José Hernández and Lisa Castlebury - USDA, Agricultural Research Service, Systematic Botany and Mycology Laboratory (ARS, SBML) Beltsville, MD 20705-2350.

Mary Palm - USDA, Animal and Plant Health Inspection Service (APHIS), SBML, Beltsville, MD 20705-2350

Daylilies (Hemerocallis spp., Liliaceae) are one of the most important cultivated perennial plants in the United States of America (U.S.A.). Daylily rust, a serious disease caused by Puccinia hemerocallidis Thüm., was observed in Georgia (U.S.A.) in August 2000 and was found in at least 20 other states and in Costa Rica in 2001. It was originally described from Russia, reported throughout the Japanese archipelago, and recorded from China (Manchuria), Korea, and Taiwan.

Among the rust fungi, only Puccinia hemerocallidis is known to infect Hemerocallis spp. This study was undertaken because initial observations of variation in urediniospore morphology and the presence of many non-septate teliospores (mesospores) in the rust in the Americas suggested that it might be different from the Asian rust and that there might even be heterogeneity within the American rust. The type specimen of P. hemerocallidis from Siberia, Russia, was examined and compared with both recently and previously collected specimens from China, Costa Rica, Japan, Russia, Taiwan and the United States. This report provides an expanded description with photomicrographs of the fungus causing daylily rust.

Additionally, the internal transcribed spacer (ITS) region of the ribosomal DNA were sequenced for specimens from Costa Rica, Japan, Russia and the United States to compare the rust fungus from the Americas with recently collected Asian specimens of P. hemerocallidis.

Herbarium specimens from the U.S. National Fungus Collections (BPI), Arthur Herbarium (PUR), and Herbarium of Systematic Mycology, Ibaraki University, Japan, were examined. In addition, fresh specimens were obtained from colleagues in Russia and Japan, and from the U.S.A. and Costa Rica through USDA, APHIS interceptions and state surveys conducted in 2001 (see specimens examined). These collections were deposited at BPI.

Morphology. The range of variability of certain morphological characteristics found in this study is greater than indicated in the literature. Telia in collections from the Americas were smaller, less dense, and had many non-septate teliospores compared to those in the Asian collections in which telia were dense and with mostly 1-septate teliospores. The ratio of non-septate to 1-septate teliospores was variable between different sori within one specimen and among specimens. Some of the teliospores in the recent Japanese collections were found to be 2-septate and longer than those in the specimens from the Americas and Russia. Both teliospore and urediniospore sizes varied among specimens from different geographical regions, but the ellipses formed in scatterplots overlapped. Hiratsuka et al. mentioned brown paraphyses in the telia of P. hemerocallidis, but no paraphyses were observed in any of the specimens examined.

The following description of Puccinia hemerocallidis is based on examination of numerous specimens and expands the known morphological variation of this species on daylily.

Puccinia hemerocallidis Thüm., Bull. Soc. Imp. Nat. Moscow 55: 81. 1880.

Uredinia are first evident as hypophyllous, small, dark, circular to irregularly shaped, interveinal lesions that are initially less than 1 mm in diameter and 2 mm or more at maturity. A corresponding chlorotic area can be seen on the adaxial leaf surface. Uredinia are subepidermal, becoming erumpent, and often have a narrow, dark margin. The broken epidermis surrounds the mature uredinial sori, which are round to elongate and pale yellowish to yellow to orangish yellow. On older or otherwise chlorotic leaves, the yellow sori often are surrounded by a green halo. When the leaves are heavily infected the sori often become confluent and the lower leaf surface appears bright yellow due to the numerous urediniospores.

Urediniospores are yellow, globose to ellipsoid, (13.5-) 21-26.5 (-36) × (12-) 18.5-22.5 (-29.5) µm (mean = 24 µm ± 2.8 by 20.5 µm ± 2.2, n = 1041). The urediniospore wall is hyaline, echinulate, variable in width, measuring 1-2.5 µm when young and 2-3.5 (-4) (mean = 2.6 µm ± 0.6, n = 128) µm at maturity, with five to six obscure germ pores observable with cotton blue. Urediniospores are subtended by a non-persistent pedicel that is infrequently attached to the spore. No paraphyses were observed.

Telia are primarily hypophyllous, subepidermal and either remain covered by the epidermis, as in most Asian specimens, or erumpent, as in some U.S. specimens. Telia are round to slightly elongate and 0.5-1.5 mm in diameter. In American specimens telia appear brownish and less dense compared to the telia in Asian specimens which are blackish brown, dense and compacted. No paraphyses were observed.

Teliospores are variable but mostly ellipsoidal to clavate with an apical papilla, or angular with an eccentric papilla. Teliospores are nonseptate to 1-septate, rarely 2-septate, and usually slightly constricted at the septa. Non-septate teliospores measure (21.5-) 27.5-38.5 (-46.5) × (10-) 13-16.5 (-19.5) µm (mean = 33 µm ± 5.3 by 14.6 µm ± 1.9, n = 95) and 1-septate teliospores are (28.5-) 36-51.5 (-66.5) × (10.5-) 14.5-19 (-22.5) µm (mean 43.9 µm ± 7.7 by 16.6 µm ± 2.3, n = 233). The teliospore wall is smooth, brownish, darker brown at the apex, 1-1.5 µm at sides, and (1.5-) 3-8 (-10.0) µm (mean = 5.6 µm ± 2.5, n = 34) at apex. In each probasidial cell there is one germ pore near the apex in the upper cell and one germ pore adjacent to the septum in the lower cell.

The ITS region has been used to determine identities and phylogenetic relationships with other rust species as well as many other fungi and is easily amplifiable with rust specific primers even in the presence of host DNA. Virtually all available sequences in GenBank for rust fungi are for the ITS region. For the six specimens sequenced, ITS variation within the American specimens or within the Asian specimens was approximately equal to variation between specimens from the two broad geographic areas and indicates that the specimens are the same species. Two fixed substitutions and one insertion/deletion were present in the ITS regions that distinguished the two Asian specimens from the four American specimens. However, because of the limited sampling and the absence of significant morphological differences between specimens from the two broad geographic areas, no conclusions about the significance of these substitutions can be made.

Puccinia hemerocallidis has been reported from Austria, however after examining the specimen (Austria, Niederoesterreich, Tulln, Baumschule Gebhard & Fussel, on Hemerocallis sp; 23 Jul 1984, R. Fischer s.n. PUR N1738 [II]) we conclude that the fungus and host were misidentified. The urediniospores of the Austrian rust have 3-4 prominent, more or less equatorial germ pores with hyaline caps whereas those of P. hemerocallidis have 5-6 obscure, scattered germ pores with no caps. Urediniospores of the Austrian specimen had more dense and evenly distributed echinulations than those of P. hemerocallidis. Additionally, the urediniospores of the former were found to be significantly larger than those of P. hemerocallidis (mean = 29 µm ± 3.2 by 21 µm ± 2.2, n = 21; cell wall 2.1 µm ± 0.5, n = 14). No telia were observed in the Austrian collection The morphology of the leaf was inconsistent with that of species of Hemerocallis (C. Feuillet, pers. comm.). Therefore, the report of P. hemerocallidis in Europe is erroneous.

The center of origin of the daylily (Hemerocallis spp.) is eastern Asia. Puccinia hemerocallidis was described from Russia (Siberia) and, until 2000, known only from eastern Asia. Rusts are obligate parasites that usually coevolve with their host and therefore Asia is likely the center of origin of P. hemerocallidis. Puccinia hemerocallidis is reported to be heteroecious, producing the spermagonial and aecial stages on Patrinia (Valerianaceae), also native to Asia. To date, no rust infections have been reported on Patrinia in the U.S.A. where, although that host is neither native nor common, it is becoming more popular as a cultivated plant.

At present, P. hemerocallidis is reported from eastern Asia and many states in the United States as well as from Costa Rica. The disease first was observed in Georgia in the summer of 2000. Although there are reports from Florida that the rust had been present in that state for several years, no voucher specimens are available for confirmation. In the past years daylilies have been shipped from the United States to Costa Rica and other Central American countries to be multiplied during the North American winter. Trimmed cuttings are subsequently shipped back to several southeastern states where they are sold throughout the United States and to other countries. Additionally, daylilies are grown and traded extensively by hobbyists.

All evidence suggests that P. hemerocallidis inadvertently was introduced into the Americas quite recently although where it was first introduced is uncertain. The widespread movement of daylilies in commerce and among enthusiasts contributed to the rapid spread of this rust in the continental United States. It has also recently spread to Hawaii, Canada and Australia. General information about daylily rust, including control measures, can be found at http://www.aphis.usda.gov/npb/daylily.html; http://www.ncf.ca/~ah748/rust.html