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- Author or Editor: Jean L. Williams-Woodward x
- HortScience x
Daylilies (Hemerocallis sp.) have traditionally been considered to be pest-free. However, a rust disease caused by Puccinia hemerocallidis Thüm. has become an increasing problem in the United States since 2000. The objective of this study was to evaluate daylily cultivars for resistance to daylily rust. From a greenhouse evaluation of 84 inoculated cultivars, 14 (17%) were classified as resistant; 13 (15%) were classified as moderately resistant; 22 (26%) were classified as moderately susceptible; and 35 (42%) were classified as fully susceptible. Several cultivars displayed very high levels of resistance and may be utilized by breeders to develop cultivars with improved resistance to daylily rust. Information about the resistance and susceptibility of cultivars also will help commercial growers and gardeners select cultivars that have the potential to dramatically reduce damaging outbreaks of rust.
The eriophyid mite, Phyllocoptes fructiphilus, vectors the causal agent, Rose rosette virus (RRV), that results in rose rosette disease. Parts of the southeastern United States have remained free of the disease, except for infected plant material introductions that were eradicated. A survey of sampling points through Alabama, Georgia, and Mississippi (n = 204) revealed the southeastern border of RRV. The presence of RRV in symptomatic plant tissue samples (n = 39) was confirmed by TaqMan-quantitative reverse transcription polymerase chain reaction (RT-qPCR). Samples were also collected at every plot for detection of eriophyid mites, specifically for P. fructiphilus. Three different species of eriophyid mites were found to be generally distributed throughout Alabama, Georgia, and Mississippi. Most of these sites (n = 60) contained P. fructiphilus, found further south than previously thought, but in low populations (<10 mites/gram of tissue) south of the RRV line of incidence. Latitude was found to be significantly correlated with the probability of detecting RRV-positive plants, but plant hardiness zones were not. Plot factors such as plant size, wind barriers, and sun exposure were found to have no effect on P. fructiphilus or the presence of RRV. The reason for the absence of RRV and low populations of P. fructiphilus in this southeast region of the United States are unclear.