Abstract:
Species of Colletotrichum are considered important plant pathogens, saprobes, and endophytes on a wide
range of plant hosts. Several species are well-known on citrus, either as agents of pre- or post-harvest infections,
such as anthracnose, postbloom fruit drop, tear stain and stem-end rot on fruit, or as wither-tip of twigs. In this study
we explored the occurrence, diversity and pathogenicity of Colletotrichum spp. associated with Citrus and allied
genera in European orchards, nurseries and gardens. Surveys were carried out during 2015 and 2016 in Greece,
Italy, Malta, Portugal and Spain. A total of 174 Colletotrichum strains were isolated from symptomatic leaves, fruits,
petals and twigs. A multi-locus phylogeny was established based on seven genomic loci (ITS, GAPDH, ACT, CAL,
CHS-1, HIS3 and TUB2), and the morphological characters of the isolates determined. Preliminary pathogenicity
tests were performed on orange fruits with representative isolates. Colletotrichum strains were identified as members
of three major species complexes. Colletotrichum gloeosporioides s.str. and two novel species (C. helleniense and
C. hystricis) were identified in the C. gloeosporioides species complex. Colletotrichum karstii, C. novae-zelandiae
and two novel species (C. catinaense and C. limonicola) in the C. boninense species complex, and C. acutatum s.str.
was also isolated as member of C. acutatum species complex. Colletotrichum gloeosporioides and C. karstii were
the predominant species of Colletotrichum isolated. This study represents the first report of C. acutatum on citrus
in Europe, and the first detection of C. novae-zelandiae from outside New Zealand. Pathogenicity tests revealed
C. gloeosporioides s.str. to be the most virulent species on fruits. The present study improves our understanding
of species associated with several disease symptoms on citrus fruits and plants, and provides useful information
for effective disease management.
