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United States Department of Agriculture

Agricultural Research Service

Title: In vitro inhibition of soilborne fungi by “SPK”, a novel pesticide

item Iriarte, Fanny
item Rosskopf, Erin
item He, Zhenli
item Lin, Youjian

Submitted to: Proceedings of Methyl Bromide Alternatives Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/11/2011
Publication Date: 10/28/2007
Citation: Iriarte, F.B., Rosskopf, E.N., He, Z., Lin, Y. 2007. In vitro inhibition of soilborne fungi by “SPK”, a novel pesticide. Proceedings of Methyl Bromide Alternatives Conference.

Interpretive Summary:

Technical Abstract: A novel combination of organic compounds, referred to by the name “SPK”, is currently under development by the University of Florida and USDA, ARS. In previous studies, the material showed pesticidal activity and no detrimental effect on pepper and tomato seed germination when used at a concentration of 0.5%. SPK was tested in vitro for the control of Phytophthora capsici, Pythium aphanidermatum, Pythium myriotilum, Fusarium oxysporum, Sclerotinia sclerotiorum, Sclerotium rolfsii, Colletotrichum acutatum, Verticillium albo-atrum and Rhizoctonia solani. A 0.7 cm diameter plug of a 4 - 6 day old culture of the different fungal isolates were transferred to Petri plates with ¼ potato dextrose agar containing a range of SPK concentrations from 0 to 1 %. Fungal radial growth was measured after the 3rd, 6th, and 9th day of incubation at 26 oC under continuous light. Complete inhibition of mycelial growth of P.aphanidermatum and V. albo-atrum occurred at an SPK concentration of 0.2%, S. sclerotiorum, P. capsici, R. solani and C. acutatum at 0.3%, and P. myriotilum and S. rolfsii at 0.4 %-0.5%. Hence, two additional experiments were carried out, one with SPK concentrations of 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 % (Exp.1) and another with SPK concentrations of 0.0, 0.1, 0.15, 0.20, 0.25 and 0.30 % (Exp.2). Three replications per fungus for each SPK concentration were included in each experiment and each experiment was performed twice. Percent kill was calculated based on radial growth of two replicate experiments combined and IC50 values were calculated using the Probit analysis for toxicology separately for each range of concentrations. In the greenhouse assays, no phytotoxicity was observed nor were there any significant differences in the size of tomato or pepper plants transplanted 5, 10 or 15 days after potting soil was drenched with 30 ml of 0.0, 0.5, 1.0, 1.5, 2.0, or 2.5 % SPK solution. Further greenhouse evaluations are underway to determine SPK concentrations that are effective for control of Phytophthora blight of pepper and Fusarium wilt of tomato. Preliminary investigations indicate that further research is warranted on this compound. If similar results are obtained under field conditions, SPK could be a promising component to an integrated control program for the control of soilborne pests of numerous crops without causing phytotoxicity. Advantages of using SPK would include a short plant back interval and the very low concentrations needed to provide effective soilborne disease control.

Last Modified: 06/27/2017
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