As it was previously reported (MNL 60:82), we are working on an introgression project of wild germplasm into maize, with the purpose of increasing heterosis and to produce greater variability in the cultivated species. Perennial teosinte (Zea perennis) has been used as donor of wild germplasm through advanced progenies derived from interspecific hybrids with Gaspe (see MNL 60:82). We have employed a great diversity of maize stocks as recurrent parents, especially inbreds, commercial hybrids and whole populations. As a result of controlled introgression carried out according to the scheme given in the last issue (MNL 60:82), we could obtain a perennial-teosinte-introgressed population of maize that constitutes the second back-cross progeny (SBCP).
Only two backcrosses with maize were necessary to recover the specific traits of the cultivated species. Nevertheless, the plants of this population still maintain as their main characteristic a high prolificacy, which is typical of the hybrid progenies between maize and perennial teosinte.
The SBCP was cultivated in several locations, to study its behaviour. It was subjected to an evaluation through the quantitation of some agronomic traits in two locations of the province of Buenos Aires (Pergamino and Santa Catalina). The results obtained are shown in Tables 1, 2 and 3. Generally the SBCP plants are extremely precocious.
It really calls attention to the fact that, though they are short cycle plants, some of them have a luxuriant development joined to a high yielding capacity. Some plants' yield is really unusual in such early individuals. Protandrous value is low, though quite variable, as there can be chosen plants with protogynous (like teosinte) up to those with remarkable protandrous levels. Tillering still perpetuates in the SBCP plants, but tillers are really scarce and almost as vigorous as the principal stalk and able to flower at normal plant densities. Cropping the studied population with a density of 57,000 plants/ha does not constitute any obstacle to the expression of a high prolificacy. These plants' prolificacy is not only the result of the existence of several tillers, but of the developing capacity of several productive nodes per tiller. Ear size is not big, but is acceptable if we consider that there is a greater number of ears per tiller than in common maize.
The majority of all those traits studied points out a high variability among the SBCP plants for different traits combinations, and let us suppose that there is enough base to improve significantly the population, especially for its yield.
The average values resulting from the evaluation of different traits (see Tables 1 and 2) arise from computing in a sample taken at random, including little-developed plants with small ears and highly sterile, susceptible to insects and disease damage, up to those plants which join the greatest part of those traits which define the maize ideotype. These exceptional plants are able to produce almost half a kilo of kernels when we spread them at normal plant densities.
To date the results obtained show the potential usefulness of perennial teosinte germplasm in the genetic improvement of maize. This introgression of perennial teosinte genes or gene groups into the genetic background of modern maize can positively affect quantitative inheritance traits.
An enormous variability was generated in the SBCP as a result of introgression, and this can be explained on the basis of transgressive combinations. It is just where extreme combinations can be produced through unusual phenotypes, that a wide possibility of getting the superior individuals back is presented. Plants combining strong stalks and roots, simultaneous sex maturation, precocity and high yield do not appear in low frequency and they constitute the base of a selection process that we have already begun. Extreme individuals with exceptional yield have a potential productive capacity much greater than those maize plants actually cultivated.
Gabriela Pischedda1 and Jorge Luis Magoja
1Est. Exper. Reg. Agrop. Pergamino,
INTA
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