Black pepper is cultivated in Andaman and Nicobar Islands, India as a spice crop. During a survey performed in June of 2007 in South Andaman, two kinds of leaf anthracnose symptoms were observed. The classic symptom, angular to irregular or circular brownish lesions with a chlorotic halo and pinhead size acervuli on the leaves, was consistent with the disease previously reported on pepper caused by Colletotrichum gloeosporioides (2). This symptom also caused splitting and the production of hollow berries. The new symptom was novel, with leaves initially exhibiting pale green or yellowish green lesions. As the disease progressed, lesion margins became brown to black with slightly raised areas containing numerous acervuli. Unlike the classic symptom, the new symptom was characterized as leaf lesions that rarely caused defoliation; berries showed no lesions. The foliar disease incidence was up to 15%, but direct economic loss of berries was not noticed. This new symptom was similar to symptoms caused by C. dracaenophilum, a species identified as a pathogen on lucky bamboo (Dracaena sanderiana) (1). A fungus was isolated in pure culture from the pale green lesions and cultured on potato dextrose agar (PDA). At room temperature (28 ± 2°C), fungal growth on PDA was slow and mycelium appeared whitish at the margin with pale pink centers. A pinkish color was observed on the reverse side of the plate, reflecting profuse sporulation. The conidia were hyaline, broadly clavate to cylindrical, and measured 12.5 to 15 × 5 to 7.5 μm (average 14 × 7.5 μm). The internal transcribed spacer (ITS) region of the fungal DNA was amplified, sequenced, and submitted to NCBI GenBank (Accession No. EU744584). The specimen was deposited in the MTCC of IMTECH, Chandigarh, India (Accession No. MTCC9344). Pathogenicity was tested in five replications on 15- to 20-day-old pepper plants and repeated twice. A 1-ml conidial suspension (108 spores/ml) of the fungus was brushed on two intact leaves of each pepper plant and incubated for 2 weeks in a glasshouse at 28°C and 70% relative humidity with natural daylight conditions. Plants brushed with sterile water served as control. Similar pale green symptoms were observed only on treated leaves and the same organism was reisolated from lesions. BLAST searches of the GenBank using the ITS sequence revealed that this fungus was a member of the genus Colletotrichum, but a species level identification could not be made with these data. The fungus was most similar in sequence to unnamed endophytic strains of Colletotrichum (96% sequence identity) and phytopathogenic isolates of C. dracaenophilum (93% sequence similarity). Although the symptomatology and sequence data were most closely matched with those documented for C. dracaenophilum (1), the morphological and cultural characteristics of the black pepper anthracnose fungus differed from C. dracaenophilum and other known species of Colletotrichum (3). Together these morphological and molecular data suggest that this form of anthracnose disease on black pepper may be caused by a novel, undescribed species of Colletotrichum. Further investigations will be required to characterize this organism to the species level.
References: (1) S. G. Bobev et al. Plant Dis. 92:173, 2008. (2) P. Santha Kumari and A. Sanker. J. Mycol. Plant Pathol. 33:329, 2003. (3) B. C. Sutton. In: Colletotrichum. Biology, Pathology and Control. CAB International, Wallingford, 1992.