Ideally, grow cassava plants from semi-hardwood cuttings. Within 2-3 weeks, adventitious roots develop at the base of the cuttings. Subsequently, roots develop into a fibrous root system. Other roots develop at the base of axillary buds, or at the nodes. Fibrous roots may be up to 200 cm long. Some fibrous roots develop into 'storage roots' or 'tuberous roots', 20-40 days after planting. Tuberous root formation, or root bulking, depends on
Cassava stem cuttings (or stakes) are vulnerable to adverse climatic conditions, pests, and diseases. If exposed to sunlight, cuttings dry and lose viability. Excessive moisture causes sprouting or rotting.
Pathogens and pests are common causes of poor sprouting. Sprouting is better with freshly harvested stem cuttings. Long storage periods emphasize varietal differences in sprouting vigor.
Healthy, fresh stem cuttings from mature plants are best for planting. However, if planting is delayed because of cold weather, drought or excess moisture, farmers need reliable methods to store the stems. Stem cuttings store best in dry, well-ventilated, shaded areas away from direct sunlight.
Storage methods depend on environmental conditions. The simplest method is arranging the stems vertically under a tree, with the oldest part of the stem buried in the soil. The soil should be moist to keep the stems 'alive'. Leaves form on the upper part of the stems. After storage, discard the top and basal parts of the stems, and use the middle part as cuttings.
Under cold conditions (for example, in southern Africa; <15°C), store the stems in underground tunnels. Place stems inside the tunnel on top of a layer of dry straw, and cover them with another layer of straw and soil. Protect the tunnel from water.
The quality of cassava stem cuttings depends on
Age of stem. Take stem cuttings from plants which are between 8 and 18 months old. Cuttings from older, more mature parts of the stem give better yield than cuttings from younger parts. Cuttings from green parts are susceptible to pathogens and insects. Also, immature stems cannot be stored for a long time, because they dry rapidly. Stem cuttings from older plants are lignified, and contain only small amounts of nutrients for sprouting. Sprouts are weak.
Thickness. Use thick stems. Although any part of the cassava stem can be used for propagation, do not use thin stems. Thin stems have little nutrients and moisture. Sprouts are weak, and plants produce only few and small tuberous roots.
Number of nodes. Use 20-30 cm long cuttings with 5-7 nodes. Nodes are the origins of shoots and roots. You may obtain a plant from a small cutting with only 1 node, but the possibility of sprouting is low. Cuttings with 1-3 nodes do not sprout well because of small amounts of nutrients.
Small cuttings may also lose viability during transport, propagation, and planting. Long cuttings give higher yields than short cuttings, because long cuttings produce more stems and leaves.
Health of stems. Select planting material from healthy plants. Examine planting material carefully to prevent transmission of diseases and pests. Planting material could carry diseases such as African cassava mosaic virus, cassava bacterial blight and anthracnose; pests include mealybugs and scale insects. Do not use planting material with disease and pest symptoms.
Cut stems when you are ready for planting. Cut stems with a well-sharpened machete, knife, or saw. Avoid rough handling, otherwise the epidermis and buds may be bruised or damaged. Each wound provides entry for microorganisms.
If feasible, treat cuttings with appropriate pesticides (Table 1). Immerse stems for 5 minutes and dry them in the shade. The use of pesticides is not common among cassava farmers in Africa.
Presprouting. Presprouting stem cuttings before planting improves establishment, particularly in the humid and subhumid zones. Other advantages of presprouting are high growth vigor, a full crop stand, reduced weed pressure, and higher yield.
Presprout stem cuttings by placing hardwood or semi-mature stem cuttings in perforated polythene bags without soil. Fill each bag up to two-thirds leaving about one-third for aeration. Tie the bags with a piece of string and place in a shaded area or under a roof. Sprouting occurs in 3-5 days. Some varieties however, require a longer period for sprouting.
Table 1. Pesticides for treatment of stem cuttings.
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