FIRST REPORT OF ALTERNARIA ALTERNATA CAUSING A BLIGHT DISEASE OF EUPHORBIA LATHYRIS IN CHINA

Abstract

During 2008-2010, a blight disease was observed in caper spurge (Euphorbia lathyris L.), an important traditional medicinal plant species, in Nanjing (China). Symptoms appeared in early summer on stems as circular or irregularly shaped, small, brown-to-black spots or/and on shrivelled leaf apices. The lesions rapidly expanded around the stems or along the leaf blades in the rainy season. The disease occurred on 50 to 80% of the plants, with a mortality rate of ca. 70%. A fungus, recovered from diseased tissues, was grown on potato carrot agar (PCA) to produce conidia. These had the size of 10-52×7-16 μm (primary conidia 2552×7-16 μm; secondary conidia 10-27×7-13 μm), were brown to dark-brown, ovoid to ellipsoid, had a short conical or cylindrical apical beak, and showed 1 to 5 transverse septa and 0 to 3 longitudinal septa. The internal transcribed spacer (ITS) region (White et al., 1990) was amplified, sequenced and deposited in GenBank (accession No. HQ873733). BLASTn analysis of the 571 bp amplified product showed 100% homology with Alternaria alternata (AB470912). Based on these results, the fungus was identified as A. alternata (Fr.:Fr.) Keissl (Simmons, 1990). Pathogenicity tests were performed by spraying caper spurge seedlings with a suspension of conidia (1×106 conidia per ml). Control plants were they sprayed with sterile water. After 9 days, inoculated plants developed blight symptoms similar to those shown by naturally infected plants. No symptoms occurred on control plants. The pathogen was reisolated and identified, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of A. alternata on E. lathyris in China.