Breeding method of ultra-short corn variety

Abstract

The invention relates to the field of agricultural breeding, and discloses a breeding method of an ultra-short corn variety, which comprises the following steps: S0, mutagenizing a corn inbred line B73 through EMS; the method comprises the following steps: S1, selecting a corn inbred line with a dwarf character as a dwarf donor; s2, selecting a corn backbone inbred line with high yield, high quality and strong disease resistance as an improved receptor; s3, carrying out artificial hybridization on the low-source donor and the improved receptor; s4, carrying out selfing on the generation S0; s5, stabilizing the agronomic yield character; and S6, screening out the ultra-short corn inbred line with the plant height stabilized at 80-100 cm. F1, improving male and female parents with heterosis according to the operation method, and hybridizing and assembling the male and female parents. According to the method, the maize inbred line B73 is subjected to mutagenesis treatment through EMS, then multi-generation inbreeding and screening are carried out, the inbred line is obtained, and compared with a traditional natural variation breeding method, the genetic stability and variation probability of the dwarf character are improved.

Description

Technical Field

[0001] The present invention relates to the field of agricultural breeding, and specifically to a method for breeding a super-dwarf corn variety. Background Art

[0002] At present, corn breeding technologies mainly rely on traditional heterosis utilization breeding and molecular marker-assisted selection methods. Traditional heterosis utilization breeding involves selecting high-yield, high-quality, disease-resistant, and adaptable parents with complementary advantages and trait negotiation for hybridization and combination. F1 is identified in multiple fields and subjected to variety comparison tests to screen out new high-yield and high-quality corn varieties with strong heterosis and stable traits, which are widely used in the cultivation of hybrid corn varieties. Molecular marker-assisted selection combines genetic maps and DNA marker technologies to locate the genes controlling target traits and accelerate the breeding process. For example, corn lines are improved by selecting stress-resistant genes or yield-related genes. These technologies have made significant progress in increasing corn yield and stress resistance. The plant height of conventional hybrid corn varieties is generally about 300 cm, and the grain yield per unit area can reach 10 tons / ha or the silage yield can exceed 50 tons / ha, and the planting range covers most agricultural areas in China.

[0003] However, there are certain limitations in existing corn breeding technologies. Traditional cross-breeding relies on natural variation, the genetic improvement rate of dwarf traits is slow, and it is difficult to effectively control plant height, which easily leads to lodging of tall corn under strong wind or rainy conditions, affecting yield stability. Although molecular marker-assisted selection can improve efficiency, the precise regulation of dwarf traits is still limited by the diversity of gene resources, and the breeding cycle is relatively long, usually taking 5 - 7 years. In addition, existing corn varieties are mostly designed for tall plants, which are difficult to meet the needs of urban agriculture or small-scale planting models, with low resource utilization efficiency, high irrigation and field management costs, and poor survival rate and yield performance, especially in arid or hilly areas. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a method for breeding a super-dwarf corn variety, which solves the problems of low variation probability of dwarf traits, many accompanying undesirable traits, genetic instability, and difficulty in improvement and application in traditional breeding methods.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for breeding a super-dwarf corn variety, comprising the following steps: S0: Treat the corn inbred line B73 by EMS mutagenesis, soak the seeds in 3% and 0.5% EMS solutions in stages for a total of 5 hours, and then perform multiple generations of self-crossing and screening to obtain an inbred line with a stable plant height of 80 - 100 cm and an ear height of 20 - 30 cm; S1: Select a corn inbred line with dwarf traits as the dwarf source donor, and the plant height of the donor is 60 - 80 cm; S2: Select high-yield, high-quality, and highly disease-resistant maize backbone inbred lines as the improvement recipients, with the plant height of the improvement recipients being 150 - 180 cm; S3: Artificially hybridize the dwarf source donor and the improvement recipient to generate the S0 generation; S4: Self-cross the S0 generation to generate the S1 generation, and screen for individuals with a plant height lower than 100 cm in the S1 generation; S5: After inducing doubling of the selected individuals by haploid technology, conduct self-crossing and selection for 3 - 5 consecutive generations to stabilize the agronomic yield traits; S6: Conduct ecological adaptability identification of the selected ultra-dwarf inbred lines in a multi-point environment, and screen for ultra-dwarf maize inbred lines with a stable plant height of 80 - 100 cm; F1: According to the above operation method, improve the male and female parents with heterosis, hybridize and combine them, conduct ecological adaptability and / or yield trait tests on the hybrid combinations in a multi-point environment, and breed ultra-dwarf maize hybrids with a stable plant height below 130 cm and agronomic traits meeting production requirements.

[0006] Preferably, the dwarf source donor is the maize inbred line "19M1130" obtained by EMS mutagenesis treatment.

[0007] Preferably, the improvement recipients are two excellent maize backbone inbred lines from opposite heterosis patterns.

[0008] Preferably, in step S5, the selected individuals also need to meet the breeding conditions of inbred lines with coordinated comprehensive agronomic traits, strong disease and insect resistance, and strong adaptability.

[0009] Preferably, in step S5, during the continuous self-crossing and selection process, while maintaining the ultra-dwarf trait, optimize the plant, yield, and stress resistance.

[0010] Preferably, in steps S6 and F1, the multi-point environment includes environments such as temperate irrigation, temperate semi-arid, temperate rain-fed, and winter southward multiplication in Hainan tropical region.

[0011] Preferably, the plant height of the ultra-dwarf maize inbred line is stable at 80 - 100 cm, the plant height of the hybrid is stable below 130 cm, and it shows stable yield and stress resistance in various ecological environments.

[0012] Preferably, it also includes multi-generation propagation and trait determination of the selected inbred lines to confirm the genetic stability of dwarf plant, plant, yield traits, and stress resistance adaptability.

[0013] Preferably, the ear height of the ultra-dwarf maize inbred line is 20 - 30 cm.

[0014] Preferably, through multi-generation systematic selection and ecological adaptability screening, the wide adaptability and production application value of the ultra-dwarf corn line are ensured.

[0015] The present invention provides a breeding method for an ultra-dwarf corn variety, having the following beneficial effects: 1. In the present invention, the maize inbred line B73 is treated by EMS mutagenesis. The seeds are soaked in 3% and 0.5% EMS solutions in stages for a total of 5 hours, and then subjected to multi-generation self-crossing and screening to obtain an inbred line with a plant height stably at 80-100 cm and an ear height of 20-30 cm. Experimental data shows that the probability of the occurrence of target trait variations is greatly increased, reaching more than 25%. Moreover, the retention rates of comprehensive traits such as agronomy and yield of individuals with the target traits are relatively good, and the breeding cycle is shortened by about 3-5 years. Compared with the traditional natural variation breeding method, the genetic stability and variation probability of the dwarf trait are improved.

[0016] 2. In the present invention, multi-point environmental tests are carried out in environments such as temperate irrigation, temperate semi-arid, temperate arid, temperate rain-fed, and winter southward breeding in Hainan tropics. The irrigation water volume (irrigation + precipitation) during the maize growth period is 400 mm, 250 mm, 150 mm, etc. respectively. Combining with the molecular marker-assisted selection of the drought-resistant gene ZmDREB1A, the survival rate of the selected variety under drought conditions reaches more than 85%, and the unit area yield is stably above 4.5 tons / ha. Verified by two-year data, the adaptability covers about 80% of the main maize planting areas in the country.

[0017] 3. The plant height of the ultra-dwarf corn inbred line selected in the present invention is controlled at 80-100 cm, and the ear height is 20-30 cm. Through artificial inoculation with leaf spot disease (10 5 spores / ml) screening, the incidence rate is lower than 15%, and the lodging rate is lower than 5% under the condition of a wind speed of 15 m / s. Compared with traditional tall maize, the disaster loss is reduced by about 20%, and the field stability is improved.

[0018] 4. In the present invention, through field screening and applying 300 kg / ha of compound fertilizer, the ear length of the selected variety reaches more than 15 cm, the number of grains per ear exceeds 400, and the unit area yield is stably at 5-5.3 tons / ha. Experimental data shows that the yield is about 40% compared with conventional maize, and the coordinated development of ear traits is achieved under the condition of reduced plant height.

[0019] 5. In the present invention, the plant height of the ultra-dwarf corn is below 130 cm, the planting density is increased to 120,000 plants / ha, the irrigation volume in the arid area is reduced to 150 mm, and the field mechanized operation efficiency is increased by about 20%. Compared with traditional maize, the resource utilization rate is increased by about 15%, and the irrigation, pesticide application and labor input are reduced. Description of the Drawings

[0020] Figure 1This is a flowchart of a breeding method for a super-dwarf corn variety of the present invention. Detailed implementation manners

[0021] Next, in combination with the accompanying drawings of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] Please refer to the attach Figure 1 , the embodiment of the present invention provides a breeding method for a super-dwarf corn variety, including the following steps: S0: Treat the corn inbred line B73 by EMS mutagenesis, soak the seeds in 3% and 0.5% EMS solutions in stages for a total of 5 hours, and then perform multiple generations of self-crossing and screening to obtain an inbred line with a plant height stably at 80-100 cm and an ear height of 20-30 cm; S1: Select a corn inbred line with a dwarf trait as the dwarf source donor, and the plant height of the donor is 60-80 cm; S2: Select a high-yield, high-quality, and strong-disease-resistant corn backbone inbred line as the improvement recipient, and the plant height of the improvement recipient is 150-180 cm; S3: Manually cross the dwarf source donor and the improvement recipient to generate the S0 generation; S4: Self-cross the S0 generation to generate the S1 generation, and screen individuals with a plant height lower than 100 cm in the S1 generation; S5: After inducing doubling of the screened individuals by the haploid technology, perform self-crossing and selection for 3-5 consecutive generations to stabilize the agronomic yield traits; S6: Conduct ecological adaptability identification on the selected super-dwarf inbred lines in a multi-point environment, and screen out super-dwarf corn inbred lines with a plant height stably at 80-100 cm; F1: According to the above operation method, improve the male and female parents with heterosis, hybridize and combine them, and conduct ecological adaptability and / or yield trait tests on the hybrid combinations in a multi-point environment to select a super-dwarf corn hybrid with a plant height stably below 130 cm and agronomic traits meeting the production requirements.

[0023] Specifically, the dwarf source donor is a maize inbred line obtained by EMS mutagenesis, with a plant height of 60 - 80 cm. The improved recipient is a high-yield and strong-disease-resistant inbred line, with a plant height of 150 - 180 cm. The dwarf source donor and the improved recipient are artificially hybridized to generate the F1 generation, and the plant height shows an intermediate type. The F1 generation is self-crossed to generate the F2 generation, and individuals with a plant height lower than 100 cm are screened. After the screened individuals are induced to double by the haploid technique, they are self-crossed for 3 - 5 consecutive generations to stabilize the agronomic traits, and the plant height is 90 - 100 cm. The selected inbred lines are subjected to ecological adaptability identification in a multi-point environment, and the plant height is stable at 80 - 100 cm. Using the selected inbred line as the female parent, it is hybridized with another dwarf inbred line, and ecological adaptability and yield tests are carried out in a multi-point environment to select a hybrid with a plant height below 130 cm. Through EMS mutagenesis and multi-generation self-crossing screening, dwarfing genes are introduced and the plant height is stabilized, with the genetic variation rate controlled within 5%, the breeding cycle is shortened by about 1 - 2 years, and the genetic stability and diversity of the ultra-dwarf maize lines are improved.

[0024] The dwarf source donor is the maize inbred line "19M1130" obtained by EMS mutagenesis treatment.

[0025] Specifically, take the seeds of the maize inbred line "B73", and select plump and pest-free seeds as mutagenesis materials, with the seed weight controlled at 50 g / batch.

[0026] The mutagenesis treatment uses ethyl methane sulfonate (EMS). The specific steps are as follows: First, soak the seeds in a 3% EMS solution at a constant temperature of 25°C for 3 hours, then rinse them thoroughly with distilled water, and then continue to soak them in a 0.5% EMS solution for 2 hours, keeping the light-shielded environment to prevent photodegradation.

[0027] After mutagenesis, rinse the seeds repeatedly with clean water 6 times, 10 minutes each time, to remove the residual chemical substances, and then dry them in a ventilated place for 24 hours and sow them in the experimental field.

[0028] The first generation after mutagenesis (M1 generation) is planted in the Ningxia Pingluo experimental field, and the plant height is distributed between 60 - 120 cm. Individuals with a plant height lower than 80 cm are screened as the subsequent female parent.

[0029] Through precise EMS mutagenesis conditions, a recessive dwarfing gene is successfully induced, significantly improving the genetic variation rate of the dwarfing trait, providing diverse germplasms for subsequent breeding, and shortening the breeding cycle by about 1 - 2 years.

[0030] The improved recipient is two excellent maize backbone inbred lines from opposite heterosis patterns.

[0031] Specifically, two excellent maize inbred lines, "15H009" and "HP4664", from opposite heterosis patterns were selected as the recipients. The seeds are excellent inbred lines independently selected and bred, with a plant height of 180 cm and an ear height of about 80 cm. The average ear weight per plant is 150 g, and the disease resistance index reaches 85%.

[0032] The recipient seeds were pretreated before sowing to enhance seed vigor. The operation was to sun-dry the seeds for 1 - 2 days, soak them in a 0.1% potassium dihydrogen phosphate solution for 12 hours, and then germinate them for 2 - 3 days for standby.

[0033] Field management adopted a standardized fertilization plan, applying 300 kg of compound fertilizer per hectare with a nitrogen - phosphorus - potassium ratio of 15:15:15, and controlling the irrigation amount at 400 mm to ensure the healthy growth of the recipients.

[0034] Select typical plants of the recipients to harvest fresh pollen for artificial pollination.

[0035] The excellent traits of the two excellent maize inbred lines "15H009" and "HP4664" provided a high - yield and disease - resistant gene basis for improving the offspring, significantly enhancing the genetic gain and adaptability of the improved offspring and their derived inbred lines.

[0036] Specifically, the S1 generation was planted in the experimental field, using a large population of more than 1000 plants of multiple ear lines, with a planting density of 120,000 plants per hectare.

[0037] In step S5, the selected individuals also need to meet the inbred line selection conditions such as coordinated comprehensive agronomic traits, disease and pest resistance, and strong adaptability.

[0038] Specifically, during the field observation period, the phenological period, adaptability such as disease and pest resistance, and the plant lodging resistance ability were recorded, and plants with well - developed roots and no lodging or breakage in the early stage were selected for self - crossing and generation addition to further improve the traits of the improved materials.

[0039] The ear length and the filled length were measured using a vernier caliper, accurate to 0.1 cm. The number of ear grains was counted manually by counting the number of grains on a mature single ear, and the data of self - crossed super - dwarf plants without diseases and pests in the field were statistically analyzed.

[0040] The screening criteria were individuals with a plant height ≤ 100 cm, an ear length ≥ 15 cm, and the number of ear grains ≥ 400 grains. Fifty plants meeting the conditions were preferably selected and marked.

[0041] Through strict selection in multiple ecological environments and selection criteria, the agronomic yield traits of the improved inbred materials were significantly improved, while the ability to resist wind disasters and heavy rains was enhanced, avoiding or reducing the impact of natural disasters.

[0042] In step S5, after doubling is induced by haploid technology, during the continuous self-crossing and selection process, while maintaining the ultra-dwarf trait, the plant, yield, and stress resistance are optimized.

[0043] Specifically, for 3 - 5 consecutive generations of mixed-pollination and self-crossing, small-scale isolated planting can be adopted, with a planting area of 0.1 hectare per generation. An isolation belt is set up to prevent cross-pollination by foreign pollen during the same period, and strict self-crossing is ensured to prevent the genetic basis from being mixed.

[0044] Yield is optimized through the management of epistasis in field planting. After selecting yield traits using molecular markers, self-crossing materials with outstanding yield trait performance are selected in the field to improve ear length, filled length, number of grains per ear, and 100-grain weight.

[0045] Stress resistance is optimized by artificially simulating drought and high-temperature environments. Under drought conditions, the irrigation volume is reduced to 150 mm, and under high-temperature conditions, the temperature is raised to 35 °C by covering the film. Individuals with a survival rate ≥ 85% are screened.

[0046] The plant height, yield, and disease resistance index are recorded for each generation, and plant lines with a plant height of 90 - 100 cm, a yield ≥ 5.2 tons / ha, and a disease resistance rate ≥ 80% are preferably selected.

[0047] Multi-dimensional optimization improves the comprehensive stress resistance of the strain, increases the drought and high-temperature survival rate by 15%, enhances yield stability, and expands adaptability to harsh environments.

[0048] In step S6: F1, the multi-point environments include temperate irrigation, temperate arid and semi-arid, temperate rain-fed, and Hainan tropical winter southward breeding environments, etc.

[0049] Specifically, the test sites are selected as the temperate yellow river irrigation area in the Ningxia Plain (soil pH 8.0, annual rainfall 200 mm), the temperate semi-arid hilly area in Ningxia (soil pH 8.0, annual rainfall 200 mm, slope 5° - 10°), the rain-fed area in the southern mountainous area of Ningxia (altitude 1800 m, soil pH 7.6, annual rainfall 400 mm), and the tropical area in Hainan (altitude 260 m). 0.2 hectares are planted at each site.

[0050] In the temperate yellow river irrigation area of the plain, surface flooding irrigation and full-process mechanized management are adopted, with 3 - 4 irrigations and a total irrigation volume of 300 mm; in the temperate semi-arid hilly area, drip irrigation with integrated fertilization and full-process mechanized planting are adopted, with 10 irrigations and a drip volume of about 210 mm; in the rain-fed area of the southern mountainous area, the whole-film double-ridge furrow side-sowing planting technology is adopted; in the Hainan tropical winter southward breeding area, the ridge planting with drip irrigation and integrated fertilization technology is adopted. The maize growing season is from November to March of the following year, with 10 irrigations and a drip volume of about 250 mm.

[0051] The improved ultra-dwarf inbred materials are systematically selected at each site, and the ultra-dwarf corn varieties are selected and identified at each site. The traits of plants, resistance, yield, and grains per ear are observed and recorded for two consecutive years, and selection is based on this.

[0052] Ultra-dwarf corn inbred lines with a plant height stable at 80 - 100 cm and hybrid varieties with a plant height stable below 130 cm are screened out, and they show stable yield and stress resistance in various ecological environments.

[0053] Specifically, the plant height stability is achieved through multi-generation measurements. Sowing is carried out in spring (March - April) on the mainland every year and in winter (October - November) in Hainan every year. The plant height and ear height are investigated at the milk ripening stage of corn. Materials with relatively stable plant height and ear height between years and environments are selected. The plant height of ultra-dwarf corn inbred lines is stable at 80 - 100 cm, and the plant height of hybrid varieties is stable below 130 cm.

[0054] The yield stability is tested in 4 environments over 2 years. Artificial or mechanical harvesting is used, and the corn yield per unit area at standard moisture content is statistically analyzed to ensure that the yield is relatively stable between years and environments.

[0055] The stress resistance test includes artificial inoculation with leaf spot disease (concentration 10 5 spores / ml) and simulated drought (irrigation amount 100 mm), and individuals with a disease incidence rate lower than 15% and a survival rate ≥ 85% are screened out.

[0056] Two excellent ultra-dwarf corn inbred lines with heterosis, "H2139" and "H2149", have a plant height stable at 80 - 100 cm. Ultra-dwarf corn varieties are obtained through hybrid combination, with a plant height stable below 130 cm, and they show stable yield and stress resistance in various ecological environments.

[0057] The selected ultra-dwarf corn variety "Yu'ai No. 1" has a plant height below 130 cm. The planting density is increased to 120,000 plants / ha, the irrigation amount in the arid area is reduced to 100 mm, and the field mechanized operation efficiency is increased by about 20%. Compared with traditional corn, the resource utilization rate is increased by about 15%, and irrigation, pesticide application, and labor input are reduced. The stable plant height and stress resistance reduce the planting risk. Especially under variable climates, the yield guarantee rate is increased by 20%, providing reliable planting options for farmers.

[0058] It also includes multi-generation propagation and trait determination of the selected inbred lines to confirm the genetic stability of dwarf plant, plant, yield traits, and stress resistance adaptability.

[0059] Specifically, multi-generation propagation uses aseptic seedling raising technology. Seeds germinate in the greenhouse and are transplanted to the experimental field for continuous planting for 5 generations, with an area of 0.3 ha for each generation.

[0060] Trait determination includes plant height (measured with a vernier caliper), ear weight (weighed with an electronic scale), and lodging resistance (lodging rate at a wind speed of 15 m / s). 200 plants are sampled in each generation.

[0061] Genetic stability is detected for the dwarfing gene (such as the d1 gene) through molecular marker technology to ensure that the genetic variation rate is less than 5%.

[0062] The results show that after 5 generations, the plant height is stable at 90 ± 5 cm, the ear weight is 250 g, and the lodging rate is less than 5%.

[0063] Multi-generation verification ensures the reliability of trait inheritance, reduces the risk of degradation in future planting, and increases the germplasm purity by about 15%.

[0064] The ear height of the ultra-dwarf maize inbred line is 20 - 30 cm.

[0065] Specifically, the ear height is determined by field measurement. The distance from the ear of each plant to the ground is measured using a laser rangefinder, and the average value is calculated by sampling 300 plants.

[0066] During the breeding process, individuals with lower ear positions are selected for self-crossing, combined with the expression of the dwarfing gene, to gradually stabilize the ear position at 20 - 30 cm.

[0067] Field management optimizes irrigation and fertilization, maintains the soil moisture at 60% - 70%, and promotes ear development without affecting plant height.

[0068] Preferably, the average ear height of the ultra-dwarf maize variety is 25 cm, the ear length is 16 cm, and the number of kernels per ear is 450.

[0069] The lower ear position facilitates mechanized harvesting and manual operation, reduces the labor intensity by about 30%, and at the same time maintains the photosynthesis efficiency of the ear, with the yield loss controlled within 5%.

[0070] Through multi-generation systematic selection and ecological adaptability screening, the extensive adaptability and production application value of the ultra-dwarf maize inbred line and variety are ensured.

[0071] Specifically, combined with the haploid technology, multi-generation cycling includes 2 - 4 generations of self-crossing and selection. In each generation, individuals with a plant height ≤ 100 cm, an ear height ≤ 20 cm, and normal ear trait development and growth are screened, and the cycling period is 2 years / generation.

[0072] Ecological adaptability screening is carried out in the Ningxia Plain, the Ningxia mountainous area, the arid zone of Ningxia, and Hainan. Extreme weather simulations (such as 35°C high temperature during the ear stage, no effective precipitation and no irrigation) are set up and tested continuously for 2 years.

[0073] Molecular-assisted breeding technology introduces drought-resistant genes (such as ZmDREB1A), and the gene expression is detected by PCR to enhance the stress resistance of the strain.

[0074] For the final strain "Yu'ai No. 1", the average plant height is 125 cm in 4 locations, the yield is 5.2 tons / ha, and the survival rate is over 85%.

[0075] Multi-generation backcrossing and ecological screening have improved the genetic stability and environmental adaptability of inbred lines and hybrids. The promotion area has expanded to over 80% of the suitable maize-growing areas across the country, and the economic benefit has increased by about 5%.

[0076] The following is an introduction in combination with specific embodiments: Example 1 Experimental purpose: To obtain ultra-dwarf maize inbred lines with a plant height of about 100 cm through EMS mutagenesis and systematic breeding.

[0077] Materials and methods: Basic materials: The dwarf source donor maize inbred line "19M1130" was obtained by mutagenesis breeding from the excellent maize inbred line "B73", with 50 grams of seeds; the dwarf source receptor improvement materials were the excellent inbred lines "15H009" and "HP4664", with 50 grams of seeds.

[0078] Mutagenesis treatment: The seeds of "B73" were soaked in 3% EMS solution at 25 °C for 3 hours, and then soaked in 0.5% EMS solution for 2 hours, with light avoidance treatment. They were rinsed with water 6 times, and after 24 hours of germination, they were sown.

[0079] Obtaining the dwarf source donor: The mutagenized seeds were planted, artificially self-pollinated, and treated with the single haploid technology. Individuals with a plant height ≤ 100 cm were selected and continuously self-crossed and identified to obtain the dwarf source donor "19M1130".

[0080] Constructing the dwarf line improvement population: In winter 2018, the dwarf source donor "19M1130" and the dwarf source receptor improvement materials "15H009" and "HP4664" were planted in Hainan. To ensure the coincidence of flowering periods, sowing was carried out at different times multiple times. During the flowering period, the fresh pollen of the typical plants of the receptor was artificially pollinated onto the silk of the strictly bagged female ears of the dwarf source donor "19M1130", and the S0 generation seeds were harvested when mature; in April 2019, the S0 generation seeds were sown in Ningxia, and excellent plants were selected for artificial bagging and self-crossing to pairwise construct the dwarf line improvement population.

[0081] Single haploid technology: The two dwarf line improvement populations were induced for haploids, and the selected haploids were doubled in chromosomes.

[0082] Selection of excellent traits: The double haploid seeds were self-crossed and propagated, and selection was carried out continuously for 2 years in 4 ecological environments. Traits such as plants, resistance, yield, and grains per ear were observed and recorded in the field. Two excellent ultra-dwarf maize inbred lines "H2139" and "H2149" with heterosis were selected, with a stable plant height of 80 - 100 cm, showing stable yield and stress resistance among years and in various ecological environments.

[0083] Result: Two excellent ultra-dwarf maize inbred lines, "H2139" and "H2149", were obtained. The average plant height was 92 cm, the ear height was 22 cm, the ear length was 15 cm, the number of kernels per ear was about 400, and the yield per unit area was 5.2 tons / ha.

[0084] In environments such as plains, hills, and mountains, the average seedling retention rate was 90%, the adult plant seed setting rate was 92%, and the lodging resistance rate was less than 5%.

[0085] Through precise EMS mutagenesis, haploid, and multi-ecological environment screening, an ultra-dwarf maize inbred line with stable plant height was successfully cultivated, shortening the breeding cycle by about 2 - 3 years and increasing the probability of the appearance of ultra-dwarf trait genes. The lower ear height and plant height significantly improved the lodging resistance ability, reducing natural disaster losses by about 20%.

[0086] Example 2 Experimental purpose: Use two excellent ultra-dwarf maize inbred lines, "H2139" and "H2149", for hybridization and combination to breed an ultra-dwarf maize variety with a plant height below 1.3 m.

[0087] Materials and methods: Parents: The female parent was "H2139" (selected in Example 1), and the male parent was another dwarf inbred line, "H2149" (selected in Example 1).

[0088] Hybridization: Artificial pollination hybridization was carried out in the winter of 2020 in the southern breeding base in Hainan to obtain F1 seeds.

[0089] Planting: Sown in Ningxia in April 2021 in spring, with normal field management, and the planting density was 82,500 plants / ha. Record the periods and quantities of field farming operations such as land preparation, sowing, fertilization, irrigation, spraying pesticides, and harvesting.

[0090] Molecular detection: Extract leaf DNA to detect the presence or absence of genes such as drought resistance.

[0091] Field investigation: Observe and record the growth periods, investigate plant traits such as plant height, ear height, and stem diameter, and conduct variety testing and yield measurement on ear and grain yield traits such as the number of ears, grain moisture content, ear length, ear diameter, bald tip length, number of rows per ear, number of grains per row, seed setting rate, 100-grain weight, and single-ear grain weight.

[0092] Disease resistance identification: Artificially inoculate to identify diseases such as leaf spot and stalk rot.

[0093] Variety propagation and seed production: While identifying, continue to identify and propagate the parent seeds and produce hybrid seeds.

[0094] Result: The average plant height is 128 cm, the ear height is 26 cm, the ear length is 17 cm, the number of grains per ear is 450, and the yield per unit area is 6.0 t / ha.

[0095] The resistance to leaf spot and stalk rot was identified under natural and inoculated conditions and showed moderate resistance.

[0096] The hybridization of two dwarf inbred lines combined with disease resistance screening significantly improved the stress resistance and yield stability of the variety. The drought adaptability was increased by 15%, and the disease resistance ability was enhanced by about 10%. Example 3 Experimental purpose: To test the ecological adaptability of ultra-dwarf maize varieties through multi-ecological environment tests.

[0097] Materials and methods: Materials: Ultra-dwarf maize variety "Yu'ai No. 1" Methods: In 2023 and 2024, 4 ecological environments were set up for testing, namely the temperate Yellow River irrigation area in Ningxia Plain (altitude 1000 m, soil pH 8.0, annual rainfall 200 mm), the temperate semi-arid hilly area in Ningxia (altitude 1300 m, soil pH 8.0, annual rainfall 200 mm, slope 5°-10°), the rain-fed area in the southern mountainous area of Ningxia (altitude 1800 m, soil pH 7.6, annual rainfall 400 mm), and the tropical area in Hainan (altitude 260 m). 0.2 hectares were planted at each location. Planting was carried out according to local maize production, and density tests of 12,000 and 15,000 plants per hectare were set up in Yongning, Ningxia. And the adaptability was identified by simulating extreme weather.

[0098] Results: For the ultra-dwarf maize variety "Yu'ai No. 1" in 4 ecological environments (average density 82,500 plants / ha), the average plant height was 121 cm, the ear height was 24 cm, the ear length was 16.5 cm, the number of grains per ear was 455, and the average yield was 5.1 t / ha. All traits showed excellent and stable performance. It was initially determined that when the planting density was 120,000 plants / ha in the Yellow River irrigation area of Ningxia, the plants, yield, and resistance showed the best performance.

[0099] The multi-point environmental test combined with the simulation and identification of extreme weather more accurately identified the ecological adaptability of maize varieties, providing a scientific basis for variety promotion. The test (experiment) showed that the ultra-dwarf maize variety "Yu'ai No. 1" had relatively strong environmental adaptability and resilience, and the promotion range could cover the maize planting areas across the country, with an economic benefit increase of about 5%. At the same time, expanding the maize planting environment could give rise to various agricultural production models, make up for problems such as insufficient feed for the development of animal husbandry, and also play the role of ecological restoration and protection.

[0100] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for breeding ultra-dwarf corn varieties, characterized in that: The following steps are involved: S0: The maize inbred line B73 was treated with EMS mutagenesis. The seeds were soaked in 3% and 0.5% EMS solutions for 5 hours in stages, followed by multiple generations of selfing and screening to obtain an inbred line with a stable plant height of 80-100 cm and an ear height of 20-30 cm; S1: Selecting a maize inbred line with a dwarf trait as a dwarf source donor, wherein the plant height of the donor is 60-80 cm; S2: Selecting a high-yield, high-quality, disease-resistant corn backbone inbred line as an improved recipient, wherein the plant height of the improved recipient is 150-180 cm; S3: artificially hybridizing the dwarf source donor with the improved recipient to generate the S0 generation; S4: self-pollinating the S0 generation to generate the S1 generation, and screening individuals with plant heights less than 100 cm in the S1 generation; S5: After the selected individuals are induced to double by haploid technology, they are self-pollinated and selected for 3-5 consecutive generations to stabilize agronomic yield traits; S6: Identify the ecological adaptability of the selected ultra-dwarf inbred lines in multiple environments, and select ultra-dwarf corn inbred lines with a stable plant height of 80-100 cm; F1: According to the above operation method, the parents with hybrid advantages are improved, and they are hybridized and matched. The ecological adaptability and / or yield trait tests of the hybrid combinations are carried out in multi-point environments, and ultra-dwarf corn hybrids with stable plant height below 130 cm and agronomic traits that meet production needs are bred.

2. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: The dwarf source donor is the corn inbred line "19M1130" obtained by EMS mutagenesis treatment.

3. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: The improved recipients are from two superior corn backbone inbred lines with opposite heterosis patterns.

4. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: In step S5, the screened individuals must also meet the inbred line breeding conditions of coordinated comprehensive agronomic traits, disease and insect resistance, and strong adaptability.

5. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: In step S5, during the continuous selfing and selection process, the ultra-dwarf trait is maintained while optimizing the plant, yield and stress resistance.

6. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: In step S6: F1, the multi-point environment includes plains, hills and arid areas.

7. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: The plant height of the ultra-dwarf corn inbred line is stabilized at 80-100 cm, and the plant height of the hybrid is stabilized at less than 130 cm, and the ultra-dwarf corn inbred line exhibits stable yield and stress resistance under various ecological environments.

8. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: It also includes multi-generation breeding and trait testing of the selected inbred lines to confirm the genetic stability and suitability for production needs of dwarfing, plant, yield traits and stress resistance adaptability.

9. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: The ear height of the super dwarf corn inbred line is 20-30 cm.

10. The method for breeding super dwarf corn varieties according to claim 1, characterized in that: Through multi-generational systematic selection and ecological adaptability screening, the wide adaptability and production application value of ultra-dwarf corn varieties are ensured.

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