Ammonia and Nitrous Acid from Nitrogenous Amendments Kill the Microsclerotia of Verticillium dahliae

Abstract

This study examined the mechanisms by which nitrogenous amendments such as meat and bone meal kill the soilborne plant pathogen Verticillium dahliae. The effect of nitrogen products from the amendments on the survival of microsclerotia of V. dahliae was examined by solution bioassay and soil microcosm experiments. Ammonia and nitrous acid but not their ionized counterparts, ammonium and nitrite, were toxic to microsclerotia in bioassays. In microcosms, addition of meat and bone meal (2.5%) to an acidic loamy sand resulted in the accumulation of ammonia and death of microsclerotia within 2 weeks. At lower concentrations (0.5 and 1%), microsclerotia were killed after 2 weeks when nitrous acid accumulated (>0.03 mM). In an alkaline loam soil, microsclerotia survived at 3% meat and bone meal and neither ammonia nor nitrous acid accumulated. The toxicity of ammonia to the pathogen was verified by increasing the concentration of meat and bone meal to 4% or addition of urea (1,600 mg of N per kg) to the loam soil resulting in the accumulation of ammonia (>35 mM) and death of microsclerotia. The toxicity of nitrous acid was verified by adding ammonium sulfate fertilizer to an acidic sand soil. Inhibiting nitrification with dicyandiamide revealed that nitrous acid was generated as a result of the accumulation of nitrite and an acidic pH. Thus, levels to which the toxins accumulated and the effective concentration of amendment were dependent upon the soil examined. Of the two mechanisms identified, accumulation of nitrous acid is the more promising strategy to control plant diseases in acidic soil because it is more toxic than ammonia and is formed at lower concentrations of amendments.

Growth, yield and physiology of Verticillium-inoculated pepper plants treated with ATAD and composted sewage sludge

“…Leoni and Ghini (2006) and Dos Santos and Bettiol (2003) established negative correlations between EC and the incidence of Phytophthora nicotianae in citrus and Sclerotioum rolfsii in bean, respectively. Tenuta and Lazarovits (2002) observed a decrease in the viability of Verticillium microsclerotia as a consequence of the accumulation of nitrogenous compounds. In the present study, sludge application decreased soil pH and increased EC, as well as the concentration of N-NO 3 − .…”

“…Concerning the use of organic amendments, several cases of controlling this pathogen have been reported in the literature. Tenuta and Lazarovits (2002) demonstrated that ammonia and nitrous acid from liquid swine manure and nitrogenous amendments inhibited microsclerotia germination. Goicoechea et al (2004) suggested that organic amendments could stimulate defence mechanisms, providing an ecological and efficient means for the control of pepper wilt caused by V. dahliae.…”

Diversity, Pathogenicity, and Management of Verticillium Species

“…When the pH drops below 5.5, NO 2 − is converted to HNO 2 (nitrous acid) (pK a occurs at pH 3.3). Nitrous acid is approximately 300-500 times more toxic to microsclerotia than NH 3 (155) and is also toxic to many plant pathogens. most influenced by soil buffering capacity (156) as nitrification lowers soil pH only in poorly buffered soils.…”

“…most influenced by soil buffering capacity (156) as nitrification lowers soil pH only in poorly buffered soils. Both ammonia and nitrous acid were highly effective at reducing the microsclerotia in acidic soils (155). Because of the sitespecific nature of soil pH and organic matter, efficacy of these products in pathogen suppression is inconsistent.…”

Ammonia/Ammonium Toxicity Root Symptoms Induced by Inorganic and Organic Fertilizers and Placement

“…Adverse effects of organic nutrient sources on seed germination have correlated with the concentration of NH 4 + in amendments, for example, chicken manure (Wong et al, 1983), while sources high in cation exchange capacity such as peat can help ameliorate the toxic effects of NH 4 + relative to inorganic NH 4 + sources, thereby improving root development at moderate rates of application (Abbès et al, 1995). Ammonia was also suggested to be a biotoxic causative factor in controlling verticillium wilt (Verticillium daliae) with organic amendments (Tenuta and Lazarovits, 2002).…”