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Evaluation of Arrowleaf Clover for Tolerance to Bean Yellow Mosaic Virus. I. J. Pemberton, Technician II, Texas Agricultural Experiment Station, TAMU Agricultural Research and Extension Center, Overton 75684; G. R. Smith, and M. R. McLaughlin. Associate professor, Texas Agricultural Experiment Station, TAMU Agricultural Research and Extension Center, Overton 75684, and research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Crop Science Research Laboratory, Forage Research Unit, Mississippi State 39762. Phytopathology 79:230-234. Accepted for publication 14 September 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-230.

Seventy-eight half-sib families of arrowleaf clover (Trifolium vesiculosum) were evaluated in the greenhouse for tolerance to bean yellow mosaic virus (BYMV). Inoculated seedlings of five families exhibited more tolerance to BYMV than seedlings of reference cultivar Yuchi. These five and seven families with equal or less tolerance than Yuchi were selected for further comparisons. The 12 selected families and Yuchi were rated on symptom severity and dry matter production. There was a significant negative correlation between symptom severity and dry matter yield, r = -0.92 (P = 0.01). The effects of BYMV on growth and survival of plants inoculated at different ages were determined. The age of arrowleaf clover plants at inoculation significantly (P = 0.001) affected cumulative dry matter production compared with controls. The younger the plants were when inoculated, the greater the yield reductions. Overall, 92% of the inoculated A64 plants survived the resulting infections, while only 55% of the inoculated Yuchi plants survived. Yuchi plants inoculated at 17 wk of age were particularly sensitive to BYMV infection, with only 25% surviving. We conclude that tolerance to BYMV is present in the germ plasm of arrowleaf clover and that evaluation of inoculated seedlings based on symptom severity is a conservative, effective selection method.