Four antioxidants, i.e. ascorbic, citric, oxalic and salicylic acid and eight bioagents, i.e. Bacillus megaterium, B. subtilis, Pseudomonas fluorescens, Serratia marcescens, Trichoderma album, T. harzianum, T. lignorum and T. viride were tested in vitro, under greenhouse and in vivo against Rhizoctonia damping-off of snap bean plants. In vitro, all the tested bioagents caused significant reduction to the linear growth of R. solani. T. viride caused the highest reduction followed by T. lignorum then T. harzianum, respectively. Under greenhouse conditions, sowing soaked bean seeds in the tested antioxidants or coated with the tested bioagents in soil artificially inoculation with R. solani significantly reduced the incidence of pre- and post-emergence damping- off with significant increase in the fresh and dry weight of roots and shoots compared with control treatment. Salicylic acid and S. marcescens gave the highest percentages of survived plants. S. marcescens induced the highest increase of fresh and dry weight of shoots followed by B. megaterium then salicylic acid and T. viride. S. marcescens followed by B. megaterium and T. viride resulted in the highest increase in the fresh and dry weight of roots. In general, all the tested antioxidants and bioagents significantly reduced the incidence of damping-off and root-rot under field conditions. The obtained results showed that, the use of antioxidants and bioagents caused considerable increase in the activity of peroxidase, polyphenol oxidase, chitinase and β-1,3-glucanase enzymes that play an important role in plant defence mechanisms against pathogens infection. |
