First Record of Grey Leaf Spot on Pepper Caused by Stemphylium lycopersici in Syria

Peppers (Capsicum annuum) are an important crop grown in greenhouses in the coastal region of Syria, with 15,166 greenhouses covering 607 hectares and annually producing approximately 30,000 tonnes (Syrian Ministry of Agriculture 2023). In the autumn of 2023, symptoms of grey leaf spot appeared on pepper (cv. Sirad 2) grown in greenhouses in Nahout, south of Tartous city (34.729798″N–36.070476″E). Initially, symptoms on the leaves appeared as small reddish-brown spots. As the infection progressed, the spots enlarged, and their centre turned grey-white with dark brown margins. The diameter of the spots ranged from 0.5 to 5 mm and sometimes merged to form a larger spot. Some of these lesions cracked, creating a ‘shot-hole’ appearance (Figure 1A). Heavy infections led to leaf yellowing and premature defoliation (Figure 1B). The spots also appeared on the petioles and stem as well as the pedicles and calyxes (Figure 1C,D). No symptoms were noted on the fruits. Small pieces were cut from the margin of spots, the surface was disinfected with 1% sodium hypochlorite for 2 min, then washed three times with sterile distilled water and dried on sterile filter paper. The pieces were placed in the centre of potato dextrose agar (PDA) plates (9 cm) and incubated at 25°C ± 2°C in the dark. Colonies were initially cottony grey, becoming reddish-brown as they aged (Figure 2). Conidiophores were solitary, septate, transparent to pale olive and had apical vesicular swellings, 50–180 × 4–6 µm (Figure 3A,B). Conidia were solitary, oblong, cylindrical or with a conical apex, warty, light brown, with 1–4 darkened, constricted transverse septa and several longitudinal septa [(21-)32-57 (-64) × 13–20 µm (Figure 3C). On the basis of morphological criteria, in particular, the shape of the conidia (some with a pointed, pyramidal apex) and the colony's appearance on PDA, the fungus was identified as Stemphylium lycopersici (Kim et al. 1999; Woudenberg et al. 2017). Pathogenicity testing was performed by spraying a conidial suspension (1 × 105/mL) on detached 40-day-old healthy leaves of pepper (cv. Sirad 2) placed on moist sterile filter paper in 14 cm diameter Petri plates. The negative control was sprayed with sterile distilled water. The leaves were incubated at 24°C. Symptoms appeared on the inoculated leaves after 3 days and developed fully within 10 days, similar to those observed in greenhouse production (Figure 4). No symptoms appeared in the controls. The fungus was re-isolated using the same method as before and had the same morphology on PDA as the original isolate. S. lycopersici has been reported to infect leaves of tomato and pepper (Kim et al. 2004; Huang and Tsai 2017; Sun and Huang 2022). To our knowledge, this is the first report of S. lycopersici causing grey leaf spot on pepper in Syria.