Disease threatens African banana industry

Experts concerned with Africa's banana sector are trying to increase production of the crop that currently feeds about 100 million people in sub-Saharan Africa. But their efforts are threatened by diseases that result in banana farmers across the continent losing half their yields – and sometimes even more. Scientists warn that this could soon lead to more severe food shortages in some parts of Africa. For many on the continent, the green boiling banana is a staple food, and they depend on it to save them from hunger.

Bananas are particularly susceptible to disease, says Dr. Irie Vroh, a molecular geneticist with the International Institute of Tropical Agriculture. He explains that this is because bananas grow directly from "mother plants," and not from seeds.

"From the roots of the mother plant grow many small progenies…. They are clones of the mother. So, if the mother is sensitive to a disease, the progenies are also automatically sensitive to that disease," Vroh tells VOA from his office in Ibadan, Nigeria, where he leads his organization's West African banana program. "Disease is one of the main problems affecting banana and plantain…. Diseases and pests are a major problem for these clonally propagated crops."

Thomas Dubois, a Belgian scientist with the Consultative Group on International Agricultural Research, adds that when farmers take cuttings from banana plants they're unaware are infected with disease, and replant them, or sell or exchange them with fellow growers, they unwittingly spread plant sicknesses. In so doing, he says, their crops are often "wiped out."

In Kampala, Uganda, Dr. Fen Beed studies diseases afflicting African banana crops.

"I try to determine how exactly the disease spreads and how it infects plants, and try to identify interventions based on this," he says.

Beed explains that bananas in Africa, and especially in East Africa, are currently succumbing to a disease that was first diagnosed in Ethiopia in 2001.

Wilt attacks African bananas

Bacterial wilt – scientific name, Xanthomonas – causes banana plants to literally waste away. The leaves of infected plants turn yellow, and ooze yellowish fluid. Bunches of bananas ripen prematurely and rot. Beed says the disease has destroyed up to seventy percent of crops in afflicted areas. As a result, some countries aren't producing enough cooking bananas to feed their populations.

"(Bacterial wilt) has spread right across Uganda, and more recently has spread into Rwanda, Tanzania, Kenya, Congo and is suspected in Burundi," says Beed.

He says the disease has "devastated" banana production in Uganda, which harvests 10 million tons a year, making it the world's second largest banana producer after India. Analysis of the situation in the East African nation reveals that the disease, if uncontrolled, will result in the loss of almost 60 percent of production in the near future.

The scientific website, Science Development Net, has quoted a Ugandan government official saying bacterial wilt could cost his country up to eight billion dollars in the next five to ten years, with the majority of the population likely to be in danger of hunger.

Incurable disease

Experts say no matter what measures are taken by Africa's agricultural sectors against bacterial wilt, the disease is extremely difficult to prevent and control. Beed says the sickness affects banana plants at such a "rapid" rate that by the time farmers become aware that there's something wrong with their crops, it's too late to respond effectively.

Certain insects are also carriers of the disease, and most African farmers can't feasibly spray their banana crops with chemicals to protect them against infection by pests. Dubois says because of the "immense" size of banana plants, the crops would require a lot of chemicals, and this proves too expensive for the vast majority of African farmers – even in places where such pesticides are available for sale.

Scientists say plants infected with bacterial wilt can't be cured; the best farmers can do is to take preventive measures to control the disease.

"We advise farmers to uproot infected crops," Beed states, but then continues, "one of the things that was most disappointing was that once we did recommend the removal of infected plants, there wasn't a system in place within the national frameworks of the countries in which we're operating to actually replace this infected material with new, clean material."

Beed says African banana farmers are trying to get clean plants in an effort to resume production. But in most cases, they're too poor to do this.

"And that system wasn't in place to try and combat the losses that they'd suffered. That's actually resulted in some farmers moving away from banana to growing cassava and maize; this is true of central Uganda."

Beed acknowledges, though, that impoverished African farmers are hesitant to destroy their only means of livelihood. Yet even when they've taken this radical step, the negative consequences have mounted.

"The perennial qualities of the banana enable the soil to be maintained. This prevents erosion and environmental degradation, retains the structure and the water within the soil. So when bananas are removed as a consequence of disease, it's not just damaging to the banana industry, it's damaging to the environment…. It causes erosion," Beed explains.

Scientists are constantly advising that farmers not use implements that they've used on infected plants on other plants, and to sterilize their tools. But Beed says information about preventive measures such as this often doesn't reach farmers, most who live in very isolated areas.

He posits that the wilt "catastrophe" offers evidence that "no system is ever that durable because the pathogens can always adapt, or new pathogens can be introduced. This is particularly apparent when we see that both trade and commerce of agricultural products is increasing all the time, so there's always this risk of a disease coming in (to a country)."

Other diseases set to hit Africa

Beed warns as well that Panama disease, one of the "most notorious" of all plant diseases, is set to strike in Africa in the near future. This sickness has wiped out production in South America of the previously popular "Gros Michel" dessert banana.

Beed says Panama disease is particularly hard to control, as it's constantly mutating and is set to threaten production of the Cavendish dessert banana in Africa.

"The difficulty we're facing now is that there's another race of Panama disease, which is called tropical race four, which is present in Asia and will come to Africa at some point, and this will knock out Cavendish, because the Cavendish doesn't have any resistance to this particular form of the disease," Beed tells VOA.

Dr. Irie Vroh adds that black sigatoka, a leaf spot disease caused by fungus, is also having a "devastating impact" on banana production in sub-Saharan Africa.

Beed also warns as well of the intensification in Africa of banana bunchy top virus that causes the stunting of banana plants.

"It seems to be attacking all types of banana. This is particularly worrying because we're not quite sure why it has started to spread," Beed says.

Scientists say no banana variety is resistant to this virus, with infected plants largely unable to bear fruit.

"We're doing surveys and investigating and analyzing its molecular constitution, to try to determine why it is now becoming more of a problem than it ever was before," says Beed. "We're trying to determine what the main parameters are encouraging the spread of this… such as climate, location and so on. If we can do that, then we'll better be able to identify control interventions."

Tissue culture solution

Dubois says a potential long-term answer to the disease danger facing Africa can be found in the laboratories of international agricultural research organizations.

"What farmers nowadays can do – and what is being done all over the world except in Africa – is something called tissue culture. This is a technique by which you produce small little plants in a laboratory, in a sterile condition (and in so doing) you make clean planting material," he explains. "You get rid of the pests and diseases that normally associate with banana plants before you plant them in the field. This is also a very quick way to very rapidly multiply lots and lots of bananas."

Dubois says bananas also grow much faster through the use of tissue culture.

"It gives farmers the chance to get more income, to market the products they get as a result of those tissue cultures," he enthuses.

Dubois, though, acknowledges that plants raised from tissue cultures are a "bit fragile" and require further scientific modification to enable them to survive under harsh African conditions.

"To put them in fields that are burdened by pests and diseases and that are suffering from bad management in Africa, these plants need something extra. So I put microbes in those plants, to bolster them and make them into a kind of super-plants, to stimulate their immune system," he says.

But Dubois and other scientists agree that such technological advancements are presently beyond the reach of the majority of African banana producers, who in the near future are set to continue to suffer the wrath of diseases.


Source: voanews.com

Publication date: 1/20/2009