Effects of Supplemental Irrigation and Biofertilizers on Yield, Chlorophyll Content, Rate and Period of Grain Filling of Rainfed Wheat

Introduction The yield of wheat in Iran is very low as compared to the other wheat producing countries. One of the most important effective factors is water shortage. Water shortage can damage pigments and plastids, reduce chlorophyll a, chlorophyll b, rate and grain filling period. One approach to improve the salt stress problem is the use of plant growth promoting rhizobacteria (PGPR) and Mycorrhiza. The PGPR are a group of rhizosphere colonizing bacteria that produce substances to increase the growth of plants, synthesize different phytohormones including auxins, cytokinins, and gibberellins, synthesize enzymes that can modulate plant growth and development. Arbuscular mycorrhizal fungi (AMF) symbiosis is considered a valuable component in most agricultural systems due to its role in plant nutrition and soil health. Therefore application of biofertilizers and supplemental irrigation can improve crop yield and water productivity especially during critical crop growth stages. Materials and Method A factorial experiment was conducted based on randomized complete block design with three replications in Agricultural Research Station of Ardabil in 2016. Experimental factors included irrigation levels (no irrigation as rainfed, supplemental irrigation at booting and heading stages or according with 45 and 61 BBCH code, respectively) and four levels of biofertilizers application (inoculation with Azospirilum, Mycorrhizal, Mycorrhizal+Azospirilum, and without application of biofertilizers as control). A two part linear model was used to quantify the grain filling parameters. In this study, total chlorophyll, chlorophyll a, b, carotenoid, grain filling components and yield of wheat were investigated. Grain dry weight and grain number were used to calculate the average grain weight for each sample. Total duration of grain filling was determined for each treatment combination by fitting a bilinear model: Effective grain filling duration (EGFD) was calculated from the below equation: EGFD = highest grain weight (g)/rate of grain filling (g day-1). Results and Discussion The results showed that application of both biofertilizers (Mycorrhiza and Azosprilium) and supplementary irrigation at booting stage increased chlorophyll a, b, total chlorophyll and carotenoids (76.6, 42.26, 49.57 and 100% respectively) compared with no application of biofertilizers under rainfed condition. Also, both application of Mycorrhizae and Azospirilium and supplemental irrigation at booting stage increased grain filling rate, grain weight, grain filling period, effective grain filling rate and grain yield (15.26, 51.35, 14.04, 35.92 and 35.27% respectively) compared with no application of biofertilizers under rainfed conditions. Conclusions Based on this study, the application of Azospirillum and Mycorrhiza and supplemental irrigation at booting stage can improve the content of chlorophyll a, b, total chlorophyll, carotenoids, grain filling rate, grain weight, grain filling period, effective grain filling period and grain yield compared with no application of biofertilizers under rainfed conditions. Based on the results, it seems that application of biofertilizers and supplementary irrigation can be suggested as modulators of drought stress in wheat under rainfed conditionss.