Carbon source-dependent efficacy of anaerobic soil disinfestation (ASD) in suppression of Rhizoctonia root rot of apple

Abstract

Rhizoctonia solani AG-5 is a significant component of the pathogen complex that incites apple replant disease (ARD). A non-fumigant alternative, such as anaerobic soil disinfestation (ASD), is highly desired for control of ARD. We examined the influence of carbon input as a determinant of ASD efficacy in the suppression of apple root infection by R. solani AG-5. Pasteurized (P) and non-pasteurized (NP) R. solani infested orchard soil was amended with rice bran (RB), Brassica juncea seed meal (SM), ethanol (ET), steer manure (M) or grass clippings (GR). Pots were inundated to field capacity, bagged, incubated for two weeks, aerated and then planted with five 9 weeks old ‘Gala’ seedlings per pot. After 5 wks, plants were harvested, and biomass and R. solani root infection were determined. To examine activity of ASD-generated volatiles against R. solani, pure cultures of the pathogen were placed on the surface of similarly amended NP soil and incubated in sealed bags during the anaerobic phase. Among treatments, GR and SM yielded the highest seedling weights and, with the exception of M, all treatments significantly reduced root infection compared to the no treatment control. Disease was higher in P than NP soil. Volatiles from all C amended ASD soils significantly retarded colony growth compared to control, but volatile composition differed.