The effects of mycorrhizal fungi and nano zinc oxide on yield, dry matter accumulation, rate and duration of grain filling of wheat under soil salinity condition

Salinity is one of the major environmental stresses that decreases water availability to plant roots through reduced osmotic potential in the soil. The most important response of plants to saline soils or salty irrigation water is a reduction in growth. Salt stress causes disturbance in photosynthetic processes by ionic toxicity and also decreases photosynthetic area by osmotic stress, leading to reduced plant growth period and increased grain-filling rate (Pessarakli, 1999). One of the suitable ways to improve crop yield under salinity is to use mycorrhizal fungi. These fungi employ various mechanisms, such as enhancing plant nutrient and water status or maintaining sodium-potassium ratio, to improve salt tolerance of host plants. Another impact of water scarcity is the disruption of plant nutritional equilibrium, particularly, in relation to micronutrients. A complementary supply of micronutrients through foliar spraying can enhance plant growth under stressful conditions. In this regard, nanoparticles are considered to be superior over other forms due to being light and having high solubility and mobility, which increase their chances of contacting plants (Salehi and Tamaskoni, 2008). The aim of this study was to evaluate the effects of bio-fertilizers and zinc on yield, dry matter accumulation, rate and duration of grain filling in wheat under soil salinity
condition.
A factorial experiment was conducted based on randomized complete block design with three replications in research greenhouse of the Faculty of Agriculture Sciences, University of Mohaghegh Ardabili in 2015. Experimental factors were soil salinity at three levels (no salinity application as control, salinity of 40 and 80 Mm as NaCl) and mycorrhizal inoculation in two levels [no application, application of mycorhizal (Glomus mosseae)] and foliar application of nano zinc oxide in three levels (no spraying of nano zinc oxide, application of 0.4 and 0.8 g lit-1). To investigate grain filling parameters in each sampling, two plants in each pot were taken. The first sampling was taken on day 13 after heading, and other samplings were taken in 3-day intervals to determine grain weight. We calculated total duration of grain filling for each treatment combination through fitting a bilinear model: Where GW is the grain dry weight, a– the GW-intercept, b– the slope of grain weight indicating grain filling rate. Effective grain filling period (EGFD) was calculated from the following equation: EGFD = the highest grain weight (g)/ratio of grain filling (g day-1)Conversely, an increase in kernel weight in filling period was calculated by using the above-cited equation in statistical software SAS via Proc NLIN DUD method.
The results showed that all the measured traits for wheat were significantly affected by mycorrhiza inoculation, salinity stress and nano zinc oxide application (Table 1). Increasing salinity level from 0 to 80 Mm reduced yield and yield components of wheat plant. The highest yield (0.45 g. per plant) was obtained from combined treatments of foliar spray of zinc nano oxide (0.8 g.lit-1) and mycorrhizal inoculation without salinity application. The lowest yield (0.32 g.per plant) was associated with the greatest concentration of salinity where no foliar spraying and no mycorrhiza were applied (Table 3). Likewise, the highest grain weight (0.0606 g) and grain-filling rate (0.0022 g.day) were achieved by combined treatments of no salinity, mychorrhizal inoculation and foliar application of zinc nano oxide (0.8 g.lit-1) and the lowest values for these traits (0.0252 g and 0.0011 g.day) were respectively obtained from the highest salinity level with no application of nano zinc oxide and mycorrhiza (Table 3). Simultaneous application of mycorrhiza and nano zinc oxide (0.8 g.lit-1) with no salinity treatment resulted in the greatest grain filling period (28.55 days) and the highest effective grain filling period (28 days). Baniabbass (2012) stated that Zn increases plant photosynthetic capacity and consequently leads to increased carbohydrate amount in plants, which in turn, results in greater dry matter production that is stored as reserves in grain. This is attributed to the vital role of zinc in phosphoenolpyruvate carboxylase structure and also its importance in direct synthesis of growth hormones such as auxin.
Our findings suggest that nano zinc oxide application together with mycorrhiza can improve yield and biomass performance in wheat under salinity stress.