Growth-Promoting Endophytes as Immunity Booster for Brassica juncea against Insect Attack

Endophytes play a pivotal role in plant growth, metabolism, and defense mechanisms. Many of these endophytes are known to promote plant growth and/or contribute in stress alleviation by producing an array of secondary metabolites and phytohormones. In agroecosystem, plants are continuously exposed to various biotic stressors which affect their growth and development as well as quality and quantity of the crop. This study for the first time, focuses on the growth promoting bacterial potential of endophytes in enhancing plant resistance against the polyphagous pest Spodoptera litura in Brassica juncea (Indian mustard). A total of the 30 bacterial and fungal endophytes were isolated from B. juncea and ten isolates namely, Acinetobacter sp. WEL105, Acinetobacter sp. WEL1051, Acinetobacter sp. WEL1052, Acinetobacter sp. WEL1072 and Acinetobacter sp. BJWEL1, Zasmidium sp. PWEL1031, Cladosporium sp. PWEL1032, Cladosporium sp. PWEL1033, Cladosporium sp. PWEL1034 and Cladosporium sp. PWEL104 were shortlisted based on their plant growth-promoting potential. Among these, Acinetobacter sp. WEL1072 and Acinetobacter sp. BJWEL1 supplementation showed significant increase in biomass, phytohormones production (indole acetic acid and gibberellic acid), phenol and condensed tannins concentrations. Endophyte-treated plants exhibited improved biomass and increased production of defence compounds, namely phenols, condensed tannins and serine protease inhibitors. Our study thus highlights the dual potential of endophytes in enhancing plant growth and strengthening defence mechanisms, thus offering a sustainable approach to agricultural pest management.