Stemphylium vesicarium (wallr.) E.G. Simmons: An onion plant pathogen and options for suppression

Pestic. Phytomed. (Belgrade), 38(2), 2023, 43–53 DOI: https://doi.org/10.2298/PIF2302043T UDC 632.4:632.952:635.25 Review paper Stemphylium vesicarium (wallr.) E.G. Simmons: an onion plant pathogen and options for suppression Ana Takač 1* and Slavica Vuković2 1Kite DOO Novi Sad, Međunarodni put 162A, 21233 Čenej, Serbia 2University of Novi Sad, Faculty of Agriculture, Trg Dositeja Obradovića 8, 21000 Novi Sad, Serbia *Corresponding author: Received: 5 March 2023 Accepted: 3 August 2023 SUMMARY Onion (Allium cepa L.) is one of the most important vegetable species grown worldwide, including the Republic of Serbia. Leaf blight, caused by the fungus Stemphylium vesicarium, is a serious and destructive disease of onion leaves around the world, which limits the quality and quantity of bulbs and seeds. Yield decrease occurs due to a reduced photosynthetic area, which leads to the formation of smaller bulbs of poorer quality. The recommended strategy for control and reduction of SLB inoculum includes crop rotation with other vegetable species or cereals that are not hosts of these fungi, the use of resistant onion genotypes, weed removal, adequate use of nitrogen fertilizers, control of thrips (Thrips spp.), as well as seed treatment, considering that seeds play a significant role in the spread of pathogens. Timely and correct application of foliar fungicides is certainly the key strategy. The timing of application of fungicides with different modes of action is crucial for controlling Stemphylium vesicarium in onion. Keywords: plant pathogenic fungi, plant disease suppression, onion, leaf blight, fungicides INTRODUCTION Onion belongs to the monocotyledon family Amaryllidaceae, genus Allium (Yusupov et al., 2021). This genus includes about 1250 perennial bulbous plant species that are used as food and spice, but also as honey-bearing, ornamental, medicinal and industrial plants. It is characterized by a distinct nutritional value and is present in our diet throughout the year (Gvozdanović-Varga, 2011). Cultivation and use of onion has been known for the past 4000 years (Kazanova, 1978; Brewster & Rabinowitch, 1990). Onion production in the Republic of Serbia is widespread and the main production regions are Northern Banat and Bačka, Podrinje, the environs of Prizren, Pirot and Belgrade (Miladinović et al., 1997). In the Republic of Serbia in 2022, areas under onion crops amounted to 4114 hectares with an average yield of 8.5 t/ha, while 1364 hectares were sown/planted with onion in the Serbian Province of Vojvodina, with an average yield of 12.2 t/ha (Statistical Office of the Republic of Serbia, 2022). 43 Ana Takač and Slavica Vuković Causal agents of onion disease Diseases are one of the most important limiting factors in onion production. Onion diseases are caused by dozens of pseudofungi, fungi, bacteria and viruses (Koike et al., 2007). Literature shows that onions are susceptible to at least 66 diseases caused by different pathogens: 36 types of fungi, about 10 different types of bacteria, a large number of viruses and one phytoplasma (Bulajić, 2015). Among them, pseudomycosis and mycosis, which occur during the growing season, but also during storage, stand out for their importance. The presence of pathogens depends on climatic conditions during the growing season, genotype and region of cultivation. In the Republic of Serbia, the most important causal agents of onion diseases are phytopathogenic fungi listed in Table 1, and the drying of onion leaves caused by a fungal pathogen in the genus Stemphyllium has become frequent in recent years. STEMPHYLIUM VESICARIUM (WALLR.) E.G. SIMMONS – THE CAUSAL AGENT OF LEAF BLIGHT Importance Stemphylium leaf blight and stalk rot of onion are caused by the hemibiotrophic fungal pathogen Stemphylium vesicarium (Wallr.) E.G. Simmons (teleomorf: Pleospora herbarum [Pers.] Rabenh., sin P. allii) of the genus Stemphylium. Depending on agroecological conditions and geographic growing region, it is described as a very significant disease of onion (Allium cepa L.) and garlic (A. sativum L.) (Gupta et al., 1994; Miller & Schwartz, 2008; Mishra & Singh, 2017). S. vesicarium (SLB) leads to premature leaf blight (leaves droop after necrosis), thus making it more susceptible to post-harvest diseases (Paibomesai et al., 2012). In onion production, SLB can be easily confused with purple blotch symptoms, caused by Alternaria porri (Suheri & Price, 2001). Uddin et al. (2006) reported that S. vesicarium is first to initiate infection, which is then followed by infection with A. porri, and hence the disease is designated as the purple blotch complex (PBC). The mentioned fungi are very well described in international literature as significant pathogens of onion (Mathur & Sharma, 2006) having economic impact on onion production worldwide (Gupta et al. 1994). The presence of this pathogen under Serbian agroecological conditions has been recorded on annual basis in recent years, and it causes significant economic damage in some onion producing regions of Vojvodina Province. So far, there has not been enough recorded data about the ecology and distribution of SLB in the territory of the Republic of Serbia. The presence of S. vesicarium in onion was first described in the United States (Miller et al., 1978), then Table 1. Onion diseases caused by phytopathogenic fungi (Mijatović et al., 2007) Disease name Pathogen or causal agent ROOT NECROSIS Root rot Pythium spp. Onion Stunting Rhizoctonia solani (Kühn) White rot Sclerotium cepivorum (Berk) Botrytis leaf fleck Botrytis cinerea (Pers. ex Fr) Smut Urocystis cepulae (Rabenh. ex Fuckel) Onion smudge Colletotrichum circinans (Berk.) Voglino Pink root of onion Pyrenochaeta terrestris (J.C. Walker & Larson) BASAL ROT Fusarium basal rot Fusarium oxysporum f. sp. cepae (Snyder & Hansen) LOCAL NECROSIS OF ABOVE-GROUND PARTS OF PLANTS Downy mildew Peronospora destructor (Berk). Caspary Purple blotch Alternaria porri (Ellis) Cifferi Rust Puccinia porri, P. allii (DC) Rudolph Onion smut Urocystis cepulae (Hansen) Botrytis leaf blight Botrytis squamosa (Walker), B. alli (Munn) 44 Pestic. Phytomed. (Belgrade), 38(2), 2023, 43–53 Portugal (Tomaz & Lima, 1988), India (Gupta et al., 1994), Korea (Cho & Yu, 1998), Venezuela (Cedeño et al., 2003), Egypt (Hassan et al., 2007), Canada (Paibomesai et al., 2012), Japan (Misawa & Yasuoka, 2012) and New Zealand (Wright et al., 2018). Yield and quality losses of up to 90% have been reported in Texas and New York State (Miller et al., 1978; Lorbeer, 1993), while losses of 80-85% have been reported in seed crops in Portugal (Tomaz & Lima, 1988). Extensive damage has also been reported in Egypt (Hassan et al., 2007), India (Rao & Pavgi, 1975), Japan (Misawa & Yasuoka, 2012), New Zealand (Suheri & Price, 2001), South Africa (Aveling et al, 1993) and Spain (BasalloteUreba et al, 1999). Premature plant mortality under conditions of high dis (...truncated)