Response of Different Cultivars of Wheat Plants (Triticum aestivum L.) to Inoculation by Azotobacter sp. under Salinity Stress Conditions

Abstract

Salinity is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Therefore, cope with this problem we should be develop strategies to enhance salinity tolerance in different crops. One of these modern strategies is to use plant growth promoting rhizobacteria (PGPR) which can help plants to withstand under harsh environmental conditions. The present study was evaluated six isolates of Azotobacter sp. (Az1-Az6) which tested in vitro for growth, PGPR traits such as indole-3 acetic acid (IAA) production and nitrogen fixation, germination indicators for different wheat cultivars i.e. Misr 1, Gemmiza 12 and Sakha 95 under different levels of NaCl. Also, the efficacy of inoculation with two superior isolates in different wheat cultivars in a Gnotobiotic Sand System and greenhouse experiment for improving growth dynamics, physiological attributes, nutrient uptake and antioxidant enzymes under different levels salinity of sandy soil (0, 4, 8 and 12 dS m-1).
 Out of 6 isolates, two isolates (Az2 and Az6) could show salinity tolerance and exhibited PGPR traits as well as improvement germination tests. Both the bacteria could promote growth in 3 cultivars of wheat tested in terms of increase in fresh weight, dry weight, root and shoot length as well as root colonization compared to uninoculated control under Gnotobiotic Sand System experiment. 
 Under greenhouse experiment conditions, inoculation treatment with Az6 showed a significant increase of vegetative growth, physiological and biochemical parameters of different wheat cultivars under different salinity stress treatments. Also, Az6 treatment recorded the highest N% from wheat plants attained 2.64, 2.51 and 2.43% at 4 dS m-1 for Misr1, Sakha 95 and Gemmiza 12 cultivars, respectively but the highest K+, K+/Na+% and the lowest Na+% were obtained from plants that grown in soil salinized with 8 and 12 dS m-1. The same trend was observed for antioxidant enzymes. Thus, inoculation with Azotobacter isolates Az2 and Az6 could be efficiently used to partially or completely eliminate the effects of salt stress on growth of different wheat cultivars.