Location: Citrus and Other Subtropical Products Research
2020 Annual Report
Objectives
1. Identify natural products and crop production systems that contribute to management of soilborne diseases, weeds, and nematodes.
1a. Develop combinations of commercially-available allylisothiocyanates (AITC) with organic amendments and other crop protection tools to improve weed, disease, and nematode control.
1b. Develop strategies to eliminate obstacles to the use of dimethyl disulfide.
2. Optimize application of anaerobic soil disinfestation (ASD) for application in vegetable and ornamental production.
2.a. Determine minimal input requirements and optimize organic amendments for effective application of ASD.
2.b. Increase environmental benefit of ASD through incorporation of reclaimed water.
3. Identify rootstocks for use with grafted vegetables with resistance or tolerance to pathogens and root-knot nematodes.
3a. Characterize rootstocks and associated microbiome for resistance or tolerance to soilborne pathogens of importance in the Southeastern U.S.
3b. Determine nutritional requirements and capacity of grafted plants to mitigate abiotic stress related to water quality.
Approach
The loss of methyl bromide for soil fumigation, limited registration of new chemical fumigants, and increased regulation of existing chemical fumigants has caused significant changes to crop production practices, including the registration and utilization of biofumigants and non-fumigant systems. Newly registered compounds, used alone or in combination, do not provide the same level of pest control resulting from the use of methyl bromide. Recognizing that some of the currently-registered chemical fumigants may, in the future, follow the same path as methyl bromide, the emphasis of the current research project will be to enhance the efficacy and understand the mechanisms of biologically and culturally-based management strategies for pathogens, weeds, and nematodes impacting vegetable and ornamental crops. Efficacy of management components will be examined individually and in combinations to achieve improved control of pathogens previously managed through soil fumigation using methyl bromide and to mitigate abiotic stress. Although some tactics have shown significant efficacy against individual pests or problems, integrated systems that address pest complexes are limited. It is critical that broad-spectrum pest control is achieved and approaches are compatible with the USDA, ARS mission to sustain a competitive agricultural economy by addressing pests that impact crop production as well as improving the health of the agro-ecosystem. Developed strategies will be built upon to gain a better understanding of pest biology, plant nutrition, pathogen and non-pathogen microbial interactions, and the impacts of pest control practices on the development of disease, weed, and nematode suppressive soil. Laboratory, greenhouse, and field experiments will be conducted independently, and in cooperation with ARS and University researchers, and through agreements with industry to broaden the scope of the research. Continued engagement with grower and industry partners will ensure effective transfer of technology which will include more efficient and environmentally compatible crop production systems that minimize health risks to workers and bystanders, and reduce inputs and environmental pollution from pesticides and fertilizers.
Progress Report
ARS researchers at Ft. Pierce, Florida, completed second year field trials for the evaluation of allylisothiocyanate (AITC) in cut flowers for multiple species. AITC was applied alone or in combination with herbicide active ingredients dithiopyr, oxyfluorfen with isoxaben, or a formulation containing trifluralin, isoxaben, and oxyfluorfen. Significantly fewer weeds emerged when AITC was applied with an herbicide partner. No phytotoxicity was observed in sunflower, however stunting and poor growth of snapdragon again resulted from treatments that included the application of the formulation of trifluralin, isoxaben, and oxyfluorfen.
ARS researchers at Ft. Pierce, Florida, completed first year field trials on the impact of totally-impermeable film selection on the efficacy of anaerobic soil disinfestation to control yellow and purple nutsedge and strawberry crop productivity. First year carbon replacement trials were completed and most effective pathogen control was achieved with a standard rate of pelleted poultry litter combined with liquid molasses as the carbon source. Potential for nitrogen release, either as a nitrous oxide or through leaching potential, was impacted by carbon source selection.
The first small plot field trial combining oak biochar for odor mitigation of dimethyl disulfide was completed. Application of biochar had a significant impact on the detection of dimethyl disulfide through the plastic at the soil surface. The odor mitigation did not detrimentally impact nematode mortality levels, but poor weed control occurred in all treatments.
ARS researchers at Ft. Pierce, Florida, completed an assessment of resistance to root-knot nematodes of 18 tomato rootstock accessions and eight cucurbit rootstock accessions. Commercial field trials were completed on the use of ‘heirloom’ tomato scions grafted onto rootstocks containing the Mi gene as well as variable resistance to Fusarium oxysporum f.sp. lycopersici races. Two field locations were identified in which resistance to root-knot nematode was broken. One experiment was conducted to determine if the incidence of foliar disease could contribute to resistance breaking but the results were not conclusive due to the variability of disease in the field. One controlled growth chamber experiment was completed in which field collected single and multiple species of Meloidogyne were inoculated alone or co-inoculated at multiple temperature regimes. Temperature did not impact resistance or susceptibility but mixed populations did have an impact on galling.
Accomplishments
1. Combining herbicides with allyl isothiocyanate for improved pest control. The loss of methyl bromide has left growers with few soil fumigant options, particularly for buffer zone areas in which standard fumigants cannot be applied due to potential for bystander exposure. A newly registered biofumigant in the United States with active ingredient allyl isothiocyanate (AITC), is currently under evaluation for use as a pre-plant soil treatment for both conventional and organic crop production. In recent field trials, the biofumigant provided root-knot nematode control equivalent to that achieved with methyl bromide, but had inadequate weed control. AITC treatments were applied by researchers at Ft. Pierce, Florida, with or without registered herbicides for tomato and bell pepper production. Application of the biofumigant resulted in lower incidence of bacterial wilt (Ralstonia solanacearum) of tomato and soil populations of root-knot nematodes (Meloidogyne spp.). There was no improvement in nutsedge control with soil treatments, but both herbicides (fomesafen and halosulfuron) were effective in reducing nutsedge germination. Combining AITC with an herbicide provided broad-spectrum control of pathogens and weeds. The active ingredient AITC has well established potential as a biofumigant and the availability of a commercial formulation that can be combined with labeled herbicides provides a greatly needed pest control option.
2. Improved tolerance to biotic and abiotic stress through vegetable grafting. Bell pepper is the second leading vegetable crop in Florida. The profitability of bell pepper has been endangered by the increasing incidence of Phytophthora capsici, an important soilborne plant-pathogen known for its destructive potential, especially in subtropical areas. While periods of high rainfall and raised water levels are considered major causes of P. capsici outbreaks, the incidence of the disease is also favored by salinity stress, a condition increasingly affecting the coastal areas of South Florida, where a significant amount of bell pepper production occurs. Vegetable grafting is a tool that has the potential to address these issues. ARS researchers at Ft. Pierce, Florida, conducted studies to evaluate plant growth, nutrient accumulation, yield, and stress response of different bell-pepper grafting combinations to P. capsici under increasing salinity conditions. Non-grafted and self-grafted plants of a susceptible pepper cultivar were compared with plants grafted onto resistant rootstocks. In infested soil, non-grafted and self-grafted susceptible plants showed consistently higher incidence of Phytophthora blight compared to those grafted onto resistant rootstocks. Moreover, plants grown under moderate salinity had a higher disease incidence. Irrigation with moderately saline water may increase the incidence of Phytophthora blight in susceptible cultivars of bell pepper, however, commercial rootstocks resistant to P. capsici will control the disease with no, moderate, or moderately-high salinity levels, providing pepper growers an important tool for mitigation of this disease.
3. Role of temperate and carbon input for anaerobic soil disinfestation is key for Fusarium control. Anaerobic soil disinfestation (ASD) involves incorporation of organic amendments to provide labile carbon (C) to stimulate microbial activity in moist soils mulched with polyethylene. ARS researchers at Ft. Pierce, Florida, conducted multiple studies to evaluate the effect of ASD amendment C:Nitrogen (N) ratio on survival of introduced inoculum of the important tomato pathogen, Fusarium oxysporum f. sp. lycopersici (Fol). Control of this pathogen by ASD has been variable based on region. A series of greenhouse and field studies were conducted in which total C and C:N ratios were varied and applied under different temperature regimes. At higher soil temperatures, all ASD treatments significantly suppressed Fol. In the field, all ASD treatments reduced survival of Fol compared and application of amendments at C rates of 4 mg C g-1 soil at a C:N ratio of 20:1 and 30:1 increased anaerobic soil conditions and resulted in higher mortality of Fol inoculum compared to a lower C rate (2 mg C g-1 soil). Soil temperatures of at least 25-35°C improved treatment efficacy, which could be achieved in areas with lower temperatures by combining ASD with soil solarization and by increasing carbon input.
4. Anaerobic soil disinfestation carbon input modifications for improved nutsedge control. Anaerobic soil disinfestation (ASD) applications have primarily targeted control of soilborne plant pathogens, but can also impact weed propagules. Nutsedges are a weed of principal concern in areas in which ASD is being adopted for annual crop production. ARS researchers at Ft. Pierce, Florida, conducted experiments 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 with increasing carbon quantities. Wheat bran used as the carbon source resulted in significantly fewer sprouted nutsedge tubers as well as a reduction in the number of tubers produced. ASD treatment with wheat bran-based amendments at lower C:N ratios reduced nutsedge tuber sprouting and reproduction.
5. Potential for herbicide degradation under anaerobic soil disinfestation. ARS researchers at Ft. Pierce, Florida, investigated Fumigated and organic-amended soil management strategies as potential methyl bromide (MBr) alternatives for controlling diseases, nematodes, and weeds in soil. Nutsedge and broadleaf weed control using the herbicide fomesafen has been reported to be comparable to MBr. Information on the fate of fomesafen using alternative amendment practices does not exist. ARS researchers at Ft. Pierce, Florida, developed methods to investigate dissipation of fomesafen under anaerobic soil disinfestation (ASD) treatments. For treatments using organic amendments, reductions in fomesafen concentrations were positively correlated with lower redox potentials and soil organic matter content. Due to increased losses of the herbicide through microbial degradation and subsequent reduction in weed control, fomesafen would not be recommended for weed control using anaerobic soil disinfestation (ASD) technique. However, due to this rapid dissipation under ASD, this tool has potential for application in herbicide contamination mitigation.
6. Improving early detection of soil pathogens through analysis method selection. Research on the soil microbiome is important, as soilborne microbes are associated with both plant health and disease. To study the soil microbiome, the microbial deoxyribonucleic acid (DNA) is extracted from the soil, sequenced by using high throughput sequencing (HTS) techniques, and then analyzed by using various statistical methods. It is often difficult to identify plant pathogens from the vast amounts of data obtained from HTS. A soilborne plant pathogen, Ralstonia solanancearum, was artificially inoculated in soil and soil was sampled at one and seven days post inoculation. ARS researchers at Ft. Pierce, Florida, used thirteen different statistical methods to determine which approach could differentiate a statistical difference and be optimized for rare species. Distance-based resemblance measurements, such as Euclidean and Chi Squared, showed that 24 hrs post inoculation the soil samples were significantly different from each other, while the other methods did not detect a change in the microbiome. Employing these techniques should assist in improved early detection of soilborne pathogens.
Review Publications
Shi, L., Wang, J., Gao, Z., Zhao, X., Digioia, F., Guo, H., Hong, J.C., Ozores, H., Rosskopf, E.N. 2019. Economic analysis of anaerobic soil disinfestation for open-field fresh-market tomato production in Southwest and North Florida. HortTechnology. https://doi.org/10.21273/HORTTECH04332-19.
Di Gioia, F., Petropoulos, S., Ozores, H., Morgan, K., Rosskopf, E.N. 2019. Zinc and iron agronomic biofortification of selected Brassicaceae microgreens. Agronomy Journal. https://doi.org/10.3390/agronomy9110677.
Garcia-Chance, L.M., Albano, J.P., Lee, C.M., White, S.A. 2019. Runoff pH influences nutrient removal efficacy of floating treatment wetland systems. HortTechnology. 29:756-768.
Levia, J.A., Wilson, P., Albano, J.P., Nkedi-Kizza, P., O'Connor, G.A. 2019. Pesticide sorption to soilless media components used for ornamental plant production and aluminum water treatment residuals. ACS Omega. 4:17782-17790.
Pisani, C., Patel, P.C., Rosskopf, E.N., Abbasi, Mehrdad, Aime, M.C. 2019. First report of downy mildew caused by a Plasmopara halstedii on Ageratum houstonianum in the United States. Plant Disease. https://doi.org/10.1094/PDIS-06-19-1331-PDN.
Li, Z., Di Gioia, F., Hwang, J., Hong, J.C., Ozores-Hampton, M., Zhao, X., Pisani, C., Rosskopf, E.N., Wilson, P.C. 2019. Dissipation of fomesafen in fumigated, anaerobic soil disinfestation-treated, and organic-amended soil in Florida tomato production systems. Pest Management Science. 10.1002/ps.5558.
Paudel, B., Digioia, F., Zhu, Q., Zhao, X., Ozores-Hampton, M., Swisher, M., Sattanno, K., Hong, J.C., Rosskopf, E.N. 2019. Implementation of anaerobic soil disinfestation in Florida tomato production. Extension Digital Information Source (EDIS). https://doi.org/10.1017.
Hong, J.C., Di Gioia, F., Jones, J.B., Turechek, W., Johns, C.W., Finley, N.L., Ozores-Hampton, M., Mccollum, T.G., Rosskopf, E.N., Burelle, N.K. 2020. Defining anaerobic soil disinfestation through changes in the microbiome. Acta Horticulturae. https://doi.org/10.17660.
Zhao, X., Di Gioia, F., Delate, K., Rosskopf, E.N., Guan, W. 2019. Advances in organic cultivation of vegetables. Organic Vegetable Production. http://dx.doi.org/10.19103.
Rosskopf, E.N., Di Gioia, F., Hong, J.C., Ozores-Hampton, M., Zhao, X., Black, Z., Gao, Z., Wilson, C., Thomas, J., Jones, J., Butler, D.M., Shrestha, U., Sattanno, K., Delong, A., Swisher, M., Burelle, N.K., Wang, J., Li, Z., Shi, L., Pisani, C., Guo, H., Zhu, Q., Paudel, B., Johns, C.W., Finley, N.L., Muramoto, J., Albano, J.P., Shennan, C. 2020. Anaerobic soil disinfestation: Areawide project on obstacles and adoption. Acta Horticulturae. https://doi.org/10.17660.
Rosskopf, E.N., Hong, J.C., Burelle, N.K., Pisani, C., Di Gioia, F., Jones, J., Booker, B., Keely, M., Yates-Yarbrough, S., Sances, F. 2020. Evaluation of Dominus® (allyl isothiocyanate) for tomato and bell pepper production. Acta Horticulturae. 1270.41. https://doi.org/10.17660/actahortic.
Di Gioia, F., Hong, J.C., Ozores-Hampton, M., Zhao, X., Wilson, C., Albano, J.P., Li, Z., Pisani, C., Guo, H., Paudel, B., Butler, D., Rosskopf, E.N. 2020. Anaerobic soil disinfestation: Nutrient cycling and potential environmental impact. Acta Horticulturae. https://doi.org/1270.
