Effects of Nano Silicon Concentrations and Bio-fertilizer on Yield and Grain Filling Components of Wheat in Different Irrigation Regimes

Introduction   Water limitation can damage pigments and plastids, reduce chlorophyll a, chlorophyll b, rate and grain filling period. One approach to improve the water stress problem is the use of plant growth promoting rhizobacteria (PGPR) and Mycorrhiza. The PGPR are a group of rhizosphere colonizing bacteria that produces substances to increase the growth of plants, synthesize different phytohormones, including auxin, cytokinin, and gibberellin, 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 their role in plant nutrition and soil health. Silicon (Si) is considered as quasi-essential for plant growth and development, and alleviates toxic effects caused by various environmental stresses in plants. So, it seems that application of nano silicon and bio-fertilizer can improve wheat yield under water limitation conditions. Materials and Methods In order to study the effect of nano silicon and bio-fertilizer on yield and grain filling components of wheat in different irrigation levels, a factorial experiment was conducted based on randomized complete block design with three replications at the research farm of faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili in during 2018-2019. The experimental factors were included irrigation in three levels (full irrigation as control, moderate water limitation or irrigation withholding at 50% of heading stage; severe water limitation or  irrigation withholding at 50% of booting stage) based on codes 55 and 43 of the BBCH scale, foliar application of nano silicon (foliar application with water as control, 30, and 60 mg L-1) and bio-fertilizer (no application as control, mycorrhiza application, both application of flavobacterium and pseudomonas, both application of flavobacterium and pseudomonas with mycorrhiza). Mycorrhiza fungi (mosseae) was purchased from the Zist Fanavar Turan corporation and soils were treated based on method of Gianinazzi et al. (2001). Psedomunasand flovobacterium were isolated from the rhizospheres of wheat by Research Institute of Soil and Water, Tehran, Iran. A two part linear model was used to quantifying 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 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 = the highest grain weight (g)/rate of grain filling (g day-1).   Results and Discussion      Means comparison showed that highest grain filling rate (3.04 mg day-1), grain filling period (37 day), effective grain filling period (30.44 day) and grain yield (4593 kg ha-1) were obtained at foliar application of 30 mg L-1 nano silicon, both application of flavobacterium and pseudomonas with mycorrhiza under normal irrigation. Also, maximum of chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content (2.04, 0.93, 2.87 and 9.89 mg g-1 FW-1 respectively) were obtained at foliar application of 60 mg L-1 nano silicon in seed inoculation with flavobacterium and pseudomonas under normal irrigation. Maximum of volume and root dry weight were obtained at foliar application 60 mg L-1 nano silicon and mycorrhiza application fungi under normal irrigation. The highest leaf area index was obtained at both applications of flavobacterium and pseudomonas with mycorrhiza, foliar application 30 mg L-1 nano silicon under normal irrigation.  Conclusions    Generally, it seems that application of bio-fertilizers and nano silicon can be recommended as appropriate management factors for increasing grain yield and grain filling components of wheat under water limitation conditions.