Effects of Holding Irrigation at Reproductive Stages and Putrescine and Bio Fertilizers Application on Grain Filling Period, Chlorophyll Content and Yield of Wheat (Triticum aestivum L.)

Drought is the most severe abiotic stress factor limiting plant growth and crop production. Many physiological processes in plants are impaired by drought stress. Also, this stress can damage the photosynthesis of plants, pigments and plastids reduce chlorophyll a, chlorophyll band other carotenoids, hydrolyze proteins and prevalent photochemical reactions in most plants. The response of plants to drought stress depends on several factors such as developmental stage, severity, duration of stress, and cultivar genetics. Several strategies have been developed in order to decrease the water limitation-induced toxic effects on plant growth, among them use of bio fertilizers and putrescine play a key role in yield improvement. The aim of this study was to investigate the effects of irrigation withholding during reproductive stage and putrescine and bio fertilizers application on grain filling period, chlorophyll content and yield of wheat.

A factorial experiment was conducted based on randomized complete block design with three replications at the research farm, faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili during 2018-2019. Factors experiment were included irrigation at three levels (full irrigation as control, irrigation withholding in 50 percent of heading stage and irrigation withholding in 50 percent booting stage as moderate and severe water limitation respectively) and bio fertilizers at four levels (no bio fertilizer, application of mycorrhiza (Glomus Intraradices), both application Psedomunas(Psedomunas Putida Strain 186)and Flavobacterim Spp, application of mycorrhiza  with Psedomunas and Flavobacterim), foliar application putrescine in three levels (foliar application with water as control and foliar application 0.5 and 1 mM of putrescine). Mycorrhiza fungiwas purchased from the Zist Fanavar Turan corporation and soils were treated based on method of Gianinazzi et al. (2001). Psedomunas and flovobacterium were isolated from the rhizospheres of wheat by Research Institute of Soil and Water, Tehran, Iran. 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).

Means comparison showed that maximum of grain weight (0.0641 g), grain filling rate (2.28 mg.day-1), grain filling period (39.7 day) and effective grain filling period (28.14 day) were obtained in full irrigation, application of mycorrhiza with Psedomunas and Flavobacterim and foliar application 1 mM of  putrescine and the least of these traits (0.0361 g, 1.6 mg. day-1, 33.15 and 22.57 days respectively) were obtained in irrigation withholding at booting stage and no application of putrescine and bio fertilizers, there were an increase about 77.56%, 42.5%, 19.76% and 24.68% in this treatment compounds in comparison with withholding at booting stage and no application of putrescine and bio fertilizers. Full irrigation, both application Psedomunas and Flavobacterim withmycorrhiza and foliar application 1 mM of putrescine increased volume and root dry weight 124.37 and 123.47% respectively. Grain yield under irrigation withholding in heading and booting stages decreased in comparison with full irrigation. The highest grain yield was obtained in full irrigation (682.68 g.m-2), both application Psedomunas and Flavobacterim(686.42 g.m-2) andfoliar application 1 mM of putrescine (618.02 g.m-2).

Based on the results of this study, it seems both application of mycorrhiza with Psedomunas and Flavobacterim and foliar application 1 mM of putrescine with full irrigation can increase grain yield of wheat due to improve biochemical and physiological traits under water limitation condition in reproductive stages.