Histopathology of Leaf Rust Infection and Development in Wheat Genotypes containing Lr12 and Lr13

Evidence exists that certain genes for resistance to leaf rust in wheat\ e[g[ Lr02 and Lr23\ may interact with other genes to condition higher levels of resistance than that conferred by each gene individually[ In this study\ the hypothesis that Lr01 and Lr02\ both genes for adult plant resistance to Puccinia recondita Roberge ex[ Desmaz f[ sp[ tritici Eriks[ and Henn[\ interact to confer an improved level of resistance\ was investigated using ~u! orescence and phase!contrast microscopy[ Flag leaf seg! ments of monogenic and digenic Thatcher lines\ sampled 53 and 139 h post!inoculation\ were stained with Uvitex 1B and screened\ using ~uorescence microscopy\ for development of infection structures or host response[ To study cell wall appositions\ specimens were stained with trypan blue and a solution of picric acid in methyl salicy! late[ Aborted penetration\ consisting of nonpenetrating appressoria and aborted substomatal vesicles\ showed that inhibition of fungal growth in wheat lines containing Lr01 and:or Lr02 was activated\ to a certain degreebefore haustoria were formed[ At 139 h after inoculation colony size indicated that fungal colonies in the Lr gene combination lines were generally smaller than in the par! ents\ but not necessarily smaller than those in a line with Lr02 only[ Host cell necrosis was more frequently associated with infection sites\ speci_cally of pathotype UVPrt1\ in the combination lines than in the parents[ The morphology of cell wall appositions varied considerably from a narrow\ luminous zone slightly wider in the centreto a thick central part opposite the haustorium mother cell\ sharply decreasing towards both ends[ Histological assessments could\ however\ not conclusively prove pro! nounced resistance enhancement or unconventional resistance mechanisms due to combining the genes Lr01 and Lr02[ U[ S[ Copyright Clearan