Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea

The study includes isolation, characterization and evaluation of actinobacteria for plant growth promotion in cowpea. Actinobacteria were isolated from four soil and three compost samples on starch casein agar and total 50 morphotypes were maintained including 21 isolates from the Department of Agricultural Microbiology repository. All 50 isolates were subjected to screening for direct plant growth promoting (PGP) activities including nitrogen fixation, phosphate, potassium and zinc solubilization and production of indole-3-acetic acid. Indirect PGP activities including production of hydrogen cyanide, ammonia and siderophores were also tested under in vitro conditions. Compatibility among isolates was tested via cross-streak method and five actinobacterial consortia were developed for further in planta studies. A total of 29 actinobacterial isolates were obtained from rhizosphere soil and compost samples, with cowpea rhizosphere soil exhibiting the highest population density. Based on in vitro screening and PGP ranking of all the 50 isolates, 15 isolates with PGP ability were selected for further cultural, biochemical and morphological characterization. The evaluation of five compatible consortia led to significant improvement in growth and yield parameters of cowpea compared to treatment of PGPR Mix 1 and control ( P  ≤ 0.05). T ₂ consortium ( Streptomyces fumigatiscleroticus and Streptomyces sp. strain PAS3) recorded significantly higher number of pods (23.8), number of seeds per pod (12.1), test weight (22.8 g), fresh (120.2 g) and dry weight (15.6 g) of pods, indicating their potential benefits for plant growth and yield. This research suggested actinobacterial consortia as viable biofertilizers, enhancing cowpea growth and contributing to environmentally sustainable agriculture.