EFFECTS OF INOCULUM DENSITY AND TEMPERATURE ON 3 COMPONENTS OF LEAF RUST RESISTANCE CONTROLLED BY LR34 IN WHEAT

Different inoculum densities had negligible effects on latent peri od, uredinium density and uredinium size measured on flag leaves of adult RL6058 (Thatcher* 6/PI58548 [Lr34]) plants kept at low (17.5 degrees C) post-infection temperatures in a glasshouse. In a qualitative assessment of rust severity at higher (24.6 degrees 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.