Pinellia ternata, a medicinal plant widely cultivated for its tubers, faces significant challenges during its growth cycle, especially between the 8th and 10th months of the year. This period coincides with the mildew season, when the second, third, and fourth generations of Pinellia develop. The early spring-planted bulbs and the summer generation form new generations, with the second-generation bulblets growing rapidly, forming tubers while the original stems also enlarge. This is the most vigorous growth phase for the tubers, but it is also when their resistance to disease is at its weakest.
As the tubers grow larger, their ability to resist pathogens decreases, whereas smaller tubers tend to be more resilient. During this rapid underground growth, the tubers require large amounts of oxygen and organic matter from the soil. At the same time, microorganisms in the soil become highly active, consuming oxygen and releasing harmful gases and substances. When there is continuous rain or heavy soil moisture, gas exchange between the soil and air is restricted, creating an environment conducive to rot development.
In such conditions, the protective outer layer of the tubers becomes less effective, allowing harmful bacteria and gases to penetrate and cause rapid decay. In severe cases, up to 80% of the tubers may rot within a week, leading to total crop failure in just a few days. The affected fields emit a foul odor, and by summer, the entire crop may be completely rotten, leaving only a few small buds and tiny tubers at harvest time. This rot disease has long been one of the major obstacles in Pinellia production.
The initial signs of infection include irregular black spots on the tubers, which quickly expand and merge, invading the inner parts of the tuber. As the disease progresses, the roots shrink, and the above-ground leaves turn yellow and wither. Within a week, the tubers become soft and filled with black water, leading to the death of the entire plant. The infection spreads rapidly, affecting the whole field and causing widespread rot. The soil and air around the infected area begin to emit a strong, unpleasant smell.
To manage this issue, several control measures can be implemented:
1. **Selecting Resistant Varieties**: Plant Pinellia cultivars with strong disease resistance, such as "Leaflet" or other leaf-shaped varieties. Use disease-free tubers or bulb buds for planting.
2. **Stem Treatment**: Before sowing, treat the stems with drying or disinfecting methods to prevent bacterial infections from the start.
3. **Land Selection**: Choose well-drained loam or sandy loam soils with a pH between 6.5 and 7. Avoid areas that have previously suffered from root rot or similar diseases. In rainy regions, select sloped plots (at least 20% slope) to improve drainage. In flat areas, create drainage ditches (30 cm wide and deep) to ensure proper water runoff.
4. **Soil Cultivation**: During wet periods, cultivate the soil regularly to break up compaction and allow better gas exchange. This helps reduce the buildup of harmful gases and improves oxygen availability.
5. **Timely Harvesting**: If heavy rain and high soil moisture are expected, monitor the crop closely. If signs of rot appear, harvest immediately rather than waiting for the scheduled time. Delayed harvesting can lead to rapid spread of rot, reducing yield or even causing total loss. After harvesting, process the tubers promptly to prevent internal rot, as unprocessed tubers can spoil within 1–2 days.
By implementing these strategies, farmers can significantly reduce the risk of tuber rot and improve the overall success of Pinellia cultivation.
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