Variation within teosinte: numerical analysis of agronomic traits

As part of a project whose purpose is the evaluation of wild genetic resources of maize, especially the study of possibilities offered by teosinte as a genetic diversity source, a series of agronomic traits in wild taxa of Zea were quantified. During the last few years, a great deal of information about teosintes has been given by several authors, including us (see MNL 59:61, 1985; MNL 60:79, 1986 and MNL 61:67, 1987). All this information is based in large part on the study of specific important traits.

All the available information has contributed to strengthening some ideas or putting into action some other ones about phylogenetic relationships among teosintes and between teosintes and maize. Nevertheless, the characterization of teosintes for non-specific features or those of apparent non-taxonomic significance, for example common agronomic traits, has not deserved the same attention. Consequently, the purpose of these investigations is to gather all the teosintes in clusters on the basis of agronomic traits, and then compare these groupings with those derived from the utilization of specific traits.

The wild taxa of the genus Zea (teosintes), Z. perennis (Zp), Z. diploperennis (Zd), Z. luxurians (Zl), Z. mays ssp. parviglumis var. parviglumis (Zmpp), Z. mays ssp. parviglumis var. huehuetenangensis (Zmph) and Z. mays ssp. mexicana (Zmmx) constitute the 6 operational taxonomic units (OTU's). These 6 OTU's are part of a complete randomized block design with 3 replicates and they were cultivated during the 86/87 growing season in our experimental field.

This experiment gave enough information to compare teosintes among themselves. The average values for each trait were used to make analysis by numerical techniques.

Twenty-two traits were measured in each one of the OTU'S:

(A) Evolutive cycle traits: (1) days to tassel, (2) days to silking, (3) days to pollen; (B) Prolificity traits: (4) number of productive nodes per tiller, (5) number of female spikes in the uppermost node, (6) number of female spikes per tiller, (7) number of female spikes per plant, (8) number of fruit cases per spike; (C) Plant traits: (9) total number of tillers, (10) number of tillers with spikes, (11) plant height (cm), (12) number of leaves per tiller, (13) leaf width in the uppermost productive node (cm), (14) leaf width in the 10th node (cm), (15) leaf length in the uppermost productive node (cm), (16) leaf length in the 10th node (cm), (19) stalk diameter in the uppermost productive node (cm), (20) stalk diameter in the 10th node, (21) whole plant protein content at tillering stage (%), (22) whole plant protein content at stalk forming stage (%).

The average values obtained for each one of the traits were set into a basic data matrix (BDM) (see Table 1).

With these results, we built phenograms derived from correlation index matrix and mean taxonomic distance matrix (MTD), OTU x OTU, using the UPGMA method (see Figure 1).

Finally, the results obtained through these measurements and evaluation procedures point out that when the different taxa are clustered on the basis of these agronomic importance traits, they are partially congruent with the clusters derived from specific characters (see MNL 60:81, 1986). This fact is suggesting that possibly these chosen traits have taxonomic significance. It must be specially emphasized that one of the teosintes of the Sect. Luxuriantes (Z. luxurians) is more similar to the taxa belonging to the other taxonomic section (Sect. Zea) than to the ones of its own when we analyze the studied traits. This fact agrees with the general impression that one generally has about Guatemala teosinte when it is compared with Zmpp and Zmph, and without considering those specific traits that make the difference among themselves.

One wonders if Z. luxurians could be the link between Sect. Luxuriantes and Sect. Zea, as those teosintes belonging to the first are the most primitive, but the ones included in Sect. Zea are the most evolved.

We finally think that as more information is collected, new questions would be brought out; then it is necessary to go on researching until it is possible to have a better understanding about phylogenetic relationships within teosinte.

Table 1. Basic data matrix (BDM): agronomic traits.

Figure 1. Phenograms of 6 OTU's resulting from: (A) UPGMA cluster analysis of the OTU x OTU correlation matrix; (B) UPGMA cluster analysis of the OTU X OTU distance matrix. r: cophenetic correlation coefficient.

Monica B. Aulicino1 and Jorge L. Magoja

1Fellow, Cons. Nac. Inv. Cient. Tkni. (CONICET)


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