D. L. Long

Virulence and Diversity of Wheat Leaf Rust in the United States in 1993 to 1995

Isolates of Puccinia triticina were obtained from wheat leaf collections made by cooperators throughout the United States and from cereal rust field surveys of the Great Plains, Ohio Valley, and Gulf Coast states in 1993, 1994, and 1995. Sixty-two virulence/avirulence phenotypes on 14 host lines that are near-isogenic for leaf rust resistance were found among 681 single uredinial isolates in 1993, 42 phenotypes were found among 683 isolates in 1994, and 51 among 701 isolates in 1995. As in previous surveys, regional race distribution patterns showed that the central United States is a single epidemiological unit distinct from the eastern United States. The distinctive racial composition of collections from the Southeast, Northeast, and Ohio Valley indicates that populations of P. triticina in those areas are discrete, suggesting epidemics originate from localized overwintering sources.

Races of Puccinia graminis in the United States in 1989

Oat stem rust was present in light amounts throughout most of the United States in 1989, and yield losses were nil. Disease onset was 1 mo later than the 40-yr average. The principal race in the United States was NA-27, virulent to resistance genes Pg-1, -2, -3, -4, and -8. NA-27, NA-5, and NA-16, respectively, made up 97, 1, and 1% of the isolates from the United States. No virulence was found for Pg-9, Pg-13, Pg-a, or Pg-16 in the 1989 oat stem rust population

Virulence of Puccinia recondita f. sp. tritici in the United States during 1988-1990

Isolates of Puccinia recondita f. sp. tritici were obtained from wheat leaf collections made by cooperators throughout the United States and from cereal rust field surveys of the Great Plains, Ohio Valley, and Gulf Coast states in 1988, 1989, and 1990. Forty-one virulence/avirulence phenotypes were found among 618 isolates in 1988, 45 among 983 isolates in 1989, and 53 among 906 isolates in 1990 on 14 host lines with single designated genes for leaf rust resistance. The frequencies of virulence to lines with Lr11 and Lr26 during 1988-1990 were greater than in previous years(.)

Races of Puccinia graminis in the United States and Mexico during 1987

Disease generally developed more than a week later that the 40-yr average. The principal race in the United States and Mexico was NA-27, virulent on hosts having resistance genes PG-1, -2, -3, -4, and -8. NA-27 made up 93 and 100% of the isolates from the United States and Mexico, respectively

Races of Puccinia graminis in the United States in 1988.

Disease development was a month later than the 40-yr average. The principal race of the pathogen was NA-27, which is virulent on hosts having resistance genes Pg-1, -2, -3, -4, and -8. NA-27 accounted for 83% of the isolates and NA-16 for 7%. No virulence was found for Pg-a or Pg-16 in the 1988 oat stem rust population. Wheat stem rust overwintered in trace amounts from southern Texas to southern Georgia. A probable overwintering site was found in a plot in northeastern North Dakota leeward of a shelterbelt. Stem rust inoculum spread northward, but little disease developed because of a severe drought throughout the central and northern Great Plains (...)