The new division of the genus Zea proposed by Doebley and Iltis (Amer. J. Bot. 67:982, 1980) is based upon morphological characteristics of the male inflorescence. Among other characteristics, we have studied heredity, in hybrids between perennial teosinte (Z. perennis) and Gaspe (Z. mays), of three of these: (a) tassel branch number, (b) tassel branching axis length and (c) lateral tassel branch internode length. It is our intention to make known here the inheritance of those three quantitative traits of the tassel which are specific, and which distinguish maize from perennial teosinte.
On at least two mature tassels of each plant belonging to perennial teosinte, Gaspe and its progenies F1 and F2, measurements were carried out. The four populations studied were cultivated during spring-summer in the years 1982/83.
(a) Tassel branch number (TBN): The number of tassel branches was evaluated upon 151 perennial teosinte plants, 31 Gaspe plants, 85 F1 plants, and 429 F2 plants. TBN represents all primary and secondary branchings, providing they have 4 or more spikelets. As can be observed in Table 1, perennial teosinte has a low TBN, but Gaspe also has a low TBN for a Z. mays species, although definitely higher than teosinte. In the F1 TBN does not differ significantly from Gaspe (Table 3). The average TBN of F2 is higher than for F1, and an ample variability can be observed for TBN (Figure 1). In F2 there are plants which have no branches in the tassel (TBN=O) up to plants which have 25 branches. Broad sense heritability calculated upon the results presented in Table 2 is high (0.80), and the genetic variance of F2 is great in comparison to environmental variance (5:1).
The results shown in Tables 1, 2 and 3 indicate that: (1) TBN is inherited quantitatively; (2) high TBN (GASpe) is dominant to low TBN (perennial teosinte); (3) the distribution of frequencies for TBN in F2 represents a type of transgressive inheritance, which indicates a significant heterosis effect.
(b) Tassel branching axis length (TBAL): TBAL covers the central axis part of the tassel which presents branching. This characteristic is closely associated with TBN; when TABL is long, there is high TBN and vice versa. TBAL was evaluated on 21 perennial teosinte plants, 11 Gaspe plants, 69 F1 plants, and 427 F2 plants. Perennial teosinte has a significantly lower TBAL than Gaspe (see Tables 4 and 6). The TBAL value of the F1 is nearer to Gaspe than to teosinte, and in F2 the average value of TABL is greater than that of F1 (see Tables 4 and 6). In F2 there exists an ample TBAL variability, with plants with TBAL=O (without branching) up to plants with long TBAL (14 cm) (see Figure 2). From the results shown in Table 5, broad sense heritability was calculated (H=0.77).
The results obtained indicate that: (1) TBAL is inherited quantitatively; (2) TBAL average of the F1 does not differ significantly from the mid parent value; (3) the distribution frequencies for TBAL in F2 is transgressive, especially in the positive direction, so that the obtained mean exceeds the theoretical mean, indicating a significant heterotic effect similar to that found for TBN; (4) in F2, TBAL correlates significantly with TBN (r=0.78).
(c) Lateral tassel branch internode length (LTBIL): LTBIL may vary from short, with male spikelets densely overlapping, to long, slightly superimposed. LTBIL was evaluated in 21 perennial teosinte plants, 10 Gaspe plants, 101 F1 plants and 427 F2 plants. In Table 7 it can be seen that perennial teosinte has a short LTBIL, while in Gaspe it is long. F1 and F2 averages are alike and intermediate with respect to their progenitors. The differences between the four population averages are summarized in Table 9. The distribution of LTBIL frequencies shown in Figure 3 represents an intermediate F1 with less variation than in F2, where LTBIL varies between 2 mm and 7.5 mm. LTBIL heritability is 0.61 and was calculated from the data presented in Table 8.
The results obtained indicate that: (1) LTBIL is inherited quantitatively; (2) the F1 has a LTBIL near the mid parent value; (3) the F2 has a LTBIL that does not differ significantly from the theoretical mean, from which it may be deduced that genes with additive effect predominate; (4) the distribution of frequencies in F2 is transgressive in both ways.
Analyzing the results presented with regard to heredity of tassel traits it is deduced that TBN and TBAL are inherited in a similar way and are closely associated, because of their possibly being conditioned by the same genes.
On the other hand, LTBIL is inherited in a distinctly independent manner from TBN and TBAL (LTBIL does not correlate significantly with TBN and TBAL).
TBN and TBAL are very changeable characteristics in maize, and frequently there is observed, as in the Gaspe case, a low TBN and short TBAL, resembling a perennial teosinte. On the contrary, LTBIL allows a better way to distinguish maize from perennial teosinte and consequently it is the most specific (to our knowledge) of all three characters studied.
Ida Graciela Palacios and Jorge Luis Kagoja
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