SPRING WHEAT YIELDING AND THE CONTENT OF PROTEIN AND ZINC IN ITS GRAIN DEPENDING ON ZINC FERTILISATION

Fariborz Shekari¹, Hossnieh Mohammadi¹, Alireza Pourmohammad¹, Armen Avanes², Mohammad Bagher Khorshidi Benam^3
1 Dept. of Agronomy and Plant Breeding, Agriculture Faculty, University of Maragheh, Iran
² Dept. of Chemistry, Basic Sciences Faculty, University of Maragheh, Iran
³ East Azarbaijan Agricultural and Natural Resources research Centre, Iran

ABSTRACT

In crops, Zinc deficiency is an important problem, causing decreased crop production and food quality. Cereals have significant role in satisfying daily calorie intake, but they very low in Zn contents in grain specially when grown on Zn-deficit alkali soils of Iran. Amendment in seed zinc content through agronomic biofortification is one of the most important agronomic strategies to overcome Zn deficiency in human. This study was conducted to evaluate the effects of Zn application on yield, yield components, seed zinc and protein content as randomized complete block design based factorial with three replications. Three spring wheat cultivars (Darya, Tadjan and N-80-19) with five fertilizer levels including; 0 (control), 25 kg ha^-1 (soil application of zinc sulfate in planting time), 0.5% zinc sulfate (spraying in booting stage), 0.5% zinc sulfate (spraying in booting and milk stages) and 0.5% zinc sulfate (spraying in milky and dough stages), were used. The results showed that there were significant difference among cultivars in seed number per spike, max seed number per spikelet, biomass, seed protein and Zn content, thousand kernels weight and yield. Zinc application showed significant effect on spike number per m^-2, maximum seed number per spikelet, biomass, seed protein and Zn content, and yield. Interaction effect of zinc on cultivar was only significant on seed protein and Zn content (P≤0.01). Zinc sulfate application at the planting time had the most significant effect on number of spikes number per m2. Zinc foliar application had no significant impact and there was no difference between those treatments and control. Number of seed per spike was the highest in Darya with zinc application at planting time. Darya showed highest seed number per spikelet with significant difference with N-80-19 and Tadjan. Only Zn application at boot stage had no effect on maximum seed number per spikelet and soil application and dual application of Zn increased significantly maximum seed number per spikelet. The highest 1000 kernel weight was belonged to Tadjan and N-80-19 cultivars, but, there was no significant difference with diverse zinc applications. This may be explained by the highest number of seeds with “Darya” spikes and with reverse relationships between 1000 kernel weight and seed number per spikes. Zinc application had no considerable effect on 1000 kernel weight. Zinc application significantly influenced total yield of plants. Highest seed yield was recorded with zinc sulfate application at the planting time and with Darya and Tadjan cultivars. Considering, soil based application of Zn surely affects the quality and protein content of grains. Interaction effects of variety and zinc application were significant (P≤0.01) on grain protein content. Zinc application during milky and dough stages led to the highest Zn accumulation with Darya. Furthermore, the highest protein accumulation was traced at Tadjan with the soil application of zinc sulfate.  Further experiments at diverse environments are needed to explore the different responses of varieties to Zn different types and times of application. According to ours, the highest seed yield and protein content were belonged to soil based application of Zn treatments, however, based on Zn biofortification, foliar spray of Zn treatments during the milky and dough stages had the most promising effects. These results showed that agronomic biofertification method appear to be essential in maintaining adequate Zn transport to the grains specially during reproductive growth stage.

Key words: ZnSO₄, TKW (thousand kernels weight), seed zinc, seed protein, zinc application stages.

INTRODUCTION

Zinc as an essential micronutrient in biological systems holds pivotal physiological roles in protein biosynthesis and several fundamental processes [6]. A large group of proteins need to be functional in biological systems. Approximately, 2800 types of proteins in human body are associated to zinc, an amount equals 10% of human proteome [1]. The unbalances in zinc equilibrium or its deficiency cause cute cellular disorders, immune system disturbance, and sensitivity to several infectious diseases [1]. Zinc is an essential micronutrient for the integrity and function of biological and acts in the detoxification of free radicals in plants [6]. This element has strategic role in membranes stability, phytochrome activity and tryptophan biosynthesis [26]. Various enzymes are responsible for carbohydrate metabolism and protein biosynthesis, that their activation and kinetics are intrinsically Zn dependent [9]. Commonly, zinc deficiency is prevalent in plants cultivated in poor soils with low organic matter and especially under calcareous soil actions. Zinc deficiency is a widespread organic restraint with calcareous and alkaline soils of arid and semi-arid regions of Iran [25].

Wheat production with 659 million ton is the most dominant cereal in the world [11]. Nearly, 50% of staple food in Iran is supplied by wheat and its products. However, zinc content is very low at cereal seeds and mainly in wheat seed [6]. In addition, some compounds such as Phitic acid, fibers and polyphenols prevent the absorption and utilization of the seed contained Zinc [33].

Biofortification is the easiest and the most confident way to increase the grain zinc content. Other methods of increasing seed zinc content or absorption efficiency need huge costs and are risky to human health [5, 30]. Zinc biofortification is increasing Zn content in seeds by biological strategies and mainly by agronomical and breeding practices [6]. Today, biofortification employed by various forms consisting of soil based fertilizer application and foliar application. Several experiments with cereals revealed that Zinc fertilizers application increased productivity and seed Zn content [6]. Zinc application essentiality for wheat yield improvement and zinc content has been improved by various researchers [4, 7, 13, 17, 18, 27, 31]. The most common form of zinc employed is zinc sulfate [26]. Cereal crops, especially wheat, are more sensitive to zinc deficiency [2, 34]. There are contradictory results beyond the further application of zinc on seed quality and the output is mainly dependent upon the variety and the method of Zn application [6]. Generally accepted, zinc foliar application during the late growth stage has been the most effective treatment for grain zinc content improvement.

In present experiment, the effects of different amounts and forms and application time of zinc sulfate have been studied on yield, yield components, seed zinc biofortification and protein content of several spring wheat cultivars.

MATERIALS AND METHODS

This experiment was conducted at the Malekan agricultural research station, East Azerbaijan province, Iran, during spring 2009 as factorial based on RCB design with 3 replications. Three spring wheat varieties (Darya, Tadjan and N-80-19) and 5 fertilizer application regimes (control, 25 kg ha^-1 in planting time, spraying with 0.5% zinc sulfate in booting, milk and dough stages) were employed. Nitrogen and phosphate basal amounts at 100 and 43 kg∙ha^-1 were employed based on soil analysis results (Tab. 1). Each block was consisted of three 5 m × 1.5 m plots. Each plot consisted of 6 rows with 20 cm distance. Wheat was the forecrop, soil type was sandy loam with pH=8.04. Year precipitation was 300 mm. Altitude is 1285 m.

Table 1. Physical and chemical analysis of soil samples in 2010

Cu [mg∙kg-1]	Zn [mg∙kg-1]	Mg [mg∙kg-1]	Fe [mg∙kg-1]	K [mg∙kg-1]	P [mg∙kg-1]	Organic carbon [%]	neutral materials [%]	pH	EC×103	texture	depth [cm]
1.72	0.96	5.40	2.28	230	13.16	1.53	14.75	8.04	0.82		0–30

No potassium was used. Super phosphate triple as 45 kg ha^-1 and 1/3 of Urea in cultivation. 1/3 urea in wheat tillering, and 1/3 of 100 kg ha^-1 at stem extension stage was used. Spike number per area unit, seed yield and biomass measures on one m2 area. After harvest number of seed per spike, max seed number per spikelet, TKW, seed protein and zinc content measured from 20 plants.

The grain zinc content was measured with wet ashing method [32]. The grain protein evaluated by Zeltex (ZX-50 USA) system [36]. The data were analyzed by MSTAT-C and means were compared by Duncan multiple range test at 5% probability

RESULTS AND DISCUSSION

Anova table showed that there were significant difference among cultivars in seed number per spike, max seed number per spikelet, biomass, seed protein and Zn content, TKW and yield. Zinc application showed significant effect on spike number m-2, max seed number per spikelet, biomass, seed protein and Zn content, and yield. Interaction effect of zinc on cultivar was only significant on seed protein and Zn content (Tab. 2).

Table 2. Results of analysis of variance of traits in spring wheat by zinc treatment

Mean Squares								df	source of variation
tkw	seed yield	grain zinc content	protein content	biomass	Seed no per spikelet	Seed no per spike	Spike no per area
1.622486	11802.99	0.003323	0.1815	676719.7	0.054	9.491286	596.9656	2	rep
33.38939**	1155200**	74.92495**	3.7625**	2014288**	0.366**	70.32588**	674.0515	2	cul
8.447293	1576132**	188.0183**	0.47425**	7479248**	0.331444**	26.14107	6644.642**	4	zn
6.822848	29766.18	7.228311**	0.518125**	170461.7	0.024611	0.176882	161.807	8	Z*C
7.041078	125616	0.07216	0.000786	364243	0.01519	8.227586	602.5121	28	e
** and * means significant at P≤0.01 and P≤0.05, respectively

The highest number of spikes per m2 belongs to soil application of zinc (357.22). Zinc foliar application had no significant impact and there was no difference between those treatments and control as well (Fig. 1). Thus, soil based zinc application during vegetative period significantly increased the spike production potential mainly by its effect on fertile tillers emergence. Yilmaz et al., [34] showed that zinc application significantly increased seed yield and yield components of wheat and the effect was more prominent on spike number per m2.

Fig. 1. No of spikes per area affected by Zn application

Mean comparisons for the cultivars showed that the highest seed number per spike (22.68) was belonged to “Darya” and “Tadjan” (Fig. 2). In case of fertilizer application form, the soil application of zinc sulfate during planting time and control treatment without significant difference with spraying treatments had the highest (23.81) and the lowest (19.87) number of seed per spike, respectively (not shown). Seed number in spike is the most important yield component in wheat, and any increase in that intensified partitioning of assimilates to seed than vegetative organs [28] by flag leaf and the leaf beneath of that in three weeks just before anthesis. Indeed, reproductive stage (after double ridges appearance), and concomitant with internodes development, the terminal spike will be in initiated. During this growth stage, need for essential nutrients would be at its highest level. This event, besides elaborated photosynthesis rate and photo assimilates availability nourishes the seeds at the highest rate [16].

Fig. 2. No of seed per spike in different cultivars

Darya showed highest seed number per spikelet with significant difference with N-80-19 and Tadjan (Fig. 3). It has been proved that there were differences among cultivars. Only Zn application at boot stage had no effect on max seed number per spikelet and soil app and dual app of Zn increased significantly max seed number per spikelet (Fig. 4). Ziaeian and Malakooti [37] showed that zinc application meaningfully increased the seed number per wheat spikelets and spike numbers. Moreover, zinc foliar application increased the seed number per pod in bean [20].

Fig. 3. Differences in seed no per spikelet among cultivars

Fig. 4. Differences among Zn application stages in no of seed per spikelet

Darya produced highest biomass which only significant with N-80-19 (Fig. 5). But only Zn soil application increased significantly biomass in compare to control (Fig. 6). Results showed that plants with sufficient Zn content had higher photosynthetic enzyme activity and produced higher biomass [14].

Fig. 5. Differences in biomass production among cultivars

Fig. 6. Differences among Zn application stages in biomass production

Thousand kernel weight of “Tadjan” and “Darya” were the most (37.34 g) and the lowest (34.37 g), respectively (Fig. 7). This may be explained by the highest number of seeds with “Darya” spikes and with reverse relationships between 1000 kernel weight and seed number per spikes [12]. Zinc application had no considerable effect on 1000 kernel weight (Tab. 2). Owing to the increased number of seeds, the constant and/or reduced quantity for 1000 kernel weight may be due to unbalances in photo-assimilation and subsequent partitioning during the simulations increase in grain number and seed filling stage, all these goes to lighter grains [28, 29]. Moreover, the relations between seed number and 1000 kernel weight in spike may be due to diverse grain filling rates at the basal and ends of rachis and tip of rachila. It is well evident that the difference will be more highlighted with any increase in seed number per spike [28, 29]. A research noted that the unchanged 1000 kernel weight was a result of high availability of zinc in the soil of experiment site [14].

Fig. 7. Differences in TKW among cultivars

Mean comparison revealed that the seed yield (2194 and 2434 kg ha^-1) belonged to “Tadjan” and “Darya” (Fig. 8) and there was a significant difference with ‘N-80-19’ (1984 kg ha^-1). Rengel and Graham [23, 24] documented that difference in zinc use efficiency among of wheat cultivars may be due to diverse root potential of the plants for zinc absorption. Because there are great differences between intensity of zinc mobile sidrophors release among cultivars. Ekiz et al., [8] related this differences to zinc absorption and efficient use of water and drought tolerance of cultivars. Another possible explanation for the divergent response of plants to zinc has been defined as the physiological differences in the Zn availability at the cellular level.

Fig. 8. Differences in seed yield among cultivars

Zinc application significantly influenced total yield of plants (Tab. 2). Kalayci et al. [15] reported that zinc application during a two year experiment led to 31 and 32% increase in the seed yield of plants. The highest grain yield (3.34 ton ha^-1) was related to soil based Zn application during planting time and lower yield with no difference was recorded in control and foliar spray treatment (Fig. 9). Belali and Malakooti [3] demonstrated that different methods of Zn application positively affect wheat yield. It is worthy of note that, micronutrients deficiency apart from reduced yield leads to low zinc content in seeds and also decreased viability and germination potential during subsequent cropping [22].

Fig. 9. Differences among Zn application stages in seed yield

Interaction effects of variety and zinc application were significant (P≤0.01) on grain protein content (Fig. 10). According to mean comparisons, the highest protein content (17.9%) was traced in ‘Tadjan’ with soil based application of zinc. ‘N-80-19’ had the least amount (16.3%) for with Zn foliar application during booting and milky stages (Fig. 11). It is well defined that, Zn actively affects and is involved in nitrogen metabolism [9], and in contrast with carbohydrates the main source for grain nitrogen content is the redistribution of the reserved nitrogens compounds that have been accumulated during the vegetative growth stage and before translation to the reproductive stage of growth. Besides, Zn is a mobile element, in case of need distributes from the old basal leaves towards up to the new leaves and grains [10]. Considering, soil based application of Zn surely affects the quality and protein content of grains. Ziaeian and Malakooti [37] similary noted that zinc application correspondingly increase the protein content of grains. Belali and Malookti [3] reported a new trend so that, pretreatment along with foliar spray increased the protein content of grain about 6.7% greater than soil based Zn application.

Fig. 10. Seed protein content differences among cultivars in Zn different stage application

Fig. 11. Seed zinc content differences among cultivars in Zn different stage application

Interaction effects of cultivar*Zn application were meaningful on seed Zn content in a way that foliar spray prominently increased the grain Zn content (Tab. 2). Mean comparison for the grain Zn biofortification showed that Zn application at the milky and dough stage led to the highest accumulation of Zn in grains with ‘Darya’ (21.3 mg kg^-1). The least data for this trait was recorded in control at ‘N-180-19’ (5.6 mg kg^-1) (Fig. 11). Yilmaz et al [34, 35] and Marschner [19] reported the promotive effects of Zn application on grain Zn content with several grain cultivars. In line, Ziaeian and Malakooti [37] documented the same results with soil based application of different zinc containing fertilizers and compounds. Ozturk et al [21] found that foliar application of zinc during the milky stage had the most promising effect on zinc content of grains. In contrast, Cakmak [6] reported that foliar spray during any booting, milky and dough stages led to acceptable and same results regarding grain Zn content. The difference with growing stages may be due to the effected of diverse environments and also the cultivars employed.

CONCLUSIONS

Regarding the results, if the aim is to increase the seed yield, then Zn spraying during early growth stages of wheat plants will be promising. By contrast, Zn biofortification mainly can be enhanced by the application of the Zn treatments during the late growing stages. Seemingly, mutual soil based and foliar application of Zn treatments will improve total yield and seed Zn content. Further experiments at diverse environments are needed to explore the different responses of varieties to Zn different types and times of application. According to ours, the highest seed yield and protein content were belonged to soil based application of Zn treatments, however, based on Zn biofortification, foliar spray of Zn treatments during the milky and dough stages had the most promising effects.

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Accepted for print: 25.02.2015

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Fariborz Shekari
Dept. of Agronomy and Plant Breeding, Agriculture Faculty, University of Maragheh, Iran
Maragheh 55181
Iran
email: shekari_fb@yahoo.com

Hossnieh Mohammadi
Dept. of Agronomy and Plant Breeding, Agriculture Faculty, University of Maragheh, Iran
Maragheh 55181
Iran

Alireza Pourmohammad
Dept. of Agronomy and Plant Breeding, Agriculture Faculty, University of Maragheh, Iran
Maragheh 55181
Iran

Armen Avanes
Dept. of Chemistry, Basic Sciences Faculty, University of Maragheh, Iran
Maragheh 55181
Iran

Mohammad Bagher Khorshidi Benam
East Azarbaijan Agricultural and Natural Resources research Centre, Iran
Tabriz
Iran
email: mb.khorshidi@yahoo.com

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