Diploperennial teosinte introgressed population of maize: isozyme variation

--I. G. Palacios and J. L. Magoja

The study of morphological and physiological traits--in its greatest part of agronomic importance--we have done on a diploperennial teosinte (Z. diploperennis) introgressed population of maize has revealed that, as a product of the interaction between the wild and cultivated germplasm, there is great variability for most of the quantitative traits, especially those associated with grain yields. With the purpose of giving a better measure of the whole genetic variation partially detected through the study of agronomic traits, we have initiated some studies to be able to establish isozyme variation.

One hundred ears (plants) obtained by controlled pollination and representative of that population (see MNL 60:82, MNL 61:65 and MNL 62:84) were used to obtain, through starch gel electrophoresis, the patterns of four systems: esterases (EST), alcohol dehydrogenase (ADH), malate dehydrogenase (MDH) and leucine aminopeptidase (LAP). With the purpose of obtaining a measure of variation and on the basis of presence-absence of each band revealed in the gel, it was considered that when the band was present in all the individuals, it belonged to a monomorphic locus and if it was present or absent according to the individual, is considered polymorphic. All the observed phenotypes and the frequency in which one of them appeared in the population, are drawn in Figure 1.

To make the comparisons of polymorphism easier, the polymorphic index (PI) is the frequency of each band and the number of loci for each isozymatic system. Bearing in mind that PI varies from 0 and 0.25, the values found for ADH and MDH represent a high variation. The same pattern was observed in all the individuals analyzed in the EST and LAP systems. Considering that LAP does not show any variation in maize and that only a few systems were tested, the results can be considered congruent with the variability observed for agronomic traits.
 
Isoenzymatic system PI
EST 0.00
LAP 0.00
MDH 0.15
ADH 0.12
   

The future availability of more information from the study of other systems that we are analyzing, in comparison with normal populations (without introgression), will let us deduce the variation generated by the introgression of wild germplasm.

Figure 1.  Phenotypic frequencies of MDH, EST, LAP, and ADH.


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