Biological control of Phomopsis leaf blight of brinjal (Solanum melongena L.) with combining phylloplane and rhizosphere colonizing beneficial bacteria

Abstract

Beneficial phylloplane colonizing bacteria (PCB) and rhizosphere colonizing bacteria (RCB) were evaluated individually and in combinations for plant growth promotion and control of Phomopsis leaf blight of brinjal (Solanum melongena L.). Bacteria from the leaf surface of brinjal plants were isolated and screened, and four PCBs were selected based on their ability to colonize phylloplane and inhibit the growth of Phomopsis vexans. All PCB and RCB strains were characterized for their beneficial traits and their leaf and root colonizing ability were confirmed through SEM. Under greenhouse conditions, individual applications such as seed treatment with Pseudomonas putida Has-1/c (RCB) and foliar application of Bacillus subtilis Br/ph-33 (PCB) significantly increased the plant growth and leaf surface area, respectively. Among 16 combinations of PCB and RCB tested, seed treatment with Pseudomonas fluorescens 2apa-pf followed by foliar application of B. subtilis Br/ph-33 significantly increased root length (6.3cm) and shoot length (23.2cm), fresh weight (2.51g) and dry weight (0.373g) of seedling. Individual application of PCB strains recorded significant decrease in disease incidence and severity over control. Among various combinations tested, Has-1/c+Br/ph-11 significantly reduced the disease incidence (18.0%) and severity (0.54) in comparison with distilled water treated control (91% and 6.0). The results suggested that combined application of biocontrol agents is more efficient in improving plant growth and controlling the disease over their individual application. The research findings could be beneficial in replacing agrochemicals in brinjal cultivation and also promising in suppressing leaf blight disease caused by P. vexans in brinjal.