Screening potential bacterial biocontrol agents towards Phytophthora capsici in pepper

Abstract

A total of 1,487 bacterial isolates were obtained from the rhizosphere, phyllosphere, endorhiza and endosphere of field-grown pepper. In a dual assay, 232 isolates displayed the antagonistic activity towards Phytophthora capsici L.; 36.6 % and 39.2 % of them were obtained from the rhizosphere and phyllosphere, respectively. 40 of the 232 antagonistic isolates producing inhibition zones of at least 5 mm in diameter were assessed for production of siderophores and chitinase, cellulose, and protease activity. These 40 isolates fell into 15 groups according to 90 % similarity of the banding patterns obtained by amplified ribosomal DNA restriction analysis (ARDRA). Seventeen isolates spanning the 15 groups were evaluated in greenhouse tests for their ability to control Phytophthora blight of pepper. Biocontrol efficacy ranged from 0.7 % to 92.3 %, with three isolates (B1301, R98, and PX35) exhibiting maximum ability to reduce the disease severity (83.5 %, 92.3 % and 83.5 %, respectively). Based on 16S rDNA sequencing, these isolates were identified as Bacillus cereus (B1301), Chryseobacterium sp (R98) and Bacillus cereus (PX35). This is the first report that Chryseobacterium sp. (R98) can function as a biocontrol agent of Phytophthora blight.