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Andres Sanabria MSc Thesis.pdf (2.91 MB)

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EFFECTS OF ANAEROBIC SOIL DISINFESTATION COMBINED WITH BIOLOGICAL CONTROL ON ROOT-KNOT NEMATODE AND LETTUCE DROP

Sanabria, Andres, SANABRIA
http://rave.ohiolink.edu/etdc/view?acc_num=osu1534496965018979

Abstract Details

2018, Master of Science, Ohio State University, Agricultural, Environmental and Developmental Economics.
Lettuce is one of the most important leafy vegetables produced on muck soils in Ohio. The fungi Sclerotinia minor and Sclerotinia sclerotiorum cause lettuce drop, a disease that results in the complete wilting and death of the plants. These pathogens produce large overwintering structures called sclerotia that are resistant to environmental extremes such as cold and heat, and can persist in the soil for several years. Another soilborne pathogen that limits lettuce production is the root-knot nematode (Meloidogyne hapla). Vegetable growers require sustainable approaches to manage these soilborne pathogens. Moreover, anaerobic soil disinfestation (ASD) appears to be a very promising management technique for smallholder farmers in developing countries like Paraguay. We evaluated the effectiveness of biocontrol bacteria and anaerobic soil disinfestation (ASD) as management tools for these pathogens. This is the first study of the effect of these tactics on the survival of Sclerotinia’s resistant overwintering structures in Ohio and Paraguay. The potential of biocontrol bacteria to suppress the viability of the survival structures (sclerotia) of Sclerotinia sclerotiorum and Sclerotinia minor was evaluated during laboratory experiments. The antagonism of forty-five bacterial strains (one Streptomyces sp., two Bacillus spp., and forty-two Pseudomonas spp.) was tested using the dual culture and sclerotia germination inhibition methods. We also evaluated a new soil disinfestation technique called anaerobic soil disinfestation (ASD) and its efficacy in suppressing Sclerotinia and root-knot nematode in Ohio and Paraguay. This technique consisted of incorporating an organic amendment into the soil followed by saturation with water and covering with plastic mulch for four weeks. During this procedure, levels of oxygen decrease and complex microbial processes, including production of organic acids, reduce the viability of the pathogens. During growth chamber trials, muck soils containing sclerotia placed in mesh bags and root-knot nematode eggs were treated with ASD using one of four organic amendments (molasses, wheat bran, or mustard greens at 20.2 Mg/ha, or 2% ethanol). Organic acids produced during the disinfestation process were characterized. After four weeks, sclerotia were removed and tested for viability, and lettuce plants were grown in treated and control soils for five weeks to determine root-knot severity. Field trials were conducted in Ohio muck soils and Paraguay red (oxisols) soil as well. Plots were amended with wheat bran (20.2 Mg (metric tonne)/ha), molasses (10.1 Mg/ha), wheat bran (20.2 Mg/ha) plus molasses (10.1 Mg/ha) or maintained unamended (control). Sclerotia in mesh bags were buried in the plots, which were then saturated and covered. After four weeks, sclerotia of both fungal pathogens were recovered and their viability evaluated. Biocontrol bacteria including Pseudomonas and Bacillus strains reduced the viability of the survival structures (sclerotia) of the fungal pathogens >70% during in vitro trials. ASD reduced the viability of the sclerotia >80% obtaining similar results from field trials in Ohio muck soils and Paraguay red soils. Complete suppression of root-knot nematode was observed in soils treated with ASD, regardless of carbon source during growth chamber trials. Organic acids produced during ASD were deleterious to sclerotia viability. Concentrations of these organic acids varied depending on the carbon source employed for ASD. The carbon sources for ASD that allowed highest production of organic acids were molasses followed by wheat bran and ethanol, being mustard greens the least effective in regards of organic acids production. When P. chlororaphis 14B11R was applied and anaerobic soil disinfestation (ASD) was conducted in those soils, no bacterial growth was observed. On the contrary, populations of B. subtilis QST 713R did not differ from populations of B. subtilis QST 713R in the positive, non-ASD control, whether applied to the soil before or after ASD treatment. The combination of biocontrol agent (BCA) application with ASD soil treatment did not lead to a significantly higher reduction of sclerotia viability compared to ASD alone for both S. minor and S. sclerotiorum. Future work will focus on determining if the biocontrol bacteria will be similarly effective when inoculated into the soil and/or on the roots of the plants. These bacteria can reduce the number of sclerotia by producing fungal inhibiting compounds and growing in association with the plant roots. Anaerobic soil disinfestation is currently being adopted by farmers in Ohio and in Paraguay. Future research will focus on optimizing ASD for soilborne pathogen management in different soils and with additional readily available organic amendments.
Miller Sally A., Dr. (Advisor)
Taylor Christopher G. , Dr. (Committee Member)
Paul Pierce A. , Dr. (Committee Member)
228 p.
Plant Pathology
ASD, biocontrol bacteria, IPM, soilborne pathogens, soil disinfestation

Recommended Citations

Citations

  • Sanabria, SANABRIA, A. (2018). EFFECTS OF ANAEROBIC SOIL DISINFESTATION COMBINED WITH BIOLOGICAL CONTROL ON ROOT-KNOT NEMATODE AND LETTUCE DROP [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534496965018979

    APA Style (7th edition)

  • Sanabria, SANABRIA, Andres. EFFECTS OF ANAEROBIC SOIL DISINFESTATION COMBINED WITH BIOLOGICAL CONTROL ON ROOT-KNOT NEMATODE AND LETTUCE DROP . 2018. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1534496965018979.

    MLA Style (8th edition)

  • Sanabria, SANABRIA, Andres. "EFFECTS OF ANAEROBIC SOIL DISINFESTATION COMBINED WITH BIOLOGICAL CONTROL ON ROOT-KNOT NEMATODE AND LETTUCE DROP ." Master's thesis, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534496965018979

    Chicago Manual of Style (17th edition)

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