Flower World: Chrysanthemum Variety Improvement —— From Cross Breeding to Biotechnology Application

Chrysanthemum belongs to Compositae, with about 100 to 200 species, which is a perennial herb. It is mainly distributed in Asia and continental Europe in the northern hemisphere, and a few species are distributed in South Africa.

Chrysanthemum originated in China and is one of the traditional famous flowers in China. It has been cultivated for 3000 years. Later, it spread to Japan, Europe in the17th century and America in the19th century. In modern times, Europe, America and Japan constantly improved and bred chrysanthemum varieties. In addition to actively introducing chrysanthemum varieties from all over the world as seed sources, traditional cross breeding and new technologies such as mutation breeding and gene transfer have been adopted. Therefore, new varieties appear constantly, and the number increases sharply, reaching thousands at present. Due to the progress of breeding technology, the understanding of chrysanthemum ecological habits and the continuous research and improvement of cultivation techniques, chrysanthemum has gradually changed from traditional cultivation to exquisite cultivation in facilities or greenhouses.

Chrysanthemum is one of the three major flowers in Europe and America, and it is the most important cut flower crop in China, Taiwan Province and Japan. Chrysanthemum has become an economically cultivated flower because of its long vase life, many colors, easy adjustment of production period and year-round cultivation. In addition to cut flowers, chrysanthemum can also be used as potted flowers or bedding plants, which is a widely used flower.

Chrysanthemum is the largest cut flower crop in China Taiwan Province Province over the years, with an annual output of more than 300 million plants, covering an area of 1.600 hectares. In addition to supplying the domestic market, it is also exported to Japan, Hong Kong and Southeast Asia, and once had an export performance of tens of millions of pieces a year. Although there are many varieties of chrysanthemum cultivated in this province at present, they are all imported from abroad, and there are no excellent varieties suitable for subtropical climate cultivation in Taiwan Province Province, so that under the pressure of fierce international competition, the export volume has been declining in recent years. In recent years, variety patents have been paid more and more attention. With China's entry into the World Trade Organization and its agriculture stepping onto the international stage, it is imperative to cultivate new native chrysanthemum varieties for the sustainable development of chrysanthemum industry in China.

Growth and flowering habits

The result of chrysanthemum cross breeding and selection is mainly autumn chrysanthemum that blooms in autumn and winter. Except for special varieties with heat or cold tolerance, the suitable growth temperature of most varieties is between 10 ~ 30℃. In nature, chrysanthemums have different growth patterns due to the change of seasonal climate. For example, after flowering, chrysanthemums will form a cluster state when they enter the low-temperature climate in winter, but after breaking dormancy through low-temperature vernalization, they will enter a young state, the internodes will become longer, the number of leaves will gradually increase, and then they will enter the photosensitive period. At this time, chrysanthemum can regulate flower bud differentiation and even blossom by controlling the day length. If they stay in long sunshine, they will not bloom or delay flowering.

Chrysanthemum is a short-day plant. In autumn and winter, the sunshine time becomes shorter, and flower buds will differentiate and bloom under natural conditions. In commercial cultivation, chrysanthemum is often used for artificial lighting at night to inhibit the formation of flower buds and delay flowering; Or use a dark curtain to shade the light for a short time, so as to advance the flowering period and achieve the purpose of annual cultivation. However, due to the hot summer in Taiwan Province Province, China, there is no short-day cultivation mode.

Temperature and day length will not only affect the flowering habit of chrysanthemum, but also affect the characteristics of flowering day length, flower type and inflorescence. At present, the cultivated chrysanthemum is a hybrid of many parents for many years, and the conditions such as temperature and sunshine length required for growth are very different. It is necessary to do field observation tests to understand its growth and flowering habits.

Most chrysanthemum varieties in Taiwan Province Province of China were introduced and planted by farmers themselves. According to different responses to photoperiod, for example, varieties that can bloom in a short time of six to eleven weeks belong to early-maturing varieties; The varieties that need short sunshine from 12 to 15 weeks are late-maturing varieties; Generally, commercial varieties are mainly from nine to eleven weeks.

Because the nursery management and cultivation technology of chrysanthemum industry have gradually matured, diversified varieties can be used for rotation to realize annual cultivation and production and meet the needs of consumption. However, for many years, the varieties of chrysanthemum planted in Taiwan Province Province of China were all imported from abroad, and there was a lack of excellent varieties suitable for local cultivation. In recent years, the international community has paid more and more attention to the protection of agricultural intellectual property rights and the rights and interests of new varieties, and it will be more and more strict to obtain new varieties from abroad in the future. In view of this, Taichung Agricultural Reform Farm has actively invested in the research and development of new chrysanthemum varieties in recent years. In addition to the traditional hybrid breeding of excellent parents, radiation is also used for mutation breeding to increase genetic variation, and at the same time, foreign genes are transformed to develop new varieties.

New variety development

There are many methods for breeding new chrysanthemum varieties, such as traditional cross breeding, natural bud mutation selection, radiation or chemical agent mutation breeding, somatic cell variation, protoplast culture and biotechnology gene transfer. Because chrysanthemum is one of the three largest cut flowers in the world, in order to seize the opportunity of this vast market, various research institutions and breeding companies have made every effort to develop new varieties of chrysanthemum.

Traditional hybrid breeding is the most basic method to select different genotypes of parent combinations, and it is the most widely used breeding method in chrysanthemum improvement. Chrysanthemum cross breeding often needs to cultivate a large number of offspring to increase the chances of selecting offspring with the best characteristics of parents. One of the hybrid parents should be improved, and the other should have excellent characteristics that the improved parents lack. The selection principles of parents are: parents that meet the target flower pattern; Parents who meet the target color; The flowering period is early and late, and the offspring of early varieties usually produce more early offspring, while most late varieties produce intermediate offspring, some are early and some are late offspring; For varieties with few petal types, few petals and few parental petals, most offspring have few petals. If you want to choose double flowers, at least one parent must be a double flower variety.

For example, chrysanthemum varieties suitable for annual cultivation should have the characteristics as close as possible to the ideal genetic type: strong terminal bud advantage in vegetative growth period; The terminal buds and lateral buds can quickly differentiate into flower buds in a short time; Under the condition of long sunshine, the leaf differentiation rate and leaf number are high; Long internodes, fast elongation in short-day environment; In a short time, the flower buds developed very fast and the pedicels stretched just right. It is insensitive to temperature, that is, when it is higher or lower than 15.6 degrees Celsius, the flowering is slightly delayed or not delayed; Cuttings are easy to take root and stored at low temperature for at least ten days; Flowering stems and pedicels have high strength and good water absorption; With large and horizontally extending blades; Pink flowers; The same variety has a growth law, and the competition among plants is low when cultivated.

The primary election is very important, except for the well-behaved seedlings, everything else should be abandoned to avoid huge human and material expenses in the future. Therefore, the misjudgment of early selection may lead to the loss of excellent genotypes, and it is usually necessary to plant some fixed varieties at the same time for comparison. The factors that affect the selection are: environmental factors, repetition times, boundary effect, plant competition, planting density and so on.

In the selection of chrysanthemum hybrid offspring, the quality traits are discontinuous variation, which is less affected by environmental variation and has high individual selection effect. Quantitative traits are continuous variation, which is greatly influenced by environmental variation. Many pairs of genetic factors often control the same trait, and there are secondary factors in a single factor, so the selection effect is not high. Selection should be based on the heritability of traits, and individuals with high heritability of traits have great selection effect.

In cross breeding, in order to cultivate varieties suitable for the characteristics of day length, temperature and humidity in subtropical areas, maintain the freshness and quality after harvest, and be able to withstand storage and transportation, Taichung District Agricultural Reform Farm initially selected more than 100 excellent hybrid offspring, conducted annual cultivation and flowering habits investigation, and selected four excellent autumn and winter strains in the main chrysanthemum producing areas in the winter of 1998 for regional trial planting. According to the preliminary investigation and evaluation, the leaf shape, flower pattern and color of Dahuaihua 94 180 have great potential for the development of Japanese market. The comparative tests of regions and varieties will be carried out in the future, and it is expected that domestic self-owned chrysanthemum varieties will be established one after another in recent years.

Mutation breeding of asexual crops can increase somatic genetic variation, which has the potential to improve varieties, especially in ornamental plants, because any induced mutant can be directly used as long as it has ornamental value, or it can be propagated and utilized in large quantities through asexual propagation and tissue culture. For example, any color change caused by mutation can be used asexually as long as it has commercial value. The main advantage of mutation is that it can quickly obtain plant somatic variation, and although it may also cause other traits to mutate, the target variety can also be selected in a short time by selecting the traits that breeders hope. Successful mutant individuals can become commercial clones through asexual reproduction.

The agricultural improvement farm in Taichung District not only carries out traditional cross breeding of chrysanthemum, but also carries out mutation breeding and develops new flower varieties. Since 1980s, radiation mutation breeding of chrysanthemum has been carried out, that is, many scholars have conducted research one after another and selected somatic mutants. Chrysanthemum is generally propagated asexually by cuttings. Mutants with different colors or petals can be induced by irradiating chrysanthemum plants with γ -rays during flower bud differentiation. Somatic variation often appears on petals, which can be easily observed by naked eyes. Tissue culture with petals with color mutation can induce adventitious buds and obtain plants without flowers and leaves, and then field observation and comparative experiments are carried out to select varieties that meet the breeding objectives. If 1000 Ryder (Rade is the unit of radiation absorbed dose) is used to irradiate chrysanthemum seedlings, it will induce mutant buds and produce mutant branches and flowers with different colors. This deformed flower can be easily observed by naked eyes, and then a new strain with color mutation can be obtained through vegetative propagation of branches.

In the aspect of chrysanthemum mutation breeding, chrysanthemum varieties such as Xiufang, Heixinhuang, Holland White, Harley, Ji Tao, Hongmeiren, Flower World were irradiated with γ-rays to induce somatic mutation. Huang Xiufang only observed some mutations, while Black Heart Huang did not find any mutations. The mutant petals combined with tissue culture technology were used to produce individuals, and the red beauty mutant 10, Ji Tao mutant 2 and Halley mutant 2 were preliminarily screened out, and their application potential was observed and evaluated.

Although domestic chrysanthemum breeding started late, recently, agricultural improvement farms in Taichung have successively established the technical basis of cross breeding and mutation breeding, and selected many excellent offspring for strain test and market evaluation. In the future, we will strengthen the breeding of heat-resistant strains of Xia Ju, cold-sensitive strains of Dongju and diversified new color strains, cultivate our own varieties suitable for the climate in Taiwan Province Province, China, and establish a chrysanthemum breeding and variety approval system in Taiwan Province Province, China.

The culture of plant cells, tissues or organs belongs to the field of biotechnology, which can be applied to the change or reproduction of horticultural crops, especially in the change of genetic characteristics or the screening, maintenance and proliferation of some mutant species. Plant tissue culture is to put a small piece of plant tissue on a culture medium or culture solution under aseptic conditions. This tissue is called a culture body. The culture preferably belongs to the outer cortex or dividing tissue, which can divide and grow cells indefinitely. For the development of plant cells, its culture medium needs to contain some plant growth hormones, and its conditions are different according to different plants and tissues in different parts of plants.

The main purpose of gene transfer is to overcome the difficulties of traditional breeding methods, such as the inability to cross breeding or the absence of the target gene in the seed source, and the target gene has commercial value. Chrysanthemum pests are serious, and pesticides are used in large quantities during the growing period, so eggs cannot be detected in exported chrysanthemums. Therefore, insect-resistant plants can be obtained through gene transformation.