Assessment of beneficial microorganisms: Trichoderma, Actinomycetes, and Bacillus in anaerobic soil disinfestation (ASD)

View the project final report

• 2014 annual report

Commodities

• Vegetables: tomatoes

Practices

• Pest Management: biological control, integrated pest management
• Soil Management: soil microbiology

Studies on anaerobic soil disinfestation (ASD), a non-chemical alternative to soil fumigants for controlling many soilborne diseases, have shown that it enhances populations of beneficial microorganisms against plant pathogens, including increased presence of the biocontrol agent Trichodermaas sclerotial parasites of Sclerotium rolfsii. However, studies on ASD effectiveness paired with beneficial mycoparasites and commercial biofungicide applications are lacking. This study compared the effect of ASD and incorporation of antagonists separately or in combination, at the initiation of ASD treatment, against the sclerotial germination and parasitism. The effect of ASD amendment on soil populations of endophytic isolates of Trichoderma,actinomycetes, and Bacillus spp. were also assessed. The anaerobic condition was also determined during ASD treatment in growth chamber studies. The root nodules of cowpea and plant biomass (cowpea and tomato) after ASD treatment were also recorded in greenhouse study. In contrast to the negative effect of ASD on sclerotial population, we observed positive or no effect on the population of beneficial microorganisms. Further, ASD enhanced the mycoparasitic and bacterial colonization of sclerotia;however, ASD followed by addition of antagonists did not increase sclerotial mortality or parasitism of sclerotia.

Introduction

Anaerobic soil disinfestation (ASD) or biological soil disinfestation is a practical and relevant soil treatment to replace chemical fumigant pesticides to control soil borne pathogens. It is also applicable to places where other environmentally friendly approaches, such as flooding, solarization, and biofumigation techniques, are not effective or economically feasible. ASD uses locally available organic materials as a carbon source and can improve soil quality, increase populations of beneficial soil microorganisms, in addition to numerous other agronomic and environmental benefits. In ASD, the carbon source from organic amendments increases microbial activity leading to consumption of available soil oxygen; microbial populations shift to those adapted to oxygen-limited environments and release various compounds along with organic acids, e.g. butyric acid and acetic acid that significantly contribute to the soil disinfestation process (Momma et al., 2006).

Anaerobic condition that result from ASD mainly increases the number of anaerobic bacteria of clostridia groups (Mowlick et al., 2012), while there is some research on effect of ASD on bacterial communities, studies on ASD impact on beneficial fungal populations are lacking. It is important to find effective ASD treatment methods to control plant pathogens without effecting the population of beneficial soil organisms. Hence, the SARE-funded graduate research project based at The University of Tennessee examined the ASD treatment effect on the soil beneficial microbial organisms such as Trichoderma, Actinomycetes, Bacillus and root colonizers (Rhizobia) and investigated combined effect of ASD and microbial biocontrols at the initiation of ASD treatment on germination and parasitism of sclerotia of Sclerotium rolfsii.

1. Examine the efficacy of incorporation of endophytic Trichoderma and two commercially available biofungicides Trichoderma harzianum (RootShield®) and Streptomyces riseoviridis (Mycostop®) in ASD treatment against sclerotial germination and parasitism.
2. Evaluate the effect of ASD amendment on populations of Trichoderma, actinomycetes Bacillus and nodulation by Rhizobia
3. Compare yield of plant biomass among ASD, biocontrols, and ASD in combination with biocontrols.