Antifungal Trait and Plant Growth Promotion Potential of Bacillus Spp. from Rhizosphere Soils of Black Aromatic Rice, ‘Chakhao’

Abstract

Manipuri black aromatic rice, ‘Chakhao’, is a nutrient rich unique local rice cultivar of Manipur, India. Rhizosphere bacteria may have potential as antifungal agent and seedling growth promoter. Hence, the current investigation was aimed at screening, for the above traits, using bacteria, Bacillus spp., isolated from the soil of Rhizosphere of six Chakhao rice cultivars. Altogether, 323 bacterial isolates were obtained from the rhizospheric soils of 6 different cultivars of Chakhao, namely Chakhao Amubi (CA), Chakhao Poireiton (CP), Chakhao Sempak (CS), Chakhao Angoubi (CAng), Chakhao Angangbi (CR) and Chakhao Wairi (CW). All the rhizobacterial isolates were screened for antifungal activity against 5 rice fungal pathogens viz. Rhizoctonia solani (RS), Fusarium oxysporum (FO), Curvularia oryzae (CO), Pyricularia oryzae (PO) and Aspergillus niger (AN). The isolates were also subjected to PGP (plant growth promotion) assays such as ammonia, indole acetic acid (IAA), siderophore and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and phosphate solubilization. Of 323 isolates obtained, 64 were found to exhibit antifungal activity while 69 showed PGP traits. Twenty-five (25) isolates were found to be positive for both antifungal and PGP traits. Of 25 bioactive isolates, 4 (CR12, CW11, CA2 and CP2) potent isolates were shortlisted for further studies. The shortlisted potent isolates were subjected to quantitative estimation of PGP activities like phosphate solubilization, IAA and siderophore production. The strains could produce significant amount of IAA and siderophore and solubilize phosphate. Molecular characterization by 16S rDNA sequence analyses revealed the identity of the isolates: CR12: Bacillus subtilis (Accn. No.OM866257), CW11: Bacillus paralicheniformis (Accn. No.OM868047), CA2: Bacillus sp. CCMB1014 (Accn. No.OM868070) and CP2: Bacillus licheniformis (Accn. No.OM892495). Seedling vigor assays of the shortlisted potent strains were carried out on Chakhao Amubi rice. The isolates exhibited higher seedling vigor indices (CR12: 668.00, CA2: 618.66, CP2: 510.92 and CW11: 478.91) over the control (164.48). These rhizospheric strains have the potential to be developed as bioinoculants or biostimulants for enhancing Chakhao rice growth.