Differential antioxidative responses of three different rice genotypes during bacterial blight infection

Abstract

Using three rice genotypes exhibiting different disease symptoms towards bacterial blight (BB) disease, O. longistaminata (BB-highly resistant), IRBB21 (BB-resistant) and Pusa Basmati 1 (BB-sensitive), we investigated the variable antioxidant profile and oxidative damages resulting from bacterial blight infection to elucidate the antioxidative protective mechanism governing differential BB resistance. Rice genotypes were grown in growth chamber and after 45 days of transplantation in pots, they were inoculated with Xanthomonas oryzae pv. oryzae (Xoo) isolate DX133 following the leaf clipping method. Different biochemical assays were performed with leaf samples collected on 5th day after infection (5th DAI) 10th DAI and 15th DAI. The results showed that O. longistaminata exhibited higher level of total chlorophyll (̃4.42±0.09 mg/g fw) and carotenoid (̃2.74±0.04 mg/g fw) pigments throughout the studied periods of infection when compared to other genotypes. At 5th DAI, the higher production of non-enzymatic antioxidants including total phenolic content (10.82±0.01 mg GAE/g fw) and flavonoid content (18.60±0.03 mg QE/G fw) was observed in highly resistant genotype O. longistaminata, compared to Pusa Basmati1 and IRBB21. The activity of catalase (CAT) was increased in all the three genotypes under BB infection. However, O. longistaminata showed highest CAT activity on later stages of infection (15th DAI). The level of total antioxidant and ferric reducing power (FRAP) increased in the infected plants compared to controls on the onset of infection. The present study clearly demonstrates higher level of antioxidative protection in the highly resistant wild genotype O. longistaminata and can significantly contribute to understand the physiological mechanisms in rice conferring BB resistance.