Abstract:
Species in Diaporthe have broad host ranges and cosmopolitan geographic distributions, occurring as
endophytes, saprobes and plant pathogens. Previous studies have indicated that many Diaporthe species are associated
with Citrus. To further determine the diversity of Diaporthe species associated with citrus diseases in China,
we conducted extensive surveys in major citrus-producing areas from 2017–2020. Diseased tissues were collected
from leaves, fruits, twigs, branches and trunks showing a range of symptoms including melanose, dieback, gummosis,
wood decay and canker. Based on phylogenetic comparisons of DNA sequences of the internal transcribed spacer
regions (ITS), calmodulin (cal ), histone H3 (his3), translation elongation factor 1-alpha (tef1) and beta-tubulin (tub2),
393 isolates from 10 provinces were identified as belonging to 36 species of Diaporthe, including 32 known species,
namely D. apiculata, D. biconispora, D. biguttulata, D. caryae, D. citri, D. citriasiana, D. compacta, D. discoidispora,
D. endophytica, D. eres, D. fusicola, D. fulvicolor, D. guangxiensis, D. hongkongensis, D. hubeiensis, D. limonicola,
D. litchii, D. novem, D. passifloricola, D. penetriteum, D. pescicola, D. pometiae, D. sackstonii, D. sennicola, D. sojae,
D. spinosa, D. subclavata, D. tectonae, D. tibetensis, D. unshiuensis, D. velutina and D. xishuangbanica, and four
new species, namely D. gammata, D. jishouensis, D. ruiliensis and D. sexualispora. Among the 32 known species,
14 are reported for the first time on Citrus, and two are newly reported from China. Among the 36 species, D. citri
was the dominant species as exemplified by its high frequency of isolation and virulence. Pathogenicity tests indicated
that most Diaporthe species obtained in this study were weakly aggressive or non-pathogenic to the tested
citrus varieties. Only D. citri produced the longest lesion lengths on citrus shoots and induced melanose on citrus
leaves. These results further demonstrated that a rich diversity of Diaporthe species occupy Citrus, but only a few
species are harmful and D. citri is the main pathogen for Citrus in China. The present study provides a basis from
which targeted monitoring, prevention and control measures can be developed.
