CONICET and CIC
Perennial teosinte introgressed population of maize: behavior of half sib families and S1 derived lines
--J. L. Magoja
One hundred eight S1 lines and 108 half-sib families derived from a perennial teosinte introgressed population of maize (Z. perennis) (see MNL 60:82, MNL 61:66 and MNL 62:83) were tested during 87/88 in Llavallol, as part of an augmented randomized complete block design. Two commercial precocious hybrids (controls), with a similar evolutive cycle to one of the most studied progenies, also were part of the test.
A whole of 30 traits were evaluated, and 19 of them are the object of this article: (1) days to tassel (T), (2) days to pollen (P), (3) days to silking (S) - measured in days after emergence (dae)-, (4) protoandrous (PR=S-P) (days), (5) tassel branch number (TBN), (6) plant height (PH) (cm), (7) uppermost ear insertion height (EIH) (cm), (8) number of leaves (NL), (9) number of leaves above uppermost ear (LAE), (10) number of tillers (NT), (11) number of tillers in plants with low competence (TLC), (12) lodging resistance (LR) (0 = susceptible to, 2 = resistant), (13) ears per plant (EP), (14) ears weight per plant (EWP) (g), (15) kernel weight per plant (KWP) (g), (16) cob % (C), (17) uppermost ear weight (UEW) (g), (18) average ear weight (AEW) (g), and grain yield (Y) (kg/ha). The plants were grown at a density of 57,143 pl/ha and they were not sprinkled nor fertilized. Table 1 summarizes the results obtained and gives the inbreeding depression values (ID) resulting from the comparison among the S1 lines and half-sib family averages for each trait.
The evolutive cycle traits (T, P and S) show that the progenies tested are precocious, most as much as the commercial hybrids used as controls and some even more precocious.
The fact that the original population has arisen from hybridizations between perennial teosinte and Gaspé and then it was backcrossed with precocious maizes, conferred this particular characteristic to the material. These traits are the less variable ones, while most of the other traits show a relatively wide variation. The difference between the male and female flowering (PR) has an appropriate value, though it must be remarked that there is wide variation, from protogynous progenies (teosinte) up to variable protoandrous as in most maize.
Tassel branch number is relatively high, especially when the short evolutive cycle of the plants is considered. The high mean value of this trait and its wide variation are associated characteristics--as in the case of prolificity--to the heterotic expression conditioned by the wild germplasm (Palacios and Magoja, Rev. Fac. Agrn. UNLP 59:81, 1983). Plant height is one of the less variable traits, the plants are relatively low, which is possibly and strongly associated to the evolutive cycle length and also with the number of leaves. The high variation for the uppermost ear insertion height could be possibly related to the different levels of prolificity of these plants.
The number of leaves (NL) and the number of leaves above the uppermost ear (LAE) are not very variable and they are adequately related to evolutive cycle and plant height. The plants have a low number of tillers (NT) when they are exposed to competence, but when the competence degree is low (plants disposed at the head of the plots), all the tillering capacity derived from teosinte is expressed and then a great part of the progenies are able to produce several fertile tillers (see TLC trait). It could be said that lodging resistance is good enough although very variable, and because of this it can be expected to find plants which tumble easily up to those which remain perfectly erect at harvest time.
Prolificity is the most remarkable trait among all those studied. This trait distinguishes the introgressed population of maize from the rest, through the number of ears per plant (EP). EP has a high value and it is really very variable. Probably this trait constitutes the main cause by which can be explained the high potential yield of some progenies. As repeatedly pointed out, prolificity is the most remarkable expression of the enormous heterosis produced by the interaction between wild and maize germplasm. The traits EWP, KWP, C, VEW and AEW are together with prolificity components of the grain yield and they also show a wide variability range. The average grain yields both for the S1 lines and the half-sib families are not too high, but the great variability between the S1 lines and half-sib families suggests that an adequate selection could engender a synthetic population with an enormous potential yield.
Considering the results obtained and bearing in mind that the commercial hybrids used as testers produced 10,119 kg/ha and 7,563 kg/ha, it can be deduced that 58 half-sib families (53.7% of the whole) and 11 S1 lines (10.2% of the whole) yielded significantly more than the less yielding tester while 18 half-sib families (16.7% of the whole) and 2 S1 lines produced significantly more than the most yielding commercial hybrid.
The inbreeding depression value, as seen in Table 1, is low and nonsignificant for some traits. All the opposite, that value is high when we consider yield and some of its components. A critical test for a better evaluation of the ID value consisted in comparing the S1 lines and the half-sib families derived from the same plant. For that, the first ear was self-pollinated and the second one was pollinated with a mixture of pollen taken from the whole population. The yield of the progenies derived from this was individually compared (Table 2). The S1 line yield is not related to the half-sib families (r = 0.04 nonsignificant). In mean, the S1 lines show an inbreeding depression value of 44%, which is very close to the estimated value considering the S1 lines and half-sib families have arisen from different plants of the population (see Table 1).
The results obtained to date document the usefulness that the wild germplasm has in the search for higher variability and the attainment of high yields. Bearing in mind that, as several authors point out, modern maize arose from a spontaneous introgressive process of its wild relatives (the teosintes) and that from the enormous variation produced by this primitive man led the evolution of the cultivated species, though with an empiric sense, the repetition of those events but managed with another criterion, can actually let us produce great expectancy for higher yields. As the variation produced in interspecific hybrids between maize and teosinte is well known, and as the female inflorescence (ear) has possibly been the base of selection of primitive man, it is easy to foretell the operated changes that led up to a modern maize with only one stem and one big ear. Probably, primitive man handled the criterion of the size of the edible organ and not yield per unit of area.
Actually, the variability generated in wild germplasm introgressed populations of maize possibly resembles the one available to primitive man, a long time ago. Then it is only necessary to get advantage of the fact, using a scientific criterion. Considering that one desires a more productive maize plant, then one with a different architecture cannot be discarded.
The results obtained let us infer that possibly those plants with multiple ears and tillers (though these characteristics are moderately expressed), homogeneous maturation and growing at low densities, probably express the maximum potential yield of the species. The high production shown by some of those half-sib families tested (almost 18,000 kg/ha), without water supply or fertilization techniques are not usual in the traditional maize crop area of Argentina. This fact, obtained on the basis of prolific plants, constitutes one more evidence of the significant advance that can be obtained in maize breeding by using wild germplasm.
Table 1. Relevant traits of S1 lines and half sib families derived from a maize population introgressed with perennial teosinte.
2. Comparison of grain yeild between S1 and half sib
families derived from the same female plant.
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