Effective Formulations to Improve the Efficiency of Bacterial Inoculum as Biological Control Agents against Some Root Diseases

Abstract

Fungi that cause root diseases are the most common pathogenic fungal groups, which affect a wide range of plant species and suits different environmental conditions. The most important of these pathogenic fungi are Rhizoctonia solani Kühn; Fusarium semitectum, and Macrophomina phaseolina which isolated from eggplant (Solanum melongena). This research was concerned with studying the
effectiveness of some endophytic bacterial isolates, isolated from Medicago sativa; Rosmarinus officinalis and Vicia faba, as biological control agents. Bacterial isolates were identified as Pseudomonas aeruginosa, Pseudomonas alcaligenes, and Pseudomonas mendocina based on 16S rRNA and evaluated for their ability to inhibit these fungi individually or in mixtures under greenhouse and laboratory conditions. Eighteen different formulations of biological control agents were evaluated based on their base and additive combinations. The different bases used were Talk, Diatoms, and Clay, while the additives were Alginate, Arabic gum, and beef extract. The results showed that using of bacterial mixtures against pathogenic fungi was more effective than using each bacterial isolate
individually. The most effective bacterial formulations were; 1- Diatoms with Arabic gum and Beef; 2- Clay with Alginate and Beef; 3- Clay with Arabic gum and Beef; 4- Clay with Arabic gum; 5-Talc with Arabic gum and Beef; 6-Talc with Arabic gum. All selected bacterial formulations significantly reduced root rot on Eggplant (Solanum melongena) under greenhouse conditions and positively affected the
level of total phenolic compounds and total antioxidant activity in tested host plant. The study recommended carrying the tested biological control agents on ecofriendly materials to maintain the effectiveness of bacteria and reduce the incidence and severity of root rot diseases.