Nova species, new records and pathogenicity of Diaporthe species associated with symptomatic citrus in Thailand.

Citrus trees are among the most important fruit crops grown worldwide; however, they are also susceptible to numerous fungal plant pathogens. A range of symptoms, including melanosis, leaf and fruit spots, stem end rot, and twig blight, has been observed. The survey and collection were conducted from December 2021 to January 2022 in citrus orchards in northern Thailand. Thirty-three isolates of Diaporthe were obtained and identified based on morphological characteristics and molecular data. Subsequently, a representative subset of 18 isolates was subjected to multi-locus phylogenetic analysis based on four gene loci: ITS, TEF1, TUB2, and CAL. The combined datasets were used to construct phylogenetic trees using both Bayesian and Maximum Likelihood methods. The study identified seven Diaporthe species associated with Citrus spp. in Thailand, including a new species: Diaporthe citrithailandica, new host records for Diaporthe sojae, Diaporthe tectonendophytica, Diaporthe tulliensis, Diaporthe ueckeri, and Diaporthe vitimegaspora, and a known species, Diaporthe arecae. The pathogenicity of the isolates was tested by artificial inoculation of mandarin and acid lime fruit, leaves and young branches using a mycelial plug, which revealed varied virulence. This study enhances our understanding of the Diaporthe species associated with Citrus diseases in Thailand. By enabling improved pathogen identification and management, our findings contribute to better plant disease control, supporting food security and helping to reduce post-harvest losses.