Expression of Defense Related Enzymes in Rice Near Isogenic Lines IRBB4 and IRBB7 Challenged with Xanthomonas Oryzae Pv. Oryzae at Elevated Temperature

Bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae ( Xoo ) is an important disease of rice causing significant yield losses. Currently, there are ten highly diverse pathotypes of Xoo prevalent in Punjab state of India. Breeding for and deploying host plant resistance is the most economical approach for the management of this disease. But pathogen variability coupled with uncertainties in prevailing weather conditions due to climate change poses serious threat to the durability of R genes and makes the plant vulnerable to attack by the pathogen. During the current study, biochemical basis of resistance of two R genes, Xa4 and Xa7 was studied at different temperature regimes and five pathotypes of Xoo viz . PbXo-4, PbXo-7, PbXo-8, PbXo-10 and Sgr-1001. Level of resistance in Xa4 and Xa7 genes was observed to be highly correlated with the expression of three defense related enzymes viz . peroxidase, polyphenol oxidase and phenylalanine ammonia lyase. It was further observed that the expression of Xa4 and Xa7 was influenced by temperature as Xa4 showed increased effectiveness at lower temperature while Xa7 was more effective at high temperature. The differential pattern of lesion length progression on these near isogenic lines in response to different temperature regimes also suggests the level of quantitative resistance imparted by these genes.