Detailed Explanation of Carnation Hybrid Breeding Methods and Key Technical Points
Carnation (Dianthus caryophyllus), also known as carnation, belongs to the family Caryophyllaceae, genus Dianthus. Its flower colors are delicate and brilliant, and a single flower has a relatively long blooming period, making it an important cut flower plant of the modern era. Carnation originated in southern Europe, the northern coast of the Mediterranean, and the area from France to Greece, and is now widely cultivated around the world, with major production areas in Italy, the Netherlands, Poland, Israel, Colombia, the United States, and others. With the commercialization of carnation production, many companies specializing in breeding and propagation have emerged. These companies each have their own advantages in variety types and can introduce a certain number of new varieties every year to enhance market competitiveness, while also injecting stronger vitality into the sustainable development of carnation cut flowers. China's carnation breeding work started relatively late, and most varieties popular in the domestic market are introduced foreign varieties. At present, the Shanghai Flower Breeding Center, after years of breeding research and development, has developed several carnation varieties with independent intellectual property rights. Based on the author's practical experience, the most commonly used and most effective method for breeding new carnation varieties - hybrid breeding - is briefly introduced below.
Before breeding, breeders must have an understanding of the habits, classification, breeding objectives, and development status of carnations.
Variety Classification
Carnation varieties can be classified according to various standards. By use, they can be divided into two major categories: potted flower (flower bed) carnations and cut flower carnations. The former was all the rage 150 years ago, and currently only a few varieties remain, but there is a trend of growth; the latter is currently the main category cultivated and used. By flowering pattern (inflorescence), carnations can be divided into standard carnations or single-head carnations (Standard carnation) and spray (multi-flowered, small-flowered) carnations (Spray carnation). The former retains one flower per stem; the latter has multiple branches and multiple flowers per stem. By flower stem size, they can be divided into four categories: large-flowered (8-9 cm), medium-flowered (5-8 cm), small-flowered (4-6 cm), and miniature-flowered (2.5-3 cm). By flower color: solid-color carnations (Clove), with no variegation on the petals, mainly white, peach red, rose red, scarlet, deep red to purple, cream yellow to yellow, orange, and other colors; bizarre carnations (Bizarre), which have two or more different colors on one background color, with spots or markings distributed directly from the petal base toward the edges; flake carnations (Flake), which have only one contrasting color on one background color distributed from the petal base toward the edges; picotee carnations (Picotee), whose petal edges have a very narrow band of contrasting color, with the rest being solid color. By origin, they are mainly divided into two major groups: the Sim group and the Mediterranean group.
Breeding Objectives
In addition to ornamental traits, carnation breeding objectives also include horticultural traits. Ornamental traits require vivid flower color, outer petals that do not droop, no visible pistil, fragrance, petals that fully open and bloom simultaneously; calyx that does not easily drop, and good flower durability; straight peduncles, stiff, flexible stems that do not break easily; relatively large leaves with a waxy layer, not curling, not drying out; uniform flower branches, low node position of axillary bud sprouting, and early secondary flowers; and a strong root system. From the perspective of ecological breeding, carnation breeding in Europe aims at growth and flowering under weak light in winter, Japan focuses on breeding heat-tolerant varieties whose growth quality does not decline under high summer temperatures, and China needs both. From the perspective of disease-resistance breeding, Fusarium wilt caused by Fusarium is severe in Europe, bacterial spot caused by Pseudomonas is a greater problem in Japan, and leaf spot caused by Alternaria is currently relatively common and severe in China. Disease-resistance breeding has become an important objective in carnation breeding. In addition, heat tolerance, early maturity, and high yield are also important objectives in carnation breeding research.
Hybrid Breeding Techniques
Pollen is an important condition for selecting the paternal parent. Carnations are double-flowered, formed by stamens transforming into petals, so pollen is not easy to collect; the pistils of most varieties are normal. Using existing varieties, interspecific hybridization can be carried out with original species of Dianthus that possess disease resistance. Hybrid breeding requires years and months of unremitting effort, and division of labor and cooperation among all parties is very necessary.
The main operational process of hybrid breeding is:
Parent selection and combination -> crossing -> seed collection -> seedling growth -> selection at flowering -> vegetative propagation (cutting)
Basic hybridization techniques:
1. Usually, when the petals of the maternal parent show color, the petals and stamens should be carefully removed, and then a paper bag should be put on to completely prevent contamination by foreign pollen.
2. Pollination is suitable when the air is dry and the temperature is 18 degC-25 degC, from 10:00-14:00 in September-November and March-April. The suitable period for pistil pollination is the middle to late stage of flowering, pollinating when the stigma forks, is shiny, and has mucus; it is better when the stamens are 40%-50% open. A larger amount of pollination gives better results, and the method of repeated pollination can be used.
3. After each flower is pollinated, the pollination tool (tweezers or brush) must be sterilized with 75% alcohol; bag it promptly and hang a label stating the name of the parental cross combination, the crossing date, and so on.
4. Generally, about 10 days after hybridization, the bag can be removed to facilitate the development and growth of the ovary. For the hybridized plants, fertilizer and water management and pest and disease control should be strengthened, especially increasing the application of potassium and boron fertilizers, which is beneficial for seed maturation. Usually after 40-50 days, when the top of the swollen ovary changes from green to brown, it indicates that the seeds have matured and should be harvested promptly. The harvested seeds should be stored separately by combination together with the label to prevent mixing, and the seeds should be kept in a desiccator.
5. The treated seeds are sown in a greenhouse, either in flower pots or seedling trays, maintaining a room temperature of 20 degC-25 degC. When the seedlings grow 2-3 pairs of true leaves, transplant them once. After transplanting, spray nutrient solution on the leaves once a week. When the seedlings grow to 8-10 cm, they can be planted out into the cultivation bed.
6. Plant treatment: After planting out, manage the small seedlings carefully, do not pinch, leave 4-5 lateral buds at the base, and let the terminal bud flower first. For useful hybrids, continue selfing or backcrossing to stabilize traits, and use vegetative propagation to expand the production of seedlings. Individuals among the seedlings that grow poorly and are not vigorous should be removed as early as possible. Due to the heterozygous genetic composition of carnations, progeny individuals different from both parents will be obtained. At flowering, conduct the first selection, propagate the selected individuals with excellent flower color and flower shape by cuttings, and then carry out further selection (this is clonal selection), finally obtaining new varieties with excellent comprehensive indicators, and promote them through tissue culture production.