Traits-Based In vitro and In vivo Evaluation of Plant Growth-promoting Bacterial Isolates from Piper nigrum and Piper colubrinum

Abstract

Black pepper (Piper nigrum L.) is a valuable commercial crop of India, particularly in Kerala, with Wayanad district serving as a major hub for its cultivation, where farmers in these hilly regions heavily rely on chemical fertilizers to maintain crop productivity. However, prolonged use of these fertilizers can degrade soil health, disturb the microbial balance, and limit nutrient availability over time. In the pursuit for eco-friendly alternatives, plant growth-promoting bacteria (PGPB) have gained attention for their ability to enhance plant health while preserving soil integrity. The present study explored the potential of bacterial isolates from both wild and cultivated Piper species as PGPB. Many of the bacterial isolates exhibited multiple beneficial traits, including nitrogen fixation, phosphate and zinc solubilization, production of phytohormones such as indole-3-acetic acid (IAA) and gibberellic acid (GA), and ACC deaminase activity. Based on these characteristics, seven strains primarily belonging to the genus Bacillus, including Bacillus sp., B. amyloliquefaciens, B. drentensis, B. velezensis, and B. subtilis were selected and formulated into microbial consortia. In vivo evaluations were conducted using black pepper plants grown in polybags under greenhouse conditions, with regular monitoring of growth parameters such as number of leaves, branches, shoot length, root length and dry matter production. The consortium derived from Piper colubrinum (PCCB) significantly enhanced plant growth metrics, indicating its superior efficacy. These findings underscore the potential of native bacterial isolates as bioinoculants for sustainable black pepper cultivation, particularly in challenging environments like the hill ecosystems of Kerala. The development of such microbial consortia could reduce dependence on chemical inputs and offer a scalable, eco-friendly strategy for improving crop productivity and soil health.