Characterization and in vitro efficacy of Bacillus subtilis and Pseudomonas aeruginosa as biological control against wilt causing Fusarium species of Sugarcane

Abstract

Wilt is a threatening disease of sugarcane caused by various Fusarium species. Many rhizospheric isolates have studied for their plant growth promotion and biocontrol potential against wilt causing Fusarium species in sugarcane. This study is focused on a gram-positive and a gram-negative bacterial antagonist, isolated from the rhizosphere of the sugarcane field located in the South Gujarat region, India and studied for their plant growth-promoting (PGP) and antagonistic activity against major sugarcane wilt pathogens prevalent in the region. Based on the results of phenotypic characterization and 16S rRNA gene sequencing, the isolates were identified as Bacillus subtilis strain IAM 12118 (RB32) and Pseudomonas aeruginosa strain ATCC 10145 (RB42). Several mechanisms are accounted for the control of plant patho-gens, RB32, and RB42 were screened for their PGP characteristics and hydrolytic enzyme capabilities. Both the isolates tested positive for the production of indole-3-acetic acid (IAA), ammonia (NH3), siderophores, Hydrogen cyanide (HCN) and phosphate solubilization, while only P. aeruginosa had the capability for the Nitrogen fixation. Quantitatively IAA was measured higher in RB32 (34.56±0.32 mg\L) as compared to RB42 (19.26 ± 0.61 mg\L), phosphate solubilization was also higher in RB32 (9.06 ±.0.22 mg\L) as compared to RB42 (3.35 ± 0.21 mg\L). Siderophore production is an important mechanism for biocontrol activity, RB42 produced more siderophores (78.88±1.14 %) than RB32 (62.71±1.58 %). Among both the rhizospheric isolates, P. aeruginosa strain ATCC 10145 (RB42) gave a higher mycelial inhibition of 64.63± 1.22% mean than B. subtilis strain IAM 12118 (RB32) of 57.69±1.28% mean against Fusarium species. The objective of this study is to isolate indigenous organisms from the sugarcane rhizosphere and use them as an alternative source of chemical fungicides to manage major sugarcane diseases.