Can we beat the Banana Bunchy Top Virus?!

Banana growing countries across the world are at risk of invasion from the boisterous Banana Bunchy Top Virus!

 

Surprisingly, Invasive Alien Species can come in the form of micro-organisms, like the Banana Bunchy Top Virus. First recorded in Fiji in 1889, it has now invaded more than 120 countries worldwide, and scientists are trying to find a way to control this dangerous disease and prevent further spread in banana plants! 

What does this dreadful disease actually do?

The classic symptoms of infected banana plants include an overall dwarfed effect, bunching up of leaves, lack of fruit production and dark green streaks on the leaves, as reported by Kumar et al. In the image below, the 'In' shows the infected plant compared to the healthy 'He' one. 

The stunted growth and reduced fruit production cause detrimental economic and health effects. Worldwide production of bananas exceeds 100 million tonnes, and it is the 4th most important food crop behind rice, wheat and maize according to Cook et al., making it fundamental to millions of livelihoods. 

What is the main mechanism of invasion?

The Banana Bunchy Top Virus (BBTV) either gets transmitted by the aphid, Pentalonia nigronervosa (as shown by the image to the right) or by infected plants coming into contact with healthy ones. In Hawaii specifically, Almeida et al. believe that the movement of contaminated plant material across and between the islands led to this epidemic destroying large amounts of their crops. 

Almeida et al. describe the human transportation of these plants to new sites, both with and without the aphid being present upon them, as a type of Pathogen Pollution. This invasion of virus' into places outside their native area cause the host (the banana plant in this case) to be at a new risk of infection and hence human activity is causing major spreads of diseases and not just in the banana plant! 

With the world's population size continuing to grow rapidly, the demand for food is ever increasing meaning that more banana plantation sites are being formed. The set-up of theses farms requires the transfer of crops from previous areas, and this is where the cross-contamination occurs. Also, as mentioned in another blog post, improved transportation efficiency is allowing plants, animals and micro-organisms to spread to new invade-able areas meaning that diseases like BBTV can spread even more easily thanks to our increased trading and travels. Bananas generate both an income and a food source for people all over the world and so the management and control of diseases that destroy them is highly important, but how is it done? 

Methods of management?

The Cooperative Extension Service of the University of Hawaii says there are two ways of controlling such a disease either by killing the aphid's that carry the disease of removing all the infected banana plants from a particular site. 

For the Banana Bunchy Top Virus in Australia, Cook et al. predicted the amount of area that would be affected by BBTV if no management strategy was enforced (Nil Management) vs, a plan of Active Containment. This Active Containment plan involved destroying any previously infected crops and as soon as the infection was detected locally, to stop further spread. As the graph to the left shows, the Active Containment reduces the amount of land diseased drastically, with the variance shown being due to the risk of re-emergence and eradication is not 100% effective. 

However, these plans and policies are very effective in theory but when it comes to practising them, it is never as successful. For instance, in 1993 in Australia a five-year programme was carried out to eradicate Banana Bunchy Top Virus but did not fully work and by the end, not all of the disease was removed and so spreading began again. 

In sub-Saharan Africa BBTV is also widespread but due to different socioeconomic conditions, long-term, wide-scale programmes like done is Australia are as suitable, even if they did become entirely effective. As a result, Kumar et al. proposed some new ideas on how to control BBTV in sub-Saharan Africa:

• Educate farmers on how to efficiently destroy diseased crops 
• Supply clean, BBTV free planting material to farmers 
• Improve monitoring schemes 
• Deploy rapid removal responses to the detection of the disease 

The schemes suggested are not mutually exclusive but can be used together to detect, destroy and prevent re-infection in plantations efficiently. Such epidemics require cooperation between the governments, local authorities and the farmers themselves in order stand any chance of effective control.

 Do you do think the consumer has any responsibility for making sure they buy bananas from farms that actively try to reduce the spread of BBTV? Should this information be made available?

Whatever your view,  next time you buy a banana, just remember how lucky you are that that one escaped the grasp of the famous Banana Bunchy Top Virus!!