Reactive oxygen species generating and scavenging systems play critical role in conferring leaf spot disease resistance in Withania somnifera (L.) Dunal

Leaf spot disease caused by Alternaria alternata severely affects the growth and yield of a high repute medicinal plant, Withania somnifera(L.) Dunal. Thus, to substantiate the growing demand of this plant, it is critical to develop suitable strategies to combat the effects of leaf spot disease. Reactive oxygen species (ROS) modulation is one of the key mechanisms for achieving biotic stress tolerance as it evokes multiple stress adaptive pathways in plants. Hence, in the present investigation, ROS generating and scavenging systems have been evaluated together in leaf spot disease resistant and susceptible accessions of W. somnifera. The levels of various types of ROS have been detected using different staining methods and biochemical assays have been performed to estimate the enzymatic activities of ROS generating and scavenging enzymes. The results of enzymatic activities have been consolidated at the transcript level using real-time PCR. Results show that leaf spot resistant accession has higher basal levels of hydrogen peroxide due to the increased enzymatic activities of nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase and superoxide dismutase (SOD) enzymes. Hydrogen peroxide is well known as a signaling molecule that regulates a plethora of biotic stress-responsive pathways. The threshold levels of this molecule are maintained by the action of a series of antioxidant enzymes which also showed increased levels in the present investigation. Different oxidative stress markers including proline and malondialdehyde (MDA) have also been analyzed. Our study demonstrates that ROS dynamics in leaf spot resistant accession of W. somnifera due to the coordinate action of ROS generating and scavenging system could be one of the reasons for resistance against A. alternata. Hence, modulation of ROS machinery could a feasible approach for achieving leaf spot disease resistance in W. somnifera.