Plant Growth Promoting Activity of Actinomycetes Isolated from Soybean Rhizosphere

Plant Growth Promoting Rhizobacteria (PGPR) is considered as the biological agent for improving plant growth. One Group of PGPR that have an important role in growth promoting of plant is Actinomycetes. The objective of this study was to isolate and screen Actinomycetes isolated from soybean rhizosphere as growth promoter of soybean in vitro. Fifty-three Actinomycetes isolates have successfully been isolated from soybean rhizosphere using two media, mainly Humic acid Vitamin Agar (HVA) and starch casein agar (SCA). Among 53 isolates, 18 (34%) isolates were able to produce IAA in range of 2.08 ppm to 16.70 ppm. Growth promotion test of soybean in vitro using Ragdoll method resulted 7 Actinomycetes isolates that significantly enhanced 3 plant growth parameters, including hypocotyl and radicular length as well as the number of lateral roots. Of those 7 isolates of Actinomycetes, 5 isolates were able to grow on nitrogen-free medium and solubilize phosphate. Those 5 isolates also were found as non-pathogenic, based on the negative reaction in hypersensitivity test. Based on 16S rRNA sequence analysis, 5 selected Actinomycetes isolates were highly homolog with Streptomyces genera in different taxa of species and strains (similarity ≥99%). Our finding reveals a potent application of 5 Actinomycetes isolates as plant growth promoter in soybean agriculture.