Paper mulberry, Broussonetia papyrifera (L.) Venten. (family Moraceae), is a fast-growing tree with luxuriant branches and leaves. Because of strong adaptability and tolerance to unfavorable environmental conditions, it is an important tree species for shade or shelter and reforestation in mined areas and on hillsides. During the summer of 2010, brown-to-black spots were observed on leaves of paper mulberry in Baiwangshan Forest Park in Beijing, China. Early symptoms were round or elliptic, light brown, small lesions that later extended to round or irregular spots (4 to 6 × 4 to 8 mm) that were dark brown or black in the center with brown or light brown margins. Several dozen spots were found on severely infected leaves. Leaf tissues (2 × 2 mm), cut from the margins of lesions, were surface disinfected in 0.5% NaOCl solution for 3 min, rinsed three times with sterile water, plated on potato dextrose agar (PDA) and incubated at 25°C with a 12-h light and 12-h dark period. Numerous waxy subepidermal acervuli with setae were observed after 3 days. Acervuli were brown or black, round or elongate, and 100 to 250 μm in diameter. Setae were dark brown, erect straight or slightly curved, and 60 to 74 × 4 to 8 μm with one to two septa. Conidiophores were hyaline or light brown, short with no branches, and cylindrical with dimensions of 12 to 21 × 4 to 5 μm. Conidia were 11 to 21 × 3 to 6 μm, hyaline, aseptate, and cylindrical. Mycelia on PDA were off white-to-dark gray on the reverse side of the colony. Six isolates (BP21-1 to BP21-6) were obtained from different infected leaves and identified as Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. (teleomorph Glomerella cingulata (Stonem.) Spaulding & Schrenk) on the basis of reverse colony color, dimensions and colors of acervuli, conidiophores, and conidia (3). ITS1-5.8S-ITS2 rDNA sequence analysis was performed on all six isolates. The resultant sequences were identical (GenBank Accession No. HQ 654780) and revealed 99% similarity (100% coverage) with C. gloeosporioides isolates in the GenBank (Accession Nos. EU371022.1 and AY376532.1) (2). Pathogenicity was demonstrated using six potted 3-month-old paper mulberry trees. Isolate BP21-2 was grown on PDA for 14 days and conidia were harvested to prepare a suspension of 106 conidia/ml. Three plants were sprayed with the conidial suspension and three were sprayed with sterile water. All trees were covered with plastic bags for 24 h to maintain high humidity and incubated at 25°C for 6 days. All conidia-inoculated trees showed identical symptoms as the infected leaves in the park, while the control trees remained symptom free. Reisolation of the fungus confirmed that the causal agent was C. gloeosporioides. C. gloeosporioides is distributed worldwide causing anthracnose on a wide variety of plants including members of mulberry family Moraceae, e.g., mortality of stem cuttings and death of saplings on mulberry (Morus alba L.) in India (1). To our knowledge, this is the first report of C. gloeosporioides causing black spots on paper mulberry in China.
References: (1) V. P. Gupta et al. Indian Phytopathol. 50:402, 1997. (2) K. D. Hyde et al. Fungal Divers. 39:147, 2009. (3) J. E. M. Mordue. No. 315 in: Descriptions of Pathogenic Fungi and Bacteria. CMI. Kew, Surrey, UK, 1971.
