Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2006
Publication Date: 6/1/2007
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2007. Microscopic and Macroscopic Studies of the Development of Puccinia hemerocallidis in Resistant and Susceptible Daylily Cultivars. Plant Disease. 91:664-668. Interpretive Summary: Daylily rust, caused by Puccinia hemerocallidis, is a newly introduced disease in the United States. The objective of this study was to investigate varying resistance mechanisms utilized by eight daylily cultivars, ‘Buttered Popcorn’, ‘Mary Todd’, ‘Chorus Line’, ‘Chicago Apache’, ‘ Blue Eyes’, ‘Stella De Oro’, ‘Bertie Ferris’ and ‘Pardon Me’. The eight daylily cultivars were grouped into five categories, based on the size of lesions, the length of time before the fungus produced spores in the lesion, and the amount of spores produced. Differences in infection types and resistance components among daylily cultivars suggest that different resistance mechanisms exist in the daylily-rust pathosystems. The results provide scientists and breeders with information that can be used to further evaluate daylily rust resistance and provide growers and consumers with a disease resistant rating for currently available cultivars.
Technical Abstract: Infection and colonization of eight daylily cultivars, which varied in resistance to daylily rust, by Puccinia hemerocallidis was studied macroscopically and microscopically. After germination of urediniospores, appressoria formed at the tip of germ tubes and the fungus penetrated the host through stomatal openings 2 days after inoculation (DAI). Under the infection sites, intercellular hyphae aggregated and formed uredia, which released urediniospores 8 DAI. Resistant cultivars, characterized by the development of rapid death of host cells, were separated into three qualitative categories based on absence and presence of necrotic lesions without or with sporulation. In highly resistant cultivars ‘Prairie Blue Eyes’ and ‘Bertie Ferris’, no macroscopic disease symptoms were observed on leaf surfaces although a few collapsed cells were detected microscopically. Both resistant and moderately resistant reactions were characterized by necrotic lesions with many collapsed cells under infection sites. The difference between these two reactions was that uredia and urediniospores were observed in the moderately resistant cultivar ‘Chicago Apache’, but not in resistant cultivars, ‘Buttered Popcorn’ and ‘Stella De Oro’. Susceptible cultivars, characterized by the absence of a hypersensitive response, were separated into two qualitative categories based on restriction of intercellular hyphal growth that delayed development of uredia and formation of urediniospores. Compared to the susceptible cultivar ‘Pardon Me’, moderately susceptible cultivars ‘Mary Todd’ and ‘Chorus Line’ had delayed latent period and reduced amount of sporulation. The results indicate that hypersensitive cell death is one of the resistance responses to daylily rust. Necrotic lesions on leaf surfaces are associated with the number of collapsed host cells. Delayed latent period and reduced sporulation that resulted from restriction of intercellular hyphal growth could represent another type of resistance response in the daylily rust pathosystem.