Evaluation of some antagonistic bacteria in biological control of Gaeumannomyces graminis var tritici causal agent of wheat take-all disease in Iran

Take-all is a disease of wheat root caused by the soil borne fungus, Gaeumannomyces graminis (Sacc) Von Arx and Oliver var tritici Walker (Ggt) all over the word. There has been considered biological control using the microorganisms departed from suppressive soils or wheat roots, widely. In this study, strains of Bacillus (B. subtilis and B. pumilus),Pseudomonas (P. fluorescent, P. putida and P. aeruginosa) and Chromobacteria sp., separated from wheat rhizosphere, were assessed for their ability to control this disease. Three fungal isolates (23, 35 and 45) were used in all experiments. Out of 45 bacterial strains in laboratory conditions, 15 strains were selected for isolates 23; 14 strains for isolates 35, and 25 strains for isolates 45 based on dual culture tests. In volatile metabolites test, for isolate 45 the most effective bacteria were strains 132 (P.fluorescens) and 159 (P. putida) and for isolates 23 and 35, strains 73 (P. fluorescens) and 10 (P. putida) were the best, respectively. Antibiotic production results indicated that for isolate 23 strains 93, 196, 142 (P. fluorescens) and 106 (P. putida); isolate 35, strain 10 (P. putida) and isolate 45, strain 66 (B. subtilis), 68, 103, 159 (P. putida), 173, 93 (P.fluorescens) and 78 (P. aeruginosa) reduced pathogen growth significantly (p<0.05). Regarding siderophore production, among fluorescent pseudomonads, strains 189, 87, 5 and MP were selected. The effectiveness of bacteria on take-all was assessed in test tubes and greenhouse by seed treatment, too. Disease severity was assessed based on 0-6 scale and in all three fungal isolates, there were significant differences between treatments (p<0.01). In growth chamber experiments for isolate 35, P. fluorescens (VN) was the best one and for isolates 23, wheat treated with P. fluorescens strains VN and 196 showed less disease. Finally, for isolates 45, the most effective strains were VN, 132, 39, 73, 189, 196, MP (P. fluorescens), 53, 103 and 147 (P. putida). According to greenhouse results, in isolate 35 wheat treated with strains 10 (P. putida) and VN (P. fluorescens) showed no infection indicating bacterial effectiveness in fungal inhibition. Isolate 23, strains 100 (P. putida), 196, 5, VN (P. fluorescens) and 65 (B. pumilus) and in isolate 45, strains VN, 132, 93 (P. fluorescens) and 53 (P. putida) were the most effective ones. In these cases there was no infection as well. The role of bacteria in promoting plant growth was assessed. There was no difference in growth indices between intact plant and plant treated with bacteria (without any fungal inoculation), so bacteria cause growth enhancement by disease control.   Key words. Gaeumannomyces graminis var tritici, Bacillus, Pseudomonas, Chromobacteria, take-all, biological.