Differential Response of Potato Toward Inoculation with Taxonomically Diverse Plant Growth Promoting Rhizobacteria.

Tahir Naqqash,Muhammad Kashif Hanif,Asma Imran,Sohail Hameed,Jan Dirk Van Elsas,Afshan Majeed

doi:10.3389/fpls.2016.00144

Abstract

Rhizosphere engineering with beneficial plant growth promoting bacteria offers great promise for sustainable crop yield. Potato is an important food commodity that needs large inputs of nitrogen and phosphorus fertilizers. To overcome high fertilizer demand (especially nitrogen), five bacteria, i.e., Azospirillum sp. TN10, Agrobacterium sp. TN14, Pseudomonas sp. TN36, Enterobacter sp. TN38 and Rhizobium sp. TN42 were isolated from the potato rhizosphere on nitrogen-free malate medium and identified based on their 16S rRNA gene sequences. Three strains, i.e., TN10, TN38, and TN42 showed nitrogen fixation (92.67–134.54 nmol h-1mg-1 protein), while all showed the production of indole-3-acetic acid (IAA), which was significantly increased by the addition of L-tryptophan. Azospirillum sp. TN10 produced the highest amount of IAA, as measured by spectrophotometry (312.14 μg mL-1) and HPLC (18.3 μg mL-1). Inoculation with these bacteria under axenic conditions resulted in differential growth responses of potato. Azospirillum sp. TN10 incited the highest increase in potato fresh and dry weight over control plants, along with increased N contents of shoot and roots. All strains were able to colonize and maintain their population densities in the potato rhizosphere for up to 60 days, with Azospirillum sp. and Rhizobium sp. showing the highest survival. Plant root colonization potential was analyzed by transmission electron microscopy of root sections inoculated with Azospirillum sp. TN10. Of the five test strains, Azospirillum sp. TN10 has the greatest potential to increase the growth and nitrogen uptake of potato. Hence, it is suggested as a good candidate for the production of potato biofertilizer for integrated nutrient management.

Highlights

Potato (Solanum tuberosum L.), of the family Solanaceae, is the third most important food crop in the world after rice and wheat
We describe the potential of Azospirillum for growth promotion of potato
Five bacterial strains were purified from enrichment culture on Nitrogen-free malate (NFM) semisolid medium

Summary

Introduction

Potato (Solanum tuberosum L.), of the family Solanaceae, is the third most important food crop in the world after rice and wheat. More than a billion people worldwide consume potato, and global crop production exceeds 350 million metric tons (Food and Agriculture Organization, 2014). It is a high fertilizer-demanding crop, which requires 250 kg ha−1 of nitrogen and 150 kg ha−1 of phosphorus to get an optimum yield. Potato PGPR Inoculation Effect In vitro (George and Ed, 2011). These requirements increase the cost of production and cause severe environmental problems (David et al, 2002). Soil microbes constitute a largely unexplored biochemical wealth which have a profound role in biogeochemical cycles and may directly or indirectly impact on the nutrient status of soil (Khosro and Yousef, 2012)

Methods

Results

Conclusion