The readers of this News Letter may be interested in some of my observations on maize in Mexico. I spent the months of July and August in that country, travelled approximately 8,000 miles in fifteen states and visited a number of the experiment stations,
Maize is the universal crop in Mexico. It is grown from sea level to altitudes of approximately 10,000 feet. One sees it everywhere, planted between peach and apple trees in temperate regions; between bananas and pineapples in the tropics. It is frequently encountered as an ornamental plant in front yards and parks. Volunteer maize plants appearing in a garden or field devoted to other crops are usually allowed to remain. The average Mexican apparently has the same feeling toward the maize plant which the Southern negroe exhibits toward a watermelon vine. It distresses him to see it destroyed.
The diversity of maize in Mexico is enormous. Near El Seco we saw many fields in which the plants were tasseling out at a height of about two feet. Near Monterey we saw fields irrigated with sewage water with stalks fifteen feet in height. We did not see the famous giant corn of the Jala Valley except in experimental plantings at the station near Leon.
Much of the diversity, however, is environmental. In many respects Mexican maize is quite uniform. Practically all of the maize plants of the great central plateau of Mexico are highly pubescent and uniformly pigmented either sun red or purple. Practically all of the maize in all parts of Mexico shows strong external indications of contamination with Tripsacum.
It is a common opinion in Mexico that maize reverts easily to teosinte. A very intelligent Canadian manager of a large estate assured us that teosinte-like segregates appear in the maize fields even when there is no teosinte in the vicinity to cause contamination. He is of the opinion that the potentialities for producing teosinte by recombination exist in many Mexican varieties.
A well-planned program of maize-breeding under the direction of Ing. Edmundo Taboado, Direcci—n de Agricultura, Mexico, D.F., is in progress at several stations. Ing. Eduardo Limon in charge of the Campo Experimental at Leon, Guanajuato, is one of the most enthusiastic of maize breeders.
Because of the Mexican trip, I missed for the first time in twenty years, the usual summer pollinating season. However the work carried on by J. W. Cameron during my absence has resulted in several interesting developments. The most important of these is a study of knob numbers on the chromosomes of Guatemalan varieties. Two hundred varieties were grown and knob numbers deterrained for 162 of these. The number varies from 1 to 16, and involves every previously encountered knob position in maize as well as two unusual positions on No. 10 Knob number is correlated with several other factors. Pubescent varieties had an average of 6.2 knobs as compared to 11.6 for non-pubescent types. Varieties with low knob numbers usually have tender brittle stalks which lodge easily; those with high numbers usually possess strong tough stalks. There is a relation between the altitude at which the corn was collected and knob number. Tentative averages based on the altitude data so far available are as follows:
|500 meters||12.6 knobs|
|1000 "||10.7 "|
|1500 "||10.8 "|
|2000 "||7.5 "|
|2500 "||5.5 "|
Finally, types described on the basis of the general appearance of the ear as "Andean" proved to have a low number of knobs, 4.7, as compared to the population as a whole, 7.9. The results are in general agreement with the hypothesis (Mangelsdorf and Reeves) that corn with knobless chromosomes was introduced from South America into Central America where it hybridized with Tripsacum to produce teosinte and new Tripsacum-contaminated varieties of maize with knobby chromosomes. The South American types apparently still persist in a relative state of purity at the higher altitudes in Guatemala.
P. C. Mangelsdorf