More about teosinte characterization

The taxonomy and evolution of Zea can be considered as a problem. When trying to solve a problem from different angles and using different techniques, you have the chance to obtain a global view of it. ln relation to this, Bird (Maize for Biol. Res. p. 341, 1982) correctly states that: "a careful, integrated analysis of a large and varied body of data, including studies of plant, ear and tassel morphology, chromosome knobs, isozymes, and whatever other features can be surveyed, is needed." We are determined to obtain within our possibilities, the greatest amount of information for Zea taxa characterization. For this reason, several morphological and biochemical studies are being carried out. The aim of this report is to present some results obtained in the evaluation of some quantitative traits, especially fruit and tassel traits. These studies were performed on small populations of teosintes, which were cultivated during spring and summer of 1984/85. The great number of observations done on each trait considered are summarized.

Cultivated plants of Z. perennis (Zp), Z. diploperennis (Zd), Z. luxurians (Zl), Z. mays ssp. parviglumis var. paruiglumis (Zmpp), Z. mays ssp. parviglumis var. huehuetenangensis (Zmph) and Z. mays ssp. mexicana (Zmmx) were employed for the measurements. The following 12 quantitative traits related principally to the fruit and tassel were recorded: fruit case weight (FCW), length (FCL), width (FCWD) and thickness (FCT); tassel branch number (TBN), tassel branching axis length (TBAL), central spike length (TCSL) and lateral tassel branch internode length (LTBIL); distance between the two primary lateral veins (DVL), number of veins between primary lateral veins (VBL) and total vein number (TV) of male spikelet outer glume; and number of tillers per plant (NT) (Table 1).

Assuming Doebley and Iltis' (1980) proposal that teosintes can be clustered within two sections, we have found that some traits such as TBN, TBAL, VBL and TV fit in with this separation. The remainder, especially TCSL, DLV and LTBIL, doesn't give a clear discrimination within the groups. A phenogram resulting from cluster analysis based on these traits is shown in Figure 1. From the results obtained it can be inferred that Zp, Zd and Zl form a well defined group constituted by the most primitive teosintes. Zmpp and Zmph form another group that links at a lower distance from the first than from Zmmx. Zmpp and Zmph are more closely linked to the primitive teosinte group than to the most evolved one (Zmmx). Some traits such as the fruit traits considered and TBN, TBAL and DLV allow us to cluster Zmpp and Zmph separately from Zmmx, with which they appear to have lower affinity. Some differences are shown within those clusters reported (see MNL 59:61), based on characters that were not considered previously.

For this reason, and in accordance with what we have pointed out here, not only taxonomy but also phylogenetic relationships among the taxa of Zea must be reexamined upon the basis of a multidisciplinary study of the problem. Probably, the correct way of doing it is collecting a great amount of data with the aim of studying it by means of multivariant analysis methods.

Table 1 and Figure 1.

Monica B. Aulicino and Jorge L. Magoja
 
 


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