Musa acuminata Colla and Musa balbisiana Colla
Musaceae

TAXONOMY, ORIGIN, DISTRIBUTION
Groups
Musa AA, AAA, and AAAA (AA=banana diploid; AAA=banana triploid; AAAA=banana tetraploid)

Groups
Musa BB, BBB

Interspecific groups
Musa AB, AAB, ABB, AAAB, AABB and ABBB More than 20 subgroups

Origin
South Asia, Southeast Asia and the Pacific with secondary diversification zones in West and Central Africa for the plantain subgroup, and in the East African Highlands for the Lujugira banana subgroup.

Distribution
Throughout low and mid-altitudes of the humid, wet-dry and dry tropics and subtropics (approximately 120 countries).


Five methods are commonly employed to obtain planting material for the establishment of new planting material of banana and plantain:



Bacterial diseases

Viral diseases

Fungal diseases
fusarium wilt or Panama disease Fusarium oxysporum f.sp. cubense, often referred to as Foc

Nematodes
Burrowing nematode Radopholus similis Cobb
Root-lesion nematodes Pratylenchus coffeae (Zimmerman) Filipjev and Schuurmans Stekhoven and Pratylenchus goodeyi Sher and Allen

Insects
Black weevil Cosmopolites sordidus Germar


The quality of a batch of planting material has three components that should be taken into account by the buyer, the seller and the quality controllers.

Disease. The material for planting or any associated rooting medium should not be a source of disease or insect pests. If planting material is brought from another country, region or continent, it can introduce a new insect pest or disease with devastating effects for producers. Viruses are often spread in this way. Diseases such as black leaf streak disease also can be introduced in this way, although once this disease is present in a region, planting material is no longer an important path for its local dissemination. If planting material of local origin is highly infected with commonly occurring diseases and insect pests, the grower will also experience lower yields and a shorter plantation life. Planting material prepared by different methods has different risks of pest and disease transmission.

Variety. The batch of planting material should contain only the desired variety. In addition, the material should originate from plants with superior production, resistance and quality traits. Acquisition of improved planting material is an opportunity to upgrade the production potential of the variety. Certain high rate multiplication techniques can be used to multiply carefully selected plants with elite characters.

Size and uniformity. The batch of planting material should have the size and uniformity appropriate to the objectives and resources of the grower. In cases targeting a small marketing window, the grower may want highly uniform planting material. If the planting is for home consumption or local sale, less uniform planting material may be preferable to spread the first harvest over a longer time period.

DISEASES AND INSECT PESTS
Diseases and insect pests are an important element of the quality of planting material for two reasons. First, certain diseases and insect pests are not yet present in all Musa growing regions. Extreme vigilance is therefore essential to prevent the spread of these phytosanitary problems to new regions, especially through planting material or other means. These quarantine diseases include moko disease, xanthomonas wilt, fusarium wilt, tropical race 4, banana bunchy top disease and banana bract mosaic disease. Planting material and other plant parts contaminated with sigatoka disease or black leaf streak disease also can potentially spread the diseases to non-infected areas.

Second, diseases caused by bacteria, fungi, virus, nematodes and insect pests infect plantain and banana planting materials reduce bunch size, stand density and stand productive life. Ideally, both the planting material and the field where the new plantation is to be established should be free of these diseases and pests. In practical terms, it only may be possible to minimize these problems in the planting material without achieving completely clean seed. Appropriate practices for the quality of planting material should be decided upon according to the phytosanitary problems present and the multiplication method to be used.


Common methods for multiplication of planting material
Five methods are common for obtaining planting material for the establishment of new plantings of banana and plantain. Each method has specific requirements in terms of facilities and equipment, generates planting material at a characteristic rate and has particular risks of pest and disease contamination. The methods range from a few suckers extracted from backyard gardens, to small seedbeds with a few hundred seedlings distributed at the local level, to a manufacturing unit for producing several million in vitro plants per year. The five techniques are described below. Good practices for different stages of plant multiplication are described in later sections.

SUCKERS EXTRACTED FROM BANANA AND PLANTAIN FIELDS IN PRODUCTION
Fields in production have numerous types of planting material. Sword and maiden suckers are generally considered the most reliable and productive planting material for direct extraction from production fields. The suckers are 0.5–1.0 m long, with a cone-shaped growing stem and small narrowing to the most expanded leaves. However, any shape or type of sucker or the main corm can be used, either intact or cut into pieces, to plant a new plantation, although harvest intervals may be lengthened by less satisfactory material. After extraction with hand tools, suckers or corm pieces must be subjected to diverse practices (described in Table 1) to minimize the transfer of pests and diseases, and then planted directly into a new field. Depending on the variety, each mat in a plantation may yield 1–3 suitable suckers. Over-extraction or careless extraction of suckers may result in weakened plant support and stem toppling.

SUCKERS EXTRACTED FROM BANANA AND PLANTAIN FIELDS IN PRODUCTION
Fields in production have numerous types of planting material. Sword and maiden suckers are generally considered the most reliable and productive planting material for direct extraction from production fields. The suckers are 0.5–1.0 m long, with a cone-shaped growing stem and small narrowing to the most expanded leaves. However, any shape or type of sucker or the main corm can be used, either intact or cut into pieces, to plant a new plantation, although harvest intervals may be lengthened by less satisfactory material. After extraction with hand tools, suckers or corm pieces must be subjected to diverse practices (described in Table 1) to minimize the transfer of pests and diseases, and then planted directly into a new field. Depending on the variety, each mat in a plantation may yield 1–3 suitable suckers. Over-extraction or careless extraction of suckers may result in weakened plant support and stem toppling.

Suckers reproduced in multiplication plot
Suckers or corm pieces are used to plant a high density stand. When the plants reach the stage of flower differentiation – well before flower emergence – decapitation or false decapitation is used to stop further flower development.

TABLE 1
Key banana plant multiplication steps

Steps	Suckers selected from production field	Suckers grown in a sucker multiplicatonplot	Microcorms	PIBS	Tissue culture
Sucker selection	x	x	x	x	x
Sucker preparation	x	x	x	x	x
Field selection		x
Field management		x
High humidity chamber				x
Tissue culture laboratory					x
Weaning nursery					x
Hardening nursery			x	x	x

This action stimulates the emergence of 10–20 suckers per stem. These suckers are then extracted and prepared to avoid pest and disease multiplication and transfer.

Microcorms
Small, cone-shaped suckers from 200–300 g, called “peepers”, are extracted from a production field or a sucker nursery, treated and then planted into a nursery for 6–8 weeks, until plants reach an appropriate size for transplanting.

PIBS
Sword corms (minimum 12–25 cm diameter or 150–400 g) or pieces of larger corms, peeled and stripped completely of leaf sheathes, are placed in wet sawdust in a humidity chamber made of plastic sheeting. The destruction of the main growing point of the sucker releases the axillary buds at the base of each leaf sheath for sprouting. The resulting shoots are carefully excised and transferred to nursery bags, under similar conditions to microcorms, until the plants are ready for transplanting. A single sucker can produce 15–60 shoots.

Tissue culture
Under controlled laboratory conditions, small corms are pared down and disinfected prior to the extraction of the shoot tips. Each shoot tip can be used to produce up to 1 000 in vitro plants, which are weaned at high humidity and relatively low light and then transferred to a nursery to be grown on before transplanting into the field.


Good multiplication practices must be employed in the five methods mentioned to produce plants of superior production potential with a minimum risk of pests and disease. These practices can be categorized by key steps common for two or more techniques as shown in Table 1.

Sucker selection


For suckers or other derived planting material destined for local or within country sale or exchange, the above diseases should be completely absent from the field and all surrounding fields. The farther these diseases are from the source of the planting material, the lower the risk of contamination of the seed material.

Other pests and diseases, especially nematodes, weevils and other viral and bacterial diseases, should be absent or have a low prevalence in the field from which planting material is extracted. This should be confirmed by regular field inspections.

If the sucker is to be used in tissue culture, virus index leaf samples from the mother plant and from all the extracted suckers. Virus indexing also can be used for PIBS to ensure virus-free material for a well-planned and executed multiplication programme.

Sucker preparation

Plate 1 PIBS sucker prepared with x.

Plate 2 PIBS sucker with numerous shoots.

HIGH HUMIDITY CHAMBER FOR PIBS
Multiplication techniques using a high humidity chamber include PIBS and corm fractioning such as sett and minisett multiplication techniques. The sanitary quality of the substrate and the conditions of humidity, light, temperature and drainage in the chamber are critical to ensuring quality material production. The high yield of plants from a single sucker makes this a useful technique for local multiplication of superior or new clones. When viruses are present, initial testing of foundation suckers is necessary. The following practices contribute to high quality PIBS.


LABORATORY TECHNIQUES FOR TISSUE CULTURE MULTIPLICATION
Tissue culture production is a specialized operation. It requires experience and strict procedures to minimize risks from contamination, somaclonal variation and virus activation and, at the same time, to keep production costs within acceptable limits. The cost of in vitro plants is the primary factor that limits wider spread use of this method.

The presence of BSV endogenous pararetrovirus (EPRV) in the genome of interspecific triploid (AAB) and tetraploid (AAAB) varieties results in severe limitations on the use of tissue culture multiplication. The tissue culture process itself is suspected of activating BSV EPRVs in virus-free shoot tips, especially in plantain species. In vitro techniques are not recommended for the multiplication of the AAB varieties, especially plantains, and AAAB varieties. These varieties can be multiplied from local mother plants for distribution to farmers within the same region. However, tissue culture plants of these cultivars should not be exchanged between countries. Other varieties, especially those with the Musa acuminata genome, present no risk of BSV EPRV activation during tissue culture.

For high quality tissue culture plants, the laboratory should be equipped with the necessary equipment to complete the following three phases. Specific protocols and procedures should be followed. The traceability of the shoot tip should be maintained throughout the in vitro multiplication process.


For phases 2 and 3, the recommended temperature range is 20 °C to 35 °C. Artificial lighting should be provided from cool white fluorescent tubes for 12 to 16 hours each day. The laboratory should adher e to set procedures to maintain the sterility of the tissue culture laboratory including no footwear from outside, and required wearing of cap and gown.

Plate 3 In vitro plants ready for planting.

At this point, the plantlets can be commercialized either within the country or exported if they can be guaranteed free of pathogens. To limit the risk of contamination and maintain the quality of the plantlets, they should be transported in sterile conditions with no exterior contact. This recommendation should be compulsory when the tissue culture plants are exported to another country. Rooted plants in non-sterile soil or other media should not be moved between countries (Plate 3).

The importing country may quarantine the material to make observations for signs of diseases within eight weeks, during which time the plantlets should be maintained in quarantine nurseries isolated from all other banana or plantain plantations. Any plants or symptoms associated with quarantine diseases (BBTV, BBrMV, TR4 fusarium wilt, ralstonia and xanthomonas bacterial wilts) should be subjected to further testing. If tests are positive, the entire shipment of tissue culture plants should be destroyed.


The practices below are necessary only for in vitro plantlets. By the end of four weeks, plantlets will have rooted and have three to four green leaves.



The three types of planting material to be processed in hardening nurseries are tissue culture plants that come from a weaning nursery, PIBS shoots produced in a high humidity chamber and microcorms. This phase is intended to bring the plantlets to the stage where they are ready to be planted in the field. Properly hardened plants are ready for transplanting when the last fully emerged leaf measures 20–30 cm in length. No off-type plants should be present. The plants should be of one variety only.


TABLE 2
Risk of transmission of pests and diseases by multiplication method with 100 percent use of good practices

Pest/disease	Suckers selected from field in production	Suckers grown in a multiplication plot	Microcorms	PIBS	Tissue culture
	0 = zero risk; 1 = low risk; 2 = moderate risk; 3 = high risk
Bacterial diseases*	2 (3)	1.5 (2.5)	1 (2)	2 (2)	0.5 (1)
BBTV*	2 (3)	1,5 (2.5)	1 (2)	2 (2)	0 (3)
BSV	1 (2)	1 (2.5)	1 (2)	2 (2)	2 (3) (plantain)
Foc*	2 (3)	1,5 (2.5)	1 (2)	2 (2)	0.5 (0.5)
Other viruses	2 (3)	1.5 (2.5)	1 (2)	2 (2)	0.5 (1)
Nematodes	1 (3)	1 (2)	0 (2)	0 (2)	0 (2)
Weevils	1 (3)	1 (2)	0 (2)	0 (0)	0 (0)

* If the pest or disease is not present in the region or country, the risk is substantially lower
Note: bracketed figures indicate results with limited use of good multiplication practices



Risks of pest and disease infestation
The multiplication practices described above are designed to minimize the risks of transmitting pests or diseases through the planting material produced (Table 2). It is therefore essential to follow each step and specification closely (Plate 4).

Plate 4 Root nematode damage. Bioversity. 2006

Quality standards for planting materials
The quality standards outlined below provide guidance to buyers who are placing an order or receiving a batch of suckers for direct planting or plants produced in a nursery. If the batch exceeds the proposed tolerance limits, then it should be rejected. Once the batch has been acquired, suckers or plants with defective qualities still can be eliminated to improve the quality and uniformity of the resulting plantations. This selection can occur when the plants are being loaded for transport, moved to the field or transplanted.

Size and weight
Suckers and corm pieces for direct planting

Plants produced in nursery

Summary tables of standards TABLE 3 Suckers/corms for direct planting
Suckers/corms health	Removal of roots/peeling to reduce contamination with pests/diseases	Tolerance of corms with partial or total roots: 3 % of corms
	Creamy-white corms resulting from elimination of insects galleries, nematodes, bacterial/fungal diseases	Tolerance: 2 % corms with more that 1/3 corm removed or not totally creamy-white colour
Pseudostems	Cross section without off-coloured rings or liquid or brownish spots	Tolerance of cross sections with offcoloured rings: 0%
TABLE 4 Plants produced in the nursery
Plant size	Last leaf 20-cm length, oldest leaves larger than young ones	Tolerance of plants not reaching size criteria: 1 %
	Height of plant not to exceed two times height of pot	Tolerance of plants not reaching size criteria: 5 %
Off types	Dwarfism, gigantism, mosaic-like, variegated, chlorotic/necrotic leaf patches, droopy leaves	Tolerance off types: 1 % Container Damage/loss of substrate Tolerance: 2 % plants
Container	Damage/loss of substrate	Tolerance: 2 % plants

Other quality planting material standards applicable to a batch of seed or plants
Suckers for direct planting (Table 3)


Plants produced in nursery (Table 4)



The major challenge for the production of clean, high quality planting material is choosing the appropriate technique for the local pest and disease problems and then planning the production process for timely planting. This is especially important in rainfed plantations where planting can be completed during only a few months in the year.

Alternative programmes to produce 50 000 plants when quarantine diseases are present
The use of locally produced suckers for direct fields planting, sucker multiplication plots, microcorms or PIBS brings with it a very high risk of multiplication of the quarantine diseases that may be present. The only options available depend on in vitro multiplication with clean shoot tips thoroughly indexed as free of virus. The initial emphasis of these multiplication programmes should be on diseasefree material but, over a period of 5–10 years, the selection process should also include the identification of superior clones with a high and uniform production potential.

Option 1, in Table 5, is more applicable where in vitro plants are inexpensive and the re-infection rate is high. This approach is used in areas where there is a threat from Foc or where BBTV pressure is very high. Under such conditions, the use of sucker multiplication plots represents a high risk of re-infection before PIBS can be implemented. Option 2 may be applicable where the risk of re-infection is lower and where tissue culture plants are more expensive.

Alternative programmes when major quarantine diseases are absent
In regions where there are no quarantine diseases present, there are numerous options to produce clean planting material. The major challenge in such regions is developing superior clones with a high and uniform production potential. The use of in vitro multiplication is not illustrated among the options in Tables 6, 7 and 8, but may be very effective once superior clones have been identified.

TABLE 5
Options for planting material multiplication where quarantine diseases are present

Option 1. In vitro plants			Option 2. In vitro plants, sucker multiplication plot, PIBS
Steps	Time (months)	Factors in multiplication	Steps	Time (months)	Factors in multiplication
Selection, indexing, cleaning of 55 virusand disease-free shoot tips of desired variety	1–12	Small losses due to shoot tip survival and multiplication	Selection, indexing, cleaning of 2 virus and disease-free shoot tips of desired variety	1–6	Small losses due to shoot tip survival and multiplication
Production of 53 000 in vitro plants	6	1 shoot tip yields 1 000 in vitro plants	Production of 210 in vitro plants	6	1 shoot tip yields 1 000 in vitro plants
Hardening and weaning nursery to produce 50 000 plants	6	Loss of 3% offtypes, damaged containers, plants not surviving transplant	Hardening and weaning nursery to produce 205 plants	6	Elimination of 3% off-types and damaged containers
			Protected sucker multiplication plot to produce 2 000 suckers	8	1 plant yields 10 suckers
			High humidity chamber with 2 000 suckers	6 months	1 sucker yields 25 PIBS
			Weaning nursery with 50 000 plants	6 months	Small loss of damaged containers and plants not surviving transplant

TABLE 6
Planting material multiplication from fields in production (quarantine diseases absent)

Option 3. Suckers from plantation for direct planting			Option 4. Microcorms from plantation into weaning
Steps	Time (months)	Factors in multiplication	Steps	Time (months)	Factors in multiplication
15–20 ha field (1 000 plants/ha) planted for production from which suckers extracted	10	1 plant yields 2 to 5 suckers	15–20 ha field for production from which microcorms are extracted	8	1 plant yields 2 to 5 suckers
50 000 suckers pared and treated for planting	0.5	Small losses of suckers not sprouting	Microcorms pared, treated and grown out in nursery	2	Very small losses of plants not surviving transplant

TABLE 7
Planting material multiplication from sucker multiplication plots (quarantine diseases absent)

Option 5. Sucker multiplication plot			Option 6. Microcorm multiplication plot, microcorm nursery
Steps	Time (months)	Factors in multiplication	Steps	Time (months)	Factors in multiplication
2 ha field planted for production from which suckers extracted	10	1 plant yields 2 to 5 suckers	2 ha field planted for production from which suckers extracted	8	1 plant yields 2 to 5 suckers
1 ha sucker multiplication plot (5 000 plants/ha) from suckers pared and treated	10	1 plant yields 10 suckers	1 ha microcorm multiplication plot (5 000 plants/ha) from suckers pared and treated	8	1 plant yields 10 microcorms
			Microcorms pared, treated and grown out in nursery	2	Very small losses of plants not surviving transplant

TABLE 8
Planting material multiplication with PIBS (quarantine diseases absent)

Option 7. PIBS from suckers from a field in production			Option 8. PIBS from a sucker multiplication plot
Steps	Time (months)	Factors in multiplication	Steps	Time (months)	Factors in multiplication
1 ha field planted for production from which suckers extracted	10	1 plant yields 2 to 5 suckers	100 plants planted for production from which suckers extracted	10	1 plant yields 2 to 5 suckers
2 100 suckers into high humidity chamber	6	1 sucker yields 25 PIBS	250 suckers in multiplication plot from suckers pared and treated	8	1 plants yields 10 corms
Weaning nursery with 50 000 plants	6	Small loss of damaged containers and plants not surviving transplanting	2 100 suckers into high humidity chamber	6	1 sucker yields 25 PIBS
			Weaning nursery with 50 000 plants	6	Small loss of damaged containers and plants not surviving transplanting