Development and Characterization of Efficient K-Solubilizing Rhizobacteria and Mesorhizobial Inoculants for Chickpea

Ali Raza Siddiqui,Gadah Albasher,Awais Shakoor,Tahira Yasmeen,Rizwana Kausar,Saad Alkahtani,Muhammad Ashraf,Sher Muhammad Shahzad

doi:10.3390/su131810240

Abstract

The use of mineral fertilizers has long been associated with the improved growth of crop plants as well as increased yield potential per unit area. However, the incessant practice of imbalanced fertilizers application has increased the economic and environmental costs for the agricultural sector. The deficiency of potassium (K) has been identified as a primary crop production challenge in certain semi-arid regions where soil-K reserves are increasingly being depleted. This study aimed to isolate and characterize K-solubilizing bacterial strains from the rhizosphere and root nodules of chickpea. Initially, 50 rhizobacterial strains and 50 rhizobial strains were isolated using Aleksandrov’s medium. Each of these collections was narrowed down to 25 strains, following a rigorous qualitative screening based on different physiological, morphological and biochemical tests. From these, five strains each of rhizosphere and nodule origins were selected based on qualitative as well quantitative determination of various growth promoting traits. In addition to efficient potassium and phosphate solubilization, the selected strains displayed better growth conditions, as evident by glucose substrate use at 25 °C and pH 7. In this study, we found that strains SKB3 (rhizosphere) and JKR7 (rhizobia) were the most efficient K-solubilizers. Additionally, they possessed diverse plant growth promoting traits such as root colonization, the synthesis of siderophores, exopolysaccharides, chitinase activity, indole-acetic acid production and 1-aminocyclopropane-1-carboxylic acid deaminase activity. Overall, our results suggest that the application of bacterial K-solubilizers could be employed as a useful K-supplement in K-limited agroecosystems. Moreover, the use of these K-solubilizers may help lead in alleviating the negative environmental impacts associated with chemical fertilizer.

Highlights

A series of laboratory studies were carried out for isolation, purification and characterization of K-solubilizing rhizobacteria (KSR) and rhizobial strains from rhizosphereic soil and root nodule samples of chickpea (Cicer arietinum L.), respectively, in the Department of
50 well-grown and morphologically distinct colonies of each rhizobacteria and rhizobial strain having the K-solubilization trait were selected for purification
Bacterial strains were tested for their K-solubilization on a qualitative basis using waste mica (WM) as the K source

Summary

Introduction

Pakistan is the second largest chickpea producer in the world. In 2017–2018, chickpea production increased by 3% due to increase in cultivated area and favorable weather conditions prevalent at the time of sowing [1]. Chickpea has a higher nutritional value and financial significance but its production in Pakistan is very low, at 583 kg per hectare [2]. Many factors are responsible for poor performance but among them, the use of traditional or low yielding varieties and poor adaptation of management practices are of utmost importance [3]. Many factors are responsible for poor performance but among them, the use of traditional or low yielding varieties and poor adaptation of management practices are of utmost importance [3]. 4.0/).

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