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April 17, 2000


Responses to "just a thought"


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Original message (April 15), followed by responses ….

Date:Apr 15 2000 14:05:45 EDT
From:"Ewer, J, Jonathan, Mr"
Subject:Just a thought

There seems to have been a lot of talk on the out crossing of Bt to
wild and weedy relatives of Bt crops. It has been stated that Bt
toxin would not confer a selective advantage to weeds. However, I do
feel that the insect resistance confered on these weeds (if such
weeds exist) would give them a huge selective advantge.

Although I'm in favour of GM I dont think its altogether wise to go
around cloning toxins until we can prove that the genes cannot out

Just a thought.

Date: Apr 17 2000 05:02:03 EDT
From: Rick Roush
Subject: Re: Just a thought


There has been a lot of concern about this, but I am still looking for a
plausible case that Bt will make much difference to weediness. Few if any
weeds that can outcross with crops appear to be limited by caterpillars or
other insects targetted by Bt. For example, canola might outcross with
wild radish. For other reasons, we have tried to collect a lot of
diamondback moths (Plutella) from wild radish, and although you can find
the larvae, they are clearly not at damaging densities, possibly because of
the current natural defenses in the weed.

I agree that we ought to be careful, but I'd like to see evidence that any
candidate weedy relative of crops is actually limited by herbivory from
Lepidotera or even Coleoptera, which are the only two orders that appear to
be targetted for control by Bt crops.


Date:Apr 15 2000 14:37:23 EDT
From:"Dr. José Luis Solleiro Rebolledo"
Subject:Re: Just a thought

Well, sure you need to think twoice, but science provide the tools for resistance management, doesn't it?

José Luis Solleiro

Dear Mr. Jonathan:

Your thought certainly is reasonable in theory. It is logical and is mechanism-based.

However, it is highly unlikely to be a practical significance. As you can guess, the frequency of
gene transfer in your model will be a function of the natural outcrossing frequency to "wild and
weedy relatives." For most crops in the United States, there aren't any.

In Mexico, where the "wild and weedy relatives" of maize do exist, inter-breeding is rare:

"Nonetheless, in the wild, introgressive hybridization does not occur because of differences
in flowering time, geographic separation, block inheritance, developmental morphology and
timing of the reproductive structures, dissemination, and dormancy (Galinat, 1988).

A more distant relative of maize, Tripsacum, does exist in the US, but it is very difficult to make
crosses, which are mainly sterile:

"The closest generic relative to Zea is Tripsacum, a genus of seven species, three of which
occur in the United States (Gould, 1968). Tripsacum differs from corn in many respects,
including chromosome number (n=9), in contrast to Zea (n=10). All species of Tripsacum
can cross with Zea, but only with difficulty and only with extreme sterility (Galinat, 1988)."

The APHIS article on corn that I am citing also states:

"Corn appears as a volunteer in some fields and roadsides, but it never has been able to
establish itself outside of cultivation (Gould, 1968). Some of the other species of Zea are
successful wild plants, but have no pronounced weedy tendencies (Galinat, 1988)."

There are crops for which gene transfer to wild relatives is a more serious issue: sorghum and
canola being prime examples. However, since this possibility is of more serious concern in these
cases, it is also getting more attention from breeders and the government.

Another issue to consider is gene activity. Frequently in wide hybrids introduced genes

I hope that you will read the comments on this site about "wild and weedy relatives" for further

John Cross

Lackey, James (email: jlackey@aphis.usda.gov) January 04, 1996 "Corn"
Charms of Duckweed


Date: Apr 17 2000 13:00:02 EDT
From: "Ghislain, Marc"
Subject: RE: Just a thought

Dear all,

At the International Potato Center (CIP) we have developed transgenic events
using the Bt technology from ex-PGS now Avantis in about 10 different potato
varieties. These clones are almost ready for deployment in developing
countries where potato tuber moth (PTM) is a major pest in storage.
We have many questions that relate to deployment of transgenics and are
certainly very careful to prevent any unexpected event to occur. The one you
mention here is just one of ten important issues to deal with.

In our potato case, the Bt gene does not confer a selective advantage in
nature. PTM is not affecting significantly native potato populations in one
way or another. It is essentially a market pest in the sense that you will
hardly find any buyer if your tuber is full of insect larvae and their
dejection. Farmers control PTM using a variety of measures including
pesticides. This is where the problem is, pesticides are highly toxic,
costly, and this situation is more severe in developing countries where we
can still buy banned pesticides, and where farmers and their community have
a much lower education level to handle properly such chemicals. Not later
than last October about 25 kids died in Cusco - Peru because they had their
milk for their breakfast prepared in bottles that had contained
organophosphates. We have also conducted impact studies in Andean region on
pesticide uses and it just reinforce what I have just said, if we can avoid
the use of pesticides we should definitely promote the alternative
technology for the sake of protecting producers, consumers, and the

Bt technology is the alternative in this particular case It will contribute
to save lives, relief dependence on insecticides, increase profitability of
potato production for resource-poor farmers in developing countries. Can we
seriously consider that an hypothetical flow of a non-fitness-conferring
gene is justified to delay any further this technology?

My personal opinion is no. Benefits are largely overwhelming the
hypothetical risks. Even if we have once in a while a hybrid (rare event in
potato cultivation) containing a Bt gene, it will be totally silent and
hence environmentally-neutral.

I guess my final take-home message is to advocate to make decisions through
a benefit/risk analysis on a case-by-case basis. Things tends to be much
clearer when you face the real problems.

Sincerely, Marc Ghislain
Marc Ghislain, PhD
Biotechnology adviser
Molecular Biology Laboratory
Crop Improvement & Genetic Resources Dept.
International Potato Center (CIP)
PO Box 1558, Lima 12, Peru
Tel: 51 1 349 6017
Fax: 51 1 349 5638