More about maize introgressed with diploperennial teosinte germplasm --G. Pischedda* and J. L. Magoja

*Fellow of CONICET

Together with the development of our improvement programmes using the wild germplasm, we are obtaining an amount of information related to these new materials, which is interesting to analyze. In this particular case, we intend to provide information about the experiences we have gathered in relation with the research work begun from a population of maize introgressed with diploperennial teosinte (Z. diploperennis) (see MNL 60:82 and 61:65).

As has been previously reported (see MNL 62:84), as a consequence of a cycle of recurrent selection we obtained S1 families which were evaluated for different characters. During the 1988/89 growing season, progenies of such S1 were cultivated in Pergamino (Province of Buenos Aires) as part of a trial with 2 repetitions.

On evaluating the mentioned progenies for different characters, we completed the necessary information to make heritability estimates on the basis of the parent-offspring regression.

The results of the evaluation of some important characters in the progenitors (S1 families) and their respective progenies are summarized in Table 1. These families have as general characteristics the peculiarity of producing tillers and of being prolific (2 to 5 ears per plant). The size of the average ears is generally small, though the depression caused by inbreeding must be taken into account.

Table 1. Relevant traits in parents and offspring of diploperennial teosinte introgressed maizes.

As can be seen in Table 1, there exists an acceptable congruence between means of progenitors and progenies, but it must be particularly pointed out that, for most of the characters, there remains a similar variation from one generation to the other. The heritability estimates made (see Table 2) show from medium to low values, with the exception of prolificity (ears per plant), high heritability character for this case. On the other hand, the yield, represented in this case by ear weight per plant, is the character of lowest heritability.

Table 2. Heritability (h2) of relevant traits.

On analysing the phenotypic correlation between ear yield and other characters, contrary to what might be expected, the prolificity is not significantly associated with yield. Consequently, just as is documented in Table 3, the yield seems to be determined mainly by ear and kernel size and weight. These results are congruent with the heritability estimates for prolificity and yield: if the number of ears per plant were a main component of yield, the latter should have a high heritability, which unfortunately does not occur in practise.

Table 3. Phenotypic correlation coefficients (r) between ear weight per plant (IWP) and some other traits.

This particular relation between prolificity and yield is absolutely different from the one we have found in the perennial teosinte introgressed maize (Z. perennis). Probably, the high prolificity of all the families tested conceals the true association type between ears per plant and yield.

If the calculated associations are correct, and feasible to be verified again, we could infer that, yield being conditioned by ear size and not by the number of ears, the high prolificity would produce a unitary and total reduction of the ear weight. Our experience so far, derived from the study of these particular materials, leads us to think that there is a point of balance between prolificity and yield which must be taken into account, in order to achieve further benefits when intending to improve the grain yield.


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