First Report of Anthracnose of Digitaria sanguinalis Caused by Colletotrichum hanaui in China
Authors: Qiu H. P. , Wang Y. L. , Zhang Z. , Mao X. Q. , Jiang H. , Sun G. C. 
Published: November 2010

Hairy crabgrass (Digitaria sanguinalis (L.) Scop.) is a troublesome weed in most agricultural crops worldwide. Considerable efforts are made to limit the invasiveness and impact of crabgrass on crop productivity, including evaluation of fungi as biocontrol agents (3). In September 2005, a severe disease was observed on crabgrass plants in Zhejiang Province. Leaves and stems of the affected plant showed small, water-soaked, brownish spots that rapidly turned into longitudinal elliptic or spindle-shaped lesions, 6.5 to 8 × 22 to 24 mm, with a brown outer edge and a gray sunken central area. Coalescence of large lesions gave rise to extensive rotting and necrosis, and the stems were broken when the lesions encircled. Acervuli with brown setae and falcate single-celled spores, typical of some Colletotrichum species (2), formed on the lesions at this late stage. One fungal isolate (Col-68) was obtained from symptomatic tissues on potato dextrose agar that led to white-to-gray appressed mycelium growth with orange conidial masses at 28°C in darkness. Setae were septate, dark brown, rounded and sometimes lobed at base, 32.0 to 116.5 × 3.2 to 6.0 μm, with apices acute. Hyphae were septate, hyaline, 1.0 to 6.5 μm, and sometimes guttulate. Conidia were falcate or fusiform, apices acute or obtuse, and 8.16 to 26.37 × 2.9 to 9.2 μm with an average of 18.15 × 5.65 μm. Hyphopodial appressoria were smooth, globose to prolate, ovoid or obovoid with obtuse or cylindrical apices, edges entire, and 4.17 to 14.25 × 3.77 to 8.94 μm with an average of 7.0 × 6.9 μm. The pathogen was initially identified as a Colletotrichum species based on morphology. Suspensions of 3-day-old spores collected from potato dextrose liquid cultures (106 conidia per ml) were used to spray inoculate (15 ml per pot) three 9-cm-diameter pots of crabgrass seedlings at the three- to four-leaf growth stage. Another three pots of healthy crabgrass were simultaneously sprayed with sterilized distilled water without conidia, which served as noninoculated checks. The seedlings were kept at 25 to 28°C for 24 h under a polyethylene sheet cover in the greenhouse. Symptoms that developed in all inoculated seedlings were identical to those observed on the affected crabgrass in the field, meanwhile the seedlings inoculated with sterilized water had no significant symptoms, and the reisolated strain had the same characteristics as the original isolate. To diagnose the pathogen to the species level, three isolates were tested and an approximately 580-bp DNA amplicon of this isolate was amplified using the primers ITS1/ITS4. The sequence (GenBank Accession No. GQ456160) had 98% sequence identity with the sequences of Colletotrichum hanaui (GenBank Accession Nos. EU554101and EU554124), which is supported by phylogenetic analysis with bootstrap support. On the basis of the morphological, pathological characteristics, and phylogenetic tree, the isolated strain was identified as C. hanaui (1). To our knowledge, this is the first confirmed report of anthracnose of D. sanguinalis caused by newly described C. hanaui in China.

References: (1) J. A. Crouch et al. Mycologia, 101:717, 2009. (2) B. C. Sutton. The Coelomycetes. CAB International Publishing, New York, 1980. (3) Y. Z. Zhu and S. Qiang. Chin. J. Biol. Control 20:206, 2004.