Histology of the Infection and Development of Puccinia recondita f. sp. tritici in a Wheat Line with Lr37

The degree of adult-plant resistance conferred by the gene Lr37 in RL6081 (Thatcher*8/Lr37) to four avirulent leaf rust pathotypes was quantified by assessing histological components as well as latent period, uredinium density and uredinium size. Histological observations on the adaxial flag leaf surfaces revealed significant arrest of fungal structures in RL6081 at early infection stages. Furthermore, host cell necrosis typical of a posthaustorial host-resistance mechanism was conspicuous in sizeably reduced colonies on this genotype. Lr37 significantly decreased the rate of uredinial appearance of all four pathotypes. Compared with Thatcher, fewer uredinia of smaller dimensions developed on flag leaves of RL6081. Characterization of resistance indicated that disease development in genotypes with the gene Lr37 should be extremely limited.