Molecular Characterization and Phytotoxic Metabolite Profiling of Nigrospora oryzae and N. sphaerica Isolates from Date Palm: Implications for Food Safety and Postharvest Quality

This study investigated the phytotoxic potential of two Nigrospora species isolated from date palm leaves exhibiting leaf spot symptoms, with emphasis on their biochemical interactions with the host and implications for fruit safety. Morphological characterization combined with molecular identification based on ITS gene sequencing confirmed the identity of the isolates as Nigrospora oryzae and N. sphaerica, showing ۱۰۰% similarity with reference strains in the NCBI database (accession numbers MH۸۵۵۳۰۰.۱ and PV۱۰۷۳۳۴.۱, respectively). Phytotoxicity assessment through infiltration of culture filtrates into healthy date palm leaves revealed significant biochemical alterations indicative of stress and potential metabolite translocation. Treated leaves exhibited elevated levels of carbohydrates, free proline, and phenolic compounds, suggesting a defense response to fungal metabolites. Notably, catalase activity decreased significantly from ۱.۶ mmol/min/g in untreated controls to ۱.۵ and ۱.۰۳ mmol/min/g following N. oryzae and N. sphaerica treatments, respectively, indicating impaired oxidative stress regulation. Total soluble protein levels declined in treated leaves, while free amino acids increased markedly in N. oryzae-treated tissues (۹.۶۷ mg/g FW). Accumulation of reactive oxygen species (ROS) was evident, with hydrogen peroxide levels increasing ninefold in response to N. oryzae culture filtrates. Lipid peroxidation, measured as malondialdehyde (MDA), rose from ۲.۲۲ nmol/g in controls to ۴.۹۰ and ۳.۳۰ nmol/g in N. oryzae and N. sphaerica treatments, respectively. These findings demonstrate that both Nigrospora species produce phytotoxic metabolites capable of inducing oxidative stress and cellular damage in date palm tissues.

کلیدواژه ها:

date palm ، Nigrospora oryzae ، Nigrospora sphaerica ، Food safety ، Postharvest quality ، Mycotoxigenic fungi