Further studies of F1 hybrids of maize x diploid perennial teosinte

Last summer 152 F1 hybrid plants of maize x diploid perennial teosinte were grown in the field. The maize parent included three varieties: Chuen-Hwa, Tze-Tao-Shwei, 80-105. All of them came from China. When the plants were five weeks old, variations in vigor were apparent from cross to cross. For example, F1 plants of the cross Chuen-Hwa x diploid perennial teosinte were the most vigorous individuals and those of 80-105 x diploid perennial teosinte were the least vigorous group in terms of number of tillers produced as well as plant height. When the plants were 10 weeks old, 50 percent of the plants for each cross, approximately 25 clones, were cut off and weighed together. It was found that the cross Chuen-Hwa x diploid perennial teosinte also produced the largest fresh weight. On the average each clone weighed about 5000 grams, which is about six times the weights of the parental varieties. It was also observed that this cross produced the largest number of tillers per clone. One week after cuttings, almost 100 percent of the root stocks (rhizomes) regenerated into young shoots. Again the regenerations of the cross Chuen-Hwa x diploid perennial teosinte were the most profuse. In contrast, none of the parental maize stocks were capable of regenerations. Since regeneration of grasses is a reliable indicator of perennialism, it appears reasonable to say that the F1 hybrids of the above crosses are perennial. On the basis of this observation that all of the hybrids of the crosses were perennial, it seems that the perennial attribute is dominant.

Shaver (1964, 1967) found that F1 plants of 4n maize x 4n perennial teosinte were annual and he proposed that the perennialism in the 4n teosinte was governed by a single recessive gene (pe). If this gene became homozygous in a 20-chromosome maize by going through breeding procedures, it exerted lethal effect. In the last few years, we have crossed 4n perennial teosinte with diploid maize and the teosinte was employed as seed-parent. It was consistently observed that the triploid F1 hybrids, with two genomes from teosinte and one from maize, were perennial. During summer months, each clone produced profuse grassy tillers. Some of the clones were maintained for more than five years by transferring them to the greenhouse in the winter. However, if they were left in the experimental field here in the Boston area, they died in the winter. Hence, the above suggests that perennialism in 4n teosinte is quantitatively inherited. A triploid plant possessing two perennial genomes manifested perennial habit.

Male inflorescences of three to five F1 hybrids of each of the aforementioned crosses were collected and fixed with aceto-alcohol fixative. By standard aceto-carmine squash technique, it was found that all the terminal knobs of the chromosomes of the teosinte parent were present. No chromosome aberrations of any kind were identified. However, univalents at diakinesis, laggards at anaphases I and II of the microsporocyte divisions were observed. When pollen fertility of the F1 plants was examined with the aceto-carmine staining procedure, it showed that more than 90% of the pollen grains were normal or fertile. In order to have advanced generations of the crosses, the F1 hybrids were backcrossed as seed parent to the maize parental variety. The percentage of seed set was above 60.

Y. C. Ting and M. K. Yu

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

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