Title: Carbon source-dependent volatile production and ASD efficacy for suppression of apple root pathogens and parasites Authors
|Hewavitharana, S. -|
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2014
Publication Date: N/A
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 is 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. Disease control is believed to result from the production of certain volatiles that are generated by microorganisms that are active under anaerobic conditions. Results from this study demonstrate that the effectiveness of ASD in the control of soil-borne pathogens will be determined, in part, by the type of carbon amendment that is used in application of the ASD process. Different carbon inputs resulted in production of a battery of different volatiles that were emitted from ASD treated soils. These volatiles were identified and shown to vary in the ability to suppress growth of fungal plant pathogens and cause mortality of plant parasitic nematodes that contribute to apple replant disease. An understanding of which carbon inputs will produce anti-fungal or nematicidal volatiles ASD will enable development of an optimized ASD system for the control of apple replant disease.
Technical Abstract: Anaerobic soil disinfestation (ASD) has been shown to be effective in the control of a wide range of soil-borne plant pathogens but has not been examined as a means for disease control in perennial fruit crops such as apple. Since ASD has demonstrated a broad spectrum of biological activity, it may be well suited as an alternative to current fumigation-based control of apple replant disease (ARD) which is caused by a diverse pathogen complex. The efficacy of ASD for control of ARD was evaluated in growth chamber experiments using soils from two orchard sites having a history of the disease. Suppression of Pratylenchus penetrans apple root densities was dependent upon carbon source utilized during the ASD process. Numbers of lesion nematodes recovered from apple roots were significantly lower in ASD soils amended with rice bran (RB), grass residues (GR), ethanol (ET), or Brassica juncea seed meal (SM) compared to the no amendment control and ASD soils amended with composted steer manure. Volatiles emitted during the anaerobic phase of the ASD process from soils treated with ethanol, grass residues, or SM effectively retarded growth of Rhizoctonia solani AG-5, Pythium ultimum and Fusarium oxysporum. Each carbon amendment generated a unique volatile profile during ASD as resolved through gas chromatography and mass spectrometry analysis. Allyl isothiocyanate (AITC) and dimethyl trisulfide (DMTS) were emitted from B. juncea SM treated soils whereas the latter and 2-ethyl-1-hexanol were detected in the grass residue treatment. Decanal, dimethyl trisulfide, and allyl isothiocyanate retarded in vitro growth of R. solani AG-5, P. ultimum and F. oxysporum. Nonanal was inhibitory toward only P. ultimum and R. solani AG-5, whereas 2-ethyl-1-hexanol only suppressed P. ultimum. AITC and DMTS caused significantly higher mortality of P. penetrans compared to other tested volatiles. These findings demonstrate that carbon source-dependent volatile chemistries produced during ASD suppress certain components of the apple replant disease pathogen complex.