Study of impacts of plant growth regulators foliar spray on yield and yield components of wheat cv. Zarrin at different growth stages.
Wheat is one of the oldest field crops used by mankind and planted widely and has the highest harvest index . This crop is considered as the most important field crop in food industry and the increasing population rate and per capita consumption of bread have created an urgent need for production of wheat more than ever . The history of plant growth regulators application in terms of human's manipulation in cereals growth to increase yield traces back to four decades ago . Hormones are one of the most significant factors in regulating plant growth. The hormonal regulation of plant growth and metabolism are extremely complicated and results from interaction between hormones . Environmental and genetic factors influence the ageing process, but ABA and CK are considered as the two major factors in regulating the ageing process in plants . High concentrations of CK retard ageing process in plants [5, 6] while high concentrations of ABA accelerate ageing . ABA is known as an effective and major factor in regulating the translocation of photosynthates to the seeds or growing fruits . But contradictory findings have been reported on the role of ABA in regulating the ageing process and retranslocation of photosynthates . According to Yang et al.  on wheat and rice the retranslocation of photosynthates in the stems depends strongly on the ageing process and in this regard ABA is the most important factor.
Probably the acceleration of ageing process caused by high concentrations of ABA during grain filling is the prerequisite of accelerating retranslocation of photosynthates from secondary sources like stems and leaves to growing seeds (Zhang et al, 2005). Seed growth as a major economical factor is composed of several growth stages including cell differentiation and division and photosynthates storage . Transition from one growth stage in the seeds after anthesis doesn't occur directly but occurs gradually. For example in wheat and barley the mythosis activity of endosperm stops gradually due to cell expansion and photosynthates storage . ABA and CK are two major factors in regulating cell division and photosynthates storage. Yang et al.  showed that in rice the foliar application of CK at cell division and of ABA at linear growth of seed had the greatest positive impact on the grain yield. In such conditions probably CK and ABA increase the grain yield through impact on cell division and grain filling velocity, respectively. Yang et al.  found that the foliar application of ABA at linear grain filling of wheat increased the velocity of grain filling and retranslocation of photosynthates to the seeds. Xie et al.  found that net photosynthesis rate and soluble protein content in the stamen leaf decrease after anthesis and at the beginning of ageing and the foliar application of ABA after anthesis increases ageing rate.
The present research was done with the aim of studying the effects of foliar application of CK and ABA at pollination and grain filling on the yield and yield components of wheat CV Zarrin.
MATERIALS AND METHODS
This trial was arranged in RCBD with seven treatments and five replications and conducted in Agricultural College of Mahabad Azad University in 2013. The treatments were as follows: [b.sub.1]: No spray (Check), [b.sub.2]: CK foliar spray at pollination, [b.sub.3]: CK and ABA foliar sprays at pollination and grain filling, [b.sub.4]: CK foliar spray at pollination and grain filling, [b.sub.5]: ABA foliar spray at pollination, [b.sub.6]: ABA foliar spray at pollination and grain filling, [b.sub.7]: CK and ABA foliar sprays at pollination. Seeds were planted in vases with a 17-cm diameter and a 30-cm height. Each vase was filled with 2 kg of compost soil. At first 15 seeds of wheat cv Zarrin were planted in each vase and at 3-4 leaf stage the seedlings were thinned remaining 10 seedlings in each vase and they were kept until the end of the trial. The experimental treatments were applied in each plot and in each period through foliar spray of CK and ABA at a concentration of 100 mmol . To prepare 500 cc of 100mmol solution of CK and ABA as much as 0.0057 and 0.006 g of each was used, respectively. Then the above mentioned amounts of each hormone was dissolved in 0.5 cc of 1N NaOH and reached the volume of 1000 cc by adding distilled water.
The Tipol 0.5% was used as wetting agent (surfactant). The check plants were also treated with distilled water and Tipol (0.5 v/v) . In each phase all plants in a vase were foliarly sprayed with growth regulators using a hand sprinkler, so that the aerial parts became all wet. The measured traits were number of seeds per spike, 1000-kernel weight, biological and economical yield. Plants were harvested at full maturity. The data were analyzed using MSTAT-C and mean comparison was done by Duncan's test. The Excel program was used for drawing the graphs and tables.
RESULTS AND DISCUSION
Number of seeds per spike:
Regarding number of seeds per spike the plant hormones were significantly different at p<0.01 (Table 1). The largest number of seeds per spike belonged to the applications of CK at pollination ([b.sub.2]) and at pollination and grain filling ([b.sub.4]) that increased the number of seeds per spike by 44.5 and 42.2, respectively compared with the check. The least number of seeds per spike belonged to the applications of ABA at pollination ([b.sub.5]) and at pollination and grain filling ([b.sub.6]) that showed 18 and 15% decrease in number of seeds per spike relative to the check. The increased concentration of ABA at first stage of seed growth reduced the number of seeds per spike through negative impact on the CK  and IAA concentrations .
The results showed that the foliar application of plant growth regulators at pollination and grain filling significantly influences the 1000-kernel weight at p [less than or equal to] %1 (Table 1) so that the foliarly applied CK at pollination ([b.sub.2]) had the greatest significant effect on 1000-kernel weight by 47.1 gr which was in the same statistical group as CK and ABA foliar application at pollination and grain filling ([b.sub.3]). CK increases 1000-kernel weight through retarding ageing and increasing the seed's active growth period and positively influencing source tissues and increasing photosynthetic capacity . The ABA foliar application at pollination ([b.sub.5]) had the least effect on the 1000-kernel weight (35.30 gr) relative to the rest of the treatments (Fig. 2). According to Yang et al.  the foliar application of ABA at cell division of rice seeds reduced the cell division rate and as a result the 1000kernel weight decreased significantly. The significant impact of 1000-kernel weight on the grain yield potential has been reported by Sconfild et al. (1988).
Results showed that the plant growth regulators differed significantly (p [less than or equal to] 0.01) from each other regarding biological yield (Table 1) so that the greatest biological yield was obtained from the foliar application of CK at pollination and grain filling by 13.274 t/ha that increased by 45% relative to the check. The foliar applications of ABA at pollination ([b.sub.5]) and pollination and grain filling ([b.sub.6]) had the least biological yield by 8.140 and 8.119 t/ha, respectively without any significant difference that showed an 11% decrease in yield relative to the check (Fig. 3). The significant decrease in biomass yield in ABA treatment and increase in biomass and grain yield through foliar application of CK at first growth stage of the seed show clearly the different effects of these two plant hormones on the growth processes [8, 12]. ABA decreases biomass through decreasing photosynthesis rate and photosynthesis active period.
The analysis of variance showed no difference among the plant hormones (p<0.01) regarding the grain yield (Table 1). The foliar applications with CK at pollination ([b.sub.2]) and pollination and grain filling ([b.sub.4]) produced the greatest grain yield by 5.644 and 6.098 t/ha, respectively without any significant difference which showed increases of 50 and 60.2% in grain yield relative to the check, respectively. The least grain yield with 3.170 t/ha obtained by ABA foliar application at pollination and grain filling showing a 15% decrease in grain yield relative to the check (Fig. 4). The spray of CK on the grains during the growth stage leads to increase in CK in these organs . Increased CK concentration in seeds during cell division caused the number of endospermic cells to increase which had positive correlation with the increase in grain yield . According to the findings of Kermode et al.  and Yang et al.  the increase in ABA concentration at cell division decreased the cell division significantly. Also ABA, contrary to CK, can reduce the grain filling period via stimulation of ageing  resulting in grain yield loss. Finally, it can be assumed that ABA, contrary to CK, decreases the formation of endospermic cells of the seeds at first growth stage leading to decrease in grain yield due to source weakness in photosynthesis storage.
According to the ANOVA (Table 1) the plant growth regulators were significantly different) [less than or equal to] 0.01 at p regarding the harvest index. The mean comparison showed that the greatest harvest index was obtained by foliar application of CK at pollination ([b.sub.2]) by 48.16% so that it was in the same statistical group with no significant difference showing an 18% increase in harvest index relative to the check. The least %harvest index was obtained by foliar application of ABA at pollination and grain filling ([b.sub.6]) which was in the same statistical group as the treatments of [b.sub.5] (ABA spray at pollination) and the check (no spray) (Fig. 5). According to Saeidi  the foliar application of CK increased the source ability through the size of the source by increasing the rate of cell division in growing seeds. As a result, a greater portion of the photosynthates was allocated to the seeds and the harvest index increased .
Received 12 October 2013
Received in revised form 18
Accepted 29 December 2013
Available online 25 February 2014
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(1) Salehi Gharaviran, L., (2) Nabizadeh, E., (3) Yezdanseta, S.
(1) MSc Student, Faculty of Agriculture and Resource, Mahabad branch, Islamic Azad University, Mahabad, Iran.
(2,3) Department of Agronomy, College of Agriculture, Mahabad Branch, Islamic Azad University, Mahabad, Iran.
Corresponding Author: Nabizadeh Esmaeil, Faculty of Agriculture and Resource, Mahabad branch, Islamic Azad University, Mahabad, Iran. E-mail: firstname.lastname@example.org
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|Author:||Salehi Gharaviran, L.; Nabizadeh, E.; Yezdanseta, S.|
|Publication:||Advances in Environmental Biology|
|Date:||Jan 1, 2014|
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