High-yielding crops can only achieve their potential when the appropriate technological tools are applied and weather conditions do not impose restrictions. One such technological tool is the treatment of seeds, in which different products are used and, in some cases, cause little-known effects capable of modifying the plant’s metabolism and/or its morphology. The insecticide thiamethoxam alters the plant’s physiology and morphology, accelerating its development, thus enhancing its vigor. The objective of this study was to evaluate the influence of thiamethoxam on the physiological performance of rice seeds during storage. The research was conducted in a green-house and at the laboratory of the Department of Plant Science, Faculty of Agronomy Eliseu Maciel —UFPel (Federal University of Pelotas). Rice seeds from cultivars INIA Olimar and El Paso L144 were treated to a commercial product containing 350 grams of active ingredient thiamethoxam at doses of 0, 100, 200, 300, 400 and 500 g per 100 kg of seed. Seeds were tested for physiological quality immediately after being treated (check treatment) and at 3, 6, 9 and 12 months under storage, through germination test, cold test, accelerated aging and greenhouse emergence test. The concentration range from 200 to 400 g a.i. 100 kg<sup>-1</sup> seed yielded the highest germination and seed vigor values for both rice cultivars during the storage period.
Rice is considered one of the most important human foods worldwide, holding key economic and social roles. Brazilian produce is estimated to be some 12 million tons, of which over 65% is grown in the state of Rio Grande do Sul, where average yields go beyond 7000 kg・ha−1 [
High-yielding seed crops not only need favorable climatic conditions, but the use of technological tools, such as seed treatment to support them. Although seed coating with fungicides and insecticides is a long-known technology, it has only been basically evaluated regarding its efficiency on the control of pests and plant diseases. Some of them can exert little known effects upon plants, modifying their morphology as well as their metabolism [
The insecticide thiamethoxam is one such product, which according to [
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Since seed treatments are performed some time prior to seeding, treated seed lots may be stored for varying periods, during which eventual chemical reactions may damage the seed. [
The aim of this work was to evaluate the effects of the insecticide thiamethoxam on the physiological performance of rice seeds during storage.
The research was conducted at the Seed Laboratory (LDAS-UFPel) and glasshouse, of the Department of Plant Science, Faculty of Agronomy Eliseu Maciel (FAEM), at the Federal University of Pelotas (UFPel).
Seeds from rice cultivars INIA Olimar El Paso L144 were used at a rate of 4 kg per treatment and cultivar, with four replicates. The seeds were treated to a commercial product containing 350 grams of a.i. thiamethoxam at doses of 0, 100, 200, 300, 400 and 500 g∙100kg−1 seeds. Immediately after treatment (check) with thiamethoxam, and at periods of 3, 6, 9 and 12 months of storage, seeds were evaluated for their physiological quality through the germination test, with four 50-seed replicates per treatment. The seeds were sown in “Germitest” paper rolls, moistened with distilled water at a ratio of 2.5 times the weight of dry paper and kept in the germination chamber, set at 25˚C. The evaluations were performed according to the Rules for Seed Testing [
A 6 × 5 factorial design (thiamethoxam doses × storage period) was laid over a completely randomized design with four replicates per rice cultivar. Thiamethoxam effects were analyzed through polynomial regressions using the Winstat 1.0 statistical package [
A significant interaction was observed for all the response variables, with the exception of seedling emergence in cv. INIA Olimar, which responded only to the thiamethoxam dose. All the variables available present significance to the interaction, except emerge in greenhouse, that was made the developments, and when there are no significance to the interaction was constructed only one trend line.
Thiamethoxam’s maximum efficiency in germination was in the 200 to 400 g∙100kg−1 seed range, followed by a decrease in germination values for the 500 g・kg−1 dose (
compared to that of the check treatment (0 g thiamethoxam per 100 kg of seed) on the germination value of seeds from cultivar INIA Olimar was observed at the 300 g thiamethoxam dose, at the beginning of the storage period (0 months). This result agrees with findings by [
Throughout the different storage periods, seed germination values in both cultivars for treatments within the range 0 to 400 g thiamethoxam remained above the minimum of 80% required by Brazilian legislation [
Cultivar INIA Olimar exhibited a small linear decrease ranging from 4% to 13% germination after 12 months of storage, depending on the thiamethoxam dose used (
In general, the dose of 500 g thiamethoxam 100 kg−1 seed showed a slight decrease in seed quality (Figures 1(a)-(d)). According to [
In the cold test germination increases of 18% for rice cultivar INIA Olimar and 14% for cv. El Paso L144, compared to the check treatment, were recorded at the 300 g∙100kg−1 seed dose (
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Thiamethoxam application reduced germination decline along the storage period, with the best results for seeds of cv. INIA Olimar at doses of 300 and 400 g∙100kg−1, with a reduction of 2 and 5 percentage points, respectively, whereas for seeds from cv. El Paso L144 the best results were for doses of 200 and 300 g∙100kg−1 seed, for both of which the decrease in germination value was 7%.
Similar results to those produced by the cold test were found for the accelerated aging test, where increases of 18% to 12% on the germination values for rice cvs. INIA Olimar and El Paso L144, respectively, were observed compared to the check treatment when treated to thiamethoxam doses of 300 g∙100kg−1 seed (
The evaluation of seed vigor through rate of seedling emergence in the greenhouse showed that for cvs. Olimar and El Paso L144 there was an increase of up to 16% vigor in the dose effect between 0 and 300 g thiamethoxam 100 kg−1 seeds (
Seed vigor decreased with length of storage across all thiamethoxam doses, the same trend as that observed for germination. For both rice cultivars the greatest decline in seed vigor occurred for thiamethoxam doses 0 and 100 g (
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In rice grown at low temperatures, [
Working with low quality rice seeds, [
Generally speaking, the tests performed on both rice cultivars used on this study show that thiamethoxam had a similar positive effect on germination and seed vigor, and that the highest values for seed quality were achieved at thiamethoxam doses between 200 g and 400 g per hundred kilograms of seed.
Treatment with thiamethoxam of rice seeds from cultivars INIA Olimar and El Paso L144, prior to storage, at doses of 200 g to 400 g active ingredient per 100 kg of seeds yielded the highest values for germination and seed vigor.