Abstract
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.
Highlights
Soybean (Glycine max L.) is one of Indonesian’s most important legume crops
A total of 53 isolates were successfully isolated from the soybean rhizosphere in two different media, including Humic acid Vitamin Agar (HVA) and starch casein agar (SCA), based on each distinct morphological characters
We found that it is unlikely that high indole-3acetic acid (IAA) production in vitro would constantly result in significant growth promoting activity in planta
Summary
Soybean (Glycine max L.) is one of Indonesian’s most important legume crops. The rate of soybean production in Indonesia is still relatively low, approximately 2.37% per year. Such yield productivity is still not enough to supply soybean needs in Indonesia leading to high import demand of soybean for nearly 70% per year as reported by the MAI (2015). Modern agriculture relies on the use of some chemical fertilizers in increasing soybean productivity. The excessive use of these chemical fertilizers in long-term results in the accumulation of some chemical residues that may cause environmental damage, including groundwater contamination, soil structure alteration and ecological damage. It is necessary to increase the soybean productivity by the other approaches mainly an environmentally friendly one
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