1a. Objectives (from AD-416):
Anaerobic soil disinfestation (ASD) has demonstrated significant potential as an alternative to methyl bromide (MeBr) for the control of soilborne pathogens and nematodes. This project seeks to validate the efficacy of ASD as a MeBr alternative alone or when integrated with mustard seed meal (MSM) for control of significant soilborne diseases in two CUN cropping systems; pre-plant soil use for strawberry and tree fruit nursery production systems. These ASD systems can be utilized in urbanized areas where buffer restrictions limit the applicability of alternative fumigants and, unlike many other biologically-based alternatives, have a broad-spectrum of activity, impacting most pests that are currently controlled by MeBr:chloropicrin combinations. We have obtained consistently effective suppression of Verticillium dahliae in soils with ASD and achieved yields within 76-100% of MeBr and 95-120% of other chemical fumigants in California strawberry systems. Pre-plant application of MSM formulations has provided fumigant levels of soilborne disease control in apple production systems. Although efficacy has been demonstrated, adoption of these methods for disease control in these cropping systems requires optimization from a nitrogen management and economic perspective. Our goals are to fine tune the protocol to optimize and demonstrate efficacy and economic feasibility of ASD alone or when integrated with MSM for soilborne disease control in commercial scale field trials, garner a comprehensive understanding of the biological and chemical modes of action operative in MSM and ASD-induced pathogen suppression, and effectively disseminate this information through a variety of formats including production of webinars and an “ASD Manual for Strawberries”. Specific objectives are; 1) to fine-tune type and rate of carbon sources and N management for anaerobic soil disinfestation (ASD) in strawberry systems; 2) to demonstrate ASD in commercial scale trials and evaluate its effectiveness and economic feasibility in strawberries; 3) to examine integration of ASD and mustard seed meal (MSM) for control of soil-borne disease in apple nurseries as an alternative to methyl bromide fumigation 4) to determine whether changes in soil microbial composition are responsible for soil-borne disease suppression detected in response to ASD, and MSM; and 5) to disseminate ASD to California strawberry growers via workshop, field days, eXtension, and by publishing “ASD Manual for Strawberries".
1b. Approach (from AD-416):
1. Greenhouse studies will be conducted to evaluate different organic inputs at various rates to assess the optimal input in the application of anerobic soil disinfestation from both a resource utilization and disease control standpoint. Disease development will be monitored using culture based and molecular-based methods. 2. Based upon the results of the greenhouse trials, field experiments will be designed and implemented at three strawberry field locations in California. Disease development, growth and yield will be assessed. 3. Brassicaceae seed meal (BSM) and anerobic soil disinfestation (ASD)have demonstrated potential to control the diversity of pathogens that incite replant diseases in nursery and orchard settings. However, integration of these methods may enable a more cost effective disease control alternative with improved disease control efficacy. Controlled environment experiments will be conducted to determine minimum substrate application rates that yield effective disease control. In addition, the effect of application sequence of the two substrates on disease control and tree growth will be determined. Based upon these trials, the treatment yielding optimal disease control will be evaluated in field trials conducted at two nursery sites in Washington State. 4. To assess the role of soil biology in the suppressive activity of ASD and BSM treatments, these same studies will be conducted in pasteurized soil systems. The relative level of disease control attained in the natural and pasteurized soil systems should yield important information regarding the contribution of soil suppressiveness to the ASD/BSM induced disease control. Repeated measures of soil physical parameters of temperature, Eh and pH are taken to track physical changes that occur during the course of treatment especially with ASD. Volatile compounds produced during the incubation period will be examined using GC/MS analysis. Should data indicate a role for soil biology in the suppression of an introduced isolate of Phytophthora cactorum, Terminal Restriction Fragment Length Polymorphism (TRFLP) analysis will be utilized to examine the dynamics of soil biology in response to treatments. Should resulting T-RFLP profiles (bacterial or fungal)indicate a relationship between changes in population structure and disease suppression, pyrosequencing will be carried out to more clearly identify the changes in soil microbial populations in those treatment(s) that most efficiently yield a disease suppressive state. 5. We will disseminate results using a combination of site visits, electronic team meetings, on-farm and Research and Education Center field days, grower meetings, on-farm demonstrations, distribution of newsletters and research briefs, maintenance of an interactive project website, and a workshop series. The project website will be linked to key grower visited websites in each state. In year 3, a grower guide to ASD will be created and distributed through our workshops and local networks. These efforts will be targeted at growers, cooperative extension personnel,private pest control advisors,industry representatives and relevant state and federal agencies.
3. Progress Report:
This project relates to objective 1 of the associated in-house project, which seeks to determine the relative contribution of chemistry and soil biology to the control of soil borne diseases that is realized through soil incorporation of mustard (Brassica juncea) plant residues. Anaerobic soil disinfestation (ASD) has been studied as a potential broad spectrum soil-borne disease management practice. The effect of carbon (C) source on efficacy of ASD toward suppression of apple root rot caused by Rhizoctonia solani AG-5 was examined. Grass clippings (GR), rice bran (RB), ethanol (ET), composted steer manure (CSM) and Brassica juncea seed meal (SM) were used as the carbon inputs in the application of ASD in controlled environment studies using pasteurized and non-pasteurized apple orchard soils. There was an interaction between soil pasteurization and different ASD carbon sources in terms of resulting R. solani AG-5 root infection. In general, Rhizoctonia root infection was significantly higher in pasteurized soil than non-pasteurized soil, and all ASD treatments, except that using CSM as the carbon input, had less root infection compared to the no amendment control. Among the different ASD treatments, apple seedling weight was significantly greater for the GR and SM treatments relative to all other treatments irrespective of pasteurization. Application of ASD using GR and SM carbon inputs resulted in significantly higher shoot length compared to all other treatments. Realtime quantitative PCR analysis indicated that all ASD treatments, regardless of amendment type, significantly reduced R. solani AG-5 DNA abundance compared to the no amendment control. ASD conducted with GR or ET resulted in the greatest reduction in pathogen inoculum density and were significantly different from all other treatments. The pasteurized control had the highest quantity of R. solani AG-5 DNA. Analysis of fungal community composition by generating T-RFLP profiles of soil fungal DNA extracted immediately after ASD revealed that the communities in both pasteurized and non-pasteurized GR treatments were relatively similar compared to the fungal community detected in soils in which ASD was conducted with CSM as the carbon input or the no amendment control soil. Pasteurized and non-pasteurized no amendment control and CSM treatments possessed a similar soil fungal community profile. These results suggest that there is potential for GR based ASD treatment to recruit a fungal community that is resilient over the anaerobic phase of soil incubation, which may contribute to the suppression of R. solani AG-5 and enhanced growth of apple. Studies were conducted to determine optimal grass residue input rates in the conduct of ASD for the control of apple root pathogens. Orchard grass residues were utilized as the carbon input in ASD at a rate of 5 t ha-1 (5GR), 10 t ha-1 (10GR), or 20 t ha-1 (20GR) and the resulting effect on root infection by R. solani AG 5, population density of Pratylenchus penetrans and apple seedling growth was determined. All ASD treatments effectively and uniformly controlled R. solani apple root infection regardless of grass residue input rate. In contrast, the 20GR treatment provided control of P. penetrans that was statistically comparable to soil pasteurization and was superior to ASD conducted with the two lower rates of GR. In addition, ASD conducted with the 20GR input rate did not diminish populations of free living nematodes relative to that detected in the control treatments indicating that ecosystem function may not be demonstrably impaired in response to this treatment. These studies demonstrated a potential for using grass residues as a C input for the conduct of anaerobic soil disinfestation to control apple replant disease pathogens and parasites.