The Influence of the Non-Pathogenic Fusarium oxysporum Fo47 Strain on Flax Resistance to Pathogens

Flax (<i>Linum usitatissimum</i> L.) is a plant of high economic and practical importance valued for its fiber and oil, which have diverse applications in industries such as textiles, food, pharmaceuticals, and construction. Fungal pathogens of the genus <i>Fusarium</i>, however, pose one of the most serious threats to flax cultivation. They are responsible for a number of disease manifestations, notably <i>Fusarium</i> wilt and root rot. In the case of fusariosis, there is a lack of plant protection products, and often the only effective approach is to use resistant flax cultivars or to discontinue cultivation for several years. Currently, much attention is paid to biological methods of plant protection, which do not exert a negative influence on the environment or human health and are important for sustainable agriculture. The aim of the present study was to assess the potential of the non-pathogenic endophytic fungal strain <i>Fusarium oxysporum</i> Fo47 in protecting plants against pathogenic fungi. The results showed that pretreatment of flax plants with Fo47 increased resistance of plants to all tested fungi (<i>F. oxysporum</i>, <i>Fusarium culmorum</i>, <i>Rhizoctonia solani</i>). Fo47 was the most effective for protection against <i>F. culmorum</i> for the Jan flax cultivar and <i>R. solani</i> for the Bukoz cultivar. Pretreatment with Fo47 of flax plants inoculated with <i>F. culmorum</i> caused an increase in the level of secondary metabolites involved in plant resistance (phenolics) and photosynthetic pigments (chlorophyll a and b) compared to plants treated only with the pathogenic fungal strain. Fourier transform infrared spectroscopy revealed structural changes in the polymers of cell walls. The highest intensities of vibrations characteristic of lignin and pectin were observed for flax treated with Fo47 and infected with <i>F. culmorum</i>, suggesting the highest level of these polymers, higher than in plants treated only with pathogenic fungi. Thus, it can be concluded that application of the non-pathogenic strain strengthened the immune response of flax plants. These results highlight the strong potential of the non-pathogenic strain as a biological control agent, especially for <i>Fusarium</i> infection in flax.