How to prevent flower variety degeneration? Points to note when introducing edible fungi

With the development of flower production, the formation of industrialization, the increase in introduced and bred varieties, and unreasonable operations during seed propagation and use, the phenomenon of flower variety degeneration has become rather serious, causing great impact on the development of the flower industry and urgently requiring attention and resolution.

The phenomenon of flower plant variety degeneration

The process and manifestation of the weakening of the original superior varietal characteristics of flower plants is called variety degeneration. After a superior variety degenerates, its traits deteriorate, manifesting as morphological distortion, growth decline, disordered flower color, smaller flower diameter, reduced double-petaled character, uneven flowering period, poor resistance, and so on.

Causes of variety degeneration

There are many causes of flower plant variety degeneration, mainly the following:

1. Biological mixing

This mostly occurs in annual and biennial herbaceous flowers propagated by seed. During seed collection, seed drying, storage, packaging, transport, sowing, seedling raising, transplanting and other processes, other genotypes are mixed in, or improper distances lead to natural crossing, causing gene recombination and segregation. This phenomenon is most likely to occur among varieties with similar seed or branch and leaf morphology and strong trailing habits, such as sweet pea, petunia, lupine, and so on. Biological mixing most easily occurs among varieties or species of outcrossing plants and often-outcrossing plants, and occasionally also occurs in self-pollinating plants, such as hollyhock, cockscomb, garden balsam, pansy, marigold, China aster, snapdragon, and so on.

2. Gene deterioration

This variation is caused by mutation of alleles. For example, the red corolla of cockscomb is controlled by a dominant gene and the yellow by its allelic recessive gene. When the dominant gene controlling red mutates into an allelic recessive gene, the corolla changes from red to yellow; conversely, if the recessive gene mutates into an allelic dominant gene, the corolla color changes from yellow to red; if the mutation occurs relatively late, a red-and-yellow mosaic phenomenon appears, and some show atavistic inheritance, losing the large corolla and becoming the inflorescence of the original species Celosia argentea. This phenomenon is relatively common in flowering plants.

3. Virus infection

Virus infection is very common in flower plants, and the losses caused are also very serious. At present, it has been found that flowers whose varieties are degenerated by viruses include canna, tulip, gladiolus, lily, chrysanthemum, dahlia, cyclamen, carnation, rose, and so on. For example, after canna is infected with cucumber mosaic virus, small chlorotic spots appear on the leaves in the early stage; in severe cases the leaves curl and become deformed, the flowers become broken in color, the plant becomes dwarfed, and it may even die. After lily is infected with mosaic virus, the leaves curl backward, the plant becomes dwarfed, the flowers become deformed, and it may even fail to bloom normally. Virus infection is generally spread when piercing-sucking mouthpart insects such as aphids, thrips, leafhoppers, and planthoppers feed, and can also be infected through wound contact caused by grafting, pinching, pruning side branches, and other operation and management practices.

4. Improper propagation methods

For example, the capsule size of snapdragon and petunia decreases from the lower part of the inflorescence upward; the seeds set by the ray florets of cosmos are large and heavy, while the seeds of the central disk florets are light and small. If seeds from the upper part of the inflorescence or from the central disk florets are used for propagation, the seedlings will be slender and weak and grow poorly. Another example is five-colored cockscomb and twisted-pattern garden balsam, when seeds are not collected from typical inflorescence positions; or for bicolored foliage plants such as spider plant, croton, spiderwort, silver-edged geranium, and golden-hearted boxwood, when organs from positions without typical traits are cut for cuttings, their original typical characteristics are often lost.

5. Degeneration caused by unsuitable cultivation environment

For example, cool-loving dahlia, gladiolus, and so on, if cultivated in hot and humid areas, often grow poorly, with smaller flowers and shorter inflorescences; another example is shade-tolerant flowers planted in places with excessively strong sunlight, where flower quality is greatly reduced.

Technical measures to prevent flower variety degeneration

In view of the causes of flower variety degeneration, work should be done well in practice in two aspects: preventing mixing and maintaining purity.

1. Preventing mixing

Preventing mechanical mixing: To prevent mechanical mixing, attention should be paid to the following links:

(1) Seed collection: Collect in a timely manner. Seeds that fall on the ground should rather be discarded to avoid mixing. When collecting seeds, the variety name should be marked inside and outside the collection utensils. If seeds without variety name labels are found afterward, they should be discarded.

(2) Seed drying: When drying seeds, the containers of each variety should be separated by a certain distance, and even more attention should be paid to seeds that are easily moved by wind. When the quantity is not large, it is best to place them in bags for drying.

(3) Sowing and seedling raising: Choose windless weather for sowing. If the seeds are too light, a small amount of fine soil or fine sand may be mixed in for sowing. Similar varieties should preferably not be raised as seedlings in the same bed. When irrigating the bed, slow down the speed to avoid washing away the seeds. After sowing is completed, immediately insert labels and draw a planting map.

(4) Transplanting: This process is the most prone to mixing. Seedlings must be lifted according to the planting map, and as far as possible one variety should be completely lifted and planted before another variety is lifted and planted, with labels inserted promptly and a field planting map drawn well.

(5) Roguing: Carry out roguing several times separately at each stage of field development. This is an effective measure to prevent mechanical mixing and can be done once each at transplanting, final planting, early flowering, full flowering, and late flowering stages.

Preventing biological mixing: The basic method for preventing biological mixing is isolation. There are three isolation methods:

(1) Spatial isolation: The distance for spatial isolation varies with wind force, wind direction, pollen amount, ease of pollen flight, degree of double petals, sowing area, and so on. Generally, when seed propagation is carried out in open areas with a large amount of pollen, a small degree of double petals, relatively strong wind during the propagation season, a large sowing area, and a lack of obstacles, the isolation distance should be larger. When the area is relatively small, cold frames or isolation covers can be used to prevent insect pollination. The isolation distance should also consider the natural crossing rate of the species. Among varieties with a high natural crossing rate, such as cockscomb, morning glory, marigold, calendula, zinnia, hollyhock, and dianthus, the isolation distance should be more than 300 m.

(2) Time isolation: Time isolation is the most effective method for preventing biological mixing. Time isolation can be divided into two types: cross-year and non-cross-year. Non-cross-year means sowing in different months within the same year and planting at different times, so as to stagger the flowering periods of different varieties. This method is suitable for some species that are not sensitive to photoperiod. For example, China aster can be sown in autumn and bloom in spring, or sown in spring and bloom in autumn; scarlet sage, garden balsam, morning glory, and so on have a relatively long suitable sowing period, and staggered sowing among different varieties supplemented by topping is also a feasible method for seed propagation. Cross-year time isolation means dividing all varieties into two or three groups, with the crossing rate among varieties within each group not high, sowing only one group each year, and properly preserving the seeds propagated for use over two or three years. This method can be used for species or varieties with a long effective seed storage period.

(3) Barrier isolation: Natural barriers such as woods, tall crops, tall buildings, and deliberately set isolation objects can be used to separate external pollen sources and achieve the purpose of isolation.

2. Select seeds or vegetative organs with high varietal typicality for propagation

Practice has proved that seeds at different positions in the same inflorescence produce offspring with different varietal typicality. For flowers such as cosmos, China aster, cornflower, and marigold, seeds borne on the edge of the flower disk can most accurately transmit the flower shape and color of the female parent; for vegetatively propagated flowers, typical leaves, flowers, branches, and other parts should be selected for cuttings, grafting, or tissue culture, and young basal shoots should be used for propagation as far as possible, which helps maintain the varietal characteristics.

3. Strengthen field management

Careful field management is very important for improving the varietal characteristics of flower plants, such as removing virus-carrying plants, eliminating pests, avoiding continuous cropping, strengthening fertilizer and water management, and creating environmental conditions for the full development of the traits of superior varieties; for types propagated by organs such as seed balls, bulbs, tuberous roots, and tubers, measures such as topping and pruning can increase yield and improve the quality of the seed-bearing parts.

4. Suit measures to the species and provide suitable cultivation environments for the varieties

Match flowers to the site and match flowers to the season. For cool-loving flowers such as gladiolus, cultivation can be changed to autumn in the south to prevent variety degeneration.

5. Carry out purification and rejuvenation in a timely manner

After mixing and degeneration of a variety are found, purification and rejuvenation should be carried out promptly to avoid further accumulation of undesirable traits. At each stage of flower growth and development, observe and compare, and use the method of individual plant selection for purification to achieve the purpose of rejuvenation.

Although a superior variety can recover under certain circumstances after degeneration, it is a complex and difficult matter and takes a relatively long time. Some varieties are even difficult to restore after degeneration. Therefore, in the use of varieties, the main focus should be on preventing mixing and maintaining purity, and the principle should be carried out that preventing mixing is more important than roguing, and maintaining purity is more important than purification.