As part of a project whose objective is increasing heterosis and genetic variability in maize, a perennial teosinte (Z. perennis) introgressed population of maize was obtained, in a first stage. This population was obtained using selected progenies derived from hybrids between perennial teosinte and maize, as donors of wild germplasm, and a wide diversity of maize stocks as recurrent parents (see MNL 60:82). Finally, as a result of that controlled introgression, the resulting population shows a wide variability, and unusual individuals combining exceptional characteristics can be found in it, as they combine precocity, prolificity and a high yield potential (see MNL 61:66).
During the 1985/86 growing season, we started the second stage, in search of the objectives previously pointed out, and then we initiated a first cycle of recurrent selection. A great number of plants of the population were self-pollinated. The progenies of these plants, or S1 derived lines, were grown during the next growing season (86/87). Each was crossed by two testers to measure their combining ability (c.a.), and then, among themselves, the best S1 derived lines were crossed completing the recurrent selection (cycle).
Actually, the F1's derived from cross-breedings are being evaluated through yield comparative designs, while the preliminary results for different characters of agronomic importance have let us evaluate the variability range among S1 lines.
As shown in Table 1, the quantitation of some characters let us deduce that in most cases a wide variation is detected.
Table 1. Relevant traits of S1 lines derived from a maize population
introgressed with perennial teosinte.
| Character | Mean ± SD | Range |
| Days to tassel | 62.1 ± 4.6 | 48-69 |
| Days to pollen | 67.6 ± 4.2 | 57-79 |
| Days to silking | 70.1 ± 4.2 | 60-85 |
| Protoandrous (days) | 2.5 ± 0.2 | 1-5 |
| Plant height (cm) | 180.0 ± 19.1 | 130-255 |
| Ear insertion height ( m) | 78.7 ± 17.9 | 45-150 |
| Number of tillers | 1.2 ± 0.3 | 1-3.8 |
| Number of ears per plant | 2.1 ± 0.4 | 1.1-3.2 |
| Ear lenght ( cm) | 12.6 ± 1.7 | 8-17.1 |
| Ear diameter ( m) | 3.4 ± 0.4 | 2-4.4 |
| Ear eight (g) | 64.6 ± 23.0 | 20-133.3 |
| Number of kernel rows | 12.5 ± 1.5 | 8-18 |
| weight of 50 kernels (g) | 11.5 ± 2.8 | 5-21.2 |
One of the most significant traits, and one which can be attributed to the primary effect of introgression, is the high prolificity present in most of the S1 derived lines. Some lines have, in all the cultivated plants, up to 3 perfectly developed ears per tiller. The S1 lines have on average a smaller number of ears and tillers per plant than the original population (see MNL 61:66), and the ears weigh less.
The enormous variability produced when combining wild germplasm with germplasm of the cultivated species (Z. mays ssp. mays) is not adequately reflected through those few quantitative traits measured. Qualitative variation is greater, and can be appreciated when you observe ears and plants.
As it is true that in some cases inbreeding depression has conditioned a reduction in the amplitude of variation, in other traits this amplitude is kept without significant differences when compared with the original population.
The results obtained point out that the increase of the genetic base and germplasm produced by introgression can effectively contribute to the development of new genetic resources, from which new lines able to produce better hybrid combinations can probably be obtained.
Gabriela Pischedda1 and Jorge L. Magoja
1Est. Exper. Reg. Agropec. Pergamino, INTA
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