1. Seed Breeding
1.1 Selected Seeds
The main cultivars of purple Platycodon grandiflorum are used, but white-flowered varieties are also included due to their genetic stability and high yield. However, the amino acid content and hemolytic activity are lower in white-flowered types compared to the purple ones. The two saponins found in Campanulaceae species have similar pharmacological properties. For medicinal purposes, it is recommended to use purple-flowered Platycodon grandiflorum, while the white-flowered variety is more suitable for food processing. Seeds are generally selected from healthy, vigorous plants that are free from pests and diseases. These plants are typically chosen during their second year of growth. Since the fruits of P. grandiflorum ripen from top to bottom, it's advisable to prune the upper branches in early June to redirect nutrients toward 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 avoid pod splitting. After harvesting, the seeds are dried in the sun, threshed, sieved to remove impurities, and stored at low temperatures to extend their viability (seeds stored at room temperature lose viability within a year). It is also common to introduce seeds from lowland or low-latitude areas into high-altitude or mountainous regions, which significantly improves root yield.
1.2 Seed Treatment Methods
Before planting, seeds can be soaked in warm water for 24 hours or in 0.3% potassium permanganate solution for 12 hours. Alternatively, ultrasonic treatment can be applied, which significantly increases germination rates. With these treatments, the germination rate reaches about 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 environments. 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 soils rich in organic matter. Avoid overly dry or compacted soils, as they can lead to root branching and poor growth. Prepare the land by plowing to a depth of about 35 cm, incorporating 60,000–75,000 kg/ha of farmyard manure. Create raised beds 1.3–1.7 m wide, or use ridges 1.5 m wide and 15–20 cm high if drainage is needed.
2.2 Sowing
Sowing can be done in spring, summer, or autumn, but late autumn (October to November) is ideal for broadcasting. This method results in longer growth periods and thicker roots. In northern regions, summer sowing after wheat harvest is also effective, as it maximizes land use and seed germination. Direct seeding is preferred over transplanting because it yields better root quality. Drill rows 15–20 cm apart, 5–7 cm deep, with a seeding rate of 8.5–11.5 kg/ha. For hole sowing, place seeds every 8–10 cm and cover them with ash or fine soil.
2.3 Thinning and Spacing
Once seedlings reach 2 cm in height, thinning is performed to keep strong seedlings spaced 8–10 cm apart. Each hole should have 2–3 seedlings, spaced 6 cm apart. Any missing seedlings should be replaced with new ones, ensuring good survival rates.
2.4 Fertilization and Weeding
First weeding is done when seedlings are thinning, followed by the application of 150 kg/ha of superphosphate. A diluted human urine solution (12,000 kg/ha) is also applied. At 60 days after the first fertilization, apply 25,000 kg/ha of farm manure and 18,000 kg/ha of animal manure. In the second year, before flowering, apply 23,000 kg/ha of manure and 75–105 kg/ha of urea, along with weeding.
2.5 Bud Removal and Flower Harvesting
To improve root growth, buds should be removed. Spraying 0.1% ethephon at flowering time helps control flower development. Remove side shoots, leaving only 1–2 main stems per plant.
2.6 Pest and Disease Control
2.6.1 Root Nematode Disease
Infected roots show swellings, and above-ground foliage wilts prematurely. Apply 1500 kg/ha of tea seed cake fertilizer as a base, and disinfect the soil with lime nitrogen or dibromochloropropane before planting.
2.6.2 Purple Feather Disease
This disease affects roots in mid-September, causing rotting in October. Infected roots turn red, covered with mycelium and purple sclerotia. Control involves crop rotation, removing diseased plants, and disinfecting affected areas with 5% lime water.
2.6.3 Anthrax
Common in hot, humid July–August, this disease causes stem base discoloration and eventual lodging. Prevent by spraying 20% Tuzet WP 500 times before digging. Treat with Bordeaux mixture or thiophanate-methyl at the first sign of infection.
2.6.4 Ringworm and Spot Blight
Apply 1:1:100 Bordeaux mixture or 50% carbendazim WP 1000 times in early stages, repeating 2–3 times.
2.6.5 Root Fly
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 after two years of growth or in October of the first year. Harvesting too early or too late can affect root quality. Dig up the entire root, wash, scrape the outer layer, and dry either naturally or with anthracite. Average dry yield is around 6000 kg/ha.
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