Plant Disease
October, 2004

Genes for Adult-Plant Resistance to Leaf Rust in Soft Red Winter Wheat
Yeshi A. Wamishe and Eugene A. Milus, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. Plant Dis. D-2004-0809-01R, 2004 (online). Accepted for publication 26 May 2004.

INTERPRETIVE SUMMARY

 Leaf rust caused by Puccinia triticina is an important and widespread disease of wheat that can cause significant yield loss. Resistance to leaf rust has been the most cost effective and environmentally safe means of managing the disease. Adult-plant resistance is a type of resistance whereby seedlings are susceptible but plants become more resistant as they mature. The objective of this study was to determine the genetic basis for adult-plant resistance in contemporary soft red winter wheat lines and to determine the best methods for identifying genes Lr12, 13, and 34, which confer adult-plant resistance. Of the 116 lines evaluated, more than 90% expressed adult-plant resistance when inoculated with a race of the pathogen that attacked seedlings. Genes Lr12, 13, and 34 were identified in 17, 23, and 27 of the lines, respectively. Lr12 was best identified by a distinctive reaction on flag leaves when inoculated plants were incubated under controlled conditions. Although Lr13 is considered a gene for adult-plant resistance, it was best identified by inoculating seedlings with particular isolates of the pathogen that can overcome this gene at 18.1°C but not at 25.5°C. Lr34 was best identified by evaluating lines in irrigated field plots for leaf tip necrosis, a trait known to be tightly linked to Lr34. More than 40% of the lines had adult-plant resistance that could not be attributed to genes Lr12, 13, or 34. The results of this study indicated that adult-plant resistance to leaf rust is common among contemporary soft red winter wheat lines and that genes in addition to Lr12, 13, and 34 contribute to the resistance. Furthermore, certain methods for identifying particular genes were found to be more effective than other published methods, but none of the methods were definitive.

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