First Report of Anthracnose of Malva sylvestris Caused by Colletotrichum trifolii in China.

Common mallow (Malva sylvestris L.) is a perennial medicinal plant in the Malvaceae family, which is native to Asia, Europe, and North Africa. In July 2012, typical symptoms of anthracnose disease, with a disease incidence of ~70%, were observed on common mallow in the Medicinal Herb Garden of Shenyang Pharmaceutical University, Liaoning, China. The fungus mainly infected the stalks and leaves of M. sylvestris. Pinpoint, brownish lesions initially appeared at the flowering stage and the disease spread within the field. The lesions on stems gradually enlarged and became dark brown, elliptical, and slightly concave. Concurrently, acervuli and mucilaginous conidial masses of the pathogen appeared on lesions under moist conditions. Conidia were hyaline, one-celled, cylindrical with both ends rounded, and measured 10.0 to 12.5 × 2.5 to 4.0 μm (mean 11.3 × 3.3 μm). The fungus was isolated from symptomatic tissues. Small pieces from leaves and stems were surface disinfested with 70% ethanol and 1.5% sodium hypochlorite for 1 min, then rinsed three times with sterile distilled water, and cultured on potato dextrose agar (PDA) at 25°C. The colonies on PDA had initially white aerial mycelia, and later became greenish black with regularly whorled rings. To confirm Koch's postulates, five 3-month-old plants of M. sylvestris were inoculated with a conidial suspension (10 conidia/ml) prepared from PDA cultures incubated for 14 days. Five non-inoculated plants served as controls. The plants were maintained in the greenhouse at 22 to 25°C and about 75% relative humidity under natural daylight. Typical symptoms on inoculated plants were reproduced after ~10 to 14 days, whereas control plants remained asymptomatic. The pathogen was successfully recovered from symptomatic tissues and re-identified, completing Koch's postulates. The internal transcribed spacer (ITS) and large subunit -28S (LSU) region of rDNA was amplified with primers ITS1/ITS4 and NL1/NL4, respectively, and sequenced. Phylogenetic trees (ITS and LSU) that were obtained using MEGE3.1 with the neighbor-joining method showed that both of the isolates fall in the Colletotrichum trifolii clade. The representative sequences (ITS and LSU) were deposited in GenBank (Accession Nos. KJ155692 and KJ920935). The fungus isolated from symptomatic tissues was identified as C. trifolii on the basis of morphological, cultural characteristics, and sequence analysis (2). According to previous references, C. orbiculare and C. malvarum on Malvaceae were respectively described in America and Europe (1,3,4). However, the isolate from M. sylvestris significantly differed from those of C. orbiculare and C. malvarum in cultural characteristics and sequence analysis. In this paper, the results showed that M. sylvestris is a new host of C. trifolii. To our knowledge, this is the first report of mallow anthracnose caused by C. trifolii in China. References: (1) J. A. Bailey et al. Phytopathology 86:1076, 1996. (2) U. Damm et al. Fungal Divers. 61:29, 2013. (3) K. Hyde et al. Fungal Divers. 39:147, 2009. (4) L. Tosi et al. Plant Dis. 88:425, 2004.