A novel Alternaria alternata isolate causes wheat spike discolouration and yield loss: pathogenicity and DNA sequencing evidence

This investigation aimed to identify the pathogen causing discolouration in spikes of the Gemmeiza 12 wheat variety at Gemmeiza Research Station in Gharbia Governorate, Egypt. Based on phenotypic characteristics and molecular identification using 28S rDNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene sequences, the pathogen was identified as Alternaria alternata, with GenBank accession numbers PV101490 and PV243291. Re-isolation and re-identification of the same fungus from spray-inoculated spikes, asserting Koch’s postulates in the 2024 growing season. Artificial inoculation of 26 bread and durum wheat varieties with a conidial suspension (1.0 × 106 conidia/mL) revealed significant differences in susceptibility, with bread wheat exhibiting higher disease incidence (0–100%) than durum (3.07–29.16%). Linear regression analysis indicated a strong positive relationship between disease incidence and grain yield loss % (R2 = 0.995). Principal component analysis (PCA) further demonstrated that disease incidence was significantly influenced by environmental conditions, with decreasing precipitation and relative humidity identified as the most critical factors.