I recently discovered a taxonomic error which has been propagated in at
least one published paper. The error in question lies with the USDA
accession database, and was perpetuated in Tiffin & Gaut’s paper titled
‘Molecular Evolution of the Wound-Induced Serine Protease Inhibitor wip1
in Zea and Related Genera’
(http://bgbox.bio.uci.edu/people/papers/Tiffin-MBE.pdf). The error is as follows:

In 1993, the noted maize researcher H. Garrison Wilkes submitted several
collections of teosinte germplasm to the USDA, collections he had made
in Mexico the previous year. At the time, Wilkes was still using his
outdated (and ultimately confusing) race-based teosinte classification
system. In this system, the annual teosintes are classed into ‘races’ of
Z. mays ssp. mexicana. Several of these races turned out to be ecotypes
of the same species (this species retains the designation Z. mays ssp.
mexicana), but three of the ‘races’ were classified as separate taxa by
Iltis and Doebley in the early 1980’s. Race ‘Guatemala’ became Z.
luxurians, race ‘Balsas’ became Z. mays ssp. parviglumis, and race
‘Huehuetenango’ became Z. mays ssp. parviglumis var. huehuetenangensis
(later elevated to ssp. huehuetenangensis by Doebley). Since Wilkes was
still clinging to the race designations in 1993, there are at least a
handful of accessions in the USDA germplasm system listed as ssp.
mexicana, when they are in fact ssp. parviglumis. The accession ID’s in
question are PI 566686 through PI 566692. Although they are indexed as
ssp. mexicana, the accession information clearly states they are race
Balsas. The altitudes at which the accessions were collected confirms
their identification as ssp. parviglumis.

The problem lies with the fact that apparently not all maize geneticists
are familiar with the race designations, and assume that anything listed
by the USDA as being Z. mays ssp. mexicana is just that. in the Tiffin &
Gaut paper mentioned above, they segregate ssp. mexicana and ssp.
parviglumis data (and rightly so), but two of the supposed ssp. mexicana
accessions are in fact ssp. parviglumis. If you refer to page 4 of the
paper, the tree clearly shows the mislabeled parviglumis sequences
grouping neatly with the properly labeled parviglumis sequences.

Finding bad information about the origins of maize isn’t hard. There are
still ‘professionals’ like Mary Eubanks who, as recently as 2001, were
claiming that maize was derived from a cross between Tripsacum sp. and
Z. diploperennis. It is quite common to see sites claiming that maize is
derived from ssp. mexicana, or even simply Zea mexicana, a taxon
designation that hasn’t been valid for decades. Dozens of reputable
organizations, including the USDA and NASA, have repeated Mangelsdorf’s
claim that he found 80,000 year old fossilized maize pollen (it was of
course teosinte pollen). There are still many people who believe that
the origin of maize is ambiguous, or the result of a cross between two
different taxa.

Anyway, I contacted the USDA site which curates the mislabeled
accessions, as well as authors of the paper mentioned. If anyone here
has any comments on maize misinformation, I’d love to discuss it.

Regards

Micah Mabelitini


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So exactly what is the origin of maize? I understand it is supposed to be the
descendant of teosinte, the wild form of the species. How did the habit of
making ears evolve?
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

Iris Cohen wrote:

So exactly what is the origin of maize? I understand it is supposed to be the
descendant of teosinte, the wild form of the species. How did the habit of
making ears evolve?

First, it's important to note that there are six or seven different
kinds of teosinte, so saying that maize is a descendant of teosinte is
somewhat ambiguous. General concensus nowadays, based on an overwhelming
amount of data, is that maize is a direct domesticate of Z. mays ssp.
parviglumis, the most common and highest-yielding of the Mexican annual
teosintes. Recent genetic studies strongly support that there was a
single domestication event from which all varieties of maize were
derived. There are only about 5 genes different between maize and ssp.
parviglumis, suggesting that maize may have simply been selected for by
conventional crop improvement methods (possibly from an initial mutant).
The number of genes altered throughout the diversification of maize is
far greater than the number of genes altered in the initial transition
from teosinte to basal maize.

The apparent genetic flexibility of Zea is quite impressive, and the
differences between maize and teosinte are fairly superficial. Further,
much of the apparent differences are the result of known breeding
practices which occured after the initial domestication event. Given the
amount of variability seen in modern wild teosinte populations, it is
not hard to imagine maize coming about, with or without human intervention.

Here's a few articles...

http://www.wisc.edu/teosinte/pdfs/Ma...et_al_PNAS.pdf

http://www.wisc.edu/teosinte/pdfs/Lu...oebley2001.pdf

http://www.genetics.org/cgi/reprint/150/2/863.pdf

http://www.genetics.org/cgi/reprint/158/2/487.pdf

http://www.econbot.org/journal/Vol54...t-54-1-007.pdf


Regards

Micah Mabelitini


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