Virus Diseases and Stand Decline in a White Clover Pasture. M. R. McLaughlin, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Crop Science Research Laboratory, Forage Research Unit, P.O. Box 5367, Mississippi State 39762-5367. G. A. Pederson, R. R. Evans, and R. L. Ivy. Research Geneticist, Agricultural Research Service, U.S. Department of Agriculture, Crop Science Research Laboratory, Forage Research Unit, P.O. Box 5367, Mississippi State 39762-5367; Animal Scientist, and Agronomist, Prairie Research Unit, Mississippi Agricultural and Forestry Experiment Station, Prairie 39756. Plant Dis. 76:158-162. Accepted for publication 21 August 1991. 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, 1992. DOI: 10.1094/PD-76-0158.

Linear regression analysis was used to characterize the incidence of virus diseases in white clover, Trifolium repens, and associated changes in the white clover population in a grazed pasture through four growing seasons. The incidence of diseases caused by clover yellow vein virus, peanut stunt virus (PSV), and white clover mosaic virus increased linearly through the life of the white clover stand, coincident with a steady decline in the white clover population. The predominant virus detected throughout the study was PSV, which occurred in 80% of the white clover plants sampled in the spring of the fourth growing season. By that time, the clover population had declined significantly, and by the following fall, the clover had virtually disappeared from the pasture. This association provided evidence that PSV may be a major factor in the lack of persistence of white clover. A potentially important source of resistance to PSV was identified in a white clover clone exhibiting hypersensitivity to mechanical inoculation of PSV. Alfalfa mosaic virus and red clover vein mosaic virus were present in infected white clover but at relatively low incidence. Luteoviruses not previously reported from white clover in the Southeast also were detected.

Keyword(s): forage, soybean dwarf virus.