Teosinte introgression in maize, as pointed out by several authors, has played a decisive role in the evolution of modern maize. The introgression degree in the different maizes from America is not similar and it is sometimes necessary for different reasons to recognize what races or varieties have teosinte introgression. To date, the recognition of teosinte introgression in maize has been fundamentally detected by studying certain morphological traits, especially the structure of the female inflorescence.
Considering that teosintes, especially those belonging to the Luxuriantes section (Doebley and Iltis, 1980), have distinctive traits in the tassel that make them completely different from maize, it flashed into our minds to find out if quantitative traits of the male inflorescence can be used to measure the effect of introgression. Nine quantitative traits of the male inflorescence were employed to compare two maize populations. One of them represents actually cultivated maizes and it is composed of a mixture of red flint commercial hybrids grown in Argentina. We called this population Normal (N). The other maize population introgressed by perennial teosinte (I) was obtained through the methodology previously communicated (MNL 60:82).
The traits that were sized, some of them used by Doebley and Iltis (1980) to work out the taxonomic classification of the genus Zea, were the following: tassel branch number (TBN); tassel branching axis length (TBAL); tassel central spike length (TCSL); lateral tassel branch internode length (LTBIL); distance between the two primary lateral veins of male spikelet glume (DVL); number of veins between primary lateral veins (VBL); total vein number (TV); total tassel branch length (TTBL) and tassel dry weight (TW).
Some of those same traits evaluated on perennial teosinte (Z. perennis) and its F2 and F3SM progenies (see MNL 59:70) are given in Table 1, to take them as a reference, and to note what are the changes that have taken place. Perennial teosinte has low TBN and low TBAL, when we compare it with maize. It also has short tassel internodes. In the F2 progeny (derived from hybrids with maize), those traits increase their value comparing to teosinte. In an F3 population descending from the F2, and selected for maizoid traits, TBN, TBAL and TCSL increase. F3SM was used as donor of perennial teosinte germplasm to obtain the introgressed population (see MNL 60:82).
On a sample taken at random from each population (approx. 100 tassels from each one), determinations were carried out on N and I. Results are shown in Table 2. The introgressed population does not differ from the normal one in such traits as TBN, TBAL and TCSL. On the other hand it has shorter internodes, a greater number of veins in the male glumes, a greater total tassel branch length and heavier tassels. The higher weight of the tassels belonging to the I population is the result of the greater value of TTBL, as the correlation between TW and TTBL (r=0.73) is highly significant. That higher weight also depends on the internode length, because having a higher number of spikelets increases the weight per unit. The correlation between TW and LTBIL is significant (r=-0.39). Probably the higher weight of the tassels also depends on their chemical composition (especially content of SiO2), for which we shall next make the necessary chemical analyses.
Tassel weight takes our attention because perennial teosinte has small and slight tassels, but when its germplasm is melted with maize germplasm, we obtained heavier tassels (heavier than maize tassels). In each population, the tassel weight depends on the tassel branch number, the correlation value between these traits is significant (r=0.58). Nevertheless, and as both populations do not differ in their tassel branch number, the weight mainly depends on TTBL and LTBIL. Tassel traits, as those previously pointed out, consequently let us detect teosinte introgression on maize. The shortening of internodes, the greater number of veins in male spikelet glumes and the greater weight of the tassels are particular signs of introgression.
Tables 1 and 2.
M.B. Aulicino, I.G. Palacios, G. Pischedda1 and J.L. Magoja
1Est. Exper. Reg. Agrop. Pergamino INTA
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