FIRST REPORT ON MYCOSPHAERELLA MORI ON MORUS NIGRA AND M. RUBRA IN POLAND

Abstract

In 2016 leaf spot and necrosis were observed on mulberry plants (Morus nigra and M. rubra) in house gardens and public parks in the city of Poznan and in several other locations in the west of Greater Poland district. At first, evenly distributed small, brown spots appeared on the leaves, which successively developed in oval or irregular necrotic lesions up to 18 mm in size. Infected tissues from M. nigra, M. rubra and M. alba collected from eight locations were cut to small pieces, surface-sterilized and transferred to PDA (Potato dextrose agar). Cultures incubated at 21°C for 10 days exhibited a dense, velvety, whitish to grey mycelium. Hyaline, straight or curved conidia, mostly 3-6 septate 54 (38-82) x 4.4 (4-5) µm were observed either on affected leaves or on isolates grown on PCA (Potato carrot agar). Pathogenicity tests were conducted according to Hong et al. (2011) on three M. alba plants with two isolates from M. nigra and M. rubra. Small brown spots developed only on inoculated leaves, 12 dpi, from which the same fungus used for inoculations was reisolated. The internal transcribed spacer region of 10 cultures (five M. alba, three M. nigra and two M. rubra) was PCR-amplified followed by sequencing of the amplified products (GenBank accession Nos. KX982229-31). A BLAST search revealed 100% identity of all tested amplicons with the sequence of Mycosphaerella mori (AB435069). Molecular analysis and morphological features, support the identification of M. mori as the causal agent of the disease observed on M. nigra and M. rubra. This pathogen is of wide occurrence on Morus spp. in the world (Farr and Rossman, 2017). To our knowledge this is the first report of M. mori on M. nigra and M. rubra in Poland.