Antioxidant and biochemical markers as indicators of resistance to tobacco streak virus in cotton genotypes

Abstract

Aim The study investigates the biochemical and antioxidant defense responses of five cotton ( Gossypium spp. L.) genotypes to Tobacco streak virus (TSV), an emerging pathogen threatening cotton cultivation in southern India. Study design To analyze the biochemical and antioxidant responses of different cotton genotypes upon TSV infection, aiming to identify potential biochemical markers and defense indicators suitable for resistance breeding and the development of integrated viral disease management strategies. Place and duration of the study This study was undertaken at the University of Agricultural Sciences, Raichur. Methodology A total of 107 cotton genotypes screened under AICRP trials during Kharif 2024, Raichur (From 2 May 2024 to September 2024, Wet season) were categorized by disease response, and five representative genotypes were selected for analysis. Tobacco streak virus inoculum was prepared from infected leaves and confirmed through mechanical inoculation on cowpea seedlings. Leaf samples from healthy and infected plants at 60 and 90 DAS were processed to obtain extracts. Biochemical parameters (phenols, sugars, and proteins) and antioxidant enzymes (POD, SOD, CAT) were estimated using standard spectrophotometric methods. The study followed a completely randomized design with three replications, and data were analyzed using ANOVA, correlation, and regression. Results Five cotton hybrids-JKCH 9585 BGII (moderately susceptible), RCH 1016 BGII (moderately resistant), DACH 70C70 BGII (moderately resistant), and ACH 17–2 BGII (resistant), and DACH 88S88 BGII (resistant)-were analyzed for biochemical and antioxidant enzyme responses under TSV infection. At 60 and 90 days after sowing (DAS), infected JKCH 9585 BGII showed marked increases in total free phenols and soluble proteins, coupled with reduced total sugars, reflecting reallocation of primary metabolites toward defense mechanism pathways. In Biochemical analysis, When infected compared with the healthy sample, the infection induced phenols accumulation (increase up to 27.69% at 60 DAS and 23.3% at 90 DAS),Total sugars reduced up to 17.23% at 60 DAS and 14.17% at 90 DAS, Proteins increased up to 64.62% at 60 DAS & 27.75% at 90 DAS, and RCH 1016 BGII- and DACH 70C70 BGII exhibited moderate biochemical alterations, RCH 1016 BGII- Total Phenols- increased up to 10.05% at 60 DAS & 8.53% at 90 DAS, Total sugars- reduced up to 15.11% at 60 DAS & 4.79% at 90 DAS, Proteins- increased up to 15.34% at 60 DAS & 13.61% at 90 DAS and DACH 70C70 BGII- Total Phenols- increased up to 14.28% at 60 DAS & 12.98% at 90 DAS, Total sugars- reduced up to 5.05% at 60 DAS & 6.36% at 90 DAS, Proteins- increase up to 35.65% at 60 DAS & 38.88% at 90 DAS, while resistant hybrids ACH 17–2 BGII and DACH 88S88 BGII maintained constitutively enhanced baseline levels of phenolic compounds and proteins irrespective of infection. Antioxidant enzymes, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), were highly inducible in JKCH 9585 BGII- Peroxidase activity increased up to 2-fold at 60 DAS & 89.9% at 90 DAS, Superoxide dismutase activity increased up to 61.13% at 60 DAS & 24.67% at 90 DAS, Catalase activity increased up to 16.18% at 60 DAS & 12.18% at 90 DAS, moderately elevated in RCH 1016 BGII and DACH 70C70 BGII. RCH 1016 BGII- Peroxidase activity increased up to 49.37% at 60 DAS & 21.28% at 90 DAS, Superoxide dismutase activity- increased up to 15.11% at 60 DAS & 20.71% at 90 DAS, Catalase activity- increased up to 16.01% at 60 DAS & 7.14% at 90 DAS and DACH 70C70 BGII- Peroxidase activity increased up to 8.67% at 60 DAS & 21.64% at 90 DAS, Superoxide dismutase activity- increased up to 43.69% at 60 DAS & 47.02% at 90 DAS, Catalase activity- increased up to 21.08% at 60 DAS & 8.86% at 90 DAS and constitutively enhanced in ACH 17–2 BGII and DACH 88S88 BGII. The results demonstrate that resistant hybrids possess pre-activated biochemical and antioxidant defenses that limit virus spread, whereas susceptible genotypes rely on delayed stress responses. These findings highlight phenols, proteins, and antioxidant enzymes as reliable biochemical markers for TSV resistance and provide critical insights for breeding programs aimed at developing virus-resilient cotton cultivars.