Local maize populations: sources of genetic variability for maize improvement programs --Urechean, V, Naidin, C By cultivating only some varieties and species of plants obtained by improvement methods year after year, a great part of genetic diversity has disappeared. With their reserve of ancestral genes, maize local populations are real sources of genetic diversity and variability for maize improvement programs.

A population can be improved in order to obtain specific characteristics: precocity, disease resistance, strong stalk (mechanical resistance) or a large grainís content of proteins with implications in the productionís improvement on the whole that can be used for the infusion with genes of adaptability to particular environment conditions.

In this research we studied five maize local populations (P21; P28; P68; P71; P106) which have been maintained in the genetic stock collection for twenty years, by propagation in isolated lots. Open-pollination assured the transmission of genetic variability of these populations along different generations.

A proof of this genetic diversity was the identification, as part of the same population, of plants that differ in grain color. In this way we found: P21 - yellow grain; P21 - purple grain; P28 - yellow-lemon grain; P28 - white grain; P68 - yellow-orange grain; P71 - white grain; P71 - yellow-orange grain; P106 - white grain; P106 - yellow-lemon grain; P106-yellow-orange grain. For each of these ten genotypes we analyzed the content of amino acids from the grain (Table 1).

Table 1. The variation in content of amino acids of the grains of local maize populations mg./100g.dry matter).
POPULATION-Intensity of the grain color 
Amino acid P21 y- P21 p P28

y-l

P28 w P68 y-o P71w P71

y-o

P106 w P106y-l P106y-o X c.v.
  1.2 1.5 1.1 1 1.3 1 1.3 1 1.1 1.3   %
Aspartic acid 0.825 0.788 0.801 0.916 0.634 0.824 0.850 0.794 0.866 0.840 0.814 7.00
threonine 0.417 0.427 0.472 0.462 0.331 0.426 0.470 0.438 0.453 0.472 0.437 4.03
serine 0.547 0.576 0.583 0.631 0.428 0.538 0.527 0.559 0.583 0.610 0.558 5.29
Glutanic acid 1.545 1.533 1.622 1.630 1.236 1.444 1.589 1.475 1.612 1.592 1.528 11.38
proline 0.735 0.624 0.842 0.732 0.722 0.653 0.709 0.704 0.720 0.858 0.730 6.88
cystine 0.372 0.344 0.395 0.328 0.166 0.376 0.364 0.387 0.329 0.456 0.352 7.13
glycine 0.399 0.392 0.395 0.448 0.330 0.411 0.481 0.399 0.425 0.405 0.409 3.73
alanine 0.902 0.963 0.961 0.841 0.611 0.904 0.916 0.896 0.852 0.822 0.867 9.61
valine 0.635 0.613 0.583 0.685 0.535 0.602 0.742 0.574 0.617 0.591 0.618 5.59
methionine 0.140 0.121 0.153 0.129 0.076 0.118 0.133 0.167 0.095 0.098 0.123 2.63
isoleucine 0.564 0.580 0.421 0.631 0.353 0.388 0.470 0.400 0.524 0.467 0.480 8.75
leucine 1.068 1.110 1.147 1.172 0.930 1.056 1.263 0.998 1.166 1.086 1.100 8.99
tyrosine 0.727 0.540 0.577 0.612 0.550 0.641 1.088 0.601 0.747 0.814 0.690 15.80
phenylalanine 0.782 0.641 0.606 0.750 0.548 0.750 0.967 0.827 0.917 0.837 0.763 12.70
histidine 0.623 0.445 0.483 0.631 0.623 0.574 0.629 0.624 0.549 0.618 0.580 6.38
lysine 0.519 0.562 0.383 0.513 0.462 0.733 0.638 0.605 0.568 0.602 0.559 9.20
arginine 0.707 1.122 0.913 0.800 0.561 0.797 0.800 1.001 1.016 0.823 0.854 15.51
TAA % 11.507 11.381 11.337 11.911 9.096 11.235 12.636 11.449 12.039 11.991 11.458
TAAE % 5.455 5.621 5.161 5.773 4.419 5.444 6.112 5.634 5.905 5.594 5.512
TAAE/TAA% 47.40 49.38 45.52 48.46 48.58 48.45 48.36 49.2 49.04 46.65 48.10
GLU/TAA,% 13.43 13.47 14.31 13.68 13.59 12.85 12.58 12.88 13.39 13.28 13.33
LYS/TAA,% 4.51 4.94 3.38 4.31 5.08 6.52 5.05 5.28 4.72 5.02 4.87
ASP/TAA,% 7.17 6.92 7.07 7.69 6.97 7.33 6.73 6.94 7.19 7.01 7.10
TYR+PHE/TAA 13.11 10.38 10.43 11.43 12.07 12.38 16.26 12.47 13.82 13.77 12.67

TAA -total amino acids; TAAE - total essential amino acids; GLU - glutamic acid; LYS - lysine; ASP - aspartic acid; TRY+PHE-tyrosine+phenylalanine

The coefficient of variation (c.v. %) for the ten genotypes analyzed shows a middling variation for tyrosine(15.80%); arginine (15.51%) phenylalanine (12.70%) and glutamic acid (11.38%), the other amino acids having a c.v.<10%. At the level of each population there are differences concerning the amino acid content depending on the grainís color. In this way, at P21, the content of arginine is much higher than that of the genotype with purple-colored grain, which probably assures the favorable ratio between the total essential amino acids and the total amino acids (19.38%). The yellow grain genotype (P21 with yellow grain) has a higher content of aspartic acid/TAA% (7.17%) and tyrosine+phenylalanine (TYR+PHE/TAA=13.11 %).

The white grain genotype (P28 white grain) has a higher content of lysine related with the total of amino acids (4.31%), as well as the tyrosine+phenylalanine (11.43%), the rest of the amino acids having close values. P71 with white grain and yellow-orange grain shows the greatest difference at the level of the tyrosine, the yellow-orange grain genotype hawing 1,088mg/100g dry matter and the white grain genotype 0,641mg/100g dry matter.

The total content of amino acids and essential amino acids is also higher in P71 with yellow-orange grain. The content of lysine is higher for the P21 genotype with white grain, but TYR+PHE/TAA=16.26% for the yellow-orange grain genotype is the highest of all genotypes studied.

The P106 population with P106-white grain; P106-yellow-lemon grain and P106 yellow-orange grain genotypes have the lowest total content of amino acids (TAAmg/100g dray matter.) at the white grain variant (11.449mg/100g dry matter.) but the best TAAE/TAA=49.200%. P106 with yellow-lemon grain has the highest content of glutamic acid (1.612 mg), leucine (1.166 mg) and total essential amino acids TAAE mg/100g dry matter (5.905). P106 with yellow-orange grain genotype has a higher content of proline and tyrosine but the lowest arginine level (0.823mg). Also the total content of essential amino acids is the lowest (46.65%).

All these variations of the content of amino acids reflect the genetic variability of the maize local populations on the whole and the genetic diversity existent at each populationís level. Because the quality of the grain is one of our maize improvement programs priorities we tried to establish if there was any correlation between grainís content of amino acids and the color of the grain. We used a grade scale of the grain colorís intensity:1=white grain; 1.1=yellow-lemon grain; 1.2=yellow grain; 1.3 yellow-orange grain; 1.5=purple-coloured grain. For the genotypes studied we calculated: total content of amino acids (TAAmg/100g dry matter) and color of the grain, where r = -0.128; total content of essential amino acids (TAAE mg/100g dry matter) and color of the grain, where r= -0.110. The genotypes were grouped by intensity of grain colors: genotypes with light colored grain (1 and 1.1 grade) and genotypes with dark colored grain (1.3 and 1.5 grade.

We analyzed the correlation between every essential amino acid and the light color of the grain. We found negative correlations between the level of essential amino acids and the light color of the grain (Table 2).

Table 2. Correlation between the grainís content of essential amino acids and the light color of the maize grain.
 
Amino acid Color grain coefficient of correlation
threonine 1 and 1.1 0.666
valine 1 and 1.1 - 0.375
methionine 1 and 1.1 -0.666
isoleucine 1 and 1.1 -0.002
leucine 1 and 1.1 0.562
phenylalanine 1 and 1.1 -0.125
histidine 1 and 1.1 -1.0
lysine 1 and 1.1 -0.666
arginine 1 and 1.1 0.50

 


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