Dynamics Of Reactive Oxygen Species And Antioxidant Enzyme Activity In Tomato Plants Infected With Fusarium Oxysporum F. Sp. Lycopersici

Abstract

Objective: Tomato (Solanum lycopersicum) is one of the most widely cultivated and consumed vegetable crops globally, recognized for its high nutritional value and economic importance. However, its productivity is significantly constrained by various biotic stresses, with Fusarium wilt being one of the most destructive diseases. This vascular wilt is caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. lycopersici (FOL), which disrupts water and nutrient transport within the plant. The objective of this study was to examine the associated biochemical changes occurring in tomato plants in response to infection, in order to better understand host-pathogen interactions and the biochemical basis of disease progression.
Scope: The study was carried out under controlled pot culture conditions during the period of January to April 2025 at SRM College of Agricultural Sciences, Baburayanpettai, Chengalpattu District, Tamil Nadu. Ten isolates of FOL, obtained from distinct geographic and symptomatic tomato fields, were used to inoculate healthy tomato seedlings.
Observations were made to assess disease development, and plant tissue samples (including leaves, stems, and vascular regions) were collected on the 40th day of post-inoculation for biochemical analysis. Key physiological and biochemical parameters were measured, such as chlorophyll content, soluble protein concentration, superoxide radical levels, oxalic acid accumulation, and the activity of defence-related enzymes like polyphenol oxidase and peroxidase. This comprehensive approach aimed to correlate pathogen virulence with the extent of host metabolic disruption.
Result: Among the ten isolates tested, isolate F7 was identified as the most virulent, inducing early and severe disease symptoms characterized by yellowing of leaves, stunted growth, and vascular browning as early as the 20th day of postinoculation. Plants infected with F7 displayed pronounced biochemical alterations. There was a significant reduction in chlorophyll content (0.30 mg/g), indicating impaired photosynthetic activity. In contrast, the levels of soluble proteins (151.03 mg/g), superoxide radicals (6.20 nmol g⁻¹ FW), and oxalic acid (0.600 mg/g⁻¹) were considerably elevated, reflecting heightened stress and cellular damage. Furthermore, the activity of defence-related enzymes such as polyphenol oxidase (222.00 U/g of protein) and peroxidase (58.843 U/g of leaf tissue) was notably suppressed in F7-infected plants compared to others. These findings establish a clear correlation between the virulence of FOL isolates and the intensity of host biochemical responses, offering valuable insights into the mechanisms of disease development and plant defence suppression.