Proclaiming Plant Growth-Promoting and Antifungal Properties of Pseudomonas lurida and Bacillus velezensis Isolated from Rhododendrons of Darjeeling Hills.

Abstract

Endophytes have drawn attentions due to their effectiveness in providing benefits to host and non-host plants. In this study endophytic bacteria were isolated from stem and leaf samples of medicinally important plants Rhododendron griffithianum Wight and Rhododendron arboreum Smith subsp. cinnamomeum (Wall. ex G. Don) grown at higher altitudes of Darjeeling, India. Two endophytic bacteria, Pseudomonas lurida RGDS03 and Bacillus velezensis RCDL12 were identified based on 16S rRNA gene sequencing analysis. The endophytes exhibited indole acetic acid (IAA), gibberellic acid (GA), siderophore production, phosphate solubilization, nitrogen-fixing abilities, though B. velezensis RCDL12 showed superior production of IAA (126.04 ± 0.40 µg/mL), GA (241.00 ± 0.44 µg/mL), and phosphate (74.4 ± 0.41 µg/mL) solubilization as compared to P. lurida RGDS03. Purity of extracted IAA from these two endophytes was confirmed by HPLC and LC-MS analysis. In this study, P. lurida RGDS03 inhibited mycelial growth of two tested phytopathogens Phytophthora sp. and Pestalotiopsis sp. of broad host range. However, only against Pestalotiopsis sp. did B. velezensis RCDL12 exhibit antifungal activity. Study was conducted on growth promotion capabilities of isolates on rice and mung bean seedlings. P. lurida RGDS03, B. velezensis RCDL12 and consortium of both the strains reported with promising growth promotion on both rice (85-97%) and mung bean (86-99%) in terms of their seed germination, vegetative growth (root and shoot length, fresh and dry weight), and chlorophyll content as compared to the control plants (untreated). This study has emphasized growth-promoting and biocontrol activities of endophytic bacteria from rhododendrons, and application to enhance crop development for sustainable agriculture.