Peanut plant growth and yield as influenced by co-inoculation with Bradyrhizobium and some rhizo-microorganisms under sandy loam soil conditions

Abstract

The ability of tested rhizomicrobial isolates (Serratia marcescens and Trichoderma harzianum) along with a strain of root nodule bacteria (Bradyrhizobium spp.) to exhibit some PGP-properties was evaluated in vitro conditions. The main PGP-properties, namely the ability to solubilize-P and production of IAA, as well as production of siderophores and HCN were examined. Additionally, field trials were conducted on sandy loam soil at El-Tahrir Province during two successive summer seasons to study the effect of co-inoculation with Bradyrhizobium either individually or together with S. marcescens and/or T. harzianum on nodulation, some plant growth characters, peanut yield and its yield components. The in vitro experiment revealed that all of the tested microorganisms were apparently able to trigger PGP-properties. Phosphate solubilization was the common feature of the employed microorganisms. However, T. harzianum appeared to be superior to other microorganisms, and Bradyrhizobium displayed the lowest capacity. The ability of the microorganisms to produce indole compounds showed that S. marcescens was more effective in IAA production and followed by Bradyrhizobium. Capacity of S. marcescens and T. harzianum to excrete ferric-specific ligands (siderophores) and HCN was detected, while Bradyrhizobium failed to produce such compounds. Results of field trials showed that the uninoculated peanut had the least nodulation status, N2-ase activity and all vegetative growth characters in both studied seasons. Bacterization of peanut seeds with bradyrhizobia exerted considerable improvement in number and mass of root nodules, increased the rate of acetylene reduction and all growth characters in comparison to the uninoculated control. The synergy inoculation between bradyrhizobia and any of the tested microorganisms led to further increases of all mentioned characters and strengthened the stimulating effect of the bacterial inoculation. However, the promotive action on peanut nodulation, N2-fixation performance and vegetative characters was obvious with the dual inoculation with Bradyrhizobium plus S. marcescens. The other tested treatments, Bradyrhizobium conjugated with Trichoderma or with a mixture of the examined microorganisms, occupied the second rank. Additionally, peanut yield (pods and straw) and it's components (seed and straw protein contents, hundred seed weight, as well as pod and seed weight/plant and shelling%) along the two consecutive seasons followed a similar pattern to that of the vegetative growth stage.