Copyright © 1998
ONIONS IN THE TROPICS & SUBTROPICS
INTERVIEW WITH DR. LESLEY CURRAH, NATURAL RESOURCES INSTITUTE (U.K.)
Published 1992
A case could be made that onions are one of two universal vegetables that
are cherished in almost every culture, tomatoes being the other. Both
are difficult to grow in many tropical and subtropical climates. Where
a vegetable is both popular and difficult to grow, it brings a good price.
If a way can be found to grow that crop, both local farmers and consumers
will benefit. While attending a horticulture conference in Honduras, Scott
Sherman and I had an opportunity to visit with Dr. Lesley Currah. She
travels the Third World working with onion researchers. The interview
follows. Be sure to note the offer of seed for a variety trial at the
end.
Q. Tell us more about the Natural Resources Institute where you
work.
A. The NRI is an agency of the British government, the Overseas
Development Administration. Their purpose is to use science and technology
to help people in Third World countries develop using their own natural
resources. Help is offered to any country eligible to receive British
aid.
|
Q. What is your assignment?
A. I work in the fruit, vegetable and root section. My current
assignment is an evaluation of onion production and storage in low latitudes.
A particular interest is to expand onion production in very wet climates
and on islands at sea level. Our approach is fourfold. (1) We are promoting
a network of contacts on onions in the tropics through a newsletter
called Onion Newsletter for the Tropics. (2) We evaluate onion
varieties through trials done by collaborators around the world. (3)
We provide training in how to do a trial and interpret the results.
(4) We maintain a gene bank of interesting onion accessions.
|
Q. Often a development worker from a temperate climate will plant
onion seed from home only to find that it only makes "little green onions,"
no bulbs. Explain what is happening.
A. Onions are very sensitive to day length. The kind of onion
that is grown in the higher latitudes requires long day length to form
bulbs. When onions are grown during short days it is important to plant
what are called "short day onions."
|
Q. Is there a sharp border between long and short day varieties
or are there degrees of short-day-ness?
A. There are several intermediate degrees, which would be common in
places like north Texas or Spain. A well organized seed catalog will
not just say whether onions are "short" or "long" day varieties. They
will organize them under day lengths, e.g. 11-13 hour, 12-14 hour etc.
Some varieties like Beth Alpha in Israel go to less than 12 hours. These
mature around Christmas. However, because the quality of onions harvested
at mid winter is often inferior, e. g. with more double bulbs, farmers
usually want onions to mature as days begin to lengthen but before the
rains have started.
|
Q. What does happen if you plant a long day onion near the equator?
A. As you said, they grow into little green onions. They may thicken
a little at the base. They may actually be preferable for producing
little green onions because the short day types might begin forming
bulbs too soon.
|
Q. Do onion sets exist for short day onions?
A. Many in the tropics use the set system to get onions going near the
end of the rainy season in order to extend the onion harvest forward
in time. Probably 30% of the onions in Bangladesh are grown that way.
Sets are commercially available in Zimbabwe. However, the quality of
onions grown from sets can be inferior, for example with more double
bulbs.
|
Q. How would a farmer make his/her own sets?
A. Just as the hot season is starting, sow seeds at a very close spacing.
Do not thin the onions. Harvest at * inch (1.25 cm) diameter or else
they will bolt. If they are sufficiently crowded and if it is well past
the day length where the variety would normally bulb, they will die
down naturally. It may take a few seasons of trial and error to get
it right. Keep the sets in an airy, warm place, for example, just under
the rafters.
|
Q. Under what conditions might a farmer be able to save his/her
own onion seed? 
A. This is difficult. You need a variety that will easily bolt (send
up a flower stalk) the second year. You do not want any variety that
bolts the first year because that trait would create havoc in your harvest.
Select bulbs from the best onions and store until the next season. Timing
then becomes important. If you plant too soon while daily temperatures
are increasing they may go into bulbing mode and split rather than flower.
Wait to plant the bulbs until the average daily temperatures have started
decreasing. The stalk gets a lot of diseases so, unless it is very dry,
you may need to spray a lot.
|
Q. What do you look for in a variety trial?
A. You would want most varieties in your trial to be acceptable
to local people. If onions are eaten raw, you want varieties which are
mild; if cooked, pungent onions that store well. The pungency, by the
way, depends not only on the variety of onion but also on how much sulfur
is in the soil. You would want to look for onions where a high percentage
of the harvested bulbs are marketable and where the bulbs store well.
Even the shape and color may affect marketability and price.
|
Q. How should onions be stored?
A. We are writing a bulletin on storing onions in the tropics. The humidity
should be about 75% and the temperature 25-30°
C. If the temperatures drop much below 18°
C the onions may begin to sprout. For example, in Zimbabwe we found
that stored onions began sprouting when evening temperatures dropped
to 15°
C. This is somewhat dependent upon variety, but only to a limited degree.
Light is not a very important factor. Light may cause some fading of
red onions on the surface only. Light can also cause some green color
to develop in white onions.
|
Q. Do short day onions store reasonably well?
A. Yes, but there is room for improvement. The Israeli's have been working
to select grano and granex types that will store for a long time. The
factors they select for are ability of the bulb to go into a good dormant
period and qualities in the skin that will protect the bulb. Their varieties
are being tested all over the tropics.
|
Q. I notice a lot of short day onions named "grano" or "granex,"
followed by a number. What are these?
A. Texas grano onions came from onions in Spain which over-wintering
well in the field, but have poor storage characteristics in general.
The granex series is hybrid, the grano open pollinated (non-hybrid).
|
Q. This brings up an important question. If you are working where
it is possible to produce your own onion seed, would it be a big mistake
to save seed from a hybrid onion?
A. No, if you are prepared to do a little selection, and if
the hybrid is much better than the locally available varieties, you
might end up ahead. For example, in India the Pusa Ratnar variety came
from the red granex hybrid. You might have some problems with male sterility
in early generations.
|
Q. How are onions pollinated?
A. Onion pollen is sticky, so there is not much wind pollination.
They are pollinated by insects, such as honeybees. Some seed producers
throw dead chickens in the field to attract blow flies. Some crawling
insects are also pollinators.
|
Q. Some of the special seeds that ECHO distributes have come from
members of our overseas network. Is there any way in which they might
help you?
A. I am interested in any traditionally maintained, locally
grown onion. However, the needs of our seed bank require that we obtain
about 50 g of any new accession. England is so far north that we are
unable to increase the seed ourselves. If someone has an onion that
might be of interest, they should first write and tell me as much about
it as they can, and why they value the onion. My address is: Lesley
Currah, Horticulture Research International, Wellesbourne, Warwick,
CV35 9EF, United Kingdom.
|
SEED AVAILABLE FROM ECHO
 Dr. Currah has put
together seed for a large onion variety trial that she sends to selected
researchers around the world. Most members of ECHO's network would not
have the resources to qualify to participate in such a large trial. However,
she has sent one trial for ECHO to subdivide and make mini-trials available
to you. We have divided them into five sets of six varieties each. We
will send one set at no charge to development workers assisting peasant
farmers or to university researchers. When you report the results you
can request another set. She asks that you be sure to include the best
local varieties in your trial for comparison. If you have the resources
to handle a larger trial we will consider a request for two sets, but
include a paragraph describing how they will be used. Formal researchers
who need both more varieties and more seeds of each, write to Dr. Currah
directly to inquire about joining her onion research network.
Dr. Currah is interested
in learning how the onions grown from these seeds perform in many different
environments. If you are willing to take some careful data, indicate this
in your letter. We will then send some special report forms that she has
provided, rather than ECHO's general forms.
ECHO, 17430 Durrance Rd., North Ft. Myers FL 33917, USA
Phone: (941) 543-3246; Fax: (941) 543-531
|
