Hydrogen Peroxide Prompted Lignification Affects Pathogenicity of Hemi-biotrophic Pathogen Bipolaris sorokiniana to...

Spot blotch caused by Bipolaris sorokiniana has spread to more than 9 million ha of wheat in the warm, humid areas of the Eastern Gangetic Plains (EGP) of South Asia and is a disease of major concern in other similar wheat growing regions worldwide. Differential lignin content in resistant and susceptible genotypes and its association with free radicals such as hydrogen peroxide (H₂O₂), superoxide (O₂ ^-) and hydroxyl radical (OH^-) were studied after inoculation under field conditions for two consecutive years. H₂O₂ significantly influenced lignin content in flag leaves, whereas there was a negative correlation among lignin and H₂O₂ to the Area Under Disease Progress Curve (AUDPC). The production of H₂O₂ was higher in the resistant genotypes than susceptible ones. The O₂ ^- and OH^- positively correlated with AUDPC but negatively with lignin content. This study illustrates that H₂O₂ has a vital role in prompting lignification and thereby resistance to spot blotch in wheat. We used cluster analysis to separate the resistant and susceptible genotypes by phenotypic and biochemical traits. H₂O₂ associated lignin production significantly reduced the number of appressoria and penetration pegs. We visualized the effect of lignin in disease resistance using differential histochemical staining of tissue from resistant and susceptible genotypes, which shows the variable accumulation of hydrogen peroxide and lignin around penetration sites.