Isolation and Characterization of Salt Tolerant Bacteria for Crop Improvement in Saline Agricultural Fields

Abstract

newline xi newlineABSTRACT newlineSoil salinity has emerged as a major constraint of the world that drastically affects the agricultural productivity. Natural and anthropogenic activities have intensified the problem, thereby necessitating the need to create solutions for agricultural as well as monetary deficit. Biofertilizers based on salt-tolerant plant growth promoting rhizobacteria (ST-PGPR) serve as an eco-friendly alternative to enhance crop yield and cultivation in saline soils. Towards this objective, the present study was undertaken to isolate ST-PGPR from the salt affected areas of Panipat and Jhajjar districts of Haryana, India. Ten soil samples were collected from the waterlogged saline area of Jhajjar, while eight soil samples were collected from ICAR-CSSRI Nain farm, Panipat, Haryana. All the eighteen soil samples were analysed for physico-chemical properties. The soil samples had high electrical conductivity (2.33-16.56 dS/m), confirming that the sample collection sites are affected by salt. A wide variation in concentration of major macronutrients i.e. nitrogen, potassium and phosphorus was observed amongst the soil samples, with nitrogen levels lower than the normal range of 240-480 kg/ha, except PS6 and PS7. All eighteen soil samples were enriched for salt-tolerant microbial growth and further spread plated over six types of culture media viz. nutrient agar, tryptic soya agar, Ashby s agar, Jensen s agar and King s B agar. A total of 81 bacterial isolates were obtained from soil samples of Jhajjar, while 26 bacterial types were isolated from Panipat samples. A total of 107 bacterial isolates were characterized for the PGPR activities including production of indole acetic acid (IAA), hydrogen cyanide (HCN), ammonia and phosphate solubilisation. Five bacterial isolates namely HB4A1, HB4N3, HB6J2, HB8P1and HB6P2 were found to exhibit effective PGPR activities. The five isolates also showed growth at higher salt concentrations (5 %, 7.5 % and 10 % NaCl or KCl). Molecular identification by 16S rRNA gene sequencing of three isolates was performed, which identified them as Bacillus paramycoides (HB6J2), Bacillus amyloliquefaciens (HB8P1), and Bacillus pumilus (HB4N3). The five salt tolerant PGPR isolates were optimized as biofertilizer on cultivars of Solanum lycopersicum L. (tomato) and Abelmoschus esculentus (okra) in saline soil. All the five ST-PGP bacterial isolates were found to be biocompatible and thus chosen for design of consortia. The consortia containing different combinations (treatments) were designed and pot experiments with different treatments were carried out to assess the growth of newlinexii newlineokra and tomato plants. Effect of six different treatments along with a control was studied for okra plants in saline soils corresponding to EC 2, 4, 6 and 8 dS/m. The best results of plant height and root lenth of Okra platns were observed for treatment T2 (HB6P2+ HB8P1+ HB4N3+ HB6J2) followed by T3 (HB6P2+ HB8P1+ HB4A1) and T6 (HB4N3+ HB6J2) at EC6 and EC8 dS/m as compared to control. All six treatments were found equally effective on growth of okra plants at EC 2 and 4. Based on the results of the experiments on okra, four best treatments viz.,T2, T3, T4 and T6 were selected for studies on tomato and designated as T1, T2, T3 and T4 respectively. The tomato plant height was highest for treatment T3 (63.33 ± 1.85 cm) followed by T1 (62.5 ± 0.85 cm) and T2 (61.8 ± 1.2 cm) at EC-8. Overall, it was observed that all the four treatments enhanced the growth of tomato plants at higher salt concentrations of EC6 and 8 dS/m relative to untreated control. The EC value of the pot soil of each treatment was also measured after harvesting the okra and tomato plants. No significant change in respective EC was observed for any of the treatment for okra, while slight elevation in EC value (EC-8) for each treatment was observed for tomato plants. In future, the consortia of ST-PGP isolates can be used in development of an effective bio- fertilizer and its use for improving crop yield in salt affected soils. newlineKeywords: Agriculture, crop improvement, saline soil, salt tolerant-plant growth promoting rhizobacteria (ST-PGPR), Okra, Tomato, Bacillus spp., bacterial consortia, Panipat, Jhajjar, Haryan, India.