DAYLILLY RUST

Rust on daylilies is a complex disease which goes through several different life cycle stages. Part of the life cycle takes place on daylilies and part on another Asian perennial plant known as Patrinia. A diagram of the life cycle appears below with the stages on daylily in blue, and those on Patrinia in red. A more detailed (but still somewhat simplified) description of the different stages follows the diagram.

On daylilies, the rust produces two spore types, urediospores and teliospores. A spore is a reproductive unit capable of germination and growth, somewhat similar to a plant seed. The repetition of infection on daylilies by urediospores alone is an asexual (cloning) method of reproduction which serves to build up the level of disease. The rust also has a form of sexual reproduction which cannot be completed without the alternate host, Patrinia. Both hosts are needed to fully complete the life cycle of this rust, although the rust can overwinter without the sexual cycle where conditions permit.

A daylily plant's first infection starts when a urediospore from a daylily or an aeciospore from Patrinia lands on a leaf, then grows and feeds inside the living leaf in the form of mycelium (fungal strands), eventually producing a mass of urediospores which erupt outwards through the leaf's epidermis ("skin").
These urediospores are also known as "repeating" spores or "summer" spores, and are spread mostly by the wind to leaves of daylily plants to cause more infection and produce more urediospores.
Cycles of urediospore infection and production can continue on daylilies indefinitely under suitable environmental conditions. However, the urediospores cannot infect Patrinia.
Later in the season, the rust prepares to overwinter by producing another type of spore called teliospores, also known as "winter" spores because they are typically tougher and more resistant to cold temperatures than urediospores. Teliospore masses (telia) first appear as darkened areas around the more familiar orange spots containing urediospores, and then turn black. Other methods by which rusts can overwinter are as dormant mycelium and, less commonly, urediospores.
Teliospores pass the winter in a dormant state on the dry, dead daylily leaves. In warm climates, teliospores do not appear to be necessary for winter survival of the rust since the asexual stage can continue through the winter.
In the spring, the teliospores germinate on the dead daylily leaves to produce basidiospores. Basidiospores cannot infect daylilies and must instead infect the alternate host, Patrinia.
The basidiospores produced on daylily leaves in spring are carried by wind, or other means, to Patrinia where they result in the production of dark spots called spermogonia or pycnia.
Spermogonia produce spermatia (also called pycniospores) which fertilize receptive hyphae in spermogonia of the opposite mating type.
Successful fertilization leads to the production of structures known as aecia on the other side of the Patrinia leaf.
These aecia produce another spore type, aeciospores which cannot re-infect Patrinia but must return to daylilies via the wind or other means.
When the aeciospores land on daylilies and environmental conditions are suitable, they germinate and penetrate the leaf resulting in mycelium again growing inside the daylily leaf.
Later, masses of urediospores erupt through the leaf epidermis to re-start the cycle described above.

Note: Rusts are "obligate parasites" which means that their mycelium can only grow and feed in living plant tissue. The spores, on the other hand, can live independently of live plants for varying periods of time. The longevity of the different spore types of daylily rust is not yet known. In order to germinate and infect, however, urediospores, basidiospores and aeciospores must land on living plant parts and experience suitable conditions of moisture and temperature. The requirements for urediospore germination are discussed in other links on this site. In contrast, teliospores do not need living tissue on which to germinate and produce basidiospores.

It is not yet known where and by which method daylily rust will overwinter in the different regions of North America, although it did successfully overwinter in Florida in 2000/1 and 2001/2. Only urediospores and teliospores have been reported since the rust was first identified in North America in August 2000 - the teliospores were present in Florida¹ and Georgia². Puccinia hemerocallidis was first recorded in 1880 in Siberia, Russia³. The spermogonial/aecial stage on Patrinia, and its relationship to rust on daylilies, has been documented in Russia (Tranzschel, 1913)⁴ and Japan (Hiratsuka, 1938)⁴.

Reprinted from an article by Susan Bergeron -
http://www.ncf.ca/~ah748/lifecycle.html

¹Florida Department of Agriculture - includes images
² Research by Dr. Williams-Woodward and Dr. Buck (SNA site)
³ Record of Daylily Rust in Siberia in 1880
⁴Hiratsuka, N., Sato, T., Katsuya, K., Kakishima, M., Hiratsuka, Y., Kaneko, S., Ono, Y., Sato, S., Harada, Y., Hiratsuka, T., and Nakayama, K. 1992. The Rust Flora of Japan. Tsukuba Shuppankai, Ibaraki, Japan. Pages 710-711.