Plumeria spp. are ornamental trees commonly planted in parks and gardens, and Plumeria rubra cultivars (Frangipani) is most common in Guangdong Province, China. A rust disease of P. rubra was observed on leaves of susceptible plants from August to December 2013. Ten nurseries were surveyed in September 2013, and 91% (220 of 240) of the plumeria plants were infected with rust. Symptoms first appeared as chlorotic spots (about 1 mm in diameter) appearing on adaxial leaf surfaces and then spread to whole leaf, and infection further resulted in leaf necrosis and abscission. Therefore, the ornamental value of diseased trees was greatly diminished. Bright yellow or yellow-orange uredinia were hypophyllous and produced under the epidermis. Urediniospores were catenulate, globose, ovoid or ellipsoid, and sometimes angular in appearance, ranging from 20.0 to 42.0 μm in length by 14.1 to 25.6 μm in width. Their walls were verrucose and 1.3 to 3.2 μm thick. No teliospores were observed. The rust was identified as Coleosporium plumeriae Pat. based on urediniospore morphology (2). Species identity was confirmed with a 1,551-bp sequence (GenBank Accession No. KF879087) of ITS rDNA amplified with rust-specific primers Rust2inv and LR6 (1). The amplicon had a 100% similarity to C. plumeriae (GU145555). Pathogenicity was confirmed by spraying a urediniospores suspension (15,000 spores ml−1) on five plants of P. rubra cultivar. Five leaves of each plant were inoculated and sealed in plastic bags, while five control plants were applied with sterile water. Plants were held at 28°C for 36 h in a dew chamber. All inoculated leaves developed typical rust symptoms with the uredinia appearing after 9 days, no symptoms developed on any control plants. Urediniospores were produced on infected leaves and pathogen identity was confirmed by morphology and re-sequencing of the ITS rDNA. Plumeria rust was first found in Hong Kong (4) and then in Hainan and Yunnan Provinces, China (3). However, this is the first report of plumeria rust in Guangdong Province, China. Frangipani has large, colorful flowers in the summer, and this rapidly spreading disease causes severe damage and affects their aesthetic value in the second half of the year.
References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) N. Patouillard. Bull. Soc. Mycol. Fr. 18:171, 1902. (3) Q. Wang et al. New Dis. Rep. 23, doi:10.5197/j.2044-0588.2011.023.010, 2011. (4) J. Yan et al. Mycosystema 25:327, 2006 (in Chinese).