The cause of the growth of yam deformity and its prevention
July 26 09:56:53, 2025
In the process of yam cultivation, various factors such as adverse environmental conditions, farming practices, and management techniques can lead to changes in the internal structure of the tubers, resulting in deformed or irregular yams. These abnormalities not only affect the appearance but also the quality and market value of the crop.
**I. Germplasm Factors**
**(a) Influencing Factors**
Most yam cultivation relies on yam eyes (the small buds on the tuber) or cuttings for propagation. These planting materials are often grown in the soil for at least one year, making them susceptible to root-knot nematodes, anthracnose, and brown rot. When these pathogens are present, they can cause widespread disease during the hot and rainy season (June to July), leading to deformed yams. Additionally, older yam eyes—especially those that are 4–5 years old—are more prone to mutations due to aging, which can result in forked or bent tubers. Some farmers prefer cheaper, older planting material, even though it increases the risk of deformities.
**(b) Preventive Measures**
1. Soak yam eyes or cuttings in a mancozeb solution (500–800 times diluted) or carbendazim for 3–5 minutes before planting to eliminate pathogens.
2. Use high-quality, young yam eyes (1–2 years old) for better growth and fewer deformities.
3. Select thick yam eyes or cuttings (20–25 cm long) to promote strong vine development and improve disease resistance.
**II. Soil Factors**
**(a) Influencing Factors**
Soil quality plays a crucial role in yam growth. Yams grown in black clay tend to have snake-like or tuber-shaped roots with thick, hairy surfaces, while those in sandy soils are often slender and less developed. A shallow groundwater level can cause root rot and poor growth, and continuous cropping leads to an accumulation of pests and root exudates, darkening the tuber skin and reducing quality.
**(b) Preventive Measures**
1. Rotate planting areas every 3 years to avoid soil degradation. Plant in the first year’s ridge in the second year, and in the first year’s trench in the third year.
2. Choose well-drained, deep loamy or sandy loam soils located at higher elevations for optimal growth.
**III. Planting Factors**
**(a) Influencing Factors**
Shallow trenches can cause lateral growth of the basal meristem, leading to foot-shaped or snake-like yams. Uneven soil or obstacles like stones and hard clods can cause bending or deformation. Improper placement of yam eyes may result in multiple stems, increasing the likelihood of multiple tubers forming underground and lowering quality.
**(b) Preventive Measures**
1. Dig trenches deep enough, typically 1.3 meters or more, depending on the variety.
2. Mix organic fertilizer into the top 20–30 cm of soil and use a rotary plow three times to ensure even distribution.
3. Place yam eyes at a 45-degree angle to maintain apical dominance and encourage straight tuber growth. Side shoots should be placed horizontally to support vine and tuber development.
**IV. Management Factors**
**(a) Influencing Factors**
Excessive rainfall or improper irrigation can cause waterlogging, affecting tuber shape and causing bends. Pests like cockroaches and nematodes can damage tubers or meristems, leading to insect eyes or bifurcations. Diseases such as anthracnose and stalk rot can also reduce overall quality.
**(b) Preventive Measures**
1. Ensure proper drainage during rainy seasons and avoid overwatering.
2. Compost organic fertilizer thoroughly and mix in a small amount of trichlorfon to kill pests and pathogens.
3. Soak yam eyes in a carbendazim solution (500–800 times) before planting and sprinkle a mixture of sand and trichlorfon in the planting furrow.
4. From early June, spray thiophanate-methyl and mancozeb (500 times dilution) every 15 days to prevent and control diseases.