Morphological and multilocus molecular characterization of Neocosmospora solani and Fusarium oxysporum associated with gummosis in Citrus sinensis in Veracruz, Mexico

Citrus gummosis is a complex disease primarily associated with Phytophthora spp. in Mexico, particularly P. nicotianae (syn. P. parasitica) and P. citrophthora, which have historically been recognized as the main causal agents in the country’s citrus-growing regions. However, several studies have reported additional fungal pathogens, such as Lasiodiplodia spp., involved in gummosis-like symptoms. The objective of this research was to identify phytopathogenic fungi associated with gummosis symptoms in orange orchards in Tuxpan, Veracruz. A total of 100 bark samples were collected from symptomatic trees across five representative zones of the municipality. Fungal isolation was performed on potato dextrose agar (PDA), yielding 25 isolates, from which five were selected based on morphological characteristics. Molecular identification was conducted through PCR amplification and concatenated sequencing of the internal transcribed spacer (ITS) region and the translation elongation factor 1-α (tef1) gene. The sequences were compared with reference data in the NCBI and Fusarium MLST databases. Phylogenetic analysis using Bayesian inference revealed that the isolates corresponded to Neocosmospora solani (2 isolates), Fusarium oxysporum (2 isolates), and an undescribed Fusarium species (1 isolate). The presence of N. solani and F. oxysporum as dominant species (99% sequence identity) suggests their potential role in the etiology of citrus gummosis. These findings expand the current understanding of citrus gummosis etiology in Mexico and underscore the importance of considering alternative fungal pathogens in diagnostic and management strategies.