Isolation and characterization of rhizobacteria with biocontrol activities against Faba bean (Vicia faba L.) chocolate spot disease causing Botrytis fabae

Abstract

This study has aimed at isolating and characterizing rhizobacteria having biocontrol traits against chocolate spot (Botrytis fabae L.) that attacks faba bean. Accordingly, a total of 52 rhizobacterial isolates were recovered from rhizosphere of faba bean and screened for biocontrol activities against the test pathogen using dual culture method. Of these, only 50% of them showed inhibition against the pathogen. All the 26 isolates with antagonistic activities against Botrytis fabae were characterized using standard microbiological methods. The isolates inhibited the radial growth of the pathogen at an inhibition percentage ranging to 52.5- 85.8%. Among these isolates, 17(65.38%) of them were Gram negative. Regarding the isolates’ plant growth promoting properties, 26(100%), 23(88.5) and 21(80.8%) were positive for nitrogen fixation, phosphate solubilisation and indole acetic acid production, respectively. The minimum and maximum phosphate solubilisation indexes of the isolates were 2.3 and 4.1 cm, respectively. The hydrolytic enzyme production test showed that 25(96.2%), 15(57.69%) and 14(53.84%) of isolates produced protease, chitinase and cellulase, respectively. Moreover, all (100%) and 6(23.07%) of the rhizobacterial isolates produced ammonia and hydrogen cyanide, respectively. Several isolates showed better growth at lower and higher temperature ranges and salt concentrations. Similarly, the majority of these isolates showed better resistance to the tested antibiotics and heavy metals with a decreased growth response to tetracycline and mercury. Elite isolates (WUFBI 6A and WUFBI 9D) which showed the highest performance in all the tests can be recommended as inoculants for application under greenhouse conditions and field test.