Induction of resistance to tobacco necrosis virus in bean plants by certain microbial isolates

Abstract

Four rhizosphere microorganisms (Bacillus globisporus, Candida glabrata, Pseudomonas fluorescens, and Streptomyces gibsonii) were isolated, identified, and tested for their capacity to protect Phaseolus vulgaris plants from tobacco necrosis virus (TNV) symptoms. Foliage treatment by the culture filtrate of each one of the four microbial isolates highly reduced the number of local lesions, while soil treatment by the same four microbial isolates showed lesser effects. Concerning foliage treatment, both Pseudomonas fluorescens and Streptomyces gibsonii culture filtrates showed the highest inhibitory effect to TNV infection (91.5 % and 97.2%, respectively). A number of de-novo synthesized proteins (induced proteins) was detected by Polyacrylamide-gel electrophoretic analysis in the culture-filtrate-treated bean leaves relative to the (water-treated) control. The determination of â-1,3-glucanase and peroxidase enzymatic activities in the extracted proteins showed high â-1,3-glucanase and peroxidase activities in the leaves treated with Pseudomonas fluorescens and Bacillus globisporus culture filtrates respectively, in contrast to the Candida glabrata culture-filtrate-treated leaves. However, Streptomyces gibsonii culture-filtrate-treated leaves showed the same enzymatic activities as that of the control. These results show that filtrates of the four rhizosphere microbial isolates reduced TNV incidence in bean plants through a process termed induced resistance (IR). However each microbial isolate could induce resistance by a distinct mechanism that was different from classic induced resistance against viral infection.

KEY WORDS: Induced resistance, Viral infection, TNV, Rhizosphere microbial isolates.

Egyptian Journal of Botany Vol.5 2003: 10-18