Osmopriming in Seeds of Helianthus annuus L.

Osmoconditioning stands out as an alternative treatment that aims to improve seed performance in the field. The process consists of immersing the seed in an aqueous solution containing the osmotically active compound, and thus the process of imbibition begins, which stops as soon as they reach equilibrium with the solution’s osmotic potential, allowing only the occurrence of the initial mechanisms of germination. Given the above, the objective of this work was to verify the effect of osmoconditioning on the physiological quality of sunflower seeds ( Helianthus annuus L.). For that, sunflower seeds of cultivar BRS 323 were used, which were soaked in polyethylene glycol (PEG 6000) solutions at different times of 0, 2, 4 and 6 hours. Then, the seeds were washed in distilled water and sown in trays containing sterilized sand. The following descriptors were evaluated: emergence, first emergence count, emergence velocity index, shoot length, and root length. Sunflower is a plant responsible for osmoconditioning by immersion at a potential of -2 MPa for 3.8 hours. The osmoconditioning of sunflower seeds can efficiently improve seedling performance in the stand, influencing emergence and emergence speed.


Introduction
As a result of its high adaptability, the sunflower (Helianthus annuus L.) crop is present in the most different regions of the world and is thus characterized as a very important crop from a commercial point of view (Araújo et al., 2018). In this sense, sunflower cultivation proves to be profitable, especially when considering its agronomic characteristics, such as high oil content (Dantas et al., 2015;Catão et al., 2016).
productivity (Coelho et al., 2019). Highly vigorous seeds generally germinate faster and more uniformly and can better resist the adverse effects of the environment (Scheeren et al., 2010). In this way, presowing treatments become indispensable to obtain a uniform stand, since such treatments can accelerate the germination process (Spadeto et al., 2018).
In this aspect, osmopriming stands out as an alternative treatment that aims to improve seed performance in the field (Lustri et al., 2017). The process consists of immersion of the seed in an aqueous solution containing an osmotically active compound, and in this way, the process of imbibition of the same compound begins, which is paralyzed as soon as it reaches equilibrium with the osmotic potential of the solution, allowing only the initial mechanisms of germination (Silva et al., 2020).
Among the osmotic agents used is polyethylene glycol 6000 (PEG 6000), which satisfactorily promotes the stimulation of the effects of controlled water restriction on seed germination (Breno et al., 2020). Polyethylene glycol (PEG 6000) has been highlighted as an inducer because it acts by controlling and reducing the speed of water absorption, contributing to the activation of biochemical processes, which can increase the vigor and quality of the seeds and can improve the speed, percentage and germination uniformity (Spadeto et al., 2018). These biochemical changes provide greater elaboration of solutes acting in osmoregulation, such as free amino acids, proline and total free sugars, which can improve the initial establishment of the stand (Almeida et al., 2019). Furthermore, it appears that the osmopriming technique proves to be a viable treatment alternative in the presowing phase, since its use results in an increase in the speed and uniformity of seedling emergence (Arin et al., 2011;Queiroga et al., 2011;Gomes et al., 2012;Missio et al., 2018;Silva et al., 2020).
The study of alternatives to increase the uniformity of the stand can contribute to the advancement of new industrial methods that allow the commercialization of high-quality and more vigorous seeds (Breno et al., 2020). Based on the above, the objective of this work was to evaluate the effect of osmopriming on the quality of Helianthus annuus L.

Location of the Experiment
The study was carried out in two stages. The first was conducted at the Laboratory of Seed Analysis of Campus Balsas, belonging to the State University of Maranhão. For this, sunflower seeds of the hybrid BRS 323, supplied by Embrapa Soja, produced in 2019 in its experimental field in Londrina, Paraná, were used. At this stage, asepsis and osmoconditioning of the seeds were performed. At this stage, asepsis and osmoconditioning of the seeds were performed. In the second stage, the emergency test was installed in the field in a private area in the city of Goianésia, Goiás, geographic coordinates: Latitude: 15°19′33″ South, Longitude: 49°7′2″ West, aiming to submit sunflower seedlings to environmental factors without artificial interference.

Asepsis of Sunflower Seeds
All seeds were initially disinfected. For this, they were immersed in 70% ethyl alcohol for 1 minute and in a 1% sodium hypochlorite solution for 30 seconds, followed by three washes with sterile distilled water (ADE) and drying on sterilized filter paper.
Thus, to obtain the -1 potentials, -2 and -3 MPa were used 39.24, 59.77 and 75.70 g of PEG 6000, each diluted in 500 ml of sterile distilled water. Subsequently, the seeds were placed in Erlenmeyers flasks (500 mL capacity) and immersed in each solution, at four different times of 0, 2, 4 and 6 hours, defined in order not to subject the seeds for more than 6 hours, which could take the seeds to a state of anoxia. Immersion is suggested, as it would be easily performed by farmers in the field. Then, the seeds were washed in distilled water and sown in trays containing sterilized sand.

Physiological Quality of Osmoconditioned Sunflower Seeds
For the assembly of the emergence test in sand, trays with dimensions of 7 × 21 × 29.5 cm were used, filled with 1,800 kg of sand, with granulometry between 0.05 and 0.8 mm in diameter, and 50 seeds were sown per tray. A total of 4 replicates were used per treatment. The seeds were evaluated through the following tests: Emergency: In the emergency test, the number of emerged seedlings was determined daily until they achieved complete stabilization. As emerged seedlings, those that presented the first pair of leaflets were considered.