Rpg1 is a stem rust resistance gene that has protected barley from severe losses for over 60 years in the US and Canada. It confers resistance to many, but not all, pathotypes of the stem rust fungus Puccinia graminis f. sp. tritici. A fast neutron induced deletion mutant, showing susceptibility to stem rust pathotype Pgt-MCC, was identified in barley cv. Morex, which carries Rpg1. Genetic and Rpg1 mRNA and protein expression level analyses showed that the mutation was a suppressor of Rpg1 and was designated Rpr1 (Required for P. graminis resistance). Genome-wide expression profiling, using the Affymetrix Barley1 GeneChip containing approximately 22,840 probe sets, was conducted with Morex and the rpr1 mutant. Of the genes represented on the Barley1 microarray, 20 were up-regulated and 33 were down-regulated by greater than twofold in the mutant, while the Rpg1 mRNA level remained constant. Among the highly down-regulated genes (greater than fourfold), genomic PCR, RT-PCR and Southern analyses identified that three genes (Contig4901_s_at, HU03D17U_s_at, and Contig7061_s_at), were deleted in the rpr1 mutant. These three genes mapped to chromosome 4(4H) bin 5 and co-segregated with the rpr1-mediated susceptible phenotype. The loss of resistance was presumed to be due to a mutation in one or more of these genes. However, the possibility exists that there are other genes within the deletions, which are not represented on the Barley1 GeneChip. The Rpr1 gene was not required for Rpg5- and rpg4-mediated stem rust resistance, indicating that it shows specificity to the Rpg1-mediated resistance pathway.
A broad enhancement of the form function for these shells is known to be present in the mid-frequency range. A ray model of the form function in this region was previously demonstrated for cylinders and spheres [N. H. Sun and P. L. Marston, J. Acoust. Soc. Am. 89, 1949 (1991)] and the enhancement was found to be associated with contributions to the scattering from the subsonic surface guided wave frequently designated as A<lu>0<bu>−<lux>. The consequences of this enhancement were investigated for spherical shells by synthesizing the response to tone bursts from an evaluation of the exact partial wave series over the sampled spectrum of the burst [L. Zhang, M. S. dissertation, Washington State University, 1991]. This was compared with a ray approximation for the earliest contribution for this wave, which circumnavigates only the backside of the shell. The amplitude from the ray model is ‖f0,l‖ ≊ 8πβl(c/cl)exp(−πβl), where the surface wave parameters cl and βl are found from the exact elastic equation for the roots of Dν(ka)=0. Both the Fourier synthesis and ray models show a broad enhancement which for a 2.5% stainless steel shell peaks at ka≊46 where ‖f0,l‖ ≊ 3.1 and the exact results differ by only 3%. Neglecting dispersion the peak occurs where βl=π−1. [Work supported by ONR.]
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