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The Effect of Detachment on the Development of Rust Disease and the Hypersensitive Response of Wheat Leaves Infected with Puccinia graminis tritici. S. Mayama, Laboratory of Agricultural Biochemistry, University of Nebraska, Lincoln 68503, Present address of the senior author: Laboratory of Plant Pathology, Kyoto University, Kyoto, Japan; D. W. Rehfeld(2), and J. M. Daly(3). (2)(3)Laboratory of Agricultural Biochemistry, University of Nebraska, Lincoln 68503. Phytopathology 65:1139-1142. Accepted for publication 5 May 1975. DOI: 10.1094/Phyto-65-1139.

Primary leaves of Khapli wheat and wheat lines with the Sr6, Sr6b, Sr11, Sr13 and Sr14 genes for disease reaction against race 56 of Puccinia graminis tritici were detached immediately after inoculation and floated on various solutions. Upon detachment, the normally incompatible reactions of attached leaves to this race were altered to greater susceptibility with the exception of wheat carrying the Sr6 allele for resistance. Contrary to earlier reports, kinetin did not prevent the increase in susceptibility. A hypersensitive response, measured by the number and size of fluorescent areas, was evident before 48 hours after inoculation in resistant attached leaves, but not in susceptible attached leaves. The increased susceptibility of detached leaves of resistant wheat was accompanied by a hypersensitive response of at least the magnitude observed for attached leaves of the same line. Although kinetin tended to maintain the normal appearance of detached leaves, the hypersensitive reaction sites were more numerous and larger in the presence of this compound. The results support previous studies on near-isogenic lines of wheat with the Sr6 alleles for disease reaction which indicated that the hypersensitive response of wheat to rust fungi is not a determinant in incompatibility. Rather, the response may be a general symptom of stress, and only incidental to the cellular reactions involved in host-parasite interactions.