Method for identifying high-temperature heat damage resistance of corn tassels

Abstract

The invention discloses a corn tassel high-temperature-resistant heat damage identification method which comprises the following steps: step 1, designing a test, and adjusting a sowing period to enable a corn flowering period to meet a natural high-temperature period so as to actively induce high-temperature stress; step 2, material planting: planting the to-be-identified corn material according to a preset field design; 3, performing high-temperature stress treatment to ensure that the corn is subjected to a high-temperature heat damage environment meeting a preset standard in the flowering phase; step 4, character investigation: after a corn flour loosening period, sampling and investigating tassel characters; 5, index calculation: calculating the number of effective spikelet of the corn tassel according to a formula, and calculating a high-temperature-resistant heat damage index according to a formula; step 6, evaluating heat resistance, calculating a high-temperature-resistant heat damage index, and evaluating high-temperature-resistant heat damage levels of different materials; according to the method, the heat resistance index is calculated by actively inducing natural high-temperature stress in the field and accurately quantifying the ratio of the effective spikelet number of tassels to the constant threshold value, and early-stage and efficient quantitative evaluation in the flowering period is achieved.

Description

Technical Field

[0001] This invention relates to the field of agricultural science and technology, and in particular to a method for identifying the high-temperature heat damage resistance of maize tassels. Background Technology

[0002] As a globally important food, feed, and industrial raw material crop, high and stable yields of maize are of strategic significance for ensuring national food security and agricultural product supply. However, maize is a typical warm-season crop that is sensitive to high-temperature stress, especially during its reproductive growth stage—the flowering period. Sustained high temperatures (usually referring to daily maximum temperatures ≥35℃ or even 38℃) can cause severe heat damage. High-temperature heat damage directly harms the reproductive organs of maize: on the one hand, it leads to a sharp decline in pollen viability in the tassels, reduced pollen shedding, and a shortened pollen shedding period; on the other hand, it causes a prolonged silking interval in the female ears and reduced silk activity, ultimately severely hindering the pollination and fertilization process, resulting in barren ears, missing kernels, and shriveled kernels, causing yield losses of up to 30% or more, seriously restricting maize production.

[0003] Breeding and promoting new heat-resistant maize varieties is the most economical, effective, and environmentally friendly way to address this challenge. However, efficient and accurate methods for identifying heat resistance are both the foundation and a key bottleneck for successfully breeding such varieties. Currently, existing maize heat resistance identification technologies both domestically and internationally suffer from several significant limitations: First, traditional methods heavily rely on final yield indicators, indirectly evaluating heat resistance by comparing grain yield under high-temperature stress with yield under normal conditions and calculating the yield loss rate. This method is time-consuming, highly susceptible to interference from numerous environmental factors such as soil fertility, moisture, and pests and diseases, and is a "post-hoc" assessment, unable to rapidly screen a large number of materials in the early generations of breeding, resulting in low efficiency and significant delays in the breeding process. Second, many methods rely on subjective morphological judgments, such as empirical grading based on visual observation of leaf curling, yellowing, and scorching under high-temperature stress, or the emergence of tassels and the color of husks. This method is heavily reliant on the operator's personal experience, highly subjective, and lacks unified, objective quantitative standards, resulting in poor comparability and repeatability of results between different identification units or personnel. Furthermore, some laboratory indicators are severely out of sync with actual production, such as the use of pollen in vitro culture to determine physiological and biochemical indicators like pollen viability. While these methods are relatively accurate, they require complex laboratory conditions, are cumbersome to operate, costly, and have low throughput. Moreover, the results obtained under in vitro conditions often do not fully reflect the overall pollen shedding capacity and actual fertilization effect of the tassel under complex natural conditions in the field. In addition, existing technologies lack precise quantification of core functional traits. Although some studies have focused on phenotypes such as tassel size or total spikelet number, they have failed to effectively distinguish between "effective spikelets" that function normally under high-temperature stress and "ineffective spikelets" whose development is hindered. Therefore, they cannot accurately reflect the true reproductive function of the tassel under adverse conditions. Therefore, this invention proposes a method for identifying the high-temperature heat damage tolerance of maize tassels to solve the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to propose a method for identifying the heat resistance of maize tassels. This method actively induces natural high-temperature stress in the field and accurately quantifies the ratio of the number of effective spikelets to a constant threshold to calculate the heat resistance index. This enables early and efficient quantitative evaluation of a large number of breeding materials during the flowering period, overcoming the limitations of traditional methods that rely on final yield, morphological judgment, or laboratory indicators. This provides reliable technical support for the breeding of new heat-resistant maize varieties.

[0005] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a method for identifying the high-temperature heat damage resistance of maize tassels, comprising the following steps:

[0006] Step 1: Experimental design. In areas where high temperature heat injury to maize occurs frequently, select plots with flat terrain and uniform fertility. Adjust the sowing period so that the flowering period of maize coincides with the natural high temperature period in order to actively induce high temperature stress.

[0007] Step 2: Planting of materials. The corn materials to be identified are planted according to the pre-designed field layout, and a high-temperature resistant control material is set up.

[0008] Step 3: High temperature stress treatment to ensure that the corn flowering period encounters a high temperature heat damage environment that meets the preset standards;

[0009] Step 4: Trait investigation. After the corn pollen shedding period, samples are taken to investigate the characteristics of the tassels.

[0010] Step 5: Index Calculation. Calculate the number of effective spikelets on the corn tassel according to the formula, and calculate the high-temperature heat damage resistance index according to the formula.

[0011] Step 6: Heat resistance assessment. Calculate the high-temperature heat damage index based on the high-temperature resistance threshold of the number of spikelets, the number of ineffective spikelets, and the number of effective spikelets in the corn tassel, and evaluate the high-temperature heat damage level of different materials.

[0012] The further improvement lies in the following: the field design in step two includes resource materials, hybrid combinations, and new variety combinations. The resource materials adopt a double-row zone with a row length of 3m, 3 replicates, and a planting density of 4000 plants / mu. The hybrid combinations adopt a double-row zone with a row length of 5m and a planting density of 3200 plants / mu. The new variety combinations adopt a randomized block design with 10 rows, each replicate area of ​​40 m², 3 replicates, and a planting density of 3200 plants / mu.

[0013] A further improvement is that the preset standard for the high-temperature heat damage environment in step three is the number of consecutive days with an average daily maximum temperature of ≥38℃ during the flowering period.

[0014] A further improvement is that the tassel trait survey indicators in step four include the total number of corn tassel spikelets and the number of invalid corn tassel spikelets. The number of invalid corn tassel spikelets is the number of spikelets on the inflorescence that cannot open when the corn tassel enters the flowering and pollen shedding stage.

[0015] A further improvement is made in the following: the formula for calculating the number of effective spikelets on the maize tassel in step five is:

[0016] Effective spikelet number = SN - SIVN

[0017] Wherein, SN represents the total number of spikelets in the male tassel, and SIVN represents the number of invalid spikelets.

[0018] A further improvement is made in the following: the formula for the high-temperature heat damage index in step five is:

[0019] HRI = (SN - SIVN) / TN

[0020] Among them, HRI is the high temperature heat damage index, SN is the total number of male spikelets, SIVN is the number of invalid spikelets, and TN is the high temperature tolerance threshold.

[0021] A further improvement is that the preset high-temperature resistance critical threshold TN is 700, and it is adjusted by floating based on the high-temperature resistance critical threshold 700.

[0022] The beneficial effects of this invention are as follows: This invention calculates the heat tolerance index by actively inducing natural high temperature stress in the field and accurately quantifying the ratio of the number of effective spikelets in the tassel to a constant threshold, thereby realizing early and efficient quantitative evaluation of a large number of breeding materials during the flowering period. It overcomes the limitations of traditional methods that rely on final yield, morphological judgment or laboratory indicators, and provides reliable technical support for the breeding of new heat-resistant maize varieties. Attached Figure Description

[0023] Figure 1 This is a flowchart of the steps of the present invention. Detailed Implementation

[0024] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0025] The maize tassel, or male inflorescence, grows at the top of the plant and is a panicle. Its structure mainly includes a main axis, branches, and paired spikelets attached to it, one pedunculated and the other sessile. Each spikelet is enclosed by two glumes and usually contains two florets. Each floret has three stamens. When mature, the anthers extend out of the glumes and release a large amount of pollen. The core function of the tassel is to produce and disperse pollen to pollinate the silks of the female ear. Its development status, such as the total number of spikelets, the number of effective spikelets, and pollen-shedding capacity, directly determines the pollination efficiency. It is a key reproductive organ affecting maize's seed setting rate and yield. Especially under high temperature stress, the fertility of the tassel florets is reflected in whether they can open normally, release pollen, and form effective spikelets, which becomes a key indicator for evaluating maize's heat resistance.

[0026] High-temperature heat stress assessment is a systematic agricultural technical method primarily used to scientifically evaluate the tolerance of crop varieties or germplasm resources to high-temperature stress. Its core lies in simulating high-temperature environments to observe and quantify changes in physiological and yield traits of crops during key growth stages, thereby screening for varieties with strong resistance and providing a basis for agricultural production to cope with high-temperature disasters. This assessment typically focuses on the reproductive growth stages to which crops are most sensitive to high temperatures, such as around the silking stage of maize or the heading and flowering stage of rice. It involves creating sustained high-temperature conditions 3–5°C higher than the natural environment using artificial climate chambers, greenhouse film coverings, and other facilities. Then, multiple indicators such as seed setting rate, pollen viability, inter-taper interval, and grain yield are comprehensively examined. Mathematical models such as the high-temperature tolerance index, principal component analysis, and membership function values ​​are used for quantitative evaluation. Finally, a precise evaluation of the tested materials is made according to a clear grading standard. This process provides crucial technical support for the breeding of high-temperature resistant varieties and disaster early warning.

[0027] Based on this, according to Figure 1 As shown in the figure, this embodiment provides a method for identifying the high-temperature heat damage resistance of maize tassels, including the following steps:

[0028] Step 1: Experimental Design. In areas where high-temperature heat injury to maize occurs frequently, select flat plots with uniform fertility. By adjusting the sowing period, the flowering period of maize is made to coincide with the natural high-temperature period, so as to actively induce high-temperature stress. This allows the flowering and pollen shedding periods of different maize materials to precisely coincide with the local natural high-temperature season, thereby actively and naturally inducing the required high-temperature stress environment. This lays a reliable environmental foundation for subsequent accurate identification and ensures the comparability of identification results from different batches and locations.

[0029] Step Two: Material Planting. The maize materials to be identified are planted according to the pre-designed field layout, with a heat-resistant control material included. The field design includes resource materials, hybrid combinations, and new variety combinations. Resource materials are planted in double-row plots (3m row length, 3 replicates) at a planting density of 4000 plants / acre. Hybrid combinations are planted in double-row plots (5m row length, 3200 plants / acre). New variety combinations are planted in a randomized block design (10 rows, 40 m² replicates, 3 replicates, 3200 plants / acre). This ensures a scientific and standardized field trial layout. Different planting densities and plot designs are used based on the different types of materials being identified, with a heat-resistant control material included to meet the growth needs of different materials, reduce environmental errors, and monitor and correct for annual or location-specific environmental variations, thus ensuring the high scientific validity and accuracy of the obtained experimental data.

[0030] Step 3: High-temperature stress treatment to ensure that the maize flowering period encountered a high-temperature heat injury environment that met the preset standard; the preset standard for a high-temperature heat injury environment was the number of consecutive days with an average daily maximum temperature ≥38℃ during the flowering period. The stress intensity was quantified and confirmed by continuously monitoring meteorological data to strictly confirm whether the maize flowering period encountered a high-temperature heat injury environment that met the preset standard. This ensured that the stress intensity experienced by all identified materials was clearly defined and met the standard, guaranteeing the validity and consistency of the identification results.

[0031] Step 4: Trait Investigation. After the pollen shedding stage of maize, samples are taken to investigate the characteristics of the male tassel. The investigation indicators for male tassel traits include the total number of spikelets and the number of ineffective spikelets. The number of ineffective spikelets refers to the number of spikelets on the inflorescence that cannot open when the maize male tassel enters the flowering and pollen shedding stage. This is used to accurately obtain key phenotypic data directly related to heat tolerance. By investigating the "total number of spikelets" and "number of ineffective spikelets" after pollen shedding, the substantial damage caused by high-temperature stress to the reproductive function of the male tassel is directly reflected. This provides reliable input for the next step of quantitative calculation. Yield traits include kernel moisture content, plot yield, and 100-kernel weight. Kernel moisture content: During threshing and yield measurement, the kernel moisture content is measured, averaged in three replicates, and expressed as a percentage (%). Plot yield: All ears in the harvested plot are threshed and weighed, and the yield at 14% standard moisture content is calculated, expressed in grams (g). Formula for calculating yield in a standard moisture plot: Standard moisture plot yield = Plot yield (14% moisture content) = Plot yield by weight × (100 - moisture content) / 86. 100-grain weight: After threshing, randomly select 100 seeds from each plot and measure their weight. Repeat the measurement three times and take the average. Formula for calculating the number of grains per ear in a plot: Number of grains per ear = Standard moisture plot yield / (100-grain weight / 100).

[0032] Step 5: Index Calculation. Calculate the number of effective spikelets on the maize tassel according to the formula, and calculate the high-temperature heat damage resistance index according to the formula. The high-temperature heat damage resistance index simplifies the complex heat resistance performance into a comparable value, realizing a fundamental shift from qualitative description to quantitative evaluation, making the identification results extremely objective and standardized.

[0033] The formula for calculating the number of effective spikelets on a maize tassel is:

[0034] Effective spikelet number = SN - SIVN

[0035] Wherein, SN represents the total number of spikelets in the male tassel, and SIVN represents the number of invalid spikelets.

[0036] The formula for the high-temperature heat damage resistance index is:

[0037] HRI = (SN - SIVN) / TN

[0038] Among them, HRI is the high temperature heat damage index, SN is the total number of spikelets in the male tassel, SIVN is the number of ineffective spikelets, and TN is the high temperature tolerance threshold. The preset high temperature tolerance threshold TN is 700, which is adjusted by floating based on the high temperature tolerance threshold of 700.

[0039] Step Six: Heat Resistance Assessment. The high-temperature heat damage index is calculated based on the high-temperature thresholds for the number of spikelets, invalid spikelets, and valid spikelets on the maize tassel, to evaluate the heat damage resistance levels of different materials. The evaluation criteria are as follows: HRI ≥ 1.00, rated as Level 1, extremely heat-resistant (HT); 0.80 ≤ HRI < 1.00, rated as Level 2, strongly heat-resistant (T); 0.60 ≤ HRI < 0.80, rated as Level 3, moderately heat-resistant (M); 0.40 ≤ HRI < 0.60, rated as Level 4, weakly heat-resistant (MS); HRI < 0.40, rated as Level 5, extremely weakly heat-resistant (S). By comparing the calculated high-temperature heat damage index values ​​with the clearly defined five-level evaluation criteria, the materials are classified into different levels from "extremely heat-resistant" to "extremely weakly heat-resistant". It provides breeders with clear and direct decision-making basis, enabling them to quickly screen out superior germplasm, identify excellent inbred lines or new varieties, and complete the final step from data to application.

[0040] This method is used to identify the resistance of maize tassels to high-temperature heat damage.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for identifying high-temperature heat stress tolerance of tassel of corn, characterized in that, The method comprises the following steps: Step 1: test design, in the high-temperature heat stress frequent area of corn, select the flat terrain, uniform fertility plot, through adjusting the sowing period to make the corn flowering period meet the natural high-temperature period, to actively induce high-temperature stress; Step 2: material planting, the corn materials to be identified are planted according to the preset field design, and a high-temperature resistant control material is arranged; Step 3: high-temperature stress treatment, ensure that the corn flowering period meets the preset standard of high-temperature heat stress environment; Step 4: character investigation, after the corn powder stage, sample investigation of tassel character; Step 5: index calculation, according to the formula, the effective spikelet number of corn tassel is calculated, and according to the formula, the high-temperature heat stress index is calculated; Step 6: heat resistance evaluation, according to the tassel spikelet number of corn, the tassel ineffective spikelet number of corn and the tassel effective spikelet number of corn, the high-temperature heat stress index is calculated, and the high-temperature heat stress level of different materials is evaluated.

2. The method according to claim 1, characterized in that: The field design in step 2 includes resource materials, hybrid combinations and new variety combinations, the resource materials adopt double row area, row length 3m, 3 times of repetition, planting density 4000 plants / mu, the hybrid combinations adopt double row area, row length 5m, planting density 3200 plants / mu, the new variety combinations adopt random block design, 10 row area, each repeated area 40 m², 3 times of repetition, planting density 3200 plants / mu.

3. The method according to claim 1, characterized in that: The preset standard of high-temperature heat stress environment in step 3 is that the average daily maximum temperature during the flowering period is greater than or equal to 38℃ for a continuous number of days.

4. The method according to claim 1, characterized in that: The tassel character investigation index in step 4 includes the total number of corn tassel spikelets and the ineffective tassel spikelet number of corn, the ineffective tassel spikelet number of corn is the number of spikelets that cannot open on the tassel inflorescence when the corn tassel enters the flowering and powder stage.

5. The method according to claim 1, wherein the method is characterized by: The calculation formula of the effective tassel spikelet number of corn in step 5 is: Effective spikelet number = SN-SIVN Wherein, SN is the total number of tassel spikelets, and SIVN is the ineffective spikelet number.

6. The method according to claim 1, wherein the method is characterized by: The high-temperature heat stress index formula in step 5 is: HRI = (SN-SIVN) / TN Wherein, HRI is the high-temperature heat stress index, SN is the total number of tassel spikelets, SIVN is the ineffective spikelet number, and TN is the high-temperature critical threshold.

7. The method according to claim 1, wherein the method is characterized by: The preset high-temperature critical threshold TN is 700, which is adjusted on the basis of the high-temperature critical threshold 700.

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