FIRST REPORT OF COLLETOTRICHUM KAHAWAE subsp. CIGGARO ON MANDARIN IN ITALY

Abstract

In May 2015, symptoms of light brown necrotic lesions were observed on mandarin (Citrus reticulata) leaves in Calabria region in southern Italy. The fruiting bodies (acervuli) of the fungus appeared on the necrotic tissues. Isolation was made on potato dextrose agar (PDA) from small sections (3-5 mm2) of lesions margins after surface disinfection in 1% NaOCl. The isolated fungus developed cottony, grey with aerial mycelium with stromatic acervuli producing orange masses of conidia. Conidia were hyaline, cylindrical tapering slightly from only one side measuring 16 - 20 × 3.5 - 5.5 μm. These morphological criteria matched those of Colletotrichum kahawae clade (Weir et al., 2012). Fungal identity at species level was further confirmed by amplification and sequencing of the beta-tubulin (TUB), partial histone 3 (HIS3) and internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) gene regions as described by Damm et al. (2012). The TUB sequence (GenBank accession No. KU605630) shared 100% homology with the TUB sequence of C. kahawae subsp. ciggaro (KC297082). The sequences of HIS3 (KU605631) and ITS (KU605632) were 100% homologous with KC297048 and GU174550, respectively. The isolated fungus was tested for pathogenicity on detached mandarin leaves. A 5-mm2 mycelial plugs were applied on the wounded leaves and kept for 7 days at 25°C under high relative humidity (RH). Symptoms developed were similar to those observed on the trees. Re- isolation revealed the same morphology of the original isolate. To our knowledge this is the first report of C. kahawae subsp. ciggaro on mandarin in Italy.