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Title: Detection of Suppressiveness against Rotylenchulus reniformis in Soil from Cotton (Gossypium hirsutum) fields in Texas and Louisiana

item Robinson, Arin
item Greenberg, Shoil
item Stetina, Salliana - Sally

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2008
Publication Date: 7/14/2008
Citation: Robinson, A.F., Westphal, A., Overstreet, C., Padgett, G., Greenberg, S.M., Stetina, S.R., Wheeler, T.A. 2008. Detection of suppressiveness against Rotylenchulus reniformis in soil from cotton (Gossypium hirsutum) fields in Texas and Louisiana. Journal of Nematology. 40(1):35-38.

Interpretive Summary: There are many kinds of microscopic worms called nematodes that feed on the roots of cotton and other crops, debilitating the plants and markedly decreasing yields. The direct losses to U.S. cotton farmers caused by nematodes each year are estimated by the National Cotton Council to exceed $300,000,000. The reniform nematode is one of the most important nematodes on cotton in the U.S. Cotton farmers with this nematode in their fields can reduce yield losses to nematodes in some cases by applying nematicides or planting resistant rotational crops, but these costly practices at best recover only some of the lost profit because effective nematicides are expensive and alternative crops do not make the farmer as much money as cotton. Cotton varieties with resistance to the reniform nematode are on the horizon but are not yet available. A possibly more quickly achievable solution would be the augmentation or introduction of natural enemies of the nematode, or as they are sometimes called, beneficials. Most beneficials active against nematodes are microbes, including fungi, bacteria, and special nematodes that eat other nematodes. Management of beneficials is a highly successful and widely practiced method for insect pest management that is only beginning to be explored with nematode pests. In this study, 22 cotton fields in the United States which had been identified in previous studies to have unexpectedly low populations of the reniform nematode, were assayed for the presence of biological control agents, by either autoclaving the soil to kill beneficials, or by mixing a small amount of test soil with sand, and then placing the original as well as the autoclaved and the mixed soil in pots, inoculating pots with nematodes, growing cotton plants in the pots, and then comparing the nematode population buildup in the soil. The presence of potent biological control agents was detected in five fields in Texas and five in Louisiana. Beneficials in one field were able to reduce the nematode population by 95% when introduced as only 10% of the total soil volume in the pot. Further identification and culture of these organisms may lead the way to concentrated formulations of beneficial microbes that could be applied as seed coatings, or by other means, to reduce damages caused by nematodes, with no harm to the environment.

Technical Abstract: Rotylenchulus reniformis is a major problem confronting cotton production in the central part of the cotton belt of the United States of America. In this study, the hypothesis that natural antagonists in some cases are responsible for unusually low densities of the nematode in certain fields was tested by assaying soils from 22 selected fields for the presence of transferable agents in pots containing cotton plants. In one field, soil from four different depths was tested. In the first of two types of assays, one part nematode infested soil was added to nine parts test soil with or without autoclaving and this mixture was used to fill pots; in the second type of assay, one part test soil was added to 9 or 19 parts pasteurized fine sand, and nematodes were introduced in aqueous suspension. In three experiments representing both types of assay, transferable or autoclavable agent(s) from four fields in South Texas suppressed nematode populations 48, 78, 90, and 95%. In one experiment, transferable agents in five fields in Louisiana suppressed population buildup 37 to 66%. Identification and evaluation of these agents for biological control of R. reniformis merits further study.