Università degli studi di Modena e Reggio Emilia

Pepper (Capsicum annuum L.) is one of the most important vegetables grown in Kosovo. In September 2022, 40% of pepper fruits, in two commercial fields located in the municipalities of Peja and Rahovec (Kosovo), showed typical symptoms of anthracnose. Dark lesions developed on fruits, which later appeared sunken, necrotic and surrounded by brown haloes. After isolation onto PDA, colonies and single spores morphology of both isolates revealed to be consistent with the description of Colletotrichum sp. Amplification and phylotyping of ITS, GAPDH and TUB2 gene sequences of both isolates were performed and the fungus was identified as C. scovillei. To confirm Koch’s postulates, a conidial suspension from both isolates was inoculated into healthy pepper fruits and incubated in a humid chamber. Ten days after pathogen inoculation, typical anthracnose symptoms developed, from which the fungus was successfully reisolated. No symptom was ever observed on fruits inoculated with sterile water. To our best knowledge, this is the first report of anthracnose caused by C. scovillei in Europe. Given the economic importance of the crop and the significant quality and yield losses observed, measures are urgently needed aiming at pathogen eradication or, alternatively, to ensure an efficient disease control to avoid severe damage both in the field and in postharvest. Four bacterial isolates from the UNIMORE collection were tested in vitro against C. scovillei: preliminary data showed their effectiveness in reducing mycelium growth. Studies are ongoing to test such antagonists in planta to search for sustainable alternatives to the extensive use of fungicides.

Colletotrichum scovillei is one of several species in the C. acutatum complex causing anthracnose on pepper, currently present in eastern Asia, Brazil and South Carolina (USA). A severe anthracnose infection on pepper fruits was identified in two commercial fields in Kosovo. Infection assays, morphological analyses and sequencing identified the causal agent as C. scovillei. It could be considered an emerging disease as the severe crop losses, together with the spread of the pathogen/disease to areas and regions where it was never reported in previous times. This is the first report of C. scovillei infecting pepper in Kosovo and Europe.

In July 2019, severe leaf symptoms were observed on onion plants (Allium cepa L. cv. Dorata di Parma) in a commercial field located in the municipality of Medicina (Bologna, Emilia-Romagna region), in northern Italy. Diseased leaves showed yellowish-pale-brown and oval-shaped lesions, which later coalesced in larger necrotic areas, and black leaf tips. As the disease progressed, conidia developed on the necrotizing leaves, until premature desiccation of the whole plants. Disease incidence of approximately 70% was calculated in the affected field, together with yield losses that were estimated to be above 30%. Symptomatic tissue fragments excised from the leaf lesions were surface disinfested with NaOCl 1% for 2 minutes, rinsed with sterile water and transferred onto potato dextrose agar (PDA). Fungi were consistently isolated after 5 days of incubation at 27 ± 1°C in the dark. Single spore isolation was performed on PDA to obtain 7 pure cultures, whose morphological characteristics were consistent with the description of Stemphylium vesicarium (Ellis 1971). DNA from a representative single spore isolate was extracted and the internal transcribed spacer region (ITS) of ribosomal DNA (rDNA) was amplified using the universal primers P-ITS1 and P-ITS4 (White et al. 1990). The PCR product was sequenced and deposited in GenBank (Accession No. OP144057). A BLAST search in CBS-KNAW collection bank (Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands) showed 100% identity for the ITS gene with the strain of S. vesicarium under accession number CBS 124749. Moreover, the PCR assay using the primer pair KES 1999 and KES 2000 (Graf et al. 2016) for the cytochrome b gene displayed the specific fragments of 420 bp for S. vesicarium. The isolate was tested for pathogenicity on onion (potted plants cv. Texas Early Gran, fourth leaf stage) by spraying 4 ml of a conidial suspension (1 × 104 conidia/ ml) per plant. Inoculated and non-inoculated (sprayed with sterile distilled water) plants were kept at 24 ± 1°C and 90% relative humidity with a 16-h photoperiod. Seven days after inoculation, disease assessment was performed. Inoculated plants showed typical Stemphylium leaf blight (SLB) symptoms, similar to those observed in the field. No symptoms developed on the water-inoculated plants. S. vesicarium was consistently reisolated from the artificially inoculated onion plants and identified using a PCR assay, according to Graf et al. (2016). The assay was repeated twice with the same results. SLB is currently reported worldwide and it is considered a re-emerging threat and a truly challenging fungal disease, which can result in yield and quality losses of up to 90% in onion crops (Hay et al. 2021). In Italy, S. vesicarium has been reported several years ago on pear (Ponti et al. 1982) and, more recently, on radish sprouts (Belisario et al. 2008), chili pepper (Vitale et al. 2017) and spinach (Gilardi et al. 2022). To our knowledge, this is the first report of S.vesicarium on onion in Italy. Our results stress that development and implementation of innovative Integrated Pest Management (IPM) strategies are urgently needed to ensure an effective control of SLB, since only a few moderately resistant onion varieties are available (Hay et al. 2021) and no fungicides are currently registered to specifically control SLB in Italy. Further studies are underway to elucidate the pathogen geographic distribution and assess the impact of this disease on the onion crop in Italy.