Occurrence of Rust Caused by Puccinia carthami on Snow Lotus in China

Snow lotus (Saussurea involucrata (Kar. & Kir.) Sch. Bip.) is an economically important medicinal herb increasingly grown in China in recent years. In August 2005, a rust disease on snow lotus plants commercially grown was found in the Tianshan mountain area of Xinjiang at 2,100 m above sea level. Disease incidence was approximately 15% of the plants observed in a commercial field in 2006. At the initial stage, tiny (1 to 2 mm long), orange brown pustules are formed on leaves. Later in the season, pustules turned chestnut brown to form bigger rust patches. Severely attacked leaves may die prematurely. During the growing season, rust pustules broke open to release reddish brown spores that cause secondary infection. The infected snow lotus plants were sampled, and the urediniospores and teliospores were observed for identification with a light microscope (4). Urediniospores were globose or broadly ellipsoid, 22 to 28 × 22 to 25 μm; teliospores were slightly or not constricted at the septum, 31.5 to 41.5 × 21.5 to 26.5 μm, wall was sienna to fulvous, occasionally chestnut colored, and pedicels were basal or oblique, verrucose, hyaline, and fragile. The pathogenicity test of the fungus was done by burying five leaves bearing telia around the roots of healthy safflower seedlings grown in a greenhouse under controlled conditions (25°C and 70% relative humidity) and healthy snow lotus seedlings grown under natural conditions with five replications. Symptoms were evaluated 60 days after inoculation. Similar rust symptoms were observed on both the snow lotus and safflower seedlings (1). The pycnidial and aecial stages of this autoecious rust were not observed in nature or the pathogenicity tests. The teliospores were reisolated and deposited at the Key Oasis Eco-Agriculture Laboratory of Xinjiang Production and Construction Group, Xinjiang and the Institute of Biotechnology, Zhejiang University. The causal organism of rust of snow lotus was identified as Puccinia carthami Corda on the basis of the morphology and pathogenicity test. To our knowledge, this is the first report of this rust on snow lotus (S. involucrata) (1-4). References: (1) W. L. Bruckart. Plant Dis. 83:181, 1999. (2) M. L. Deadman et al. Plant Dis. 89:208, 2005. (3) S. J. Kolte. Diseases of annual edible oilseeds crops. In: Rapeseed-Mustard and Sesame Diseases. Vol. II. CRC Press, Boca Raton, FL, 1985. (4) G. F. Laundon. N. Z. J. Bot. 8:310, 1970.