Influence of Tylenchorhynchus ewingi on growth of loblolly pine seedlings, and host suitability of legumes and small grains

Authors: FRAEDRICH, STEPHEN - Forest Service (FS); CRAM, MICHELE - Forest Service (FS); Handoo, Zafar; ZARNOCH, STANLEY - Forest Service (FS)

Submitted to: Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2011
Publication Date: 1/1/2012
Citation: Fraedrich, S.W., Cram, M.M., Handoo, Z.A., Zarnoch, S.J. 2012. Influence of Tylenchorhynchus ewingi on growth of loblolly pine seedlings, and host suitability of legumes and small grains. Nematology. 14(4):417-425.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that feed on plants and cause an estimated ten billion dollars of crop losses each year in the United States and 100 billion dollars globally. Stunt nematodes are one of the most economically important groups of plant-parasitic nematodes worldwide and have damaged pine seedling crops in southern forest tree nurseries since the 1950’s. One approach to solving the problem of designing new, safe means of controlling stunt nematodes is through the use of cover crops-plants that are not the primary crop of interest. In this study, an ARS scientist from Beltsville, Maryland in collaboration with scientists from the USDA Forest Service in Georgia and North Carolina, evaluated the susceptibility of several plant species commonly used as cover crops in pine nurseries. They discovered that legumes such as cowpeas and grains such as sorghum-sudangrass and rye are very good hosts for stunt nematodes and could greatly increase nematode populations in fields. In contrast, brown top millet was a poor host, and pearl millet was a non-host. The results are significant because they indicate that the latter two plants should be favored as cover crops in nurseries where stunt nematodes are a problem. This research will be of use to scientists, growers and extension agencies involved in stunt nematode research and control.

Technical Abstract: Tylenchorhynchus ewingi, a stunt nematode, causes stunting of slash pine seedlings and has been recently associated with stunting of loblolly pine seedlings at some forest tree nurseries in the southern USA. Experiments confirmed that loblolly pine is a host for T. ewingi and that the nematode is capable of causing severe damage to root systems. Initial population densities as low as 60 nematodes/100cc soil were sufficient to damage the root systems of loblolly pine seedlings. Populations of T. ewingi increased on pine from 2- to 16-fold, depending on the initial population density. Evaluations of various cover crops used in southern forest-tree nurseries indicated that legumes, rye and several varieties of sorghum were excellent hosts for T. ewingi. Other small grains such as ryegrass, oats and wheat were poorer hosts. A cultivar of pearl millet was a nonhost for T. ewingi, and a cultivar of brown top millet appeared to be either a very poorer host or a nonhost. Nurseries that have seedling production losses caused by T. ewingi should consider rotating with nonhost cover crops such as pearl millet or leaving fields fallow as part of their pest management program.