Heuchera spp. (Saxifragaceae) are hardy perennials, principally native to North America. In July 2004, June and November 2005, samples of ornamental Heuchera spp. and the cultivar ‘Leuchtkäfer’ showing typical symptoms of rust disease were received at the RHS. These originated from private gardens in the English counties of Surrey, Kent and Hampshire. In July 2005, CSL also identified an outbreak of the same disease on a range of cultivars (‘Hollywood’, ‘Monet’, ‘Cherries Jubilee’ and ‘Persian Carpet’) at a nursery in southern England.
In the USA, Puccinia heucherae is a common rust on Heuchera and other members of the Saxifragaceae (Farr et al., 1995). This disease has also been recorded in East Asia (Savile, 1954). In Europe, P. saxifragae is a common disease on Saxifragaceae and has been reported in the UK on the genus Saxifraga (Wilson & Henderson, 1966). In the USA, this species has also been found on Heuchera (Farr et al., 1995). Therefore the possibility was considered that the Heuchera samples were infected by one of these two rust pathogens.
Morphological and molecular comparisons were carried out with herbarium samples of both species deposited at the Royal Botanic Gardens, Kew, UK. In all the samples received, the teliospores were dark brown, two-celled with a pale conical papilla. Spore morphology was not useful for distinction between P. heucherae and P. saxifragae, as the sizes of the teliospores were very similar. According to Savile (1954), the main distinction between P. heucherae and P. saxifragae is the presence of striations on the spore walls of P. saxifragae. However, the striations of the spores are not always present (Wilson & Henderson, 1966). This character was not apparent in our samples.
For DNA analysis, the 5′end of the large ribosomal subunit (LSU) was amplified and sequenced using the primers NL1/NL4 (Maier et al., 2003). The sequences of the two Puccinia species differ at six positions, which is enough to distinguish one species from another. The LSU sequences of the RHS and CSL samples (GenBank Acc. No. DQ359701-DQ359706) were identical to that of P. heucherae (K(M)129 792, DQ359700).
This is the first record of Puccinia heucherae in the UK. It is likely that it has been imported from the USA on infected plants. At the nursery outbreak, the cultivar ‘Hollywood’ came from the USA as plugs in March 2005 and was growing in close proximity to the other three cultivars, that all originated from the UK.