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Different inoculum densities had negligible effects on latent period, uredinium density and uredinium size measured on flag leaves of adult RL6058 (Thatcher*6/PI58548[Lr34]) plants kept at low (17.5°C) post-infection temperatures in a glasshouse. In a qualitative assessment of rust severity at higher (24.6°C) temperatures, all three components of resistance indicated a susceptible flag leaf response on RL6058. In the latter environment, precise estimations of receptivity to different inoculum densities showed that adult RL6058 plants supported significantly less pustules than the leaf rust-susceptible cultivar Thatcher. In tillering plants, statistically equal numbers of uredinia developed on RL6058 and Thatcher in all paired temperature-inoculum density combinations. Growth stage-related susceptibility, and higher temperatures conducive to a shorter latent period and larger uredinia, could result in high terminal severities of Puccinia recondita f. sp. tritici on wheat genotypes containing Lr34. The reduction in receptivity associated with this gene may contribute, however, to delayed disease increase on cultivars or lines with monogenic Lr34 resistance.

The protection provided by the leaf rust resistance gene Lr34 against Puccinia recondita f. sp. tritici was studied in the field over two seasons. In leaf-rust inoculated and fungicide-sprayed control plots, yield of RL6058, the ‘Thatcher’ backcross line with Lr34, was compared to that of the susceptible cultivar ‘Thatcher’. Leaf rust severity remained low on RL6058 in both seasons, but was high on ‘Thatcher’. The latent period of wheat leaf rust isolate 3SA132 in flag leaves of RL6058 was 256 h longer than in ‘Thatcher’. The uredinium density on ‘Thatcher’ was 14.4/cm2, compared to 3.7/cm2 flag leaf surface on RL6058. Leaf rust infection of ‘Thatcher’ reduced the total grain yield per plot by 25.4% and 1,000 kernel mass by 15.6%. Leaf rust caused little or no damage on RL6058 and rusted plots outyielded the control plots by 0.3 %. Seed weight of RL6058 was reduced by 0.7%. Compared to previous greenhouse studies, the adult-plant resistance conferred by Lr34 is more clearly expressed in the field. Evaluation of milling and baking quality characteristics revealed that compared to ‘Thatcher’, RL6058 had a higher flour protein content, but that its milling, dough development and baking properties were inferior.

The effects of temperature and different isolates of Puccinia recondita f. sp. tritici on the expression of leaf rust resistance genes Lr33, LrT3, and Lr34 and gene combinations Lr33 + Lr34 and LrT3 + Lr34, all in Thatcher wheat background, were studied in seedling and adult plants. In reaction to isolates 3SA122, 3SA132, and 3SA135, the expression of low infection type by the individual genes and the two combinations in the seedling stage was best expressed at 7 C. These low infection types were largely negated at 15, 20, and 25 C. All three individual host genes, as well as the two combinations, expressed race-specific characteristics (.)

The latent period of Puccinia recondita f. sp. tritici in flag leaves of line RL6058 (with gene Lr34) was most extended at greenhouse temperatures of 13-17 C compared with that in the leaf-rust-susceptible wheat cultivar Thatcher. A day/night regime of 25-29/13-15 C also increased latent period in RL6058, but no such differences between RL6058 and Thatcher were evident at continuous 26-30 C. Uredinia per square centimeter of flag leaf surface were fewer on RL6058 than on Thatcher