Abstract:
Species of Diaporthe 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 dieback, melanose and stem-end rot on fruit. In this study we explored the occurrence,
diversity and pathogenicity of Diaporthe species 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 79 Diaporthe strains were isolated from symptomatic twigs, branches
and trunks. A multi-locus phylogeny was established based on five genomic loci (ITS, tef1, cal, his3 and
tub2), and the morphological characters of the isolates determined. Preliminary pathogenicity tests were
performed on lemon, lime, and orange plants with representative isolates. The most commonly isolated
species were D. foeniculina and D. baccae, while only four isolates of D. novem were collected. Two new
Diaporthe species, described here as D. limonicola and D. melitensis spp. nov. were found associated with
a new devastating dieback disease of lemon plants. Furthermore, one cluster of sterile Diaporthe isolates
was renamed as D. infertilis. Pathogenicity tests revealed most of the Citrus species as susceptible to D.
baccae, D. foeniculina, and D. novem. Moreover, D. limonicola and D. melitensis caused serious cankers
affecting all the Citrus species tested. This study is the first report of D. baccae and D. novem on citrus in
Europe, and the first detection of a new Diaporthe canker disease of citrus in Europe. However, no isolates
of D. citri were found. The study improves our understanding of the species associated with several disease
symptoms on citrus plants, and provides useful information for effective disease management.
