Effects of Drought Stress and Foliar Application of Boron and Zinc on Yield and Some Agronomic and Morphological Traits of Spring Type Safflower (Carthamus tinctorius L.)

Plants under natural and agronomic conditions are constantly exposed to different stresses. In this regard, drought stress is the most important limiting factor to crop yields in many parts of the world and Iran, particularly, if the water stress occurs during the flowering stage, it will affect the crop production. Drought stress disrupts the nutritional balance of plant. Proper nutrition under stress conditions can partly help plant against various stresses. Plants growth under stress can be improved by micro nutrients foliar application. Boron is important in the plant growth and its deficiency is one of the major constraints to crop production. Zinc plays a key role in the various biochemical processes of plant cells. Its deficiency will be apparent in various forms such as growth retardation, yield and concentration of the element in different parts of a plant such as seeds. The aim of this study was to investigate the effect of boron and zinc foliar application on yield and some agronomic and morphological traits of spring safflower (cv. Mahalli-e Esfahan) under late-season water deficit in Ardabil province.

The field experiment was conducted at the Research Farm of the University of Mohaghegh Ardabili, Ardabil, Iran during 2013-14 and 2014-15 growing seasons. The experimental design was a split factorial in a randomized complete block with three replications. Three irrigation treatments (S1: full irrigation until the end of season (control), S2: irrigation with holding from flowering and S3: irrigation with holding from seed filling) were randomized to the main plots and the sub-plot included factorial combination of B (B1: 0, B2: 350, B3: 700 ppm) and Zn (Zn1: 0, Zn2: 1000, Zn3: 2000 ppm). B was added as boric acid (H3BO3) and Zn as zinc sulfate (ZnSO4). The treatments were applied during flowering (when 50% of the plants were at anthesis) as foliar applications. All other agricultural practices (weeds control and irrigation), were performed when they were required and as recommended for safflower production. The measured traits included seed coat percentage, seed kernel percentage, seed coat to kernel ratio, leaf number, capitol diameter, seed length, seed width and seed yield. Analyses of variance and comparison of means at P≤0.05 were carried out, using SAS 9.1 software. The means were compared using LSD test.

Combined analysis of variance of the data showed that year, irrigation and year × irrigation interaction were significant for all the traits. Also, all traits (except leaf number) were significantly affected by B, Zn and B × Zn interaction. Seed coat percentage, seed kernel percentage and seed coat to kernel ratio were significantly affected by year×B, year × Zn and year×B×Zn interactions. Seed length and seed yield were significantly affected by year×irrigation×B and year×B×Zn interactions, respectively. During the first year, all the investigated traits influenced from deterrent impacts of drought stress. Water deficit stress at the flowering and seed filling stages significantly decreased seed yield compared to full irrigation (15.62% at flowering and 12.77% at seed filling). During the second year, there was no significant difference among all the treatments due to heavy rainfall. The results showed that B and Zn foliar application had a positive and significant effect on seed coat percentage, seed kernel percentage, seed coat to kernel ratio, capitol diameter, seed length, seed width and seed yield. The treatments of B3Zn2 and B2Zn2 had the greatest increase of these parameters in comparison with B1Zn1 (control) in both years. Boron and zinc foliar application significantly improved most traits under water stress levels.Acknowledgments We would like to thank from the Faculty of Agriculture, Mohaghegh Ardabili University, for supporting this study.