Characterization of Colletotrichum orchidophilum, the agent of black spot disease of vanilla

Abstract

Black spot symptoms were reported on vanilla plants in Reunion Island in 2011. They have repeatedly reduced annual pod production by 10% to 30%. The disease is characterized by dark spots that appear in slight depressions on flowers, pods, leaves and stems. The spots then develop into broad clearly depressed necrotic plaques. Morphological and molecular analyses, as well as pathogenicity tests, identified the fungus Colletotrichum orchidophilum (Ascomycota) as the causal agent of the disease. Inoculation tests in controlled conditions confirmed that the two C. orchidophilum strains isolated from fruit lesions are pathogenic on the leaves and fruits of Vanilla planifolia(accessions CR0001 and CR0020). However, these strains induced symptoms only when the epidermis of leaves and fruits had been punctured by a needle. In the absence of injury, no symptom appeared. Colletotrichum arxii and Fusarium proliferatum (Ascomycota) are fungal species that are also frequently isolated from black spot lesions. However, they are not pathogenic to vanilla. This is the first report of C. orchidophilum in Reunion Island. It is also the first demonstration of C. orchidophilum's pathogenicity to an orchid. Simple preventive control measures were proposed to reduce the incidence of black spot disease in vanilla plots.