Daylily is highly valued throughout the world as an easily grown herbaceous perennial for the landscape, with a proper selection of species and clonal hybrids providing an ongoing display of flowers from spring through fall. Daylily varies in growth habit; bloom season; and size, shape, and color of flowers. The robust and often fleshy roots of daylily withstand drought and their compact and sturdy, clumping growth habits allow daylily plants to tolerate competition from garden weeds (Hill and Hill, 1991; Stout, 1986). Daylily flowers may be used to flavor and garnish culinary dishes (Pollard et al., 2004).
Daylily generally has few insect and disease pests in the landscape; however, daylily rust, caused by the fungus Puccinia hemerocallidis, was observed for the first time in the United States on plants of the cultivar Pardon Me at a nursery in Georgia in Aug. 2000, apparently introduced via plants imported from South America (Williams-Woodward et al., 2001). Daylily rust spread quickly throughout much of the United States through movement of infected stock (Buck and Ono, 2012). Before 2000, the pathogen was known only from eastern Asia (Hernández et al., 2002). Multiple pathotypes of the pathogen have been identified in the southeastern United States (Buck, 2013). Disease management strategies include quarantine of new nursery stock, use of disease-resistant cultivars, scouting for signs and symptoms of rust, and use of preventative fungicides (Buck and Ono, 2012).
The daylily rust pathogen produces yellow-orange to rust-brown pustules containing urediniospores on upper and lower leaf surfaces within 1 to 2 weeks after infection (Williams-Woodward et al., 2001). Additional symptoms reported on infected plants include bright yellow-orange spots and streaks, water-soaked tan spots with darker borders, large yellow lesions, and small discrete spots (Williams-Woodward and Buck, 2001). Mueller and Buck (2003) determined that temperatures around 72 °F with 5 h of leaf wetness are required during infection; however, disease development is not as sensitive to environmental conditions once infection has taken place. Cultivar-specific resistance and partial resistance to the pathogen involve hypersensitive cell death and a delayed latent period and reduced sporulation resulting from restriction of intercellular hyphal growth (Li et al., 2007).
Identification of rust-resistant and rust-susceptible daylily cultivars is of benefit to breeders, commercial growers, and home gardeners, particularly in helping to reduce the time and expense involved in repeated fungicide applications in nurseries and landscapes. In Georgia, Williams-Woodward and Buck (2001) conducted a preliminary greenhouse study with pathogen-inoculated plants of 22 cultivars and Mueller et al. (2003) followed with a greenhouse study with pathogen-inoculated plants of 84 cultivars to assess relative resistance to daylily rust. Robbins and Vann (2002) surveyed 500 field-grown cultivars at a small commercial nursery in central Arkansas in 2001, with a follow-up survey of 500 cultivars in 2002 (Robbins, 2003), with 75% of these cultivars also surveyed in the prior year.
As of early 2015, over 78,000 cultivars have been registered with the American Hemerocallis Society (2015). Little information is available on resistance and susceptibility of daylily cultivars that have been developed and registered since 2000. This report presents results from a survey of 575 mostly modern (registered from 2000 onward) hybrid cultivars of daylily growing in a landscape in southern Mississippi under conditions favorable for daylily rust.
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