First report of alternaria leaf blight of blackberry-lily caused by Alternaria iridicola in Korea

A leaf blight disease of blackberry-lily (Belamcanda chinensis) was observed during September 1999, in a garden in Kyonggi district, Korea. Further survey of the blackberry-lily in gardens in the district of Chungnam and Kyongbuk revealed that the disease was widespread and under moist conditions was responsible for considerable damage.

Leaf lesions were elliptical to irregular oval in shape, yellow brown to dark brown, sometimes concentrically zonate with diffuse margins frequently surrounded by light coloured haloes. Infection often started at the leaf tips and progressed to the base of leaves as symptoms developed (Fig. 1). In severe infections, lesions enlarged and coalesced, resulting in blighting of the leaves.

A species of Alternaria having conidia with prominent beaks and spores produced singly or in chains of 2-4 was consistently observed on and isolated from the lesions of the plant. On PDA the fungus grew slowly, colonies reaching about 35mm in diameter in 7 days when incubated at 25°C. Conidiophores from naturally infected blackberry-lily were more or less cylindrical, arising singly or in bundles of 2-5, pale yellow to pale brown, straight or flexuous, almost colourless at the tip, sometimes geniculate with one to several conidial scars and measuring up to 120×5-7.5µm. The conidia from the host were obclavate to long ovoid, mostly straight or slightly curved, pale olive or pale brown and smooth. The number of transverse septa varied from 3-10, and 1 to several longitudinal septa were present. The conidia were slightly or sharply constricted at the transverse septa and measured 20-95×15-35µm with beaks which measured up to 90µm (Fig. 2). The isolates were identified as Alternaria iridicola J. A. Elliott (Elliot, 1917, Shimasaki, 1930). A. iridicola has been reported on Iris species in the central United States (Anonymous, 1960) and Japan (Anonymous, 1980), but little is known of this pathogen from Korea.

Pathogenicity tests were carried out in the greenhouse on 2-month-old plants of blackberry-lily, Iris germanicola and Iris nertschinskia. These were sprayed with a conidial suspension (5×10⁴ conidia per ml) of Alternaria isolated from diseased blackberry-lily; control plants were sprayed with sterilised water. Plants were covered with polyethylene bags for 2 days. Disease symptoms on blackberry-lily and Iris species appeared 3 days after inoculation. Symptoms on Iris leaves were similar to those on blackberry-lily. Control plants did not develop symptoms. A. iridicola was consistently re-isolated from inoculated plants. This is believed to be the first report of A. iridicola on blackberry-lily.