Perennial teosinte introgressed population: seed mutants and mutation rates --R. Burak and J. L. Magoja In the course of our research work related to the development of wild germplasm introgressed populations of maize, the high frequency of spontaneous mutations easily recognized in the harvested ears caught our attention. With the purpose of documenting this unusual fact in a perennial teosinte (Zea perennis) introgressed population of maize, we evaluated seven seed traits considered deviations of the normal phenotype and conditioned by genes of simple inheritance: waxy, white, floury and sugary endosperm, defective kernel, red pericarp and aleurone colour.

In the original population (P0), cultivated in the 1986/87 growing season, these mutations were recognized in a sample of 812 plants (ears) obtained at random and by controlled pollination. In the following growing season (1987/88) the progenies of said ears were cultivated. After a generation in the derived population (P1), the mutant phenotypes were recognized in a random sample of 1,617 ears. On the basis of phenotypic frequencies observed, the genetic frequencies were estimated and from the latter, the respective mutation rates.

The results drawn (see Table 1), show that the mutation frequencies, as well as their respective rates, are very high, and can be considered exceptional for maize, probably associated with the wide variability generated by the introgression.

Table 1. Genetic frequency and mutation rate (µ) in the perennial teosinte introgressed population.

If one bears in mind that the mutations found in the seeds constitute only a part of those which occur in practise (others have not been considered or detected) and that such mutations had not been observed in the materials which originated the population, it can be said as a consequence, that the presence and high frequency of the same can be attributed, as other research has pointed out (Mangelsdorf, Cold Spring Harb. Symp. Quant. Biol. 23:409, 1958), to the mutagenic effect of the teosinte introgression in maize.

We ignore the mechanisms through which these mutations occur, and we have not conducted any research work to determine it. However, we acknowledge that the wild germplasm introgression in maize conditions a wide variability that is expressed in different ways: modifying traits of quantitative inheritance, or as in this case, producing or increasing the production of variants of simple inheritance.


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