Characterization of Colletotrichum gloeosporioides, as the main causal agent of citrus anthracnose, and C. karstii as species preferentially associated with lemon twig dieback in Portugal

In the last two decades significant losses in citrus production in Portugal related to anthracnose symptoms have been recorded. These symptoms were attributed to Colletotrichum gloeosporioides, but preliminary population diversity evidence suggested that other Colletotrichum species could be involved in the disease. In this work, a field survey of the main citrus growing areas in Portugal was conducted and the pathogenicity of a group of Colletotrichum spp. isolates was studied along with morphological and genetic variability characterization [including Inter-Simple Sequence Repeats (ISSR) profiles and DNA sequence data of rDNA-ITS and β-tubulin 2 gene regions]. Colletotrichum karstii (from the C. boninense species complex) and C. gloeosporioides were identified from symptoms on leaves, branches, flowers and fruits of several citrus cultivars. However, C. acutatum, the species most commonly associated with citrus anthracnose in the Americas, was never detected. While C. gloeosporioides was isolated at higher frequency overall (87 %), C. karstii was more frequent in branches and leaves of lemon in specific geographic locations. Only C. gloeosporioides was detected in flowers. Colletotrichum karstii and C. gloeosporioides were pathogenic to sweet orange flowers and fruits and to leaves of sweet orange, mandarin and lemon, while reference C. acutatum citrus isolates were pathogenic to Key lime flowers and leaves.