|HEWAVITHARANA, SHASHIKA - Washington State University|
Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/12/2015
Publication Date: 11/8/2015
Citation: Mazzola, M., Hewavitharana, S.S. 2015. Anerobic soil disinfestation efficacy associated with altered soil microbiome and metabolome. International Conference on Methyl Bromide Alternatives and Emissions Reductions. p. 13.1-3.
Technical Abstract: Anaerobic soil disinfestation (ASD) has demonstrated potential to control numerous soil-borne pathogens in a diversity of production systems. A variety of environmental, biological and application attributes have potential to determine the overall capacity of ASD to provide effective disease control. In apple, Rhizoctonia solani AG-5 and Pratylenchus penetrans not only contribute to the phenomenon termed apple replant disease, but also rapidly recolonize fumigated soil systems leading to reduced overall fruit production in established orchards. The current study sought to examine the effect of ASD carbon(C) source input type on control of these two pathogens and to examine the specific attributes of the system that may determine the relative efficacy achieved. Different C inputs used in the ASD process yielded differential effects on resulting soil chemistry and control of root disease incited by R. solani AG-5 and P. penetrans. Among five C substrates evaluated, ASD failed to yield effective control of root infection by R. solani AG-5 only when compost was utilized as the C input. Orchard grass utilized as the ASD substrate provided the highest level of disease control based upon overall growth of apple seedlings and the amount of R. solani AG-5 detected in seedling roots. Similarly, ASD conducted using compost was less effective than ASD conducted with all other carbon sources in suppressing apple root populations of P. penetrans in multiple orchard soils. ASD conducted with ethanol, Brassica juncea seed meal, orchard grass (Dactylis glomerata) or rice bran provided similar levels of nematode suppression. Subsequent C source input rate studies indicated that orchard grass applied at 20 t ha-1 provided optimal level of control for both of the targeted root pathogens. Relative efficacy of ASD conducted with different carbon inputs was associated with differences in both composition and quantity of volatiles produced during ASD, as well as the resulting conformation of the soil microbiome. When exposed to total volatile composition produced, only the ASD-compost system failed to reduce hyphal growth of R. solani AG-5 or cause mortality of P. penetrans. Among ASD systems, the one that employed compost as the carbon input yielded the fewest volatiles with demonstrated lowest inhibitory activity against R. solani AG-5 and P. penetrans. Any biologically active volatiles detected in the ASD-compost system were typically at levels that were lower than those recorded when ASD was conducted with other carbon inputs. Active chemistries detected during ASD treated soils included 2- ethyl-1-hexanol, nonanal, decanal, dimethyl disulfide, dimethyl trisulfide and allyl isothiocyanate, among others. The ASD-compost and ASD-orchard grass systems were used to conduct a comparative analysis of ASD outcomes on the soil microbiome resulting from effective and ineffective disease control systems. The goal of these studies was to identify biological components that may have a functional role in the overall disease control achieved in response to ASD, as well as define potential bio-indicators which may be used in the future to predict ASD disease control efficacy. Pasteurized and non-pasteurized soil was artificially infested with R. solani AG-5 and subsequently ASD was conducted using orchard grass or compost as the carbon input. No significant interaction between soil pasteurization status and ASD C input was observed relative to the quantity of R. solani AG-5 DNA detected in soil post-treatment. The quantity of R. solani AG-5 DNA detected in ASD-grass treatment was significantly lower than the ASD-compost or control treatments. ASD-grass but not ASD-compost significantly improved apple seedling growth irrespective of soil pasteurization status. Terminal restriction fragment length polymorphism (T-RFLP) analysis was utilized at