EFFICACY OF SECONDARY METABOLITES AND EXTRACELLULAR LYTIC ENZYMES OF PLANT GROWTH PROMOTING RHIZOBACTERIA (PGPR) IN CONTROLLING FUSARIUM WILT OF CHICKPEA

Abstract

Plant growth promoting rhizobacteria (PGPR) and its metabolic products may play a pivotal role in controlling wilt disease in chickpea plants caused by Fusarium oxysporum f. sp. ciceris and promote plant growth under greenhouse and field conditions. The obtained data indicated that both PGPR strains viz. Bacillus subtilis and B. megaterium were able to produce indole acetic acid (IAA), siderophore, hydrogen cyanide (HCN), extracellular compound and volatile antibiotics in vitro. In addition, both PGPR strains produced mycolytic enzymes viz. chitinase, β-1, 3-glucanase and protease in growth media. Bacillus megaterium produced greater amounts of secondary metabolites than B. subtilis. Under laboratory condition, cell cultures, culture filtrates, metabolic precipitates with acetone, ethanol and ammonium sulfate inhibited mycelial growth of the target pathogen and the percentage of inhibition varied from 26.07 % to 48.82 %. Bacillus megaterium inhibited mycelial growth more than B. subtilis. Also, the metabolic precipitate significantly suppressed mycelial growth of pathogen more than cell cultures or culture filtrates and the ethanol precipitate was the most inhibitive. Under greenhouse and field conditions, both PGPR strains used as seed soaking in cell cultures, culture filtrates and/or metabolic precipitates significantly reduced area under wilt progress curve (AUWPC) compared with untreated seeds (control). B. megaterium was more efficient for controlling wilt disease in chickpea than B. subtilis and the metabolic precipitates reduced AUWPC more than cell cultures or its filtrates. Ethanol precipitate recorded the highest reduction of AUWPC either under greenhouse or field conditions. Using cell cultures, cultures filtrates and metabolic precipitates of both PGPR strains significantly increased growth parameters (plant height and number of branches per plant), yield components (numbers of pod and seed /plant, weight of 100 seed, total yield / feddan and protein content in seeds) compared with untreated seeds (control) during growing seasons 2013-14 and 2014-15 under field conditions. Ethanol precipitate of B. megaterium or B. subtilis recorded the highest growth parameters and yield components in both growing seasons. Generally, metabolic precipitation recorded the best results for controlling wilt disease under greenhouse and field conditions and improved plant growth and increased yield components more than cell cultures or culture filtrates of both tested PGPR strains.