Abstract
Tomatoes (Solanum lycopersicumL.) play a key role in ensuring food security and are an essential component of the human diet due to their rich content of vitamins and minerals. However, the stability of their production is seriously threatened by phytopathogens, especially representatives of the genus Alternaria, which cause early blight. This study provides a comparative characterization of two isolates -Alternaria alternataand Alternaria tenuissima, based on indicators of enzymatic activity and pathogenicity. The research covered five types of hydrolytic enzymes that degrade the plant cell wall: amylases, proteases, pectinases, phosphatases, and cellulases. The assessment was carried out on days 5 and 7 using indicator media to detect zones of enzymatic activity, as well as by visually measuring colony growth and degradation zones. Both isolates demonstrated moderate to moderately high levels of enzymatic activity, indicating a broad biochemical potential. When comparing enzymatic activity, it was found that both isolates exhibited the highest activity against amylolytic enzymes, with an averagevalue of 1.243, while phosphatase activity was the lowest, with an average index of 1.073. Pathogenicity test results confirmed the ability of both isolates to infect internal and external plant tissues, with no statistically significant differences between them. Nevertheless, A. tenuissimashowed more aggressive external activity, which may be critical for the spread of infection in agricultural ecosystems. The obtained data emphasize the importance of comprehensive assessment of phytopathogens in terms of both aggressiveness and biochemical activity, which is essential for the selection of resistant cultivars and breeding lines, as well as for optimizing biological protection strategies.