Planting material refers to the type of material used to establish a field or replace a banana plant. The type of planting material generally falls into one of two groups: conventional planting material and tissue-culture plantlets. The main types of conventional planting material are suckers and bits (also called corm pieces). Tissue-culture plantlets are used almost exclusively in commercial production systems, but are increasingly used by farmers making the transition from subsistence farming to income generation1 .
The main types of conventional planting material are suckers and bits (also called corm pieces).
Suckers can also be extracted from the mat for transplanting, sharing with farmers or selling, a practice that contributes to the spread of pests and diseases. The presence of pests can be reduced by paring (trimming the roots and outer leaf sheats) and boiling the sucker.
Bits are derived from dividing large parent rhizomes after harvest or by gouging out the central growing point of a smaller pared sucker to stimulate the growth of axillary buds that will grow into plants. Large rhizomes can be split into several bits, each with a prominent side bud. Several macropropagation methods have been developed to produce large quantities of this type of planting material2 .
Video on tissue-culture banana plantlets
Tissue culture is a process whereby copies of a plant's growing point are produced on a sterile culture medium3 . The basic procedure consists in isolating the apical meristem and inducing it to form shoots4 . The shoots are regularly subdivided and maintained under sterile controlled conditions (100% humidity and no direct sunlight). When plants are needed, the shoots are put on a rooting medium for a month or so to induce the formation of roots and produce banana plantlets.
Before they can be planted in the field, the plantlets produced by tissue-culture laboratories need to be weaned and hardened. The plantlets are weaned by putting them in a humidity chamber until they are 4-5 cm high. The plantlets are then placed in large bags and hardened in a shaded nursery until they are 20 to 50 cm high.
A rigorous culture process ensures that the plantlets are free of bacteria and fungi, but not of viruses which, as cell parasites, need to be removed. Intensive testing (carried out by certified indexing centres) is necessary to be reasonably confident that the plantlets are virus free. Therapies have been developed for most of the known viruses of bananas.
Conventional planting materials require less inputs and can be planted immediately in the field, unlike the more fragile tissue-culture plantlets, which need to be hardened before planting. Tissue-culture plantlets also require appropriate management practices right after being transplanted to the field1 .
Conventional planting materials grow more slowly than tissue-culture plantlets and produce smaller bunches. Besides producing larger bunches, tissue-culture plantlets reduce the time between harvests. They also grow and flower more uniformly, which makes their harvesting and marketing more predictable.
The longevity of fields planted with tissue-culture plantlets tends to be shorter than the one for fields established with conventional planting materials.
Conventional planting materials would carry any pests and diseases present in the mother plant. Methods exist to reduce pest load before planting, but not fungal, bacterial and viral pathogens. Tissue-culture plantlets, on the other hand, are free from pests, and fungal and most bacterial pathogens. If they have been properly indexed, they should also be free of viruses. However, they are easily infected with pests and diseases if transplanted in infested soils.
Unlike conventional planting materials, tissue-culture plantlets can be produced in large quantities in a short period of time.
Tissue-culture plantlets are more expensive than conventional planting materials and may not be readily available, as many countries do not have the facilities to produce them. Moreover, the number of cultivars sold by the laboratories is generally limited.
Tissue-culture plantlets have a higher rate of somatic mutations than conventional planting materials, ranging from 3 to 50% compared to 0.0001%5 .
Propagation protocols and standards for bananas, chapter in FAO plant production and protection paper 195. Also available in French and Spanish.
Trainer's manuals on banana tissue-culture plantlets published by the CGIAR Research Program on Roots, Tubers and Bananas