Disease Note.

First Report of Virulence to Wheat with Leaf Rust Resistance Gene Lr19 in Mexico. J. Huerta-Espino, Cereal Pathologist, SARH, INIFAP, CIANO, Apdo. Postal 515, 85640 Cd. Obregon, Son., Mexico. R. P. Singh, Geneticist/Pathologist, CIMMYT, Lisboa 27, Apdo. Postal 6-641, 06600 Mexico, D.F. Plant Dis. 78:640. Accepted for publication 14 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0640C.

Lr19, a gene for leaf rust resistance, was transferred to wheat (Triticum aestivum L.) from Agropyron elongatum (Host) P. Beauv. (1) and has been effective against all isolates of Puccinia recondita Roberge ex Desmaz, f. sp. tritici (Eriks. & E. Henn.) tested so far in Mexico, the United States, Canada, and in 32 countries in a worldwide survey conducted from 1987 to 1990. Lr19 has not been extensively used in cultivars. However, two released cultivars carry Lr 19, Sunnan in Sweden and Oasis 86 in Mexico. Oasis 86, released in 1986, is grown exclusively in northwestern Mexico (Sonora and Sinaloa states), where no virulence to wheat with Lr19 has ever been detected. In September 1993, leaf rust pustules were observed on seedlings of Oasis 86, which were inoculated in the greenhouse with stripe rust collected in Celaya (state of Guanajuato in central Mexico). Obviously, the stripe rust inoculum was contaminated with leaf rust. The leaf rust inoculum was isolated and used to inoculate seedlings of Thatcher near-isogenic lines, a mutant of Thatcher + Lr19 (RL6040) that lacks yellow pigment in the flour, and Oasis 86. Our results confirmed the isolate's virulence lo wheat with Lr19. This pathotype has been designated CBJ/QQ (2). We believe that CBJ/QQ could have evolved from the previously known pathotype CBJ/QL by means of a single mutation for virulence (2). Virulence lo wheat with Lr1 9 has been reported before in other countries, but no culture was ever saved for verification. This is the first confirmed report of virulence to wheat with Lr19. This pathotype is available on request from the second author.