Preliminary studies of maize vs. teosinte pollen-tube competition in short styles

The feasibility of techniques designed to determine why the pollen of modern teosinte is significantly smaller than that of its sympatric maize was tested in a pilot experiment. The following conclusions now stand: (1) Purple aleurone works satisfactorily as a marker for the fertilizing success of maize pollen in mixture with teosinte pollen. (2) Maize styles may be sheared to about a length of one inch for applications of maize-teosinte pollen mixtures. (3) In Massachusetts, at least, about 3 days after pollination of the sheared silks an insecticide dust such as Chlordane should be applied to control damage from earwigs. These insects prefer the maize-teosinte hybrid kernels. (4) Small piles of maize and teosinte pollen placed in the crease of a folded piece of paper may be rocked into a mixture. Because the maize pollen is larger in diameter than that of teosinte, the apparent size of the pile of maize pollen going into the mixture should slightly exceed that of teosinte in order to approximate a 50-50 mixture. (5) Because the actual frequency of the two types of pollen going into the mixture is only an approximation or guess, about half of the mixed pollen from a single batch used in each pollination on a sheared ear should also be used on the silks of a normal (not-sheared) control ear shoot.

In the preliminary tests so far, pollen of Hopi Blue Flour was mixed with that of Northern teosinte and then placed on the shortened styles of the dent corn hybrid B73 x Mo17. The results for five such pollinations totaled 441 blue kernels and 768 yellow kernels. Thus it would appear at first that the teosinte pollen had a greater frequency of fertilizing success in competition with corn pollen within short styles. But in mixing the pollen, adjustment in the volume was not made to account for the smaller size of teosinte pollen. Controls on long style ears should also have been made for each batch of mixed pollen. The experiment will be repeated next year taking these factors into account.

The pollen-size problem is involved in the origin of corn. Because 5 out of 14 fossil pollen grains from a drill core dated at 80,000 years are too large to be that of modern teosinte and are more similar in size to that of modern corn, it was concluded that the ancestor of corn is corn and not teosinte.

Walton C. Galinat

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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