Isolation of plant growth promoting actinobacteria from the rhizosphere of finger millet and cowpea

Abstract

Actinobacteria commonly inhabit the rhizosphere, being an essential part of this environment due to their interactions with plants. Such interactions have made possible to characterize them as plant growth-promoting rhizobacteria (PGPR). As PGPR, they possess direct or indirect mechanisms that favor plant growth. Actinobacteria improve the availability of nutrients and minerals, synthesized plant growth regulators. A total of forty actinobacterial isolates were obtained from rhizosphere of finger millet and cowpea. The isolates were characterized morphologically and biochemically. Biochemical characterization of forty isolates of actinobacterial isolates, twelve isolates were positive for casein hydrolysis, eleven isolates were positive for tyrosine, twenty isolates were positive for H2S production, seven isolates were positive for gelatin liquefaction, twenty three isolates were positive for indole test, three isolates were positive for methyl red test, five isolates were positive for Voges Proskauer test, ten isolates were positive for urease production, eight isolates were positive melanin production and seven isolates were positive for citrate production, and negative for HCN production. The average count of actinobacteria enumerated on five different media (actinobacteria isolation agar, humic acid vitamin agar, starch casein agar, Kuster’s agar and ISP-4 media) were 7.75 x 103, 6.01 x 103, 15.86 x 103, 3.04 x 103 and 7.55 x 103 CFU g-1 of sample respectively. The highest population of 29.00 x 103 CFU g-1 was observed in the rhizosphere of cowpea compared to all the other samples used for the isolation. Among the five media used for the enumeration of actinobacteria starch casein agar was found best for the growth of actinobacteria.