Identification and Prevalence of White Clover Viruses and the Resistance of Trifolium Species to These Viruses1

Abstract

White clover, Trifolium repens L., plants from 19 pastures in eight southern states were collected without regard for symptoms. Viruses infecting these plants were detected and identified by the use of differential hosts and serological techniques. Alfalfa mosaic virus (AMV) was found in 7 pastures, clover yellow vein virus (CYVV) in 15, peanut stunt virus (PSV) in 14, and white clover mosaic virus in 5. Clover yellow mosaic virus was not found. Of 636 plants sampled, 237 were infected with one to three viruses. The percentage of virus‐infected plants in a pasture varied from 0 to 86. How concentrated pastures were in the vicinity, how many years the pasture was in perennial clover, and whether the white clover persisted from year to year, as a perennial plant or by annual reseeding, influenced the amount of virus infection. Twenty‐three Trifolium species were mechanically inoculated with six or seven viruses to find resistant germplasm. Although some variation was detected, all plants of most species were infected. Clover yellow mosaic virus infected 10% of the T. ambiguum Bieb. plants inoculated, whereas no plants were infected with the other 6 viruses. A few white clover plants were resistant to mechanical inoculation with each of the three most prevalent viruses, AMV, CYVV, and PSV.