Abstract

The study was carried out in the vivo during the period from July to August and during the nursery in the period from September to December 2018 in the Department of Biology, Faculty of Education / Saber, Aden University- Yemen. The effect of biological agents, Bacillus subtilis and Trichoderma viride, on fungus pathogens in the southern coastal plain of Yemen, namely peronospora destructor, Leveillula taurica, Sclortium cepivorum, Botrytis allii, Alternaria porri, was evaluated in vitro. Vital factors have proved their ability to inhibit pathogens under vivo conditions  and  gave the most effective biological factors, compared to the witness and were of highest effectiveness of bacteria B. subtilis against the fungus peronospora destructor where the rate of inhibition to 87.5%, while the lowest efficacy of T. viride against pathogenic fungi Botrytis allii did not exceed 64.08%. As for the protection of onion seeds from these pathogenic fungi under the nursery conditions, bacteria B. subtilis and T. viride gave the highest effect against P. destructor where the germination rate of seeds was 95% and B. subtilis against pathogen S. cepivorum has also reached the rate of germination to 95%. When the seedlings were grown, the fungus was shown to be highly effective. These organisms protected the root vegetation of the pathogenic fungi, compared to the witness. The high efficacy of B. subtilis was to protect the root vegetation against P. destructor, while B. subtilis was less effective against S. cepivorum.