Sunflower Seed Protein Content in Relation to Desiccation Date and Seed Moisture

The objective of this study was to investigate the effect of desiccation date and seed moisture content on sunflower seed protein content. The experimental materials were three new parental sunflower lines of the Institute of Field and Vegetable Crops from Novi Sad, Serbia (L1, L2 and L3). Reglone forte (2 l ha-1) was used for desiccation and it was applied at 7-day intervals from the end of flowering to harvest maturity. The protein content was determined by the classical method of Kjeldahl. The stabilization of the protein content was determined in treatment that was performed 21 days after flowering (DAF) at seed moisture of about 45%. Regression analysis determined the highest and statistically significant effect of seed moisture at the moment of desiccation on seed protein content in the line L1, while the effects in lines L2 and L3 were not significant.


Introduction
Sunflower (Helianthus annuus) is the most important oil crop in Serbia (Miklič et al. 2010).It is also an important source of protein (Stanković et al. 2003).Sunflower meal as a byproduct of oil extraction is used as an excellent livestock feed.It is a source of biologically valuable proteins and if properly processed, it has a usable value of protein and amino acid composition similar to soybean meal (Lević et al. 2005).The increasing use of biodiesel will result in increased area under oil crops and increased amount of sunflower meal as a by-product (Kovčin & Stanaćev 2006).The protein content ranges from 32-38% in sunflower meal, and 13-20% in sunflower seed ( Jevtic et al. 1986).Majority of proteins present in fully developed seeds have structural or metabolic roles.Besides these roles, proteins in seeds also serve to provide a store of amino acids needed for germination and early seedling growth (Shewry et al. 1995).
Desiccation was introduced in agricultural practice as an agrotechnical measure several decades ago.The basic idea is to accelerate plant drying in order to make the crop ready for early harvest.The measure is advantageous in cool climates, where spring crops often mature in late fall, when weather conditions make harvest difficult.Chemical desiccation largely solves the problems occurring in mechanical sunflower harvest (Miklič et al. 2001).
Desiccation can be performed with chemicals such as diquat, glufosinate-ammonium, dimetipin, etc. (Đukić et al. 2007).Miklič et al. (2006) have obtained the best results with Reglone forte application (2 l ha -1 with 300-400 l of water).Diquat, which is the active substance of herbicide Reglone forte, is not soluble in oil and it is not found in sunflower meal (Hill et al. 1974).
The objective of the study was to investigate the effect of desiccation date and seed moisture content on sunflower seed protein content, i.e. to determine ending of protein accumulation in seed.

Materials and Methods
The trial was conducted at Rimski Šančevi during 2009 and included three new cytoplasmic male sterile lines of sunflower developed at Institute of Field and Vegetable Crops, Novi Sad, Serbia (L1, L2 and L3).Desiccation was performed with Reglone forte (2 l ha -1 ) applied at 7-day intervals from the end of flowering (DAF-days after flowering) to harvest maturity (control).There were 6 desiccation treatments (in the period 3 August 2009-7 September 2009) and the control (14 September 2009).Treatments were performed with a knapsack sprayer.Seed samples from several sunflower heads were collected directly before each treatment in order to test the moisture content in seed at the time of treatment.Seed moisture was determined in the laboratory by the conventional gravimetric method.When harvest maturity was reached, 12 heads were taken from each treatment to make average samples for protein content analysis.The analysis was performed by the Kjeldahl method in three replications.
The results were statistically processed.The analysis of variance of two-factorial experiment (split-plot design) and the regression analysis (quadric) were used.Significance of regression was tested with the F-test.

Results and Discussion
In all three lines there was a reduction of seed moisture content from the treatment 7 DAF to the control.Average seed moisture content decreased from 73.07% to 8.98% (Tab.1).
The highest average protein content was found in the line L1 (21.52%), the lowest in the line L3 (16.75%).The average protein content in the line L1 was highly significant in relation to the line L3.Between lines L1 and L2 there was no significant difference in the average protein content (Tab.2).The control had the highest average protein content (20.39%), while the lowest protein content was found in treatment 7 DAF (18.78%).The protein content in the control was highly significant in relation to the treatments 7 DAF and 14 DAF.Other treatments showed no significant difference in protein content in relation to the control.This result could indicate that protein accumulation in sunflower seed ends at 21 DAF (at seed moisture of 45.6%), because there was no subsequent increase in protein content.Miklič ( 2001) found the highest protein content 7 DAF, at the seed moisture of 65.58%.Gubbels & Dedio (1985) recorded that protein content reached constant level at seed moisture of 45% and 64%.Radić (2006) determined stabilization of protein content in seed at the treatment 14 DAF.Partial degradation of protein during seed maturation was reported by Bolyakina & Raikhman (1999).Steer et al. (1984), Goffner et al. (1988), Ploschuk & Hall (1997) and Jovanović et al. (2003) reported that protein accumulation in sunflower occurs at a greater rate during the first part of the seed filling.
In case of the line L1, the highest protein content was obtained with the treatment 35 DAF (23.61%), the lowest with the treatment 7 DAF (19.28%).The treatment 35 DAF had highly significant protein content in relation to all other treatments except the control, where it was significant (p=0.05).In case of the line L2, the highest protein content was obtained with the treatment 21 DAF (22.42%), and the lowest with the treatment 14 DAF (20.53%).The protein content in the treatment 21 DAF was highly significant in relation to the treatments 7 DAF, 14 DAF and 35 DAF, and significant in relation to the treatment 42 DAF.No significant difference was found among the treatments 21 DAF, 28 DAF and the control.In case of the line L3, the highest protein content was obtained with the control (17.20%), and the lowest with the treatment 7 DAF (16.01%).The control had significant protein content only in relation to the treatment 7 DAF.There was no significant difference in protein content between control and all other treatments.
Coefficients of determination, which showed the influence of seed moisture on protein content, were different between the lines.The highest impact was obtained in the L1 (0.842*), medium significant difference in protein content in relation to the control.This result could indicate that protein accumulation in sunflower seed ends at 21 DAF (at seed moisture of 45.6%), because there was no subsequent increase in protein content.Miklič (2001) found the highest protein content 7 DAF, at the seed moisture of 65.58%.Gubbels & Dedio (1985) recorded that protein content reached constant level at seed moisture of 45% and 64%.Radić (2006) determined stabilization of protein content in seed at the treatment 14 DAF.Partial degradation of protein during seed maturation was reported by Bolyakina & Raikhman (1999).Steer et al. (1984), Goffner et al. (1988), Ploschuk &Hall (1997) andJovanović et al. (2003) reported that protein accumulation in sunflower occurs at a greater rate during the first part of the seed filling.
In case of the line L1, the highest protein content was obtained with the treatment 35 DAF (23.61%), the lowest with the treatment 7 DAF (19.28%).The treatment 35 DAF had highly significant protein content in relation to all other treatments except the control, where it was significant (p=0.05).In case of the line L2, the highest protein content was obtained with the treatment 21 DAF (22.42%), and the lowest with the treatment 14 DAF (20.53%).The protein content in the treatment 21 DAF was highly significant in relation to the treatments 7 DAF, 14 DAF and 35 DAF, and significant in relation to the treatment 42 DAF.No significant difference was found among the treatments 21 DAF, 28 DAF and the control.In case of the line L3, the highest protein content was obtained with the control (17.20%), and the lowest with the treatment 7 DAF (16.01%).The control had significant protein content only in relation to the treatment 7 DAF.There was no significant difference in protein content between control and all other treatments.
Coefficients of determination, which showed the influence of seed moisture on protein content, were different between the lines.The highest impact was obtained in the L1 (0.842*), medium in the L3 (0.613), and the lowest in the line L2 (0.225).The impact in the line L1 was significant, while the impacts in the lines L2 and L3 were not significant.Miklič (2001) recorded significant and highly significant impact of seed moisture on protein content.In the lines L1 and L2 curve of regression exhibited maximum protein content at moisture contents of 11.46% and 39.63%.In the case of line L3, with decreasing of moisture content, protein content was constantly increasing (Fig. 1).Fig. 1.Effect of seed moisture on seed protein content at the time of desiccation Grafikon 1. Uticaj vlažnosti semena u momentu desikacije na sadržaj proteina u semenu

Conclusion
The following conclusions can be drawn based on the obtained results: The highest seed protein content was determined in the line L1.It was highly significant in relatio L3 and at the same level as the line L2.
The control had the highest average seed protein content, but there was no significant increas content in regard to DAF-21.This can indicate that protein accumulation in sunflower seed was complet Fig. 1.Effect of seed moisture on seed protein content at the time of desiccation Grafikon 1. Uticaj vlažnosti semena u momentu desikacije na sadržaj proteina u semenu in the L3 (0.613), and the lowest in the line L2 (0.225).The impact in the line L1 was significant, while the impacts in the lines L2 and L3 were not significant.Miklič (2001) recorded significant and highly significant impact of seed moisture on protein content.In the lines L1 and L2 curve of regression exhibited maximum protein content at moisture contents of 11.46% and 39.63%.In the case of line L3, with decreasing of moisture content, protein content was constantly increasing (Fig. 1).

Conclusion
The following conclusions can be drawn based on the obtained results: The highest seed protein content was determined in the line L1.It was highly significant in relation to the line L3 and at the same level as the line L2.
The control had the highest average seed protein content, but there was no significant increase in protein content in regard to DAF-21.This can indicate that protein accumulation in sunflower seed was completed about 21 DAF at the seed moisture of 45%, i.e. desiccation after that would not cause decrease of seed protein content.
Results of this experiment have shown that optimal time of desiccation should individually be tested for each genotype.