Effects of bio-fertilizer and putrescine on yield and some agrophysiological and biochemical traits of wheat under soil salinity stress

Salinity is one of the important and adverse environmental constraints restricting growth and development of plant particularly in arid and semiarid regions. Soil salinity induces water stress, nutritional imbalance, hormonal imbalance and generation of reactive oxygen species (ROS) which may cause membrane destabilization. Moreover, it decreases the yield of many crops by inhibiting plant photosynthesis, photosystem II efficiency (Netondo et al., 2004), protein synthesis and lipid metabolism. One approach to solve the salt stress problem is the use of plant growth promoting rhizobacteria (PGPR) and mycorrhiza. Seyed sharifi et al, (2016) reported that inoculation with PGPR enhanced proline content, relative water content, and photochemical efficiency of PSII and the activity of antioxidant enzymes of wheat under salinity stress. Large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal fungi (Glassop et al., 2005). They also impart other benefits to them, including production/accumulation of secondary metabolites, osmotic adjustment under osmotic stress, enhanced photosynthesis rate and increased resistance against biotic and abiotic stresses. In recent years, the use of growth regulators such as polyamines has been proposed to reduce the effect of biotic and abiotic environmental stresses (Kusano et al., 2008). Therefore, the aim of this study was to evaluate the effects of bio-fertilizers and putrescine on some physiological and biochemical responses of wheat under salinity stress conditions.

A factorial experiment based on randomized complete block design with three replications was conducted under greenhouse condition in 2018. Experimental factors were included soil salinity in f0ur levels [no-salt (S1) or control, salinity 40 (S2), 80 (S3) and 120 (S4) Mm NaCl], bio fertilizers at four levels [no bio fertilizer (B1), both application Psedomunas Putida Strain 186 and Flavobacterim Spp (B2), both application of mycorrhiza with Psedomunas and Flavobacterim (B3), application of mycorrhiza (Glomus Intraradices) (B4)] and putrescine foliar application in three levels (without putrescine as control (P1), foliar application of 0.5 (P2) and 1 (P3) mM). Air temperature ranged from 22°C to 27°C during the day and 18–21°C during the night. Humidity ranged from 60-65%. The wheat cultivar Gascogen was used in the experiment. Salt stress treatments were applied in two stages (3 - 4 leaf stage and two weeks after the application of the first salinity). Foliar application of putrescine was conducted in two stages of vegetative growth (4–6 leaves stage and before of booting stage).The trend of changes in flag leaf chlorophyll index at the stage of flag leaf emergence, in three samples of flag leaf were measured by chlorophyll meter (SPAD-502 Minolta of Japan). Chlorophyll fluorescence, also at the stage of flag leaf emergence, in three samples of flag leaves in each pot was randomly selected (in the period of 8-10 am) and by the device (chlorophyll fluorometer; Optic Science-OS- 30 USA) After 30 minutes of darkening by clips, F0, Fm and Fv/Fm indices were measured (Seyed Sharifi et al., 2016). The flag leaf was used to measure malondialdehyde (MDA) based on Stewart and Boley method (Stewart and Bewley, 1980) and method of Alexieva et al, (2001) was used to measure the hydrogen peroxide. In order to measure grain yield, 5 plants of each pot randomly were harvested. Analysis of variance and mean comparisons were performed using SAS9.1 computer software packages. The main effects and interactions were tested using LSD test at the 0.05 probability level.

The results showed that under soil salinity, both application of mycorrhiza with Psedomunas and Flavobacterim and foliar application of 1 mM putrescine increased maximum fluorescence, quantum yield, SPAD, yield and yield components. Also, both application of mycorrhiza with Psedomunas and Flavobacterim and foliar application of 1 mM putrescine increased about 28.57% from grain yield in comparison with no application biofertilizer and putrescine under the highest salinity level. Salinity increased malondialdehyde (MDA) and hydrogen Peroxide (H2O2), whereas application of bio fertilizers and putrescine under salinity conditions decreased (MDA) and (H2O2). both application of mycorrhiza with Psedomunas and Flavobacterim and foliar application of 1 mM putrescine under the highest salinity level decreased malondialdehyde and hydrogen peroxide 32% and 35.31% respectively, in comparison with no application biofertilizer and putrescine in same salinity level.

It seems that bio fertilizers and putrescine application can increase grain yield of wheat due to improvement of agrophysiological and biochemical traits under soil salinity conditions.