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Exposure of crown rust differential varieties of Avena spp. to 10 pphm ozone for 6 hr in the light for 10 days after infection with Puccinia coronata significantly reduced the growth of uredia. Urediospores produced on the plants exposed to ozone germinated as well, produced as many appressoria, and resulted in as much infection as spores produced on unexposed leaves. Exposure on dry leaves to 20 pphm ozone for 3 hr for 1-5 days did not affect urediospore germination, appressoria formation, or penetration. 9 references, 1 figure, 3 tables.

Lines of Pendek each containing a single Avena sterilis gene (Pc-38, Pc-39, Pc-40, Pc-41, and Pc-42) were tested to 116 isolates of Puccinia coronata var. avenae identified in Canada in 1968. None of the isolates attacked gene Pc-39 and only two isolates (races 290 and 326) attacked Pc-38. The other A. sterilis genes were not particularly effective against these crown rust isolates.

A HIGH degree of ‘field’ resistance to infection by leaf rust (Puccinia coronata var. lolii) has been developed in perennial ryegrass (Lolium perenne), an open pollinated plant, by selecting individual plants for resistance (as one of several agronomic characters) from the progenies of open pollinated strains. The strains, selected by Corkill et al., were tested for combining ability and other agronomic characters. Several were allowed to interpollinate to form the synthetic variety released as New Zealand perennial ryegrass1.

Background Adaptation of pathogens to their hosts depends critically on factors affecting pathogen reproductive rate. While pathogen reproduction is the end result of an intricate interaction between host and pathogen, the relative contributions of host and pathogen genotype to variation in pathogen life history within the host are not well understood. Untangling these contributions allows us to identify traits with sufficient genetic variation for selection to act and to identify mechanisms of coevolution between pathogens and their hosts. We investigated the effects of pathogen and host genotype on three life-history components of pathogen fitness; infection efficiency, latent period, and sporulation capacity, in the oat crown rust fungus, Puccinia coronata f.sp. avenae, as it infects oats (Avena sativa). Results We show that both pathogen and host genotype significantly affect total spore production but do so through their effects on different life-history stages. Pathogen genotype has the strongest effect on the early stage of infection efficiency, while host genotype most strongly affects the later life-history stages of latent period and sporulation capacity. In addition, host genotype affected the relationship between pathogen density and the later life-history traits of latent period and sporulation capacity. We did not find evidence of pathogen-by-host genotypic (GxG) interactions. Conclusion Our results illustrate mechanisms by which variation in host populations will affect the evolution of pathogen life history. Results show that different pathogen life-history stages have the potential to respond differently to selection by host or pathogen genotype and suggest mechanisms of antagonistic coevolution. Pathogen populations may adapt to host genotypes through increased infection efficiency while their plant hosts may adapt by limiting the later stages of pathogen growth and spore production within the host.