ABSTRACT Alternaria species is the main causative agent for black rot of citrus. 157 isolates were recovered from 150 rotten citrus samples in Upper Egypt. In this study, 150 rotten citrus samples yielded 157 fungal isolates, predominantly Alternaria alternata (150 isolates) and, to a lesser extent, A. arborescens (7 isolates) species complex. Identification was achieved through both morphological assessment and molecular techniques using the Alt a1 gene. The virulence of these isolates was evaluated exclusively on orange fruits (cv. Washington Navel) to allow direct comparison among strains from different citrus hosts. All A. alternata‐like isolates induced black rot, though disease severity varied considerably, with the average lesion diameter (ALD) ranging from 20.0 to 40.5 mm while Alternaria arborescens‐like isolates exhibited minimal variation (ALD 30.0–31.5 mm). Statistical analyses indicated no significant difference in disease severity between the two species ( p = 0.824), suggesting that pathogenicity is more closely associated with specific isolates rather than their species classification. Further analysis using high‐performance liquid chromatography (HPLC) revealed that 88.8% of A. alternata and 71.5% of A. arborescens lineages produced tenuazonic acid, with the highest level (31.02 μg/mL) detected in A. arborescens SVUAar152. These results provide a deeper understanding of the diversity and toxigenic capacities of Alternaria species linked to citrus black rot in Egypt, while highlighting the need for future multi‐locus studies to definitively resolve species boundaries within these complex lineages.
Gherbawy et al. (Sun,) studied this question.