Pucciniastrum verruculosum causing rust disease on Aster tataricus in Korea

Abstract

Aster tataricus (Tatarian aster, Asteraceae) is a perennial herb native to East Asia. The plant is used as a traditional herbal medicine for the treatment of coughs and asthma. In Korea the plant is cultivated as an ornamental, but its young leaves are also edible when cooked like spinach. In September 2016, symptoms of rust disease were found on A. tataricus in a public garden (c. 0.5 ha) in Goseong and on Taegi mountain in Hoengseong, Korea, with a disease incidence of 85% and 55%, respectively (Figure 1). Symptoms appeared as yellowish, vein-limited, polyangular, chlorotic spots on the upper surface of infected leaves, and yellow to orange-coloured pustules of the uredinial stages were revealed on the corresponding lower surfaces (Figure 2). During subsequent surveillance in 2020, two additional samples of the rust were collected in Gapyeong, and four samples from all three areas were deposited in the Korea University herbarium (Accession Nos. KUS-F29482, F29504, F31844, and F32016).The infected leaves were examined under a light microscope. Uredinia were hypophyllous, subepidermal, scattered or grouped, bright yellow to orange, round, and 100-200 µm in diameter (Figure 3). Urediniospores were initially hyaline, later yellowish, ovate to ellipsoid and (17.5-)19.3-22.1(-24.3) × (14.7-)15.3-17.5 (-20.6) µm (av. 20.7 × 16.4 µm) (Figure 4), echinulate with a thin wall of 0.8-1.5 µm (av. 1.1 µm) (Figure 5). The telial stage was not observed. The morphological characteristics were consistent with those of Pucciniastrum verruculosum