Uredinia generally hypophyllous, on petioles and midribs, pustulate, orange-yellow, subepidermal, erumpent, 1-2 mm wide;uredineospores spores greyish-yellow, globose to ovoid, 26.5-43.5 x 12.5-31.0 µm, verrucose;epispore 0.5-1.0 µm thick, hyaline.
Leaves, particularly the petioles and midribs, of Rhodoendron plants from southern and central Asia, should be examined under low power magnification for the presence of telia and uredinia. A period of post-entry quarantine should be sufficient to detect latent (overwintering) infections in such plants, although it may not be completely successful (Savile, 1973;Bennell, 1985). Perennial infections may be detected by the proliferation of shoots, or “witches’ broom” symptoms.
Related invasive species
- Chrysomyxa himalensis
Related Farm Practice
- Defoliation
Related location
- India
C. himalensis is a heteroecious rust completing different stages of its life cycle on different plants. The teleomorph occurs on Rhododendron species in the Himalayan region of southern Asia;an anamorph is reported on Picea species. Although not a major problem in its narrow native range, this rust fungus could be more damaging as an invasive on Picea and Rhododendron. The fungus is a Regulated Pest for the USA;it is considered potentially damaging to Rhododendron by CAST (2002). Small amounts of perennial or latent infection may be overlooked, therefore accidental introduction of the rust could occur through importation of infected germplasm by the horticultural industry or by flower enthusiasts.
This rust causes a “witch’s broom” of Rhododendron. Stunted shoots proliferate from infected stems. Leaves on these shoots are small, but not otherwise distorted (Barclay, 1890). Spaulding (1961) states that “it is considered to be the cause of occasional serious defoliation of spruce [ Picea ] in India and Pakistan”, but the timing of the defoliation and any symptoms preceding it are not reported.
Roane (1986) lists a few Himalayan or Tibetan Rhododendron species as susceptible, but other species from that region are not reported to be susceptible. Susceptibility of the species/hybrids of other origins is not known, and many, if not most, have not been tested. Farr et al. (1996) list four host species known from China, India, and Nepal. The rust may be limited in its host range to species in certain sections of the host genus, as other Chrysomyxa species appear to be (Crane, 2005).