Soybean Industrial Seed Treatment: Effect on Physiological Quality During Storage

The aim of this study was to analyze soybean seed physiological quality after being subjected to various mixtures of pesticides via industrial seed treatment. The experiment was performed at the seed laboratory of the company BioGrow, located at São Paulo-SP, using soybean seeds cultivar NS 6700 IPRO which were subjected to 11 different treatments. Seed treatment was carried out using a treater Momesso, model L5-K, calibrated to apply a spray volume of 0.5 L 100 kg of seeds in which the volume of each treatment was adjusted using distilled water. After treatment, seeds were spread over plastic strays for drying for a period of 24 hours under environmental conditions. Once dry, seeds were packed in paper bags and stored for 0 (control), 45, 90, 135 and 180 days, under uncontrolled conditions of temperature and relative humidity, when seed physiological quality was evaluated using the following tests: germination, accelerated aging, seedling emergence, speed of emergence index and speed of emergence. Soybean industrial seed treatment before storage for up to 180 days is practicable using the mixtures of pesticides tested for storing seeds under environmental conditions. All treatments tested contribute to the maintenance of seed quality throughout storage.


Introduction
Soybean (Glycine max L. Merrill) has wide expression in the commodity market due to a major socioeconomic value which is determined by the numerous uses of products and byproducts on human and animal feed.World production, at the 2016/2017 crop season, was of 315.1 million tons, occupying 118.1 million of hectares (USDA, 2015).Brazil is the second greater soybean world producer, with a production of 94.8 million tons and a cultivated area of 31.4 million hectares (IBGE, 2016).
Various advances in soybean production technology have allowed the increase in area and crop yield in the recent years, among them is the quality of seeds used.According to Baudet and Peske (2007), and Silva (1998), uniform seed germination and vigorous growth of seedlings at the onset of crop development are essential to guarantee the maximum yield potential genetically contained.Likewise, Baudet and Peres (2004) observed that seeds with high germination, field emergence and growth potential can produce a uniform plant stand which results in high crop yields.However, seeds are sown at the field being exposed to numerous biotic (pests and diseases) and abiotic factors which impair physiological performance, affecting germination and reducing seedling emergence uniformity.Thus, to protect seeds and seedlings against a set of adversities, phytosanitary products as fungicides and insecticides are applied to the seeds (Ludwig et al., 2011;Pereira et al., 2011).
According to Avelar et al. (2011) soybean seed treatment is economically recommended, provided that the products or mixture of products used are adequate, using the recommended dosage and are uniformly distributed throughout the seed lot.Additionally, Lucca Filho (2006) determined that an efficient chemical treatment must select a product which is able to eradicate the pathogens present in the seeds, non-toxic to the crop, humans and the environment, non-corrosive, presents high stability, adherence and coverage, low cost and easy access, besides being compatible with other products.
Concomitantly with the increasing perception of the value of seeds and of the importance of protecting/increasing performance, the availability of products for seed treatmentfor different purposes has grown, such as protection (fungicides or insecticides) or nutrition (micronutrients), aiming to improve seed performance, both physiologically and economically (Avelar et al., 2011).However, besides increasing seed protection and assisting seedling initial development, the products and mixtures of products used in seed treatment shall not interfere negatively the physiological quality of seed lots, both immediately after treatment or during the storage period.
Accordingly, the present study aimed to analyze seed physiological quality after being subjected to various mixtures of products via seed treatment.

Method
The experiment was performed at the seed laboratory of BioGrow, located in São Paulo-SP, using soybean seeds cultivar NS 7600 IPROsubjected to 11 different treatments described in Table 1.Seed treatment was performed using a treaterMomesso, Model L5-K, calibrated to apply a spray volume of 0.5 L 100 kg of seeds -1 , in which the volume of each treatment was adjusted with distilled water.After treatment, seeds were distributed over plastic trays for drying for a period of 24 hours at room temperature.Once dried, seeds were placed into paper bags and stored for 0 (control), 45, 90, 135 and 180 days, under uncontrolled conditions of temperature and relative humidity, when seed physiological quality was evaluated using the following tests: Germination: performed using germitest paper rolls wetted with distilled water, in a volume of 2.5 times de weight of the dry paper.Seeds were distributed in four paper rolls of 50 seeds each, totaling 200 seeds per repetition, which were transferred for a germination chamber and held at a constant temperature of 25 o C. Normal seedlings were counted at five and nine days after sowing accordingly to the Rules for Seed Testing (Brasil, 2009) and results were expressed in percentage.
Accelerated aging: carried outusing the gerbox method; seeds were disposed in a single layer over a wire mesh which was held suspended above 40 mL of distilled water.The gerbox were covered and transferred to a Biological Oxygen Demand (B.O.D.) chamber at 41 o C for 48 hours (Marcos Filho, 2005).Then, seeds were removed from the gerbox and placed to germinate in the conditions described for the germination test.The evaluation was performed at the fifth day after sowing, counting the number of normal seedlings and expressing the results in percentage.
Seedling emergence: performed in trays filled with sand as substrate, sowing four repetitions of 50 seeds per treatment.Sowing depth was of approximately three centimeters and irrigation was carried out daily, at early morning and late afternoon; the percentage of emerged seedlings was counted at 21 days after sowing.
Speed of emergence index (SEI): carried out alongside the seedling emergence test.The index was calculated for each repetition accordingly to the procedure proposed by Maguire (1962), using the following equation: SEI = (G1/N1) + (G2/N2) + ... + (Gn/Nn), where G is the number of normal seedlings emerged each day and N is the number of days after sowing in which the counting was performed.
Speed of emergence (SE): evaluated herewith the seedling emergence and calculated using the following equation SE = [(G1N1) + (G2N2) + ... + (GnNn)]/(G1 + G2 + ... + Gn).Where, G is the number of normal seedlings emerged at each day and N is the number of days after sowing in which the counting was carried out.
The experiment was performed as a 5 × 11 (storage periods × seed treatment) factorial under completely randomized design using four repetitions.Data processing was performed using R Software (R Core Team, 2014).Data were subjected to analysis of variance using the F-Test (p < 0.05) and, when significant differences were observed, a polynomial regression was calculated (p < 0.05) for the factor storage period and means were compared using the least significative difference (p < 0.05) for the factor seed treatment.

Results
According to the results of the analysis of variance, the storage period and the treatments applied presented a simple effect on the percentage of germination, however, there was no interaction between factors.Figure 1A presents the percentage of germinated seeds for each treatment applied where the control presented the greater percentage of germination (92.5%) which did not differ statistically from treatments TR-2, TR-3, TR-6, TR-7 and TR-10.Likewise, treatments TR-4, TR-9 and TR-11 presented a statistically lower percentage of germination compared to the other treatments.Regarding the percentage of germination throughout storage (Figure 1B), the variable was adjusted to a negative quadratic model where the maximum germination of 93% was observed immediately after seed treatment, which correspond to time zero of storage.Then, seed germination decreased accordingly with the increase of the storage time.

Table 1 .
Treatment Identification (TR); commercial product used; active ingredient; concentration of the active ingredient contained in each product; dosage of the commercial product used and class of the product