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Pathotype Variability of Rust Caused by Uromyces appendiculatus on Macroptilium atropurpureum. R. A. Bray, CSIRO, 306 Carmody Road, St. Lucia, Queensland 4067, Australia. R. M. Sonoda, and A. E. Kretschmer, Jr. University of Florida, AREC, Ft. Pierce 34954. Plant Dis. 75:430. Accepted for publication 10 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0430A.

Ten isogenic lines of the tropical pasture legume Macroptilium atropurpureum (Moc. & Sesse ex DC) Urb., all selected for resistance to an Australian isolate of the rust fungus Uromyces appendiculatus (Pers.:Pers.) Unger var. crassitunicatus and carrying resistance genes from diverse geographic origins in Central and South America, have been developed by backcrossing to the susceptible cultivar Siratro and subsequent selfing. These lines were screened against 10 single-spore isolates of the fungus-one isolate from Australia, two from Florida, and seven from Mexico. Seedlings were grown under quaran-tine conditions, with artificial light and day/night temperatures of about 23/20 C. Reaction types were assessed over a 3-wk period. All lines were resistant to the isolates from Australia and Florida, and six lines were resistant to all seven isolates from Mexico. Each isolate from Mexico produced a susceptible reaction on at least one line. Three resistant lines with genes from the state of Oaxaca in Mexico gave susceptible reactions to two isolates from that area. The results clearly show the existence of pathotype variability. The origin of the isolate from Australia is unclear, but, based on the extent of damage on Siratro, it probably is not identical to the isolates from Florida.