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Effects of Peanut Stunt Virus, Meloidogyne incognita, and Drought on Growth and Persistence of White Clover. M. R. McLaughlin, Research plant pathologists, USDA-ARS, Crop Science Research Laboratory, Forage Research Unit, Mississippi State, MS 39762; G. L. Windham, Research plant pathologists, USDA-ARS, Crop Science Research Laboratory, Forage Research Unit, Mississippi State, MS 39762. Phytopathology 86:1105-1111. Accepted for publication 5 July 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/Phyto-86-1105.

Productivity and persistence of white clover (Trifolium repens) in the southeastern United States are limited by a complex of pathogens and environmental stresses including peanut stunt virus (PSV), root-knot nematodes (Meloidogyne incognita), and drought. Determining the separate and combined effects of these factors has been hampered by the rapid natural spread of PSV to noninoculated plants. Half-sib white clover plants with and without hypersensitive resistance to PSV were used to overcome this problem. Effects of PSV, M. incognita, and drought on clover growth and persistence in the field were measured using a factorial arrangement of treatments in a split-plot design in which half of the plots were irrigated to eliminate drought stress. Data were collected in 2 consecutive years on dry weight herbage yield, stolon density, leaf area, petiole length, seed production, nematode population density, rainfall, and soil moisture. Virus infection reduced cumulative herbage yield 14% in the first year and 24% in the second year. In the first year, irrigation increased cumulative herbage yield 5 and 13% in the presence and absence of M. incognita, respectively, compared with nonirrigated control plots without M. incognita. Cumulative herbage yield in drought-stressed plots was reduced 9% in the presence of M. incognita compared with nonirrigated control plots without M. incognita. In the second year, cumulative herbage yield in the absence of M. incognita was 54% higher in irrigated plots than in nonirrigated plots, while yield in nonirrigated plots was 17% lower in the presence of M. incognita. Clover persistence, as measured by stolon density, was reduced by PSV, M. incognita, and drought, but no interactions occurred. Reductions in persistence were most severe in M. incognita treatments, resulting in nearly complete loss of stands by the end of the second year. Virus infection reduced leaf area and petiole length in all treatments, but reductions were proportionately greater in irrigated plots. Nematode infestation generally reduced leaf area and petiole length, but the effect was less than that of PSV. Mean seed yields from 100 seed heads per plot were lower in nematode-infested plots, but slightly higher in nonirrigated plots and PSV-treated plots. Drought stress, M. incognita, and PSV acted independently in reducing forage productivity and persistence.

Additional keywords: diseases losses, forage legumes, soilborne pathogens.