Sampling Intensity in Wheat and Rice Seed Lots

1. Introduction

Wheat and rice occupy a prominent position in the Brazilian agricultural scenario, due to their high demand and importance for human and animal food. Rice is a staple food for a significant portion of the population, while wheat is widely used in the production of flour, food products, and feed, especially in production systems in the southern region of Brazil (Sociedad Sul-Brasileira de Arroz Irrigado, 2022; Brazilian Agricultural Research Corporation, 2022).

Rice production has economic and social relevance, being destined for domestic supply, the formation of stocks, industry and export. In Brazil, production is mainly concentrated in the states of the South Region, especially Rio Grande do Sul and Santa Catarina, which account for a large part of the national production and Mercosur (Companhia Nacional de Abatement South Brazilian Society of Irrigated Rice, 2022).

Wheat, in turn, is the main winter crop in the country, although national production still does not fully meet domestic demand. This scenario reinforces the need for strategies that contribute to increasing production efficiency, among which the use of seeds with high physical, physiological, and sanitary quality stands out (Coêlho, 2021; Buratto et al., 2020).

Seed quality is one of the determining factors for the proper establishment of crops, as seeds with high germination, vigor and purity favor the uniformity of emergence and the initial performance of the plants. In addition, sanitary quality and the correct identification of lots contribute to reducing the risks of pathogen dissemination and varietal mixture, which are relevant aspects for the production and commercialization of seeds (Marcos Filho, 2015; Dhingra, 2022; ZUFFO et al., 2023).

In this context, seed certification plays a fundamental role in ensuring genetic identity, traceability and quality of propagative material. Sampling represents an essential step in this process, as the reliability of laboratory results depends on obtaining representative samples of the batch. Thus, the sample must contain the components of the batch in proportions like their occurrence, allowing the analyses to express the real quality of the material evaluated (Brazil, 2025).

The sampling intensity recommended by the official standards seeks to reduce errors resulting from the heterogeneity of the lots. However, in processed, homogeneous batches stored in large packages, such as big bags, the increase in the number of simple samples can increase operational time and collection costs. On the other hand, inadequate reductions in sampling intensity can compromise representativeness and generate incorrect interpretations about the quality of the lot.

Therefore, the present work aimed to evaluate the possibility of reducing the sampling intensity in wheat and rice seed lots, verifying its effects on the results of physical purity, determination of other seeds, inert material, germination and tetrazolium.

2. Materials and Methods

The study was conducted from September 2024 to May 2025, in two stages. The first corresponded to the sampling of commercial lots of wheat and rice seeds in two producing companies, located in the Campanha and Northwest regions of the state of Rio Grande do Sul. The second stage comprised laboratory analyses, carried out at the Flávio Farias da Rocha Laboratory, belonging to the Eliseu Maciel Faculty of Agronomy, of the Federal University of Pelotas, in the municipality of Capão do Leão, RS.

Sampling was carried out in 1,000 kg big bags, using a Nobbe caliper. The equipment was inserted into the center of the package, with the opening facing downwards and the tip directed upwards, forming an approximate angle of 30º in relation to the horizontal. Then, the lime was rotated 180º, so that the opening was facing upwards, and slowly removed, to allow the progressive collection of seeds along the route.

After collection, the simple samples were gathered, homogenized and reduced by three passes in a conical soil divider, followed by quartering to obtain the average sample. The samples were stored in containers with a capacity of 1,000 g and sent to the laboratory for analysis.

Lots of wheat seeds of the cultivars BRS Tarumaxi and ORS Guardião, and lots of rice seeds of the cultivars IRGA 424 RI, Pampeiro, Guri INTA CL and IRGA 431 RI, from the 2023/2024 harvest, were evaluated. The sampling intensities were defined based on the number of simple samples recommended for the lots evaluated: 40 simple samples, corresponding to 100% of the recommended intensity; 30 simple samples, corresponding to 75%; 20 simple samples, corresponding to 50%; and 10 simple samples, corresponding to 25%.

The samples were homogenized and divided into a soil divider to obtain the working samples, according to the Rules for Seed Analysis (Brazil, 2025). Physical purity analyses, determination of other seeds, inert material, germination and tetrazolium were carried out.

Physical purity was determined according to the Rules for Seed Analysis, with separation of the sample into pure seeds, inert material and other seeds. The results were expressed as a percentage of the mass of the working sample, after separation and manual counting of the components (Brazil, 2025).

The germination test was conducted with 400 seeds per sample, distributed in four replicates of 100 seeds. The seeds were placed on paper moistened with distilled water, in an amount equivalent to 2.5 times the mass of the dry paper and kept in a germinator at 25 ºC for rice and 20 ºC for wheat. The evaluations were carried out according to the periods established in the Rules for Seed Analysis, and the results were expressed as a percentage of normal seedlings (Brazil, 2025).

The tetrazolium test was performed with 100 seeds per sample, subdivided into two subsamples of 50 seeds. The seeds were subjected to soaking for 18 h in a BOD chamber, at 20 ºC for wheat and 25 ºC for rice. Before imbibition, rice seeds were hulled in Zaccaria PAZ/01-DTA equipment for 5 min. After imbibition, a longitudinal section was performed to expose the embryo, followed by immersion in 50 mL of 2,3,5-triphenyl tetrazolium chloride solution, at a concentration of 0.5%, in a BOD chamber in the dark, at 30 ºC for 4 h. After staining, the seeds were washed in running water and evaluated for viability with the aid of a stereoscopic microscope.

The results obtained at the different sample intensities were compared with the standard recommended by the Rules for Seed Analysis, represented by 40 simple samples. For comparison, the tables of germination tolerance, tetrazolium, determination of other seeds by number and verification of other cultivars provided for in the RAS (Brazil, 2025) were used. Initially, the average of the results to be compared was calculated. Then, the value corresponding to the mean and the probability of 5% was in the tolerance tables. When the difference between the results compared did not exceed the indicated tolerance, the variation was considered non-significant and acceptable.

3. Results

The results obtained for wheat seeds demonstrated that variations in sampling intensity did not significantly influence the results of the mandatory quality analyses when compared with the intensity recommended by the Rules for Seed Analysis (A40) (Table 1 and Table 2). Likewise, for rice seeds, no significant differences were observed among the evaluated sampling intensities, regardless of the lots and cultivars assessed (Table 3, Table 4 and Table 5). These findings indicate that reducing the number of primary samples did not compromise the representativeness of the samples or alter the classification of seed lots based on physical purity, determination of other seeds, inert matter, germination, and tetrazolium tests. Therefore, under the conditions evaluated, lower sampling intensities may provide results equivalent to those obtained using the standard procedure, suggesting potential optimization of sampling protocols without loss of analytical reliability.

4. Discussion

The absence of significant differences between the sampling intensities evaluated demonstrates that the reduction in the number of simple samples did not compromise the representativeness of the wheat and rice seed lots analyzed. This behavior was observed for the physical and physiological quality attributes, including physical purity, determination of other seeds and inert material (D.O.S./M.I.), germination and viability by the tetrazolium test. These results indicate that the evaluated lots had high homogeneity, an essential condition for small samples to maintain the ability to adequately represent the quality of the lot.

According to Prasad (2023), the reliability of seed analyses is directly related to obtaining representative samples, with batch homogeneity being one of the main factors that determine the accuracy of laboratory results. The International Seed Testing Association (ISTA) highlights that proper sampling and sample reduction procedures are key to minimizing variability between simple samples and ensuring that the average sample adequately represents the composition of the lot. Thus, in uniform materials with a high standard of processing, changes in the sampling intensity tend to exert less influence on the final quality classification.

In the wheat lots, the physical purity remained high at all intensities evaluated, with values close to or higher than 99%, while no other seeds or inert material were detected (Table 1). The maintenance of these results regardless of the reduction in sample intensity evidences the physical uniformity of the lots and suggests efficiency in the stages of production, harvesting, processing and classification. In addition, the values observed meet the minimum standards established for seed commercialization in Brazil (Brazil, 2013).

Similar results were described by Zonta et al. (2022), who observed high physical purity in rice seed lots subjected to different production and processing conditions, highlighting the importance of cleaning and classification steps to obtain seeds with low impurities. Thus, the absence of variation between the sampling intensities observed in this study is probably associated with the initial quality of the lots evaluated.

For wheat lots, germination remained above 90% at all sampling intensities (Table 2). The cultivar BRS Tarumaxi presented values between 91 and 98%, while the cultivar ORS Guardião varied between 90 and 94%. Although small numerical variations were observed between treatments, these differences were not enough to change the classification of the lots in terms of germination potential. This behavior demonstrates that the reduction in sampling intensity did not interfere in the evaluation of the physiological quality of the seeds.

The maintenance of high germination percentages may be associated with the physiological uniformity of the lots after processing. According to Marini et al. (2011) and Buratto et al. (2020), the physiological quality of wheat seeds can vary depending on genotype, environmental conditions during cultivation, maturation and storage; however, properly produced and processed batches have less variability between samples.

The results obtained are also in agreement with Hull, Swanepoel and Botes (2024), who highlight that wheat seeds with high physiological quality have uniform germination when produced and stored under appropriate conditions. Similar results were observed by Ortiz (2024), who found germination of more than 90% in wheat lots produced in northern Paraná, associating this performance with favorable production conditions and the high physiological standard of the seeds. Similarly, Freiberg et al. (2017) and Vilke et al. (2024) observed germination values above the minimum marketing standards in wheat seeds, corroborating the results found in this study.

The tetrazolium test confirmed the high physiological quality of the wheat lots, with viability values above 90% at all intensities evaluated (Table 2). The proximity between the results of germination and viability indicates that the reduction in sampling intensity did not compromise the interpretation of the physiological potential of the lots. The tetrazolium test is an efficient tool for rapid evaluation of seed viability, as it allows the identification of the metabolic activity of living tissues through the reduction of tetrazolium salt by respiratory enzymes (França-Neto, 2018; Santos et al., 2023).

Similar results were reported by Silva et al. (2026), who evaluated different wheat cultivars and observed percentages of viable seeds higher than 90%, evidencing the efficiency of the tetrazolium test in the physiological classification of lots. The high viability observed in this study reinforces the relationship between lot uniformity, processing quality and physiological stability of the seeds.

In the rice lots, similar behavior was observed. Physical purity remained close to or equal to 99% at all intensities evaluated, while the values for other seeds and inert material remained null (Table 3). No damaged or mechanically damaged seeds (D.O.S./M.I.) were detected in any cultivar, lot or accelerated aging treatment (0.0% in all samples); therefore, these data were not presented. The absence of significant differences between A40, A30, A20 and A10 shows that the reduction in sample intensity maintained the ability to adequately represent the physical quality of the lots.

Rice seed germination remained above 90% in all cultivars and lots evaluated (Table 4). The highest values were observed in the cultivars Pampeiro and Guri INTA CL, while some reductions were observed in the cultivars IRGA 424 RI and IRGA 431 CL. However, these variations did not present statistical significance, indicating that the lower sampling intensity did not compromise the classification of the lots in terms of germination performance.

Similar results were found by Beier et al. (2024), who observed high physiological quality in rice seeds subjected to different treatment and storage conditions, with germination values above 90%. The authors highlighted that adequate postharvest management practices contribute to greater physiological stability during storage. Similarly, Viero et al. (2023), evaluating seeds of the IRGA 424 RI cultivar submitted to chemical treatment and storage, found high germination values, reinforcing the physiological quality of this material.

The viability of rice seeds evaluated by the tetrazolium test also remained above 90% at all sampling intensities (Table 5). The cultivars IRGA 424 RI and GURI INTA CL presented the highest viability values, while the lowest percentages were observed in the cultivars Pampeiro and IRGA 431 CL. However, these differences did not compromise the interpretation of the quality of the lots, since they remained within the established statistical limits.

Similar results were reported by Tremea et al. (2024), who found high viability in rice seeds subjected to different storage periods and treatments, highlighting the influence of conservation conditions on the maintenance of physiological quality. The association between germination and tetrazolium results demonstrates that the evaluated lots had high initial quality and low physiological variability.

In general, the results obtained for wheat and rice demonstrate that the reduction of sampling intensity did not impair the evaluation of seed quality attributes in homogeneous lots with high physical and physiological standards. However, this answer should be interpreted considering the specific conditions of this study, especially the high purity, absence of mechanical damage and high germination rates observed.

In heterogeneous lots, with a greater presence of impurities, seeds of other species, mechanical damage, or different levels of deterioration, the reduction in sampling intensity may present a different behavior, since the variability within the lot can directly influence the reliability of laboratory results (Pelissari & Coimbra, 2023).

Thus, the results indicate that the optimization of sampling intensity can be an alternative to increase the operational efficiency of laboratory analyses in homogeneous commercial lots, while maintaining the reliability of the results. However, additional studies involving a larger number of lots, different storage conditions, seed categories and species are needed to expand the applicability of this recommendation.

5. Conclusions

The reduction of the sampling intensity to up to 25% of the number of simple samples recommended by the Rules for Seed Analysis did not significantly alter the results of physical purity, determination of other seeds, inert material, germination and tetrazolium in the lots of wheat and rice seeds evaluated. In processed and homogeneous lots, the reduction of sampling intensity proved to be technically feasible under the conditions of this study.