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Two Serious Bananas Diseases Emerging 

By Okolle N. Justin*

Bananas and plantains are two important food crops to many people in the world as well as a staple to many in the Sub-Saharan region especially Cameroon.  Generally, these plants are attacked by several pests (e.g. borer weevils, nematodes, mealy bugs, thrips, spider mites, caterpillars etc) and diseases (e.g. sigatokas, fusarium wilt, cigar-end rot etc). 

Infected banana sucker

In a workshop held recently in Tanzania, scientists mentioned that in banana/plantain agro-ecosystems, farmers are reporting two new serious diseases spreading within Africa (especially in the Central and Eastern regions). These two diseases are; the Banana Bunchy Top disease (BBTD) and (ii) Banana Xanthomonas Wilt (BXW).  These diseases unlike the panama or fusarium wilt are dangerous for two reasons; for BBTD, once established, it is extremely difficult to eradicate or manage it and bunches/fruits are not produced, and for BXW, fruits become inedible.

Banana Bunchy Top Disease (BBTD) is caused by the banana bunchy top virus and it is transmitted by an insect known as the banana aphid. Transmission is also by transportation of infected material. 
Alternate hosts of the vector:
Cavendish bananas are the most susceptible but no variety is resistant. The insect vectors (aphids) also feed on Heliconia and flowering ginger plants. 

Typical Symptoms and Damage
Initial symptom consists of dark-green streaks in the veins of lower portions of the mid-rib and leaf stem (series of "dots" and "dashes").  On infected plants, new leaves emerge with difficulties, and are narrower than normal. If infected plants produce bunches, the fruits are likely to be distorted and twisted. 
Management Techniques
 

(a) Managing the vector
– Frequent surveys or scouting at least twice per month. 
– Natural enemies (e.g. lady bird beetles) can be used to kill the aphids.
– Control weeds around bananas as they can serve as alternate hosts. Spray such infested hosts with suitable registered insecticides such as diazinon (an organophosphate) and an imidaclopride (a systemic insecticide)
– Control associated ants as they protect the aphids or even carry them from one area to another.

 (b) Managing infected plants
  This can be done either by injecting the plants with herbicides or rogueing (removal and destruction of infected plants).  
– Prune unwanted suckers as aphids prefer young plants to feed on.
– Use a systemic herbicide (Round Up – Glyphosate) Even if a single sucker is infected, entire mat should be destroyed.

(c) Quarantine
Countries, regions, states/provinces might prohibit importation and exportation of banana planting materials without permits. Movements of banana/plantain plants except fruits should be controlled
– Buy disease-free tissue culture plantlets or macro-propagation plants to establish plantations or farms. 
– Banana plants and potential alternate host plants should be inspected for aphids before importation/exportation and within country transportation.

Banana Xanthomonas Wilt (BXW)
The Pathogen, Disease Development & Spread
– BXW or Banana Bacteria Wilt (BBW) is caused by a bacterium referred to as Xanthomonas campestris.
– The bacterium attacks the vascular bundle of the plants making it difficult for the plants to get enough water and minerals.
– The disease is transmitted by vectors such as nectar-sucking insects, bats and birds as well as by contaminated tools.
– Other important modes of spread are (i) the planting of unclean or infected suckers in the field (ii) movement of infected plant parts, (iii) grazing animals.
Typical Symptoms and Damage

(a) External
– Premature yellowing and wilting of leaves begin from younger central leaves before extending to the outer older leaves.
– There is snapping at about 1/3 of the leaf length from the leaf tip. 
– Infected male bud may change colour from purple to dark brown; they eventually shrivel and dry up.

(b) Internal
– When the fruits are cut dark brown colour is noticed on the pulps and cut fruits might produce yellow-orange pus-like fluid.
NB: For actual confirmation of the disease (pathogen), bacterial streaking or Polymerase Chain Reaction (PCR) should be used.
Management Techniques
-The male buds should be removed as this helps to limit activities of foraging air-borne vectors such as birds, bees, etc.

– Increase surveys in banana/plantain producing zones
– Use clean suckers and clean tools when planting in the fields.  Clean planting materials are usually from stem bits (macropropagation) or from laboratory tissue cultured plants (micropropagation).  Tools should also be disinfected before use.
-Sensitizing the population especially farmers and extentionists. 
– Quarantine (as for BBTD).

Situation and Way Forward for Cameroon

In an International Workshop on BBTD and BXW held in Arusha, Tanzania on the 24th – 28th August 2009, Cameroon was represented by two researchers (Dr. Okolle N. Justin and Dr. Mouliom P Alassa of CARBAP, Njombe) and Mrs Alice Ndikontar of MINADER Yaounde. During the five-day workshop, the participants from Cameroon noted many people in the country are not aware of the diseases. 

Based on these, surveillance, diagnosis, use of clean planting materials, socio-economics analyses including public awareness were ranked as top priorities. The following were decided by the participants as major research priorities (i) epidiomology of the diseases, (ii) development of quick and user-friendly field diagnostic tools, (iii) economic and social factors affecting invasion, persistence and eradication efforts, and (iv) development of Integrated Pest Management packages for management of the diseases/vectors.

Lecturer, Department of Plant and Animal Sciences, University of Buea
Tel: +(237)74534786. E-mail: okollejustin@yahoo.com , agrovitalservices@yahoo.com
Website: www.carbapafrica.org

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