Cold Tolerance Test for Seed Vigor Determination of Tobacco Seeds

Background and Technological Evolution Analysis of YC/T 626-2025 Standard

Tobacco is an important economic crop in my country, and the quality of its seeds directly affects the stability and quality of tobacco leaf production. While traditional seed germination rate testing can reflect the germination potential of seeds under ideal conditions, it cannot accurately predict their emergence performance under field adversity (such as low temperatures in early spring). Against this backdrop, the concept of **seed vigor** emerged, comprehensively reflecting the germination, emergence, and storage stability of seeds under a wide range of environmental conditions.

The release of YC/T 626-2025, "Determination of Tobacco Seed Vigor - Cold Resistance Method," marks a new stage in my country's tobacco seed inspection, moving from a single evaluation of "germination rate" to a more comprehensive and practically applicable "vigor evaluation."

Analysis of Core Terms and Definitions

Accurate understanding of the terminology in the standard is a prerequisite for correct testing. Based on references to documents such as GB/T 21138, this standard clarifies key concepts:

• Tobacco naked seeds and pelleted seeds: The standard clearly distinguishes between the two physical forms of seeds and stipulates that the methods are applicable simultaneously, reflecting the broad applicability of the standard. The testing of pelleted seeds needs to consider the possible effects of seed coating agents on water absorption and low-temperature response.
  Seed Vigor: The definition in NY/T 3766 is adopted, emphasizing that it is "the comprehensive expression of those seed characteristics," including speed, uniformity, ability to emerge under stress, and ability to maintain germination levels after storage. This is a multi-dimensional comprehensive evaluation index. Cold Resistance Method: The two core environmental parameters of the method are clarified—the low-temperature treatment stage (5±1℃, 96h) and the recovery germination stage (25±1℃, 7d). This 96-hour cold stress is the key to stimulating differences in seed vigor. ul

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  Detailed Explanation of the Entire Determination Method and Key Control Points

  6.1 Sample Preparation: The Basis of Scientific Sampling

  After taking representative samples according to GB/T 21138, 400 net seeds should be randomly selected, with 100 seeds as one replicate, for a total of 4 replicates.

  This design meets statistical requirements, effectively reducing random errors and ensuring the reliability of the results. For pelleted seeds, it is necessary to ensure that each pellet contains a valid seed.

  6.2-6.3 Germination Medium Preparation and Bed Placement: Ensuring Uniformity

  Sponges, filter paper, or germination paper can be used as the medium. The key is to ensure that it is fully moistened and has a uniform moisture content. Using a vacuum seeder or seed plate can achieve uniform seed distribution and avoid affecting seedling growth due to local crowding or competition. Special care is required when placing seeds manually.

  6.4 Low Temperature Treatment: The Core Stress Link

  Immediately place the culture dishes after bed placement into a light incubator at (5±1)℃ for 96 hours (4 days). During this period, the medium must be kept moist to prevent additional stress to the seeds due to water loss at low temperatures. Precise temperature control (±1℃) is the key to the success of this step.

  6.5 Germination Test: Recovery and Growth Observation

  After low-temperature treatment, the seeds were quickly transferred to a germination box at (25±1)℃ for a 7-day germination period. During this stage, a light intensity of at least 1000 lx per day (12 hours) was required to promote normal seedling greening and growth. The medium was kept consistently moist.

  6.6 Seedling Identification: A Decisive Step for Accurate Results

  Identification was conducted according to Appendix A. This is the most crucial step in the entire testing process, requiring the most professional experience and meticulous observation. Identifiers must strictly distinguish between normal seedlings, abnormal seedlings, and ungerminated seeds.

  Application Case: A batch of tobacco seeds achieved a germination rate of 92% at room temperature, but the viability measured by the cold resistance method was only 68%. Analysis revealed that this batch of seeds exhibited a high proportion of "radicle atrophy" and "extremely weak seedlings" (Appendix A.2) after low-temperature stress, indicating severe damage to their cell membrane system at low temperatures. Although they could germinate under ideal conditions, their resistance was poor, making them unsuitable for sowing in areas with large temperature fluctuations in early spring. This case highlights the superiority of the cold resistance method compared to conventional germination tests. Seed vigor (V) was calculated using the formula V = (S / N) × 100%, where S is the number of normal seedlings and N is the number of seeds sown (100 seeds). The average of four replicates was calculated and rounded to the nearest whole percentage (1%) according to GB/T 8170.

  6.8 Tolerance for Error and Retesting: A Scientific Mechanism for Ensuring Data Reliability

  The standard establishes a rigorous data quality control mechanism through a two-level tolerance system in Appendix B.

  Gap Type	Based on Table	Control Objective	Remedial Measures
  Gap between 4 replicates of the same experiment	Appendix B, Table B.1	Controlling random operational errors within a single experiment	If the error exceeds the tolerance, a retest is required
  Gap between results of two experiments	Appendix B, Table B.2	Controlling systematic errors or sample inhomogeneity between experiments	Perform the second and third experiments and accept/discard results according to the complex logic specified in 6.8

  This mechanism ensures high repeatability and comparability of test results; reports are only issued when the data is statistically acceptable.

  7. Test Conclusion: Three-Level Vigor Judgment Standard

  The standard establishes a clear three-level vigor judgment system, providing a direct basis for seed quality grading and application:

  • High Vigor Seeds (V ≥ 85%): Strong resistance to adverse conditions, rapid and uniform emergence, suitable for precision sowing, sowing in adverse environments, or as raw material seeds for long-term storage.
  • Medium Vigor Seeds (65% ≤ V ≤ 84%): Have basic production value, but good field conditions must be ensured during sowing; the sowing rate can be appropriately increased to guarantee basic seedling emergence.
  • Low Vigor Seeds (V ≤ 64%): Not recommended for direct use in production; downgrading or use as processing raw material should be considered, as the risk of emergence under field conditions is extremely high.

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  Standard Implementation Recommendations and Precautions

  Laboratory Construction and Equipment Configuration

  Laboratories implementing this standard must be equipped with at least two light incubators with an accuracy of ±1℃, one for low-temperature treatment and the other for constant-temperature germination. A light intensity meter is used to calibrate light conditions. It is recommended to use a vacuum seed placer to improve seedling placement efficiency and uniformity.

  Personnel Training and Capacity Building

  Training of seedling identification personnel is crucial. It is recommended that personnel repeatedly study the pictures and text descriptions in Appendix A and practice comparisons with standard samples of known viability to standardize identification criteria and reduce subjective errors.

  Application in All Stages of the Tobacco Seed Industry Chain

  Pre-sowing

  Application Stages	Testing Purpose	Result Application Suggestions
  After Seed Production and Processing	Assess initial vigor and determine quality grade	Serving as the basis for seed pricing, grading, and packaging labeling.
  During Seed Storage	Monitor vigor changes and determine storage life	Periodic sampling and testing to establish vigor decay curves and guide warehouse management (such as turning over and priority order for delivery).
  Predict field emergence rate to guide sowing decisions	Adjust sowing date (avoid early spring low temperatures for low-vitality seeds), sowing rate, and sowing depth according to vigor level.
  Seed trade and dispute arbitration	Provide objective and scientific basis for quality judgment	The test report (Appendix C format) is a legally binding document and must be strictly implemented and issued in accordance with standards.

  Limitations of the method and future development prospects

  The cold resistance method mainly simulates low temperature stress and has limitations in assessing seed performance under other stresses such as drought and salinity.

  In the future, the tobacco seed vigor testing system may diversify, forming a combined evaluation scheme including methods such as "cold resistance method," "artificial aging method," and "electrical conductivity method," thereby providing a more comprehensive picture of seed quality. Furthermore, with the development of image recognition and artificial intelligence technologies, the automation and intelligentization of seedling identification are also promising directions, which will help further improve the efficiency and objectivity of testing. In conclusion, the promulgation and implementation of YC/T 626-2025 provides an important technical tool for improving the quality and efficiency of my country's tobacco seed industry. A deep understanding and strict implementation of this standard are of profound significance for ensuring the safety of tobacco seeds and improving the level of tobacco leaf production.