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Disease Detection and Losses

The Effects of Clover Yellow Vein Virus and Peanut Stunt Virus on Yield of Two Clones of Ladino White Clover. Cynthia K. Ragland, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695; C. Lee Campbell(2), and James W. Moyer(3). (2)(3)Associate professors, respectively, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Phytopathology 76:557-561. Accepted for publication 10 December 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-557.

Two clones, T7 and T17, of ladino white clover were examined in a transplanted clover-tall fescue system under field conditions for response to infection by peanut stunt virus (PSV), clover yellow vein virus (CYVV), and PSV + CYVV in 1982 and 1983. Plants infected by either PSV, CYVV, or the two viruses together had lower dry weight yields than plants of initially virus-free clover. PSV was the more severe virus and resulted in greater yield loss for both clones; however, clone T17 was less susceptible to yield reduction by PSV than was T7. Conversely, clone T7 was less susceptible to yield loss from infection by CYVV than was T17. The combination of both viruses led to the same yield reduction as PSV alone; however, PSV + CYVV plots exhibited the highest mortality rate during the second growing season. In the 1983 field plots, fescue had greater yield at the second and third harvest when grown with CYVV or CYVV + PSV-infected clover than when grown with initially virus-free clover. Yield and components of growth (stolons per plant, length per stolon, nodes per centimeter of stolon, rooting nodes per stolon) of virus-free, CYVV, PSV, and PSV + CYVV-infected plants of clone T17 were also evaluated in controlled-environment studies. Virus and temperature effects were significant for all components. A virus by temperature interaction (P < 0.05) occurred for final root and shoot dry weight, average number of nodes per centimeter of stolon, and average length per stolon. Reductions in components of growth due to virus infection were greatest in PSV and PSV + CYVV treatments, and overall growth of clover was greatest at 20 C. The different coat protein antigen levels, as determined by ELISA, indicated differences in titer and distribution of CYVV between plants of clones T7 and T17. Clone T17, which exhibited the greater yield reduction when infected with CYVV, had higher virus titer, in general, than clone T7. Older leaves of plants of clone T17 had higher virus titer than comparable leaves of plants of clone T7.