Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2006
Publication Date: 3/1/2007
Citation: Li, Y.H., Windham, M.T., Trigiano, R.N., Fare, D.C., Spiers, J.M., Copes, W.E. 2007. Microscopic and Macroscopic Studies on Resistance Responses to Daylily Rust. Southern Nursery Association Research Conference 51:234-238.
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 process of Puccinia hemerocallidis, the causal agent of daylily rust, and resistance responses in eight daylily cultivars were studied macroscopically and microscopically. After germination of urediniospores, appressoria formed at the tip of germ tubes and penetrated through stomatal openings. Intercellular hyphae aggregated and formed uredia under the infection sites, and released urediniospores after rupturing the epidermis. In highly resistant cultivars ‘Prairie Blue Eyes’ and ‘Bertie Ferris’, intercellular hyphal growth was restricted and uredia were not formed. No macroscopic symptoms of the disease were present on the leaf surface although a few collapsed cells were observed 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 on the moderately resistant cultivar ‘Chicago Apache’, but not on resistant cultivars, ‘Buttered Popcorn’ and ‘Stella De Oro’. Sporulation was observed on both moderately susceptible and susceptible cultivars, but latent periods were delayed and the amount of urediniospore production was reduced on moderately susceptible cultivars, ‘Mary Todd’ and ‘Chorus Line’, compared to susceptible cultivar ‘Pardon Me’. The results indicate that the hypersensitive cell death is one of the resistance responses to daylily rust, but necrotic lesions on leaf surfaces are associated with the amount of collapsed host cells. Delayed latent periods and reduced sporulation that resulted from restricted intercellular hyphal growth could represent another resistance mechanism in the daylily rust pathosystem.