Discussion on rapid selection of maize inbred lines

Zhang Junfang Dehui Zhang Ming was born in Haiqing and Haiyuan (Harbin Datian Fengyuan Agricultural Technology Development Co., Ltd.)

Tang Gui (Berry Research Institute of Heilongjiang Academy of Agricultural Sciences)

The promotion of corn hybrids has been in our country for decades. An excellent maize inbred line is the main material basis for hybrid use. The maize yield has been greatly improved. From the breeding point of view, the selection of inbred lines with high combining ability is the basic condition for breeding excellent hybrids. What method is used to quickly breed new inbred lines with high combining ability is a very prominent and realistic question before breeders. In conventional breeding, in order to speed up the stability of materials, breeders have brought the locally selected materials to Hainan for one generation to accelerate the stability of the materials in order to accelerate the selection of inbred lines and combinations. Since 1994, our company has planted the same breeding material in Hainan for two generations in winter, which has further accelerated the selection of inbred lines. Three seasons within a year, using this method of rapid cross-breeding, rapid breeding, and rapid identification, several batches of early-mature maize inbred lines containing newer germplasm resources at home and abroad have been selected, and several new hybrids have been approved and promoted. And there are many new combinations are participating in Heilongjiang province preliminary test, regional test, production test, now summarize the 15 years of practice as follows, for reference in the breeding industry colleagues and hope to give corrections.

1Technical route of one winter plus two generations of selection lines

Based on the existing heterosis theory, we use the existing local materials and combination frameworks, and introduce new and excellent materials that are late-maturing, high-combining, and disease-resistant at home and abroad as the source of change. Introduce the introduced new excellent germplasm hybrid into the local backbone inbred line, through self-segregation, strict selection, so that the selected new material retains the advantages and high combining ability of foreign germplasm, and makes it adaptable Sex and maturity meet the requirements of local early mating breeding. Generally, the first season is sown before October 5th, pollination ends in mid-November, and the harvest is completed at the end of December; the second season is sown before January 5th, pollination ends before March 10, and harvested in the middle and late April. After drying, threshing, planting and sub-packaging, returning to the local spring for planting in early May, each pollination season is equipped with basic materials, and the materials of each generation maintain continuity. While selfing, s4 or s3 was mixed with 4 to 5 local backbone inbred lines with excellent hybridization of the mixed pollen in the superior spike row and their basic materials, respectively. The hybrids are returned to local planting in the spring, and the test materials are used to evaluate the combining ability of the materials. According to the combining ability of the materials and their own agronomic traits, the retention or elimination of the newly selected materials is determined. Although this method is fast, the stability of inbred lines is carried out under different ecological conditions, so the focus of selection is slightly different from conventional selection. The materials are mainly selected in the first season of Hainan, the stability is mainly in the second season, and the local selection is strictly controlled by comprehensive selection. The following describes the different practices in the third season under different ecological conditions.

2 One winter plus two generations of specific practices

2.1 Sanya's first season ecological conditions and selection

The first season material growth time is from early October to the end of December. During this time, Hainan has high temperature and high humidity. Corn grows under strong light, high fertilizer, and sufficient water. Under short-day conditions, the growth period of nutrient growth and reproductive growth is longer. It is conducive to the development of corn. In addition to the influence of typhoons in individual years, corn grows under superior conditions, showing seedlings, strong plants, full ears, full grains, good ear development, dense green leaves, strong photosynthesis, most plants Live stalks are mature, and insects and rats are also harmless. Therefore, the selection of various traits should be strict, such as grain type, number of ear rows, grain size, etc. These traits are fully expressed, and can be selected according to the breeding goal of the breeder. Although the plant height, panicle position, number of leaves, and plant type have changed in the north and south, the correlation coefficient is relatively large and can be selected strictly. The reference materials for the growth period can be selected strictly. The selection of traits related to combining ability, such as various leaf diseases, firmness, ear stalk length, and bald tip, should also be strict. The relatively large changes in the north-south traits such as the compatibility of the material with male and female, the degree of ear abortion, the length of the fruit bract leaf, the root and stalk strength, etc. should be appropriately relaxed, and the seeding area and workload of the next season should be taken into account Affordability.

2.2 The ecological conditions and selection of the second quarter of Hainan

The second season's sowing and growing time is from early January to mid-April. The temperature in Sanya is from low to high. The seedling stage is similar to Heilongjiang conditions, but short-day sunshine and low light are more serious. The growth of maize is limited at the seedling stage, the pollination period begins with strong light and high temperature, the evaporation is large, the insects and diseases are common, and the growth is generally not as good as the first season. The plant height of the corn is reduced, the ear position is low, the filament development of the ear is not divided, the bald tip is serious, the ear is small, the grain is not full, and the interference of corn rust and insect pests makes the selection very difficult. Therefore, it is necessary to have as many varieties of ear rows as possible and pollination of multiple sets of plants to ensure that there is sufficient room for selection. This season, the selection of plant height, ear position, leaf spot and growth period should be strict. The selection of corn rust resistance, root stalk strength, firmness, bald tip, blind tip, and bract leaf length should be moderately relaxed, and yellow leaves, heavy purple seedlings, early withered plants, and malformed plants must be eliminated. On the basis of adhering to the above, the SO generation relaxes the selection. Sl and S2 should be strict, S3 and S4 should be properly reserved with more spike rows, and the selection in the row should be stricter. Generally, 3 to 5 spikes are selected. It is worth emphasizing that there are strict measures to prevent and control insect pests after emergence in this season. Spraying pesticides every 3 to 4 days, the types of pesticides should be changed frequently until the drug is stopped 15 days before harvest. This is a guarantee for the success of this season One of the measures is to prevent rust, rodent and human and animal hazards, and create favorable conditions for normal selection.

2.3 Important points for returning to local selection in spring

Planting and selection can be carried out in accordance with the breeding goals in the spring, but it should be noted that these materials are completely selected under the conditions of different places in Hainan. After returning to the local area, they must be selected and carefully selected. In the selection process, the unqualified plants or traits should be resolutely eliminated to reduce the workload of the next Southern Propaganda and enhance the accuracy of selection. The first is the selection of the material's adaptability to low temperature, drought and black soil in the north. For those seedlings that grow slowly, the seedlings do not grow purple, the bottom leaves are dry, and the plants at the later stage are tall and not suitable for low temperature, drought and high latitudes. Line firmly eliminated. Secondly, strengthen the choice of materials against silk smut, large and small gray spots. In Hainan, high temperature emerges quickly, and it does not cause disease without pathogens, so it cannot be selected. Therefore, it is best to inoculate smut strains when the materials return to the local ecological conditions. Large and small spot disease and gray spot disease should be selected strictly. The third is to strengthen the selection of growth period and root strength. Materials that are sensitive to low temperature and long daylight should be eliminated as far as possible. The short-term strong winds formed by the strong summer convective weather in the north have certain requirements on the root and stalk strength of the materials and hybrids. The selection strength of the materials that come back from the south propagation should be strengthened to resist falling, fold resistance and greenness in the later period. , Materials that are too long between the nodes, dehydrate the stem too fast, plant too high, and have too many leaves should be eliminated. The above points are all intuitive choices on the agronomics, stress resistance and maturity of the materials, and the comprehensive selection of the material combining ability through test cross species, and then decide on the choice of materials and evaluation of the use value.

3 Analysis of the advantages of the selection method of the two generations of Hainan plus two generations (hereinafter referred to as 1 plus 2 selection method) in winter

The 1 plus 2 line selection method can significantly speed up the selection progress of maize inbred lines, the material stabilization time is shortened, and the breeding speed is accelerated.

The 1 plus 2 selection method is flexible and can be used to introduce new germplasm resources at home and abroad (sometimes can be directly imported by pollen hybridization) at any time during the southern propagation period, and can be sown and hybridized to form new basic seeds at any time. Breeders ’new ideas and new ideas can be implemented immediately, with great flexibility and initiative. Also, because the material is stable for a long time, it can discover the advantages and disadvantages in time, adjust the breeding direction and improve measures.

The 1 plus 2 selection method has strong synchronization. As the stability period of this method is shortened, it can accelerate the use of the latest and best germplasm resources or hybridization models at home and abroad, so that the new combinations of selected materials belong to the latest hybrid combination model on the market, which enhances competitiveness. It can make full use of effective breeding time, save breeding funds, save manpower and material resources, and has no conflict with the working time of conventional southern propagation, does not hinder conventional southern propagation activities, enhance the efficiency and guarantee factor of southern propagation.

4 1 plus 2 selection system limitation analysis

The number of birth days of the material is very restrictive to this method. The annual available time of Nanfan in winter is from the beginning of October to the end of April. About 210d. Therefore, Hainan ’s materials for each season cannot exceed 100 days in the field. According to Hainan ’s land situation, costs, workload and other factors, the second season of Hainan should mainly focus on the reorganization of basic materials and the selection of self-crossing and s1, s2, and s3 materials. The s4 generation is put into the local and Hainan season for sowing and testing.

The 1 plus 2 system selection method also has certain requirements for the southern propagation sites in winter.

Point in the coastal zone between Sanya and Chongpo Town. These areas have high temperatures, sufficient water sources, and light natural disasters, and are suitable for 1 plus 2 selection.

The 1 plus 2 system selection method also has stricter requirements for the system selection operator. Breeders are required to have a high degree of responsibility and patience in Hainan. They must have work experience in Nanfang and return to the local area to participate in the continuous follow-up selection for many years. Frequent replacement of operators will affect the choice and fail to meet expectations. effect.

The 1 plus 2 selection system method is largely a remote selection that is free from local ecological conditions. There are some beneficial agronomic traits that can be selected intuitively and retained, but the material is resistant to physiological stress, large and small spot disease, gray spot disease, Smut and lodging resistance can only be selected by the evolutionary generation that accounts for 1/3 of the local population. It is best to choose under the ecological conditions that artificially create high selection pressure (such as artificial inoculation of large spot disease, smut, etc.) The selected materials meet local breeding goals and disease resistance requirements.

5 Summary and Discussion

The selection of three generations within one year is very effective for quickly stabilizing new maize inbred lines and improving breeding efficiency. However, most breeding units are difficult to implement this rapid breeding method due to many factors such as human resources, material resources, financial resources, resources, and systems. In addition, the limiting factor for quick results is not only the speed of selection of new materials, but also the speed limit of only one local combination test per year. How to accelerate the selection of new materials and simultaneously accelerate the pace of combination identification tests It is an indispensable supporting measure to accelerate the breeding speed by making material selection and experiment synchronously.

A Foot File is a file which is specifically designed to be used on the feet. Foot files are used to remove calluses and smooth the skin of the feet, and some people regard them as an important part of foot care. Regular use of a foot file can help to keep the feet smooth and pleasant, and it can reduce discomfort from oversized calluses.

Rough foot files can be made from metal or sandpaper. Metal foot files are used to essentially grate calluses away, and they require a delicate touch to ensure that excessive tissue is not removed from the foot. Sandpaper or emery files require less care, but they take up more time, as the course material works more slowly than a microplaning foot file. Fine files made from textured glass or very fine emery paper are designed for finishing touches only, as they are far too fine for serious calluses.

Foot File

Pedicure Tools,Foot File,Foot Files For Feet,Stainless Steel Foot File,Dead Skin Remover,Remove Dead Skin From Feet

YANGJIANG HUIHUI BEAUTY TOOLS CO.,LTD , https://www.yjhuihuibeauty.com