What causes early bolting in Angelica sinensis? How to prevent and control it
Perennial herbaceous Angelica sinensis, 0.4-1 m tall. Flowering period June-July, fruiting period July-September. Its root can be used as medicine and is one of the most commonly used traditional Chinese medicines. It has the effects of nourishing and harmonizing blood, regulating menstruation and relieving pain, moistening dryness and lubricating the intestines, anti-cancer, anti-aging, and immune support. Angelica sinensis often bolts and flowers abundantly between June and July of the second year of cultivation, with a bolting rate of 10-30% in normal years, and reaching over 80% in severe cases. In bolted and flowering plants, the parenchyma cells of the secondary xylem become lignified, and the ratio of secondary phloem to secondary xylem in the root changes from a normal 2:1 to 1:10; the fleshy root gradually becomes lignified and hollow, with a large proportion of woody tissue and lacking oil, making it unusable as medicine. Therefore, preventing and controlling early bolting is an important technical measure for improving the yield and quality of Angelica sinensis. Below is an analysis and proposed causes and control of bolting in Angelica sinensis methods.
[Causes of Bolting]
1. Genetic factors: Seedlings grown from the seeds of bolted Angelica sinensis plants, seeds retained from the main bolt of normal seed-bearing plants, over-mature seeds, or aged seeds will have a very high bolting rate, reaching over 80-90%.
2. Ecological factors: Raising seedlings or transplanting in low-altitude, high-temperature, sunny-slope, or dry areas can easily cause early bolting in Angelica sinensis. For early bolting in Angelica sinensis, the degree of correlation among various factors, from greatest to least, is altitude, annual precipitation, density, organic fertilizer, and nitrogen. Seedlings stored in shaded areas have a bolting rate about 50% lower than those stored in sunny areas; when the soil moisture content during storage is 50-60 g/kg and 50% shading is applied after transplanting, the bolting rate decreases by 60%; when the sunshine duration exceeds 14 h, the bolting rate reaches its peak.
3. Nutritional level: The early bolting rate of Angelica sinensis is positively correlated with seedling weight and size. Small seedlings with a root diameter below 0.5 cm are suitable for transplanting, but seedling size must correspond to seedling age; if the seedling weight is very small but the seedling age is old, the bolting rate will still be very high; conversely, large seedlings with very large size but young age rarely bolt. For Angelica sinensis seedlings of the same age, the greater the seedling weight, not only does the bolting process accelerate and occur earlier, but the bolting ratio also increases significantly. The early bolting rate also has a certain relationship with the nitrogen content and sugar content of Angelica sinensis seedlings, and there is a significant negative correlation between nitrogen content and early bolting rate.
4. Cultivation measures
(1) Seed maturity: Sowing with fully mature seeds or seeds from the main stem's terminal spike results in strong seedling growth after sowing, rapid sugar accumulation in the root, and a significantly increased early bolting rate.
(2) Seedling age: When the weight of Angelica sinensis seedlings is the same, the earlier the sowing, the longer the seedling age, and the higher the early bolting rate. The seedling growth period of Angelica sinensis is generally 90-110 days, with fresh weight per 100 roots of 40 g-70 g; sowing and seedling raising is generally from mid-June to mid-July, that is, sowing between the Summer Solstice and the Great Heat is more suitable, and seedling raising generally lasts until early to mid-October, that is, around Cold Dew and Frost's Descent, when the temperature drops to zero. If seedling raising is too late or seedlings are lifted too early, the seedlings will be tender and lack sufficient nutrition, and are prone to rot.
(3) Sowing density: The sowing rate of Angelica sinensis seeds is generally 60 kg-75 kg/hm2, sometimes as much as 112.5 kg/hm2.
(4) Transplanting time: For seedlings stored under the same conditions, transplanting too early makes bolting more likely, while delayed planting lowers the early bolting rate and postpones the bolting period. Seedlings with forked roots are also prone to early bolting when transplanted.
(5) Fertilization: The bolting rate increases with the use of chemical fertilizers, among which diammonium phosphate is the highest. P fertilizer has an extremely significant effect on the bolting rate of Angelica sinensis, and the application of NP chemical fertilizers accelerates the bolting process. When NK fertilizer is applied at a relatively high rate, the early bolting rate of Angelica sinensis increases significantly.
(6) Climatic environment: Angelica sinensis prefers a cool, shady, and moist climate. From May to July, if the vegetative growth period of Angelica sinensis encounters high-temperature and droughty climate, the bolting rate is generally relatively high.
[Control Methods]
1. Select and retain good seeds. Under the same cultivation conditions, seeds produced by early-bolting and flowering plants generally have early-maturity traits and are prone to bolting and flowering. According to experiments, under the same seedling and cultivation management measures, when seeds from plants that flowered and set seed in the second and third years were used separately for raising seedlings, the seedlings raised from seeds that flowered and set seed in the second year had an early bolting rate 30-40% higher than those from seeds that flowered and set seed in the third year, and bolted 10-15 days earlier. At the same time, the bolting rate of Angelica sinensis seeds is also related to seed maturity: fully mature seeds have strong vitality, grow vigorously after planting, and have a high bolting rate; tender seeds have weak vitality, and although they will not bolt early after sowing, their survival rate is low, growth is weak, and yield is low, making them difficult to use in production. Therefore, in order to improve seedling quality and reduce the early bolting rate, it is necessary in the current three-year seed-production fields to select and collect seeds that are large in root body, robust in growth, relatively late in flowering, moderate in maturity (fish-belly white), and uniform for raising seedlings. Because the development of the main stem and lateral branches of Angelica sinensis is inconsistent, in production the main stem must be cut off at the early bolting stage of seed-retaining plants to promote uniform development of all branches, so as to obtain seeds meeting production requirements.
2. Sow at the right time, fertilize reasonably, and control seedling age and seedling weight. According to production practice: Angelica sinensis seedlings not only need a certain low temperature to pass through vernalization, but also need sufficient sugar content themselves, so tall seedlings are prone to bolting and flowering, while small seedlings have a very low early bolting rate. At the same time, seedling age also has a great impact on bolting: for the same batch of seeds, when seedlings are raised at different times and the root weight is the same, seedlings with older age have a higher early bolting rate. According to data from Taibai County, Shaanxi Province, when seeds collected from three-year-old plants were used for raising seedlings, if the seedling age exceeded 130 days, the early bolting rate reached over 90%, while with a seedling age of less than 70 days, early bolting almost never occurred. However, if the seedling age is too young, the root weight of the seedlings is small, the survival rate after transplanting is low, growth is weak, yield is low, and benefits are poor. In order to control large seedlings and old seedlings and reduce the early bolting and flowering rate, the sowing date should be appropriately postponed so that the seedling age is controlled within 110 days and the weight per 100 seedlings is below 40 g; in the later stage of seedling raising, appropriately increase nitrogen fertilizer to raise the total nitrogen content of the plants, thereby reducing the total sugar content of the plants and inhibiting bolting and flowering.