Coinoculation of chickpea with Rhizobium isolates from roots and nodules and phytohormone-producing Enterobacter strains

Abstract

The aim of the present study was to isolate plant-beneficial bacteria (both Rhizobium and plant growth promoting rhizobacteria) from roots and nodules of chickpea (Cicer arietinum L.) and to study the effect of coinoculations on growth of two cultivars of chickpea. Four Rhizobium strains were obtained from roots and four from the nodules of field-grown chickpea cv. Parbat and identified on the basis of morphological characteristics, and biochemical and infectivity tests on the host seedlings. Only one type of nitrogen and carbon source utilisation pattern and DNA banding pattern of random amplified polymorphic DNA was observed in all isolates (Rn1, Rn2, Rn3, Rn4) from nodules, while two types of such patterns were detected among the isolates from roots. The isolate Rr1 from roots also exhibited a pattern identical to those of the isolates from nodules, whereas the remaining three isolates (Rr2, Rr3 and Rr4) from roots showed a different pattern. Two strains of plant growth-promoting rhizobacteria belonging to genus Enterobacter were also isolated from chickpea roots. All the Rhizobium strains and Enterobacter strains produced the plant growth hormones indole acetic acid and gibberellic acid in the growth medium. Effects of the bacterial isolates as single- or double-strain inocula were studied on two chickpea cultivars (NIFA 88 and Parbat) grown in sterilised soil. In cultivar NIFA 88, coinoculation of Rhizobium strain Rn1 with Enterobacter strain B resulted in maximum increase in plant biomass and nodulation, as compared with the control treatment (non-inoculated as well as inoculated with Rhizobium strain Rn1 only), whereas the combination of Rhizobium Rn1 with Enterobacter A was more efficient in growth promotion of chickpea cv. Parbat. In non-sterilised soil, the same combinations of the Rhizobium strain Rn1 with Enterobacter strains A and B were found to be the most effective inoculants for cvv. Parbat and NIFA 88, respectively. However, some negative effects on plant growth were also noted in cv. Parbat coinoculated with Rhizobium strain Rr2 and Enterobacter strain B.