In vitro Activity of Pseudomonas fluorescens Strains against Fusarium verticillioides, Fusarium subglutinans and Schizophyllum commune, which Cause Diseases in Sugarcane in Côte d'Ivoire

Sugar cane (Saccharum officinarum L.) is a perennial plant of the Poaceae family. It is native to New Guinea and is cultivated for its stems, which contain a sweet sap (Meslien, 2009). In 2022, global sugarcane production reached approximately 1.92 billion tonnes, accounting for 79% of total global sugar production (ChenhanTech, 2022). This sector constitutes a strategic agro-industrial sector, both for the production of sugar and for that of ethanol or energy co-products. In 2023–2024, the main producing countries were Brazil and India, with annual production ranging from 753 to 783 million tonnes and from 405 to 490 million tonnes respectively (Financial Times, 2023). Sugar cane cultivation generates economic value amounting to tens of billions of US dollars (USD). For example, the Brazilian group Raízen recorded a turnover of 47 billion USD in 2023 (Financial Times, 2023). The Illovo Sugar group (South Africa) is the leading player in Africa, exporting to the European Union, the United States and West Africa. Côte d'Ivoire is a medium-sized producer in Africa. In 2018, the country's annual sugarcane production was estimated at 1.9 million tonnes, ranking it 53rd globally and 16th in Africa (REPERCI, 2024). Within the country, sugarcane is mainly used for direct consumption or in the sugar industry. It is also used in the cosmetics and pharmaceutical sectors. Furthermore, it represents the main source of economic activity for the population in the northern part of the country (Kouamé et al., 2010). Despite the importance of sugarcane, Côte d'Ivoire continues to face a sugar deficit. This sugar deficit is generally caused by diseases affecting sugarcane cultivation, including bacterial diseases such as leaf blight caused by Xanthomonas albineans, and fungal diseases such as smut, red mould and pokkah boeng. These fungal diseases result in losses estimated at between 10 and 30 per cent of the national yield (Yao et al., 2020). Although there are no comprehensive official national data, fungal diseases cause economic losses ranging from 20 to 40 per cent of the national yield. Thus, based on an estimated national sugarcane production of around 330,000 tonnes, a 20 per cent loss equates to 66,000 tonnes, representing nearly 13 million USD in annual economic losses (Kouamé et al., 2010). These fungal diseases are characterised by symptoms such as leaf chlorosis and green mottling of varying severity. The most susceptible varieties can be literally stunted to the point of resembling tufts of grass. Sometimes the stems are covered in cankers and the internal tissues are necrotic. This deterioration of the stems leads to a reduction in their sugar content and losses in yield. These diseases have caused crop losses of up to 40 per cent in the Borotou-Koro and Zuénoula sugar complexes (Yao et al., 2020). In order to combat these pathogens effectively, pesticides – particularly synthetic fungicides from the benzimidazole, triazole and strobilurin families – are primarily used. However, the overuse of these synthetic fungicides in sugarcane plantations could lead to the emergence and rapid development of resistant strains, which would result in a resurgence of diseases (Cawoy et al., 2011). In view of these adverse consequences, it is important to find alternative solutions that will enable the continued control of plant pathogens whilst reducing the use of chemicals and also protecting the environment. These may involve the rationalisation of agricultural practices, the use of resistant plant varieties and/or the use of biopesticides (Thakore, 2006). It is against this backdrop that this study is set, the overall objective of which is to evaluate the in vitro effect of Pseudomonas fluorescens strains against Fusarium verticillioides, Fusarium subglutinans and Schizophyllum commune, which cause diseases in sugarcane in Côte d'Ivoire.