Resumen
- Cotton ramulosis caused by Colletotrichum gossypii var. cephalosporioides (Cgc) is a major disease of cotton (Gossypium hirsutum) in Brazil (Salustiano et al. 2014). During 2012-2013 growing seasons (August-February), ramulosis symptoms were observed in cotton crops in the Sinu Valley, Cordoba State, at the Colombian Caribbean region. Cotton plants in the field exhibited star-shaped lesions, necrosis of apical meristems, over-sprouting of lateral buds (ramulosis), and stunting. Small pieces up to 5 mm in diameter were removed from the star-shaped lesion margins, surface sterilized for 1 min in 1.5% NaOCl, washed twice with sterile distilled water, and plated onto V8 agar (PDA) amended with 1 g/liter amikacin sulfate and Benlate (50% benomyl) at 0.011 g/liter. Macroscopic colony characters and microscopic morphology characteristics of three isolates were developed after growth on PDA for 7 days at 25°C under a 12-h light/dark cycle. Colonies presented white cottony aerial mycelia that in two weeks turned light-tan, with numerous dark (black or brown) melanized structures similar to acervuli. Conidia were hyaline, aseptate, straight-cylindrical, rounded at both ends, and a somewhat acute apex. To confirm identity, partial sequencing of β-tubulin (TUB), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes of three isolates was performed as described previously (Templeton et al. 1992; O’Donnell and Cigelnik 1997; Weir et al. 2012). A maximum likelihood phylogenetic tree constructed from concatenated TUB and GAPDH sequences showed that the isolates reported here belong to the Cgc clade previously reported in Brazil. TUB and GAPDH sequences of isolates obtained in this study were deposited in GenBank (TUB Accession Nos. KT161253, KT161254, and KT161255; GAPDH Accession Nos. KT161256, KT161257, and KT161258). Pathogenicity tests were conducted on the susceptible cultivar LCER044 by brush inoculation of a conidial suspension (approximately 105conidia/ml). Five cotton plants brush-inoculated with water were used as control. Seven days after inoculation, star-shaped lesions appeared and a month later necrotic meristems were observed on plants inoculated with the putative Cgc isolates. The fungal pathogen was reisolated from star-shaped lesions of inoculated cotton-plants and the identity was confirmed through morphological and cultural characteristics. Cotton is an economically important crop in the Caribbean region with an acreage around 20,000 ha involving thousands of subsistence farmers (Conalgodon 2015). Reports of new emergent diseases on cotton in this region are essential for development of appropriate management strategies and quarantine measures. To our knowledge, this is the first report of C. gossypii var. cephalosporioides affecting cotton crops in Colombia.