Role of Reactive Oxygen Species in Defense Responses Against Chocolate Spot Disease in Resistant and Susceptible Faba Bean (Viciafaba) Cultivars

Abstract

Three infected faba bean (FB) plant cultivars (susceptible and resistant to Botrytis fabae Sard.) were pretreated with three tested biological inducers (Trichoderma viride, Talaromyces stipitatus and Verticillium lecanii). Disease index (DI) and disease severity (DS) were significantly reduced as a result of all treatments, Giza 40 showed less reduction compared with the infected and uninfected control. Later on activities of peroxidase (POD) and polyphenol oxidase (PPO), two infected bean cultivars were increased significantly compared with control. Treatment with the tested biological inducers resulted in significant increase in POD enzyme activity early at 24 hrs after inoculation of both susceptible (Giza 40) and resistant (Sakha2) cultivars with B. fabae, compared with the treated control. Moreover,T. stipitatus bioinducer recoded the highest POD activity values in all the tested cultivars. PPO enzyme activity significantly increased when pretreated resistant cv (Sakha2) with T. stipitatus and suceptible cv (Giza 40) with V. lecanii, compared with the other tested treatments. Increases in PPO activity were early observed in all treatments, except for T. stipitatus-Giza 40cv treatment. Increases and accumulation of reactive oxygen species (ROS), mainly superoxide (O2·-) were detected at early stages (24 hrs) after inoculation due to pretreatment with V. lecanii, compared to untreated control of Giza 40 and treated control of Sakha2, gaving the same results. At the meantime, it was found that pretreatment of Giza 40 and control with T. stipitatus significantly increased and accumulated levels of (O2·-) at late stages (72 hrs) after inoculation. It was also noted that all treatments resulted in significant increase and accumulation of O2.-, except for Giza 40 cv, which showed pronounced decrease in O2.- levels. In spite of the increase and accumulation of hydrogen peroxide (H2O2), detected in all treatments 72 hrs after inoculation, however, pretreated control of Giza 40 cv showed early increase and accumulation of H2O2 24 hrs after inoculation. Positive relationship between accumulated of H2O2 and the time elapsed after inoculation was observed in all the tested treatments.