<i>Alternaria malorum</i> , a new causal agent of cowpea leaf spot disease in Iran

Cowpea (Vigna unguiculata, Fabaceae) is an annual herbaceous legume cultivated for seed and fodder. During a survey in May 2022, cowpea leaves with leaf spot symptoms were collected from field which c. 40% of the plants diseased (Karaj City, Alborz province, Iran). Leaf spots began as small circular water-soaked lesions at centre margins expanded on occasion, coalesced. The infected tissue became pale brown necrotic. Isolation causal pathogen was performed using high humidity blotter method. After five days, growing fungi transferred fine sterile needle to 2% water agar. Pure cultures obtained hyphal tip method synthetic nutrient-poor agar (SNA) potato carrot culture media. Fungal colonies incubated 25°C 8 hour light/16 dark photoperiod seven days. A typical colony (ALT1) reached 58 mm diameter after days incubation SNA medium. olive-brown centre, white margin. Aerial mycelia sparse. Mycelia septate, smooth–walled. Sporulation abundant SNA, mostly aerial hyphae. Conidiophores arose singly mycelia, brown, erect, simple, short, smooth, frequently reduced conidiogenous cells slight swelling apices, 7–30 × 3–5 μm. Conidiogenous loci 1–3 per cell, brown. Ramoconidia 0–3 ellipsoid cylindrical, 15–32 μm, short beak (n = 50). Conidia subcylindrical, or fusiform, long acropetal chains, simple lateral branches 8–11 3–3.5 μm 50) (Figure 1). Morphological cultural characteristics recovered isolate similar description Alternaria malorum provided by Goetz & Dugan (2006) Crous et al. (2009). Molecular characterisation ALT1 done PCR amplification sequencing internal transcribed spacer (ITS) region ITS1 ITS4 primers (White al., 1990). sequence deposited GenBank (Accession No. OP006224) BLAST search showed it had 100% identity isolates A. (MW335156, LR134074, FJ839611 KY077556). Maximum likelihood analysis heuristic Mega X software. In generated phylogenetic tree 2), separated closely related species other fungal genera, clustered same group isolates. molecular confirmed morphological identification pathogen. Pathogenicity testing spraying conidial suspension (106 conidia/ml) healthy surface-sterilised without wounding, replicated three times. Sterile sprayed control plants. All covered plastic bags maintain placed glasshouse bench 12 until development disease symptoms. appeared twelve inoculation 3) resembled those observed field. re-isolated newly spots, fulfilling Koch's postulates. Iran, first reported Asgari (2004) Cladosporium Hordeum vulgare East Azarbaijan province. has also been fungus associated declining Persian oak trees (Alidadi 2018). Bagherabadi Zafari (2022) agent bark canker walnut trees. Several diseases are known infect cowpea, including anthracnose, Cercospora spot, damping off, Fusarium wilt, Sclerotium stem, root crown rot, Septoria scab (Dugje 2009). This report Iran globally. We thankful University Tehran supporting this research.