CN111528087A - Method for breeding high-combining ability and excellent germplasm of corn - Google Patents

Abstract

The invention belongs to the technical field of breeding, and in particular relates to a method for selecting and breeding high-combining ability and excellent germplasm of maize. First, an initial population is constructed by collecting excellent inbred lines, genotype identification and heterotic group division are performed, and a specific hybrid is selected as a test Evaluate the combining ability performance of each material in the initial population, and establish a genome-wide selection model; then in the heterotic group, according to the combining ability evaluation results, gradually select and breed to obtain excellent individual plants and further obtain homozygous inbred lines; Finally, the obtained homozygous inbred lines are genotyped, and their combining ability is predicted according to the genome-wide selection model, and the homozygous inbred lines with high combining ability estimates are retained, that is, high combining ability elite varieties are obtained. quality. The method of the invention has high breeding efficiency and short breeding period, and can speed up the selection and breeding process of excellent germplasm.

Description

A method for breeding high-combining ability and high-quality maize germplasm

technical field

The invention belongs to the technical field of breeding, and in particular relates to a method for breeding high-combining ability and excellent germplasm of maize.

Background technique

As the world's largest grain and feed crop, corn has important application value and status in food, feed and bioenergy, and breeding good commercial corn hybrids is crucial to improving yield.

Traditional and commonly used inbred line selection methods include recurrent selection, pedigree selection and backcross selection, but these methods often have the following problems: 1. Long breeding cycle: the performance of inbred line combining ability is based on the performance of its hybrid progeny. In addition, the line selection material needs to be selfed for multiple generations to form a pure line before it can be used for combining hybrids, so it often requires a long breeding cycle; 2. The late breeding cost is high: in the process of inbred line breeding , a large number of inbred lines need to be tested for combining ability in the later stage, and the cost of testing will increase greatly with the increase of the number of tested species and identification sites, and it is time-consuming and labor-intensive; 3. Traditional population improvement usually does not combine molecules Identification techniques and modern biostatistics provide population structure analysis and control of breeding populations, and screening for population-specific molecular markers is often not systematically performed.

Furthermore, genome-wide selection (GS) strategies are an emerging method for efficient prediction of complex quantitative traits using molecular markers covering the entire genome. With the development of high-throughput and low-cost genotype identification technology, GS technology can significantly reduce the cost of phenotype identification in the later stage of breeding, so it has broad application prospects. However, genome-wide selection strategies are not applied to the prediction of combining ability performance of inbred lines in existing breeding procedures, and historical breeding data cannot be used efficiently.

CN109536629A mentioned a method for rapid improvement of breeding population by using whole genome selection model and combining ability detection, but it only performed one mixed pollination to obtain a new population after selecting excellent plants for the training population, and did not perform phenotype selection or phenotype selection on the new population. High-density planting selection, and direct use to induce doubling to produce DH lines. In addition, the DH lines selected by GS need to be tested for combining ability and then screened out excellent individual plants for hybrid hybrids. Therefore, there are still some shortcomings in improving breeding efficiency and controlling breeding costs.

In view of this, it is urgent to apply a variety of modern breeding techniques to improve the breeding efficiency.

SUMMARY OF THE INVENTION

Aiming at the problems of long cycle, high testing and matching cost in late breeding, low efficiency, low genetic gain, etc. existing in the breeding technology in the prior art, the present invention provides a rapid and efficient breeding method for high-combining ability and excellent germplasm of maize. method.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A method for breeding high-combining ability and excellent germplasm of maize, comprising the following steps:

A) Collect excellent inbred lines to construct an initial population, and perform genotype identification and heterotic group division; select four inbred lines unrelated to the initial population material to assemble two hybrids, and use the hybrids as test species, The initial population is evaluated for combining ability, and a genome-wide selection model is established based on genotype data, combining ability identification results and heterotic group-specific combining ability-related sites;

B) in the described heterotic group, select the inbred line with excellent performance according to the evaluation result of combining ability, obtain the individual plant with good performance through the inbred line selection method, pick the seeds and carry out step C);

C) carrying out high-density planting of the seeds obtained in step B), selecting individual plants with excellent performance, and further obtaining homozygous inbred lines;

D) Perform genotype identification on the obtained homozygous inbred line, and predict its combining ability according to the genome-wide selection model, and retain the homozygous inbred line with high combining ability estimated value, that is, high combining ability and excellent germplasm.

The present invention finds that the above-mentioned method can greatly improve the breeding efficiency, shorten the breeding cycle and improve the genetic gain.

The excellent inbred lines described in step A) of the present invention can be the parent materials of single-cross varieties with a promotion area exceeding 10 million mu, deciphered inbred lines, inbred lines selected by breeders, and the like.

Preferably, in step A), a high-density SNP chip is used to identify the genotype; preferably, the high-density SNP chip has more than 10,000 SNP markers.

In step A) of the present invention, the cooperating force may be a general cooperating force (GCA) and/or a special cooperating force. Because the performance of hybrids is mainly determined by GCA effect, and GCA effect value is an important index to evaluate the excellent characteristics of inbred lines. Therefore, in the present invention, it is more preferable that the fitting force is a general fitting force.

Preferably, after the genome-wide selection model is built, cross-validation is performed to test the reliability and accuracy of the model.

Preferably, the initial population is divided into two heterotic populations, SS subpopulation and NSS subpopulation, respectively.

In step B) of the present invention, the inbred line selection method may be one of recurrent selection, pedigree selection or backcross selection. Preferably, the inbred line selection method is recurrent selection, which in the context of the present invention is combined with a variety of molecular marker aids, which can efficiently and rapidly aggregate favorable alleles, and the purpose is to screen out breeding materials with excellent combining ability. .

Preferably, in step B), when the inbred line breeding method is recurrent selection, the inbred lines with good performance are mixed pollination, and the individual plants with good performance are selected for the next round of mixed pollination, repeating After performing multiple times (at least twice), a single plant with excellent performance is obtained, and the seeds are picked to perform step C).

Preferably, when the inbred line breeding method is recurrent selection, new elite germplasm resources are added in any round, and the genotype and combining ability results of the initial population and the new germplasm are integrated to re-establish the whole genome Models are selected to expand the genetic basis of breeding populations.

Preferably, in step B), the individual plant with excellent performance refers to an individual plant with early flowering, good resistance and high yield.

Preferably, in step C), the homozygous inbred line (also called DH line at this time) is obtained by double haploid technique.

Double haploid (DH) technology is a typical representative of the development of modern breeding technology, so that the generation of pure lines does not require traditional self-pollination methods, but can obtain homozygous inbred lines after 2 generations. Compared with the traditional self-breeding which requires 6-8 generations, this method has obvious technical advantages of speeding up the breeding process. At present, DH technology has become an important technical means for seed companies to create inbred lines. The integration of DH technology and GS strategy can effectively solve the problems of rapid creation of inbred lines and large-scale phenotype identification and screening, which can further accelerate the breeding process and greatly improve genetic gain.

Preferably, in step C), the individual plant with excellent performance refers to an excellent individual plant with dense tolerance, good resistance and coordinated flowering period.

In some embodiments, the number of homozygous inbred lines obtained in step C) is more than 1000.

In addition, in the present invention, "excellent individual plants" generally refer to the top 5-10% of the individual plants, and "homozygous inbred lines with high estimated combining ability" generally refer to the top 10-15% of the homozygous estimated GCA values. Inbred lines, those in the art can adjust them according to needs.

Those skilled in the art can combine the above preferred solutions to obtain preferred embodiments of the present invention.

The beneficial effects of the present invention are as follows:

The method of the invention directly conducts molecular identification and combining ability analysis on a single heterotic group and establishes a genome-wide selection model, which can further break the unfavorable linkage, aggregate favorable alleles, and increase the frequency of favorable alleles in the population, so that the heterozygous The swarm direction is controllable, and the yield of excellent DH lines is improved. Moreover, the DH line does not need to be tested and matched at the later stage of breeding, which can effectively reduce the breeding cost and workload and improve the breeding efficiency.

Especially when DH lines are evaluated and screened for GCA effect according to the whole genome selection strategy, the breeding cycle can be shortened at least and the cost of later testing and matching can be reduced by more than half compared with the traditional breeding process. In addition, combined with the recurrent selection method, favorable alleles related to GCA can be aggregated quickly and efficiently, and the selection process of elite germplasm can be accelerated. At the same time, in this method, multiple inbred lines can be selected for breeding, and new germplasm resources can be added during the breeding period to broaden the genetic basis of the initial population and increase the aggregation strength and effect of excellent genes. Breeding projects have long carried out population improvement and breeding of inbred lines.

Detailed ways

The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

If no specific technique or condition is indicated in the examples, the technique or condition described in the literature in the field or the product specification is used. The reagents or instruments used without the manufacturer's indication are conventional products that can be purchased through regular channels.

Example 1

The present embodiment takes maize as an example, and provides a kind of method for rapid and efficient breeding of high-combining ability and excellent germplasm of maize, comprising the following steps:

1. Collect high-quality maize inbred lines, including parents of large-scale promotion varieties, decrypted inbred lines in the United States, and inbred lines selected by breeders, and divide heterotic groups according to pedigree and molecular markers. The collected germplasm was divided into two heterogenous groups, SS group: Ye 478, Tie 7922, Ye 107, Zheng 58, Liao 5114, etc. NSS group: Mo17, Jing 92, WK798-1, Chang 7-2, Ji 444 Wait. Taking the SS subpopulation as an example, two hybrids of inbred lines unrelated to the initial population were selected as the test species for testing and mating, so as to ensure that the testing and mating results were more accurate and reliable. The 20K SNP chip here is used for genotype identification of inbred line materials;

2. Combined with molecular marker data and combining ability estimation results, a genome-wide selection model was established, and cross-validation was performed, and the prediction accuracy reached 58%;

3. Carry out mixed pollination for the SS sub-population of the initial population, and carry out the work of recurrent selection. In each round, the growth period, plant height, ear position, resistance performance and yield of individual plants were investigated. Select the top 10% of individual plants ranked by comprehensive traits and enter the next round after mixed pollination, and so on for 2 rounds;

4. After the second round of mixed pollination, select the top 5% individual plants with early flowering, good resistance and high yield, a total of 400 plants, and select some seeds of the selected materials for high-density planting (10,000-12,000 plants/mu), and in each Select 2-3 individual plants with early flowering stage and good resistance in one ear row for self-pollination to obtain 1000 self-inbred ear;

5. The seeds after self-harvest are planted at high density (10,000-12,000 plants/mu), and 1-2 individual plants with good early flowering resistance in the panicle row are selected for haploid induction, and then according to chemical doubling and tissue culture. The method produces a large number of DH lines (over 2000 in total);

6. Use the 20K SNP chip to identify the genotype of the DH line, predict the estimated GCA value of the DH line according to the established genome-wide selection model for general combining ability (GCA), and select the top 10% DH with the estimated GCA value by comparison Tie.

Results 200 DH lines with high estimated GCA values were obtained from the SS subpopulation. At this time, 10 representative lines were selected from the NSS subpopulation and combined with the DH lines derived from the SS subpopulation, and excellent hybrids were selected and finally confirmed. 46 DH lines with excellent performance.

It can be seen from the results that compared with the traditional recurrent selection breeding process (population improvement-inbred line selection-testing-matching-combined hybrids-field test), the breeding cycle can be shortened from 9 years to 5.5 years, which can also be effective. Reduce the cost of testing and matching in the later stage of breeding.

Example 2

The present embodiment provides a method for quickly and efficiently breeding high-combining ability and high-quality corn germplasm. The difference from Example 1 is that the selected high-quality individual plant in step 3 enters the subsequent cycle selection program, and a total of 6 rounds of selection are performed. Further accumulation of favorable alleles.

Results After 6 rounds of selection of superior plants for mixed pollination, the frequency of favorable alleles in the population can be increased, the dominant genes can be aggregated, and the probability of breeding superior maize inbred lines can be increased. Therefore, the improved population was better than the initial population in the performance of target traits, and the 58 DH lines bred showed high combining ability, early maturity and density tolerance, and had excellent agronomic characters.

It can be seen from the results that compared with the traditional recurrent selection repeated 1-2 times, multiple rounds of selection (5-6 rounds or more) will be more helpful to break the linkage between unfavorable alleles and favorable alleles. Breeding efficiency of inbred lines, so as to give full play to the technical advantages of genome-wide selection, and predict and select molecular markers.

Example 3

This example provides a method for quickly and efficiently breeding high-combining ability and high-quality maize germplasm. The difference from Example 1 is that: after 2 rounds of mixed pollination, new germplasm of the same heterotic group as the initial population is added to expand the breeding population Based on the genetic basis, the whole-genome selection model was re-established for subsequent prediction of GCA effect of DH lines; then proceed to steps 2-6.

The new germplasms added in this example are European early durum and American Iodent. In actual operation, the parents of other market main varieties can also be added to the method of the present invention as new germplasms.

As a result, the size of the initial population (that is, the training population) was increased and historical data was accumulated, which was beneficial to improve the accuracy of genome-wide selection and prediction accuracy. Furthermore, the cross-validation prediction accuracy improves to over 65%.

It can be seen from the results that compared with Example 1, the fitting degree of the statistical model and the prediction accuracy of the breeding population can be effectively improved, thereby improving the selection efficiency of the high combining ability DH line, and can carry out long-term genetic improvement for breeding materials. .

Although the present invention has been described in detail above with general description and specific embodiments, some modifications or improvements can be made on the basis of the present invention, which will be obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention fall within the scope of the claimed protection of the present invention.

Claims (10)

1. A method for breeding high-combining ability and excellent germplasm of corn is characterized by comprising the following steps:

A) collecting excellent inbred lines to construct an initial population, and carrying out genotype identification and heterosis population division; selecting four inbred lines irrelevant to the material of an initial population to combine two hybrids, using the hybrids as test seeds, evaluating the combining ability of the initial population, and establishing a whole genome selection model by combining genotype data, combining the combining ability identification result and the heterosis population specific combining ability related sites;

B) in the heterosis group, selecting an inbred line with excellent performance according to the combining ability evaluation result, obtaining a single plant with excellent performance by an inbred line breeding method, and selecting seeds to carry out the step C);

C) high-density planting the seeds obtained in the step B), selecting individual plants with excellent performance, and further obtaining a homozygous inbred line;

D) and (3) carrying out genotype identification on the obtained homozygous inbred line, predicting the combining ability of the homozygous inbred line according to the whole genome selection model, and reserving the homozygous inbred line with high combining ability estimation value to obtain the excellent germplasm with high combining ability.

2. The method according to claim 1, wherein in step a), the genotyping is performed using a high-density SNP chip; the number of SNP markers of the high-density SNP chip is preferably 10,000 or more.

3. The method according to claim 1 or 2, wherein in step a), the mating force is a general mating force.

4. The method according to any one of claims 1 to 3, wherein in step A) the initial population is divided into two heterosis populations, respectively an SS population and an NSS population.

5. The method according to any one of claims 1 to 4, wherein in the step B), the inbred line breeding method is recurrent selection.

6. The method as claimed in claim 5, wherein in step B), when the inbred line breeding method is recurrent selection, the inbred line with excellent performance is subjected to mixed pollination, the individual plant with excellent performance is selected for the next round of mixed pollination, after repeated times, the individual plant with excellent performance is obtained, and seeds are selected for step C).

7. The method according to claim 5 or 6, wherein when the inbred line breeding method is recurrent selection, new excellent germplasm resources are added in any round, and the genotype and combining ability results of the initial population and the new germplasm are integrated to reestablish a whole genome selection model.

8. The method according to any one of claims 1 to 7, wherein the individuals with excellent performance in step B) refer to individuals with early flowering stage, good resistance and high yield.

9. The method according to any one of claims 1 to 8, wherein in step C), the homozygous inbred line is obtained by a doubled haploid technique.

10. The method according to any one of claims 1 to 9, wherein the individuals with excellent performance in step C) are excellent individuals with density tolerance, good resistance and coordinated flowering period.