Quantification of early infection structures of Puccinia recondita f. sp tritici in wheat with leaf rust resistance derived from Triticum monococcum

Using scanning electron microscopy, the formation of Puccinia recondita f. sp. tritici infection structures was studied in the Triticum aestivum line KS93U9 (pedigree: Karl(star)3//Pl266844/Pl355520), Karl (a leaf rust-suscep tible bread wheat cultivar) and the T. monococcum lines Pl266844, Pl355520 and Tm2126/5. Leaf sections infected with pathotype UVPrt9 of P. recondita f. sp. tritici were sampled 6, 12, 24, 36 and 48 h after inoculation. Infec tion structures were classified according to the following categories: germ tubes not forming appressoria, appressoria formed over stomata and elsewhe re on the leaf surface, substomatal and aborted vesicle initials, substomat al and aborted vesicles, primary infection hyphae with and without haustori um mother cells, and secondary infection hyphae, with and without haustoriu m mother cells. Indications of variable fungal behaviour on the leaf surfac e were observed among lines. KS93U9 and Tm2126/5 responded similarly in the occurrence of aborted infection structures at most sampling times. Fewer a borted substomatal vesicles or their initials, and more secondary hyphae wi th haustorium mother cells, were observed in the leaf rust-susceptible cult ivar Karl and the T. monococcum lines Pl266844 and Pl355520. Based on the f requency of aborted substomatal vesicles or their initials, the onset of le af rust resistance appeared to be as early as 6 h post-inoculation in KS93U 9 and Tm2126/5. However, vesicle abortion occurred more commonly in these l ines between 12 and 48 h post-inoculation. Scanning electron microscopy of epidermal strips allowed a precise determination of early infection structu res of P. recondita f. sp. tritici.