Objective To identify the pathogen species of newly occurring lychee brown spot, determine the biological characteristics of the pathogen, and screen biocontrol agents, so as to provide a basis for understanding the occurrence patterns of lychee brown spot and green disease control.

Method In October, 2021, leaves with severe brown spot on young litchi trees were collected. A strain of GZ1 was obtained from diseased leaves and its pathogenicity was determined based on Koch’s postulates. Morphological analysis and a phylogenetic tree based on sequences of internal transcribed spacer (ITS), β-tubulin gene (Tub2), and RNA polymerase II second largest subunit gene (rpb2) were performed to clarify the taxonomic status of this pathogen. The biological characteristics of pathogen GZ1 were determined under various culture conditions including multiple carbon sources, temperatures, and pH. Antagonistic effects of two biocontrol agents, Bacillus subtilis XX and B. velezensis BS against GZ1 were evaluated using the dual culture method and hyphal growth rate method.

Result The strain GZ1 was confirmed as the causal agent of lychee brown spot, and it was identified as Exserohilum rostratum (Drechsler) K.J. Leonard & Suggs. The optimal temperature and pH for its growth were 28 ℃ and 7. It could utilize various carbon sources, with the fastest hyphal growth observed in the presence of sucrose. The biocontrol agents B. subtilis XX and B. velezensis BS exhibited significant inhibitory effects on the growth of pathogen GZ1.

Conclusion This study reports that E. rostratum is the causal agent of lychee brown spot, thereby identifies a new lychee disease. The study can provide a basis for scientific control of lychee disease caused by E. rostratum.