|Riggs, R - UNIVERSITY OF ARKANSAS|
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 1998
Publication Date: December 20, 1998
Citation: Timper, P., Riggs, R.D. 1998. Variation in efficacy of isolates of the fungus ARF against the soybean cyst nematode, Heterodera glycines. Journal of Nematology. 30:461-467. Interpretive Summary: The soybean cyst nematode (SCN) is one of the most damaging pests of soybean in the United States. The nematode is managed primarily by the use of resistant soybean cultivars and crop rotation. However, frequent planting of resistant cultivars has lead to the development of nematode populations that are damaging even to resistant cultivars. Furthermore, many growers are not willing or able to rotate out of soybeans for the three years necessary to suppress numbers of SCN to nondamaging levels. An effective biocontrol agent would provide growers with another tactic for managing SCN. ARF is a fungus that parasitizes several stages of this nematode. Isolates of ARF, collected from different locations in the southern United States, were compared for their effectiveness in reducing nematodes in soil. Three isolates reduced numbers of SCN by 50% to 100%, whereas the other eight isolates were only moderately effective. Previous studies with ARF were conducted in pasteurized soil. Frequently, biocontrol agents perform better in pasteurized soil than in natural soil because the pasteurization process removes other microorganisms which may inhibit biocontrol. However, we found that ARF was equally effective in pasteurized and natural soil indicating that the fungus is not greatly affected by other soil microorganisms. This research has identified three effective ARF isolates which can now be evaluated as biocontrol agents of SCN under field conditions.
Technical Abstract: An unnamed fungus, designated ARF, that parasitizes eggs, sedentary juveniles, and females of cyst nematodes is being evaluated as a biological control agent of Heterodera glycines. The objectives of this study were to determine whether ARF isolates differ in their ability to suppress nematode numbers in soil, and also to compare the efficacy of ARF in microwave-heated and native soil. To determine their effectiveness, 11 ARF isolates were introduced into steam-pasteurized soil. Soybean seedlings, cv. Lee 74 were transplanted into pots containing the infested soils and inoculated with H. glycines. After 30 or 60 days, the number of nematodes and the percentage of eggs parasitized was determined. Three isolates (907, 908, and TN14), which were previously reported to be weak egg parasites in vitro, consistently suppressed nematode numbers by 50% to 100%. Of the isolates previously reported to be aggressive egg parasites in vitro, four (903, BG2, MS3, and TN12) reduced nematode numbers by 56% to 69% in at least one experimental trial and the other four had no effect on nematode numbers. The efficacy of ARF (isolate TN14) was tested in microwave-heated and native soil. Isolate TN14 reduced nematode numbers by more than 60% in both soil treatments; however, heat treatment of soil had no consistent effect on efficacy of the fungus. We conclude that: I) virulence towards nematode eggs in vitro is a poor indicator of effectiveness of an ARF isolate in soil, and II) the presence of soil microbes did not inhibit the activity of isolate TN14.