater when GR or SM was used as the carbon input relative to all other ASD treatments. Rhizoctonia solani AG-5 DNA abundance was significantly reduced in all ASD treatments, regardless of amendment type compared to the control. In independent experiments ASD conducted with grass was consistently superior to ASD-CM for limiting pathogen activity in soils. ASD treatment with a grass input rate of 20 t ha-1 provided superior suppression of P. penetrans but grass application rate did not affect ASD efficacy in control of R. solani AG-5. The soil microbiome from ASD-GR treated soils was clearly distinct from the control and ASD-CM treated soils. In contrast the microbiome from control and ASD-CM treated soils could not be differentiated. Comparative results from pasteurized and non-pasteurized soils suggest that there is potential for GR based ASD treatment to recruit microbial elements that persist over the anaerobic phase of soil incubation, which may functionally contribute to disease suppression. When ASD was conducted with GR, microbial diversity was markedly reduced relative to the control or ASD-CM or control soil suggesting that this parameter, typically associated with system resilience, was not associated with ASD-induced soil suppressiveness.