Universidad Nacional de La Plata

LOMAS DE ZAMORA, ARGENTINA

Lomas de Zamora University

Diploperennial teosinte-maize hybrids: inheritance of male spikelet outer glume traits

--V. R. Corcuera and J.. L. Magoja

According to Doebley and Iltis (1980), two characteristics of the male spikelet outer glume, number of veins between primary lateral veins (VBL) and total vein number (TV), are of such taxonomical importance that the two different sections of the genus Zea can be clearly distinguished through them. We have verified this singular observation (see MNL 60:81) when those traits were quantified in the teosintes, and we have also pointed out that both VBL and TV are characteristics which can be used to detect teosinte (belonging to Section Luxuriantes) germplasm introgression in maize (see MNL 61:64).

Bearing in mind what has previously been exposed, it can be deduced that VBL and TV are two traits which would perfectly let us discriminate the different taxa between the two sections of the genus Zea, but not within sections (see MNL 60:81). When hybrids among different taxa belonging to different sections of the genus Zea are done, the clear differences existing for those traits of the male spikelet outer glume let one study the way of inheritance of them.

Continuing the studies referred to on the inheritance or expression of specific traits or ones of agronomic importance in hybrids between diploperennial teosinte (Z. diploperennis) and maize (see MNL 62:77), we have recently evaluated VBL and TV in these hybrids and their parents.

A sample of male spikelets taken at random from the primary branches of the medium third of the tassel was used to evaluate these traits (VBL and TV) in a diploperennial teosinte population, another one of a sweet maize variety (Ever Green), and the F1 and F2 progenies resulting from the cross between the two species.

The outer glumes were diaphanized and stained with safranine and then observed with a stereomicroscope to count the number of veins. The results shown in this work were obtained after averaging all the data belonging to four male spikelet outer glumes taken from one tassel of each plant.

In Tables 1 and 2 the clear differences for the traits studied between diploperennial teosinte and maize can be seen, and the F1 and F2 mean values are nearer to maize than to teosinte. When the averages obtained for the four populations studied are statistically compared it can be deduced that the F1 and F2 mean values are significantly lower than those of the mid-parent.

The frequency distributions shown in Figure 1 show a relatively wide range of variation for the F2, but without reaching the greater extreme values (teosinte). The displacement to left of those distributions (toward maize) and the significant differences between the F1 and F2 mean values with respect to the mid-parent, suggest that both VBL and TV are quantitatively inherited, considering partial dominance of a low total vein number (maize) over high (teosinte). Both traits are strongly associated; the correlation coefficient among the mean values of the four populations considered is 0.99 (significant at 1% level) and among the F2 progeny plants is 0.77 (also significant at 1% level).

The study of the expression of these specific traits has given enough information to explain the causes by which our teosinte (belonging to Section Luxuriantes) introgressed populations of maize show higher values for VBL and TV than the normal ones (see MNL 61:64).

Bearing in mind that these populations were obtained after backcrossing them with maize (recurrent parent) and that almost all the traits of the cultivated species (maize) have been recovered, explaining the causes by which high VBL and TV values remain as introgression signs is only satisfactory on the basis of the partial dominance of high vein number over low.

Table 1.  Number of plants (N), means and range for VBL and TV traits in diploperennial teosinte (Zd), Ever green maize (Eg) and F1 and F2 populations.

Table 2.  Differences between means for VBL and TV traits in diploperennial teosinte (Zd), Ever green maize (Eg), F1 and F2 populations and mid-parent values (MP).

Figure 1. Frequency distributions for VBL (a) and TV (b) traits in diploperennial teosinte (P1), Ever green maize (P2) and its F1 and F2 populations - MP: mid-parent value.

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