The history of breeding for blast resistance in China can be roughly divided into four stages according to the evolution of breeding methods and the use of resistance sources: 1. At the breeding stage of the system, the most important method is the systematic breeding of individual plants using natural variation (or pure breeding). Mostly use local varieties as a source of resistance. 2. System breeding and cross breeding stage, this stage is characterized by systematic breeding and crossbreeding and breeding, professional institutions and the people breeding in parallel, the source of resistance used for local varieties and foreign sources of resistance. 3. Crossbreeding is the main stage, with multiple pathways in parallel, the outstanding achievement is the promotion and application of hybrid rice in a large area, and the source of resistance is mainly the IP series introduced by foreign countries, especially international rice. Another prominent feature is the use of japonica rice. Crossbred to develop high-quality, multi-resistance and higher-yield varieties. 4. With the combination of conventional breeding and new technology breeding, with the continuous development of science and technology, the breeding technology will be continuously improved and updated. In conventional breeding, the utilization of heterosis will change from "three-line law" to "second-line law" or "one-line law." The heterosis of this species can be promoted through breeding of a wide range of affinitive varieties and the use of anther culture techniques in breeding practice. The resistance to warts will be combined with high quality, high yield, resistance to other diseases and pests to constitute new and higher breeding objectives. In the new technology breeding, anther culture technology has been used in the breeding of common varieties and hybrid rice, and great progress has been made.
Disease-resistant breeding new technology refers to the application of biotechnology in disease-resistant breeding, with the following characteristics: 1. At the level of tissues, cells, or sub-cellular levels (including the nucleus, organelles), especially at the genetic level, find ways to transform the nature of the organism. 2. It may be possible to enhance the self-consciousness of directional transformation of biological organisms, especially at the molecular level, and it is possible to redirect organisms. 3. Greatly expand the scope of species hybridization and increase the frequency of species variation. 4. The seed can be quickly propagated to accelerate the homozygosity of hybrid offspring and increase the selection efficiency. Disease-resistant breeding techniques are currently widely used in the following ways:
1, embryo and ovule culture
Embryonic culture or ovary culture is the fertilization of distant plants and the degenerated embryos or ovaries are removed from immature seeds and placed in vitro. In-vitro culture and ovule culture are fertilization in vitro. That is, under sterile conditions, ovules are extracted from the ovary, placed on a culture stem containing various nutrients, and then pre-collected, sterilized pollen is collected. Granted on ovules for fertilization. After a few days, the fertilized ovules swell and the ovules are transferred to a dedicated culture stem until they grow into seedlings. The purpose of applying this technology is to obtain distant hybrid seeds that cannot be obtained by conventional methods, and it is of great significance to fight against disease breeding. It makes it possible to use the genes for resistance to heterosis rot. Some plants that are difficult to grow in anther culture, male sterile plants, and some pollen plants exhibit obvious ploidy variation and trait variation. Ovary or ovule culture is the main way to obtain haploids.
2, anther culture
It is an effective way to obtain monophyletic plants. It has been successfully applied to the practice of plant breeding. The chromosomes of haploids are doubled and the progenies are rapidly purified to shorten the breeding period. In addition, the diploid parent plants The origin, genetic composition and many other issues are also of great significance. Compared with conventional breeding, flower-cultivated species have other characteristics in addition to the shortened period of time: First, the selection efficiency is improved, and the natural doubling of haploids homogenizes the homozygous one-fold body, and the inheritance traits of offspring are rapidly and stably conducive to disease resistance. Identification and selection of types and susceptible types. Second, when the goal of the breeding target is relatively small (about 10), when the target gene position of most gene loci is stable, flower breeding species are more effective than conventional breeding. The reason for this is that cultivars of flowers can make all kinds of gametes more fully manifest at the plant level, avoid the epistatic effect of dominant genes as recessive genes, show the traits controlled by recessive genes, and appear pure The probability of the target genotype is 1.2%, which is much higher than that of conventional breeding. Third, the population (or system size) selected by the offspring of the cultivar is one-fifth of that of conventional breeding. Fourth, the medicinal source of anther culture generally comes from the individual selected, not the individual. If the double-resistance individual is used as a drug source, the chance of recombination between the parental genomes of the homozygous genotypes of the offspring of anther culture is less than that of self-recombination. If the target is linked to genes of undesirable traits, the probability of occurrence of the genotype of interest It will be reduced. At this time, anther culture breeding method can be used to break the bad linkage to accumulate superior genes of multiple parents. In addition, the cultivation ability of rice anthers varies depending on the type of rice. In general, indica rice has the highest induction rate and differentiation rate. Indica rice was the second and indica and wild rice were the lowest.
3, cell screening
The use of toxins produced by plant pathogens or other disease-resistant mutants (or variants) of similarly screened plants is a new way of artificially creating new sources of resistance and improving disease resistance. The hyphae of rice blast fungus are covered on the medium and it is difficult to distinguish between disease-resistant and susceptible calli. Therefore, only the toxins or analogues produced by pathogens are used for resistance screening. Cell screening must also be combined with field resistance in order for cells to lose their good traits while obtaining the desired traits.
4, cell fusion
Cell fusion is a new technique for obtaining somatic hybrids. Overcome the difficulties of distant sexual hybridization, break the boundaries of species classification, expand the scope of the use of germplasm resources, and create a way to introduce useful traits such as disease resistance and cold resistance from distant plants. One is to treat a heterologous biomass with a target gene with X-rays or X-rays to inactivate part or most of its nuclear DNA, and then fuse with healthy protoplasts, and choose to have a purpose from the regenerated plants. Individuals of the gene can obtain target species through backcrossing. The second is to make the donor haploid protoplasts in the pollen tetramer and then fuse with the diploid receptor protoplasts. At this time, the diploid receptor DNA also plays a leading role. This improves the ability of the plant to re-differentiate. When a triploid somatic hybrid is obtained, it is returned to the diploid level by backcrossing to increase fertility and introduce genes. Cell fusion is also applied to the direct transduction of heterologous cytoplasm, and the original protoplast of cytoplasmic male sterile line A is treated with radiation using a cell fusion technique. The nuclear DNA was completely inactivated, and the protoplasts of the transformed variety B were treated with a chemical agent. The cytoplasm is inactivated, and then the two are fused, and the regenerated plants obtained by the fused cells are the cytoplasm with male sterile line A and the male sterility line with the nucleus of the transgenic line B, such that the sterile line Transferring one year to success. The somatic hybrids obtained are also called cytoplasmic hybrids. This method still cannot avoid blindness and is far more accurate than genetic engineering. Suitable for transfer of agronomic traits for multigene control.
5. Gene recombination
The technology is to extract the target gene by chemical or biological methods. After the transformation such as trimming and splicing, the foreign gene is inserted into the recipient cell after the introduction of the vector or chemical substance into the recipient cell and can be in the recipient cell. Get expression. And can be stably inherited, the steps of gene recombination include the extraction and modification of target genes, the construction of gene carriers, the introduction of genes, the cultivation of transgenic plant cells, the selection of plant cells after gene transformation and the identification of transgenic plants, the transfer of target genes. The method is divided into two types: the carrier method and the direct method. Vector method is the most commonly used method at present. The original vector is the original plasmid in Agrobacterium tumefaciens. There is a piece of DNA on the original plasmid, ie T-DNA. When Agrobacterium tumefaciens infects plant cells, T-DNA can be inserted into the plant. In the genome of the cell, and can be stably inherited from the cells isolated thereafter, the advantage of the vector method is simple operation and stable genetic expression, but these vectors are only applicable to dicotyledonous plant genes. The direct method is the direct introduction of the gene of interest into the cells of human receptors. It includes chemical transformation methods using protoplasts as receptors, such as PEG (polydiethanol), which fuses heterologous protoplasm together using polydiethanol as the fusion agent. That is, the protoplasm fusion method. Calcium Phosphate-PEG, Improved Protoplast Fusion Method. The electroporation puncture method uses a very high voltage to quickly open a part of the cell membrane to allow foreign DNA to enter the protoplast. Microinjection is the direct injection of an injection needle into a cell. It has the following advantages. First, a cell block that can use both protoplasts as receptors and cells or cells as exogenous genes can be used as an exogenous gene. body. The second is to select cells with high recombination rates for gene transfer. The third reason is that the gene transfer is more reliable and reliable, and there is no need to screen for genetic transformation. Fourth, not only genes can be introduced but also viruses, organelles, etc. can be introduced. Later, a gene transfer method was established at the level of plant living or plant organs.
The source of resistance is the material basis of disease-resistance breeding. Whether it can open up a new situation of disease-resistant breeding, and generally raise the level of resistance of crops, depends mainly on whether there is sufficient anti-source parent. And whether reasonable use can be made of resistant parents, genetic sources are derived from disease-resistant mutants produced by local breeds, foreign varieties, distant margins, wild species, and artificial mutations. At the same time pay attention to the relationship between resistance and other traits. Select varieties that have both resistance to rickets and other good traits.
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