Effect of adding some biocontrol agents on non­ target microorganisms in root diseases infecting soybean and broad bean plants

Abstract

The present work was carried out to study effect of adding some biocontrol agents, are used to control root rot disease in broad bean and soybean plants, on non-target beneficial microorganism. These studies were carried out under laboratory, greenhouse and field conditions to confirm correlate scientific facts with application in field. Results obtained from this work could be summarized as follow: -

Isolation and identification of root rot pathogens. beneficial bacteria and some antagonists. 1- Rhizoctonia solani and Sclerotium rolfsii were isolated from rotted samples of broad bean and soybean as the main causal pathogens of root rot and damping off diseases. The nodule bacteria Rhizobium leguminosarum, and Bradyrhizobium japonicum, were also isolated from the active root nodules of broad bean and soybean, respectively.

Azotobacter bacteria were isolated also from rhizospheric soils of soybean and broad bean. The antagonists Trichoderma harzianum, T viride, Gliocladium virens and Bacillus subtilis were isolated from rhizosphere of healthy roots of broad bean and soybean plants.

Pathogenicity tests:

2- Most dangerous effects of R. so/ani and S. rolfsii singly or in combination was occurred at stage of pre-emergence damping off. Rhizoctonia so/ani caused higher pre-emergence than S. rolfsii, while S. rolfsii + R. solani caused the highest pre-emergence damping-off on both broad bean and soybean. Pre-emergence was higher on soybean than broad bean whereas the post-emergence showed the opposite trend. Post-emergence caused by R. so/ani or S. ro(fsii each alone was significantly higher than combination (S. rolfsii + R. so/ani). Finally, R. so/ani + S.