MOLECULAR ANALYSIS OF COLLETOTRICHUM SPECIES ASSOCIATED TO OLIVE IN CALABRIA.

A new molecular approach based on the use of genus-specific primers targeting the internal transcribed spacer (ITS) regions of rDNA, was developed and used to study the diversity of Colletotrichum species associated with the olive canopy in the Gioia Tauro plain (Calabria, southern Italy). Representative symptomatic and symptomless samples of leaves, flowers and fruits were collected during 2012 and analyzed by extracting total DNA and amplifying the target region with the genus-specific primers. Amplicons were cloned and sequenced in order to use the ITS as a barcode gene. No Colletotrichum species were detected in the first sampling period (May 28, 2012), whereas around 15% of the analyzed samples including leaves, dead floral parts and symptomless fruits proved to be colonized in the second (June 29, 2012) and third sampling (October 17, 2012). A significantly higher colonization rate was found in the fourth sampling (December 12, 2012) with Colletotrichum species detected in 74% of the analyzed samples, including many asymptomatic fruits and leaves. On the whole C. clavatum, C. acutatum sensu stricto and C. gloeosporioides sensu stricto were the most common species accounting for 54, 22 and 21% of the sequenced clones, respectively. Few sequences belonged to C. karstii and to a Colletotrichum sp., closely related to C. coccodes. Most samples were colonized by two or three different species. The new method proved very effective for discriminating multiple Colletotrichum species colonizing olive tissues and could be also applied to detect Colletotrichum spp. in other plant species.