1. Seed Breeding
1.1 Selected Seeds
The main cultivars used are purple-flowered Platycodon grandiflorum, although white-flowered varieties are also utilized due to their genetic stability and high yield. However, the amino acid content and hemolytic activity of the white-flowered type are lower than those of the purple variety. Despite this, the pharmacological effects of the saponins in both types are similar. For medicinal purposes, the purple-flowered variety is preferred, while the white-flowered one is more commonly used for food processing. Seed selection typically involves choosing robust, disease-free plants from the second year of growth. The fruits of P. grandiflorum mature from top to bottom, so during the first half of June, the upper branches are pruned to concentrate nutrients on the middle and upper parts, promoting better flowering and fruit development. When the fruits turn yellow-green and the seeds become dark, they should be harvested promptly to prevent pod splitting. After harvesting, the seeds are sun-dried, threshed, sieved to remove impurities, and stored at low temperatures to extend their viability (seeds stored at room temperature lose vitality within a year). Cultivating these plants in higher altitudes or cooler regions can significantly increase root yield.
1.2 Seed Treatment Methods
Before sowing, seeds can be soaked in warm water for 24 hours or treated with 0.3% potassium permanganate for 12 hours. Alternatively, ultrasonic treatment can be applied, which significantly improves germination rates. Treated seeds typically germinate at a rate of 25.5%.
2. Cultivation Techniques
2.1 Land Selection and Preparation
Platycodon grandiflorum is a deep-rooted perennial plant that thrives in sunny, cool, and moist conditions. It is resistant to cold, wind, and water. Ideal locations include mountainous areas between 450–1500 meters in elevation, with well-drained, fertile sandy or loamy soil rich in organic matter. Avoid overly dry or compacted soils, as they can lead to root branching and poor development. The land should be deeply plowed to about 35 cm and enriched with farmyard manure at a rate of 60,000–75,000 kg per hectare. Raised beds of 1.3–1.7 m wide are common, while areas with good drainage may use raised ridges 1.5 m wide and 15–20 cm high, with furrows spaced 15–20 cm apart.
2.2 Sowing
Sowing can be done in spring, summer, or autumn, but late autumn (October to November) is ideal for broadcasting, as it results in longer growth periods and thicker roots. In northern regions, sowing after wheat harvest in summer is efficient and promotes better germination. Direct seeding is preferred over transplanting because it yields higher root quality. Drill rows at 15–20 cm intervals, 5–7 cm deep, with a seeding rate of 8.5–11.5 kg/ha. For hole sowing, space holes 8–10 cm apart and cover seeds with ash or fine soil.
2.3 Thinning and Spacing
Thinning is performed when seedlings reach 2 cm in height. Strong seedlings are kept at 8–10 cm spacing, with two plants per hole spaced 6 cm apart. Additional seedlings are transplanted where gaps exist to ensure survival.
2.4 Fertilization and Weeding
Weeding is done during thinning, followed by the application of superphosphate at 150 kg/ha. A diluted human urine solution (12,000 kg/ha) is also used. At 60 days post-first fertilization, 25,000 kg/ha of farm manure and 18,000 kg/ha of animal waste are applied. In the second year, before flowering, 23,000 kg/ha of manure and 75–105 kg/ha of urea are applied, along with weeding.
2.5 Bud Removal and Flower Harvesting
To enhance root growth, flower buds are removed using 0.1% ethephon spray. Only 1–2 main shoots are left per plant, with others removed for consumption.
2.6 Pest and Disease Control
2.6.1 Root Nematode
Infected roots show galls, and above-ground parts wilt prematurely. Control involves applying tea seed cake fertilizer (1500 kg/ha) as a base fertilizer and disinfecting the soil with lime nitrogen or dibromochloropropane before planting.
2.6.2 Purple Spot Disease
This disease causes root rot in September, with red discoloration and purple sclerotia. Crop rotation and removal of infected plants are essential. Diseased areas are disinfected with 5% lime water.
2.6.3 Anthrax
Common in hot, humid July–August, this disease causes stem base browning and lodging. Prevention includes spraying 20% Tuzet WP 500 times before planting. Once symptoms appear, 1:1:100 Bordeaux mixture or 50% thiophanate-methyl 800 times is sprayed every 10 days for 3–4 applications.
2.6.4 Ringworm and Leaf Spot
Treat with 1:1:100 Bordeaux mixture or 50% carbendazim 1000 times, applied 2–3 times.
2.6.5 Root Maggot
Spray 90% trichlorfon 800 times or 50% phoxim EC 1000 times during adult mating and larval stages (May–June).
3. Harvesting and Processing
Roots are ready for harvest two years after sowing or in October of the same year. Early or late harvesting affects root quality. Roots are dug up, washed, scraped, and dried. Dried roots yield approximately 6000 kg/ha.
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