Role of Oxidative Enzymes and Biochemical Constituents in Imparting Resistance to Clusterbean Varieties against Bacterial Blight (Xanthomonas axonopodis pv. Cyamopsidis)

Abstract

Bacterial blight is associated with physiological and biochemical changes in clusterbean, and differences among varieties may be reflected in oxidative-enzyme activity and biochemical constituents. This study compared four clusterbean varieties representing susceptible (RGC-986), moderately susceptible (RGM-112), moderately resistant (RGC-1017), and resistant (RGC-1066) reactions. Healthy and diseased leaves collected 40 days after sowing were analysed for polyphenol oxidase, peroxidase, catalase, chlorophyll, total phenolic compounds, total soluble, reducing and non-reducing sugars, soluble protein, and proline. Oxidative-enzyme activities generally increased in diseased leaves. The highest polyphenol oxidase activity in diseased leaves was recorded in RGM-112, the highest peroxidase activity in RGC-1017, and the highest catalase activity in RGC-986. Total chlorophyll declined after disease development, with the highest healthy-leaf value recorded in RGC-1017. Total phenolic content increased after infection and was highest in RGC-1066. Total, reducing, and non-reducing sugars decreased in diseased leaves, while RGC-1017 retained the highest total sugar content. Soluble protein also decreased following infection, with RGC-1066 showing the highest protein content in both healthy and diseased leaves. Proline increased in diseased leaves of all varieties and was highest in RGC-1066. Overall, the contrasting varietal responses were associated with differences in oxidative-enzyme activities and biochemical constituents, indicating that these traits accompany differential bacterial blight reactions in clusterbean.