Olive anthracnose caused by Colletotrichum in Uruguay: symptoms, species diversity and pathogenicity on flowers and fruits

Olive anthracnose caused by C. acutatum, C. gloeosporioides and C. boninense species complexes, is the most widespread and economically important olive disease worldwide. The most traditional symptom is fruit rot, but more recently a high incidence of blossom blight emerged in some olive world regions as Uruguay, causing significant losses. In this work, a collection of Colletotrichum isolates obtained from different organs with symptoms attributable to anthracnose, with special emphasis in blighted flowers, was characterized. Based in the analysis of six partial gene regions (GADPH, ACT, βTUB2, HIS3, APN2/MAT-IGS and GAP2-IGS) and phenotypical characters, five Colletotrichum species were identified. C. acutatum s.s. was found as the prevalent species (n = 89) followed by C. nymphaeae (n = 14) and C. fioriniae (n = 1) all belonging to C. acutatum species complexes. The other two species found were C. theobromicola (n = 3) and C. alienum (n = 1) both belonging to C. gloeosporioides species complexes. To our knowledge, this study represents the first report of C. alienum causing olive anthracnose worldwide. Phenotypical characteristics differed mainly between the species complexes, validating their utility to separate the isolates to complex level. The tested isolates caused necrosis involving all floral organs and the typical “soapy fruit” symptom appeared regardless of the Colletotrichum species inoculated. Due the olive anthracnose being an extremely dangerous disease, further studies to development an effective management strategy are necessary to mitigate its incidence.