Plant growth promoting potential of butyl isobutyl phthalate and Streptomyces sp. from Rumex dentatus on rice.

Rice (Oryza sativa L.) is one of the most important staple foods consumed in many countries of the world. It is mostly consumed in developing countries where different chemical fertilizers are used to improve the productivity of the crop plant. In the present study, endophytic actinomycetes isolated from Rumex dentatus were identified morphologically and by scanning electron microscopy. Butyl isobutyl phthalate (BIBP) was isolated from the root endophyte Streptomyces sp. JR9 using column chromatography and HPLC methods. The compound was tested for its effect on rice seed germination. BIBP, extracts, and isolates were evaluated for their plant growth effect on rice in a growth chamber. Isolates were also screened in vitro for phosphate solubilization activity and enzyme production. Indole-3-acetic acid (IAA) and BIBP produced in extracts were quantified and detected using high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) methods, respectively. BIBP was found to increase the germination of rice seeds by 6 to 12% in treated samples and displayed potent effect at lowest concentration (0.437 µM). Both the compound and the extract depicted significant increases in almost all growth parameters at lowest concentration of 0.125 µg/mL and 62.5 µg/mL, respectively. BIBP also increased significantly shoot length, fresh root, fresh shoot, and dried shoot weight at high concentrations and was more potent than the standard phytohormone IAA. HPLC quantification showed 7.952 µg/mg and 0.371 µg/mg of IAA in extracts of Streptomyces sp. JR9 and the stem endophyte Streptomyces sp. KS3, respectively. IAA containing extract of JR9 increased significantly most growth parameters at lowest concentration (125 µg/mL). The extract of KS3 depicted significant increases in almost all growth parameters at high concentration (500 µg/mL). Our investigation showed that streptomycetes isolated from R. dentatus and BIBP are potent growth promoting agents and can be used in agriculture as bio-fertilizer to improve the growth and productivity of rice. KEY POINTS: • Butyl isobutyl phthalate (BIBP) isolated from endophytic Streptomyces sp. JR9 is a potent rice seed germination activator and promotes significantly the growth of rice • Isolated endophytes showed the ability to produce enzymes and phytohormone IAA • Isolates enhanced significantly the growth of rice.