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Techniques for Assaying Alfalfa Susceptible to Alfalfa Mosaic Virus. Pat Crill, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address of senior author: University of Florida, Gulf Coast Experiment Station, Bradenton 33505; D. J. Hagedorn(2), and E. W. Hanson(3). (2)(3)Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:1517-1520. Accepted for publication 16 May 1970. DOI: 10.1094/Phyto-60-1517.

When the relative sensitivity of three local lesion assays for alfalfa mosaic virus (AMV) was studied, the assay involving number of lesions per bean leaf was superior to those concerned with number of lesions per cowpea leaf or maximum number of lesions per square centimeter of cowpea leaf. Ten-day-old bean plants grown at 24 C developed the most discrete and readable lesions upon inoculation with AMV, as compared to beans grown longer and at other temperatures. Studies on the effect of time of day of inoculation indicated most lesions developed after beans had been exposed to at least 12 hr of light. Although alfalfa cultivars Ranger and Vernal reacted in an opposite manner, light intensities in the range 100-1,400 ft-c had no significant effect on the development of AMV. More virus developed in Glacier alfalfa under a 6-hr photoperiod than under 12 or 18 hr. There was a positive relationship between increased AMV development and increasing temperature up to 28 C.