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01/18/2006
My Endangered Breakfast Banana
Last week we talked about the impressive achievements of the
Mars rovers and orbiters. My column of October 5, 1999 began
on a different note. A Mars orbiter had been lost because of a
horrible case of someone neglecting to convert from the metric to
the English system of units, or vice versa. Actually, the main
subject of that 1999 column was the so-called charge-coupled
device, or CCD, and a chat with Willard Boyle and George
Smith, the inventors of the CCD, at a Bell Labs celebration of the
50th anniversary of the invention of the transistor. I mentioned
in the column that I told Boyle and Smith that I didn’t understand
why they hadn’t received the Nobel Prize for their work.
My comment was based on the fact that the CCD revolutionized
the acquisition of the photographic image. If you’ve ever used a
camcorder or digital camera, if you’ve marveled at spectacular
pictures of galaxies or gas clouds in the far reaches of the
universe or if you’ve had a medical endoscopy, CCDs were
likely involved. With CCDs, astronomers can see things
thousands of times fainter than they can with film or,
alternatively, see faint things with vastly shorter exposure times.
Although Boyle and Smith have not received the Nobel Prize,
they’ve just been named as the recipients of what some term the
Nobel of engineering. In February, they will receive the
National Academy of Engineering’s Charles Draper Prize. The
prize carries with it a cool $250,000 each for Boyle and Smith
and they deserve every penny of it. Another winner of the
Draper Prize was the late Jack Kilby, for his invention of the
integrated circuit. Coincidentally, in that 1999 column, I also
mentioned an embarrassing conversation with Kilby, mistaking
him for a former Bell Labs colleague at that Bell Labs
celebration. (If you’re interested in a rough description of how
the CCD works, I suggest you click on that column in the
archives.)
Well, let’s turn from the CCD to something that in the overall
scheme of things is much more important to millions of people –
the banana. According to my 1962 World Book Encyclopedia,
the banana that I ate as a child was almost certainly a variety
known as Gros Michel. Craig Canine, in an article titled
“Building a Better Banana” in the October 2005 issue of the
Smithsonian magazine, translates Gros Michel as “Big Mike”.
Today, and for the past 30 or 40 years, my breakfast has begun
with one banana blended with 2 cups of orange juice, which I
split with my wife. The blend not only tastes good but also
provides a healthy slug of potassium and makes the morning’s
dose of pills go down more smoothly. My wife, who has trouble
swallowing pills, says she couldn’t live without the added
banana.
Canine calls the banana the number one fruit in the world and
says that in the U.S. the average person consumes over 26
pounds of bananas a year. I suspect that I consume more than
that. However, for us Americans, the banana is relatively
unimportant when compared to its importance in other parts of
the world, say Uganda. There, the average person consumes
over 550 pounds of bananas a year! In fact, the Ugandan word
for banana also has a broader meaning – food. So, if you invite a
Ugandan to dinner and don’t serve any banana dishes, you
haven’t served any food! For these people, the banana is the
major source of nutrition at a price they can afford. These people
literally would have trouble living without the banana.
Back to my breakfast, that banana in my orange juice is no
longer the Big Mike, but another variety known as the
Cavendish. Almost all the bananas exported today are the
Cavendish variety, which falls in the category of a “dessert”
banana. Compared to the Big Mike, the Cavendish is thinner
skinned, more delicate and harder to handle and ship and, to
banana connoisseurs, not as tasty as was the Big Mike. So why
are we all eating the Cavendish? Therein lies a cautionary tale.
Back in the 1940s and 1950s, a soil pathogen known as Panama
disease dealt the Big Mike a deathblow. However, the
Cavendish was surprisingly immune to Panama. The United
Fruit Company (now Chiquita Brands International) led the other
major banana dealers in replanting their plantations with the
Cavendish. With the hardy Big Mikes, they could ship huge
bunches of bananas from the farm to the grocery store but with
the Cavendish bananas they had to cut them into small bunches,
wash and pack them gently into protective boxes for shipping.
OK, that’s history, what about today? As Yogi said, it’s d j vu
all over again. Now it’s the Cavendish that’s under attack,
mainly by an airborne fungus known as black sigatoka after the
Sigatoka Valley in Indonesia where the fungus was first found.
The airborne fungus has spread all over the world and attacks the
banana plant leaves, shutting down the plant. The fungus does
its job on many kinds of bananas but the Cavendish is the most
sensitive. Indonesia and Malaysia are also contributing another
more deadly strain of Panama disease known as Tropical Race 4,
which affects more varieties than the original Panama; this time
the Cavendish is also hit.
Today, 20 percent of Chiquita’s costs are spent trying to control
the Sigatoka fungus. On large plantations, the fungus is attacked
through aerial spraying of fungicides, an expensive and
environmentally distasteful approach. With the Cavendish under
siege, an urgent search is on for a disease resistant banana that
could replace it. One might think that one approach would be to
try to breed a disease-resistant Cavendish, but there’s a problem.
Like a mule, the Cavendish is a hybrid that can’t reproduce. It
has no seeds or fertile flowers to work with. It’s propagated by
the suckers that spring from its roots, has no pollen to give and
can’t be pollinated.
Every so often, you read about some animal species in danger of
extinction because of a lack of genetic diversity. A small
isolated population of animals doesn’t get a chance to mix it up
with other populations and its genes, both good and faulty, get
propagated down through generations. A history-changing
example of this in the plant field is the famous Irish potato
famine in the 1800s that spurred massive migrations out of
Ireland, many coming to the U.S.A. What happened was that the
Irish farmers all planted the same variety of potato and an
airborne fungus came along that quickly led to whole fields of
rotten potatoes. So it could be with the Cavendish.
When and if the Cavendish goes extinct, all is not lost. There are
almost 1200 varieties of bananas housed as little plantlets in a
building at the Catholic University of Leuven in Belgium.
Obviously, Belgium is not known for its bananas and that’s the
point. With no native bananas, there’s no danger of a disease
such as the Panama wiping out a nonexistent crop. The
University’s collection preserves both cultivated and wild
varieties as well as improved or hybrid varieties.
While the Catholic University’s collection consists of plants the
size of a little finger, a closer approach to reality is found in the
African state of Cameroon. Here the African Research Center on
Bananas and Plantains has a field collection of rows of plants the
size of trees. (The banana plant is not a tree.) There are over
400 varieties of bananas in this 6-acre field, including the two
wild ancestors of the Cavendish and other edible bananas. If you
cut open the fruit of these ancestors you find them loaded with
hard seeds. When these two varieties crossed or were crossed
with each other they formed the hybrid plantain, the hefty,
starchy banana favored in Africa and other tropical locales.
So, enjoy those Cavendishes while you can; they may not be
around in a few years. Hopefully, if the Cavendish does go
extinct, there will be a resistant banana to replace it. Canine
described a possible replacement, the Yangambi Km5. It has a
thin skin, making it difficult to handle and ship but it’s amenable
to crossing with other varieties and the hope is that they can get a
thicker skin, consistent with a good size of the fruit. Canine
describes the taste as “sweet, though far from cloying,” with
“hints of strawberry, vanilla and apple – perhaps even a dash of
cinnamon.” Hey, I’d love to try that Yangambi in my morning
blend with orange juice!
Allen F. Bortrum
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