Characterization and Pathogenicity of Colletotrichum gloeosporioides and C. karstii Causing Pre-Harvest Disease on Citrus sinensis in Italy

During the period from 2010 to 2013 preharvest symptoms were detected on different cultivars of sweet orange in six orchards in Catania, Siracusa and Enna provinces, Southern Italy. A total of 56 monosporic fungal isolates were obtained, and among these, 44 were identified as Colletotrichum gloeosporioides and 12 as C. karstii through morphological and molecular analysis. PCR with primers ITS1 and ITS4, primers TubGF1 and TubGR specific for b-tubulin gene, primers GDF-GDR, specific for Glyceraldehyde- 3-phosphate dehydrogenase (GAPDH) gene, were used to confirm the identification of Colletotrichum isolates from citrus. The ITS1-5.8S-ITS2 region, a portion of approximately 500 bp of b-tubulin gene and a fragment of 220 bp of GAPDH gene of the isolates were sequenced and analysed with the BLASTn program. Koch’s postulates were fulfilled by pathogenicity tests carried out on fruit of ‘Tarocco Scire’ and ‘Tarocco Nucellare’ with representative isolates of C. gloeosporioides and C. karstii. Field surveys and pathogenicity tests revealed significant differences in fruit susceptibility between ‘Tarocco Scire’ and ‘Tarocco Nucellare’ and in virulence between the fungal species. To our knowledge, this is the first report on the emergence of Colletotrichum spp. causing anthracnose in preharvest conditions