Anaerobic soil disinfestation (ASD), a biological alternative to soil fumigation, has been shown to control a wide range of soil-borne pathogens and nematodes in numerous crop production systems ...across Japan, The Netherlands and the US. A brief review of the status to the science behind ASD and its application for commercial settings is discussed for each country. Future work needs to focus on how to optimize the technique (in terms of carbon source used, temperature and degree of anaerobiosis attained) to control specific sets of pathogens, and to better which mechanism(s) are responsible for disease control in different situations. The role of observed microbial community shifts as a result of ASD in immediate disease control and long term disease suppression needs to be more fully explored. Further reductions in the costs of ASD compared to fumigant use will help increase adoption of the technique which is currently limited by cost and uncertainty about its effectiveness at controlling different pathogens across a range of environments.
Summary
Anaerobic soil disinfestation (ASD) is a cultural technique primarily targeted for control of soilborne plant pathogens, but can also impact weed propagules. A repeated pot study was ...conducted to evaluate ASD treatment impact on sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers using dry molasses‐based and wheat bran‐based amendment mixtures at four carbon‐to‐nitrogen (C:N) ratios (from 10:1 to 40:1) and compared with a non‐amended control. The mean percentage of sprouted tubers recovered after ASD treatment was lower for wheat bran‐based (42%) than dry molasses‐based (65%) amendments, and tuber production was 1.6‐fold higher in dry molasses‐based than wheat bran‐based treatments. The highest percentage of sprouted tubers (79%) and the highest mean production of large tubers (threefold higher than wheat bran‐based and 1.7‐fold higher than molasses‐based amendments) were observed for the non‐amended control. Tuber sprouting was significantly lower from all ASD treatments (regardless of amendment C:N ratio) compared with the non‐amended control at a 15 cm burial depth. New tuber production was lowest at C:N ratios of 10:1 and 20:1 and more than twofold higher in the non‐amended control. Wheat bran‐based amendments reduced above‐ground C. esculentus biomass compared with the non‐amended control and ASD treatments with molasses‐based amendments, and reduced below‐ground biomass compared with molasses‐based amendments. Above‐ground biomass was highest at amendment C:N ratio of 10:1, and below‐ground biomass was highest at amendment C:N ratio of 40:1 and the non‐amended control. ASD treatment with wheat bran‐based amendments at lower C:N ratios reduced tuber sprouting and reproduction compared with the non‐amended control, but not at rates high enough to use as a primary weed management tactic.
Copper bactericides are routinely used to control Xanthomonas perforans (XP), causal agent of bacterial spot of tomato. Given the widespread tolerance to copper in XP strains in FL, USA, ...nanotechnology-based elemental composites have gained interest for their potential applications in agriculture in part due to their enhanced antimicrobial properties and toxicity to copper-tolerant strains. However, little is known about the potential impact of conventional copper bactericides as well as nano-based elemental composites on soil microbial communities, as determined by high-throughput sequencing of the 16S rDNA. We compared the effects of 2 and 200 μg/mL of core-shell (CS), a metallic copper composite, and a conventional copper bactericide + mancozeb (Cu+Man) on the soil microbiome. These treatments were compared to three controls, the microbial profile of the soil prior to application of copper products, a water application, and spiking the soil with a soilborne phytobacterium, Ralstonia solanacearum (RS). The RS treatment was included to determine if downstream analysis could detect the artificial inoculation. Utilizing multiple β diversity measurements, each emphasizing various tenets of ecology, provided a greater perspective of the effects the treatments had on the microbiome. Analysis of HTS data revealed that the two treatments containing field applied rates of metallic copper, CS 200 and Cu+Man, had the largest impact on the soil microbiome at seven-days posttreatment compared to water. However, we simulated field applied rates of CS 200 entering the soil by treating soil with CS 2 and determined this concentration had a negligible effect on the soil microbiome.
Nanotechnology-based elemental composites have gained popularity for their potential applications in plant disease management due to their enhanced antimicrobial properties. However, little is known about their potential impact on the environment. Foliar applications of nano metallic composites upon leaching into the soil have the potential to impact soil microbial populations that in turn influence soil health. Utilizing multiple β diversity measurements, high-throughput sequencing analysis revealed that field applied rates of metallic copper (200 μg/mL) from an advanced copper composite (core-shell CS) and a conventional copper bactericide in combination with mancozeb had the largest impact on the soil microbiome compared to water and nontreated control. To simulate leaching from the leaf surface, a lower concentration (2 μg/mL) of CS was also applied to the soil and had a negligible effect on the soil microbiome. Thus, field applied rates of CS may have a minimal effect on soil microbial communities.
Anaerobic soil disinfestation (ASD, aka biological soil disinfestation) has been studied in multiple countries for the suppression of plant pathogenic fungi and bacteria. Recent work in the US has ...included studies on weed control and nematode management with this technique. Multiple mechanisms have been shown to play a role in the suppression of some studied plant pathogens, including the generation of organic acids by soil bacteria. Multiple field trials were conducted in the strawberry production region in Florida to compare this method with direct application of a novel combination of organic acids (referred to as ‘SPK’) applied through drip irrigation. Application of the organic acids consistently resulted in an increase in the native soil population of Trichoderma spp. The first year of ASD treatment resulted in a low level of cumulative redox potential and an increase in Trichoderma spp. However, in the second year, when there was a higher level of cumulative redox potential, an increase in culturable soil bacteria overwhelmed Trichoderma spp. colony isolation. Viability of introduced fungal plant pathogen inoculum was reduced in organic acid treatments when the water front carrying the acid came in direct contact with packets at the center of the bed, but not in areas with poor material movement. Introduced inoculum in the ASD-treated plots was significantly reduced compared to the untreated control regardless of packet placement.
Field trials were performed in Florida to evaluate tomato and pepper transplants amended with formulations of several plant growth-promoting rhizobacteria (PGPR) in a production system that included ...soil solarization. Transplants grown in five different formulations of PGPR were planted into plots treated by soil solarization, MeBr fumigation, or untreated soil. Treatments were assessed for incidence of several naturally occurring tomato and pepper pathogens including root-knot nematode (Meloidogyne incognita) and species of Pythium, Phytophthora, and Fusarium. Highly significant increases in tomato and pepper transplant growth occurred in response to most formulations of PGPR tested. Transplant vigor and survival in the field were improved by PGPR treatments in both tomato and pepper. Diseases of tomato caused by root-knot nematodes, Fusarium, Phytophthora, and Pythium were not affected by PGPR treatments. PGPR formulation LS261 reduced numbers of root-knot nematode galls on pepper while pepper root condition was improved with formulations LS213, LS256 and LS261. Individual PGPR strains affected the number of Pythium colonies isolated from pepper roots, but did not affect isolation of Pythium from tomato roots. Greater numbers of colonies of Pythium were isolated from pepper roots in the MeBr treatment and fewest in the solarization treatment. Numbers of colony forming units of Fusarium were significantly higher in the untreated soil than in MeBr fumigated or solarized soil with no effect of PGPR on isolation of Fusarium from either crop. Incidence of wilt symptoms on tomato was significantly lower in MeBr treated plots and highest in the untreated plots. Yield of extra large tomato fruit and total yield increased with PGPR formulation LS256. Yield of pepper was increased with formulations LS255 and LS256. Solarization combined with LS256 on pepper produced yields comparable to MeBr.
Anaerobic soil disinfestation (ASD; also termed biological soil disinfestation) is a non-chemical process which includes 1) soil incorporation of a labile carbon (C) source, 2) mulching with ...polyethylene film to limit gas exchange, and 3) drip irrigation to saturation of the topsoil or bedded area. A number of putative mechanisms have been proposed as contributing to control of pathogens, nematodes, and weeds during ASD treatment, although not all have been well-characterized. Mechanisms include formation of organic acids and volatile compounds during anaerobic decomposition of the added C source, biocontrol by microorganisms favored by ASD treatment, and changes in soil chemical constituents under anaerobic conditions. In Tennessee, USA, growth chamber, greenhouse, and field studies have been conducted to evaluate and optimize the ASD procedure for regional production systems and to evaluate pest, soil, and crop responses resulting from differing C source rates and properties. A growth chamber study conducted using soil temperatures typical to spring soil disinfestation treatment in this region (15 to 24°C), suggests that C amendment rates less than 1 mg C g-1 soil for ASD treatment do not consistently decrease viability of Sclerotinia sclerotiorum sclerotia or decrease incidence of endemic Fusarium root rot of common bean compared to an unamended control. Variability in measures of accumulated anaerobic soil conditions and an observed soil pH increase in ASD-treated soils are also indicative of ineffective ASD treatment at low amendment rates. Other preliminary work suggests that amendment rates may need to be as high as 4 mg C g-1 soil for effective soil disinfestation at moderate soil temperatures. Studies to determine optimal amendment rates and properties for consistent ASD treatment at moderate soil temperatures are ongoing.
The perceived risk of pest resurgence upon transition from conventional to organic-based farming systems remains a critical obstacle to expanding organic vegetable production, particularly where ...chemical fumigants have provided soilborne pest and disease control. Microplots were used to study the effects of soil amendments and cropping sequences applied over a 2-year transitional period from conventional to organic tomato (Solanum lycopersicum) cultivation on the incidence of bacterial wilt caused by Ralstonia solanacearum, purple nutsedge (Cyperus rotundus) reproduction, root galling by Meloidogyne incognita, and soil nematode populations. A continuation of tomato monoculture during the transitional period resulted in a disease incidence of 33%, as compared with 9% in microplots that were rotated with sunn hemp (Crotalaria juncea) and Japanese millet (Echinochloa crusgalli var. frumentacea). The benefits of disease control from a crop rotation extended into to a second season of organic tomato cultivation season, where bacterial wilt declined from 40% in microplots with a tomato monoculture to 17% in plots with a crop rotation sequence. Combining applications of urban plant debris with a continued tomato monoculture increased the incidence of bacterial wilt to 60%. During the transition period, tomato plants following a cover crop regime also had significantly lower levels of root galling from root-knot nematode infection compared with plants in the continuous tomato monoculture. Nutsedge tuber production was significantly increased in plots amended with broiler litter but not urban plant debris. Compared with a continuous monoculture, the results illustrate the importance of a systems-based approach to implementing transitional organic practices that is cognizant of their interactive effects on resident soilborne disease, weed, and pest complexes.
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