[permaculture] [Fwd: [SANET-MG] Diseases of /Musa/ spp.]
Lawrence F. London, Jr.
lfl at intrex.net
Fri May 26 15:58:41 EDT 2006
-------- Original Message --------
Subject: [SANET-MG] Diseases of /Musa/ spp.
Date: Fri, 26 May 2006 19:37:35 +0000
From: Misha Gale-Sinex <mgs2369 at COMCAST.NET>
To: SANET-MG at LISTS.IFAS.UFL.EDU
The banana/plantain is an example often offered by Dr. Raoul Robinson in his teachings on how to re-breed horizontal
resistance back into key food crops, and why this is a crucial agenda for those who depend on agricultural food systems
in a time of unrelenting growth in human numbers and destruction of ecosystem and species diversity.
Nobody seems to be listening.
Here is a very good summary article on the overall issue, from the UK /Observer/. Published last Sunday I believe. It
uses the example of the Cavendish banana.
See also this list of common /Musa/ spp. diseases, from APSnet's "Plant Pathology Online" service:
Hey, what the hell. As long as we have lottery tickets and can drive around, life's great, right?
Only lottery tickets and petrol outsell Britain's favourite fruit - and now
a deadly fungus is threatening its existence. Science editor Robin McKie
reports on a natural disaster that could change our eating habits, wipe out
eco-systems and end a worldwide industry
by Robin McKie
According to reports by biologists, the banana could be heading down the
road to extinction. To be more precise, the Cavendish -- the variety sold
in shops throughout Britain -- may be en route to oblivion.
"We are very concerned," said Ann Vezina of the International Network for
the Improvement of Banana and Plantain. "There is no doubt that the
Cavendish is facing a real problem." Virtually all bananas traded
internationally are this single variety, but biologists have discovered
that several deadly predators -- such as the black Sigatoka fungus -- are
now stalking the Cavendish. The result could be widespread devastation in
the world's main plantations of Latin America and Asia and a corresponding
massive rise in the price of the banana.
The real problem lies with the Cavendish, say biologists. It is sexless,
seedless, and sterile and can only be bred by growing plants from identical
cuttings. In short, all Cavendish bananas are genetically identical clones.
Such similarity spells danger, for plantations of doppelganger bananas lack
genetic diversity and are therefore at risk of succumbing to disease. Once
a fungus evolves past the natural defenses of one set of trees, it will
spread swiftly through the rest.
"At the moment, we have to expend a great deal of effort to fight black
Sigatoka, which attacks the banana plant's leaves," added Vezina.
"Plantations are sprayed intensively with pesticides to keep the disease at
bay. More than a 3rd of the price of a banana goes to pay for these
pesticides." However, retailers stress there is no danger posed from these
The trouble is that fungi are constantly evolving and trying to bypass the
plant's natural defenses. Far from illustrating the hand of an "intelligent
designer," the story of the supermarket banana reveals perfectly the
working of natural selection.
Indeed, it was exactly this process that did in the Cavendish's
predecessor. In the 1950s, Britons ate a different banana from the one now
munched. In those days, the banana of choice was the Gros Michel, until it
was assailed by Panama disease and was wiped out. Now the Gros Michel is an
And that is what worries biologists and banana fans. The Cavendish could
soon follow suit, they fear, and they point out that in some small
plantations, managers have discovered that the Panama fungus -- to which
the Cavendish was supposed to be immune -- has begun to attack and kill
"The fear is the disease will get into some big plantations, then we will
be in trouble," added Vezina. "Once the fungus gets in the soil, it cannot
be got rid of."
The impending crisis is akin to the Irish potato famine, say biologists. In
the 19th century, Ireland depended on a single variety of potato that was
planted over large areas of land and was ravaged by disease in one single
outbreak. The current banana crisis shows that the lessons of monocultures
have not been learned. Only unsustainable volumes of chemicals are
currently keeping black Sigatoka at bay, experts point out.
"One thing we can be sure of is that the Sigatoka won't lose this battle,"
said Dr. Emile Frison of the Consultative Group on International
In a bid to find a solution to the crisis, scientists are desperately
seeking new varieties of wild banana plants that could be grown instead of
the Cavendish or whose genes could be introduced to strengthen the
Cavendish's ability in its battle against Panama, Sigatoka, and other diseases.
But these attempts may be doomed to failure, as the UN Food and Agriculture
Organization (FAO) warned this month [May 2006]. It has found that wild
banana plant species are being wiped out at an alarming rate, as natural
forests are destroyed across the sub-continent.
"Due to ecosystem destruction, it is probable that many valuable gene
sources have now been lost," said FAO Agricultural Officer NeBambi
Lutaladio. "That could cause serious problems, because bananas,
particularly commercial varieties, have a narrow genetic pool and are
highly vulnerable to pests and diseases."
In fact, it may now be too late to do anything, he added. Many of the genes
which could have saved the Cavendish may already have been lost. For
example, India's lost bananas include a variety which is thought able to
confer genetic resistance to Sigatoka. Today, that species exists as a
single plant, which is to be found in the Indian Botanic Gardens in
Calcutta. In short, time is running out for the Cavendish.
Commentary from the ProMED list server moderator tracking this issue:
[The crop plant banana, _Musa acuminata x paridasiaca_, develops symptoms
of the disease black Sigatoka, also known as black leaf streak, when
infected by the fungus _Mycosphaerella fijiensis_. It also develops
symptoms of Panama disease (aka Fusarium wilt) when infected by the fungus
_Fusarium oxysporum_ f.sp _cubense_ .
In the developing world tropics, bananas rank 4th as a staple crop after
rice, wheat, and maize. Various different banana types are grown for these
domestic markets, and disease management does not suffer so severely from
the problems associated with monoculture of a susceptible variety grown for
the export market, which is the main topic of the article posted here.
This particular news item has been used by many of the world's journalists
in May 2006, and this article by Robin McKie is one of the better
treatments of the subject. The specific pathogens mentioned, black Sigatoka
and Panama disease, have been well covered by ProMED-mail over the years
(see archived posts below), and nothing new about these diseases is
presented here, but I have included the article because it is a reminder of
the impact of plant disease on human affairs.
Several principles of plant pathology are to be found in the worldwide
export banana industry. Over-reliance on monoculture of a susceptible
cultivar is never going to be a good thing for disease management. Overuse
of fungicides is the inevitable result, and is probably not sustainable for
cost and environmental degradation issues. New strains of pathogens with
genetic change towards increased virulence are inevitable (Panama disease
in this case). The use of non-fertile selections of a
vegetatively-propagated plant prevents crop improvement by breeding. Loss
of worldwide germplasm as a source of genes for resistance denies plant
breeders the genes they need for crop improvement. This is quite a list.
A specific observation that has triggered a focus on the banana as an
export crop is a new fungal strain, called race 4 of Panama disease, which
has struck in Southeast Asia (20050830.2565), and can kill Cavendish
bananas in the tropics. If, on top of black Sigatoka, Panama disease were
to sweep through other big banana areas, such as top export producers
Ecuador, Costa Rica, and Colombia, the Cavendish reign on supermarket
shelves could be ending.
Two solutions to the specific problem would be genetic modification of
banana for increased disease resistance, and the selection of alternate
varieties of banana from the choices that are available for the world
market. A well balanced article in Science News that discusses the
alternate sources of bananas to replace the Cavendish is presented in the
The issues raised here are discussed fully in an article by Dr Randy
Ploetz, cited in the link below on black Sigatoka. He made these closing
remarks: "In the future, products of the breeding programs [which he
discusses earlier in his article] will play increasingly important roles in
subsistence agriculture. Whether new hybrids are used eventually to replace
the Cavendish cultivars that are used by the export trades, however,
remains to be seen. The very substantial infrastructure that characterizes
export production is focused on producing only these cultivars. Converting
these operations to the production and handling of another type of banana
would be an expensive proposition. Moreover, the currently available
hybrids do not meet the very high standards for fruit quality and
post-harvest shelf life that are demanded by the trades. Yet, as fungicides
continue to lose their effectiveness against black Sigatoka, and as the
practice of fungicidal disease control becomes more expensive and less
appealing to consumers in the importing countries, the trades may
eventually be forced into making the difficult transition away from the
This spotlight on the problems in worldwide banana production may well
focus attention on the current and future breeding programs aimed at
improvement of the crop, which are summarized by agencies such as the
International Network for the Improvement of Banana and Plantain (INIBAP).
Perhaps the old vaudeville troupers were on to something when they sang
"Yes, we have no bananas."
Links: Black Sigatoka:
Panama disease: <http://helios.bto.ed.ac.uk/bto/microbes/panama.htm>
<http://www.inibap.org/> - Mod.JAD]
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