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Original Article 

Biosci. J., Uberlândia, v. 31, n. 5, p. 1319-1324, Sept./Oct. 2015 

GENETIC DIVERGENCE AMONG MAIZE HYBRIDS IN CERRADO-
PANTANAL ECOTONE  

 
DIVERGÊNCIA GENÉTICA ENTRE HÍBRIDOS DE MILHO NO ECÓTONO 

CERRADO-PANTANAL 
 

Paulo Eduardo TEODORO¹; Larissa Pereira RIBEIRO²; Caio Cezar Guedes CORREA¹; 
Flávia Alves da SILVA², Denise Prevedel CAPRISTO²; Rodrigo Araújo MARQUES², Mariana 

Conceição de SOUZA²; Francisco Eduardo TORRES
4
 

1. Discentes do Programa de Pós-Graduação stricto sensu em Agronomia - área de concentração: Produção Vegetal da Universidade 
Estadual de Mato Grosso do Sul - UEMS, Aquidauana, MS, Brasil; 2. Discentes do Curso de Agronomia da UEMS/UUA, Aquidauana, 
MS, Brasil; 3. Engenheiro Agrônomo, Dr. em Fitotecnia, Docente Adjunto do Curso de Agronomia e do Programa de Pós-graduação em 

Produção Vegetal da UEMS/UUA, Aquidauana, MS, Brasil. 
 

ABSTRACT: In maize breeding programs can arise difficulties in relation to combination capacity studies for 
determination of heterotic groups, which are highly correlated with genetic divergence among the parents. The aim of this 
study was to estimate the genetic divergence measured for nine quantitative morphological traits in eleven single-cross 
hybrids of maize cultivated in the Cerrado-Pantanal ecotone. The experiment was conducted at Universidade Estadual de 
Mato Grosso do Sul – University Unit of Aquidauana. The experimental design was a randomized blocks with four 
replications. At harvest time, it were measured the following traits: plant height, ear insertion height, ear length, ear 
diameter, stem diameter, number of kernels per rows, number of rows per ear, weight of hundred grains and grain yield. In 
the application of hybrids cluster technique was adopted the Mahalanobis’s generalized distance as dissimilarity measure, 
and for establishment of similar groups was applied the Tocher’s method. The results indicated the existence of genetic 
variability among tested hybrids. The greatest genetic divergence was observed among the pairs MAXIMUS and XB6012, 
implying in heterotic gains. Crossings of lines extracted from hybrids 2B587HX and XB6012 with lines obtained from the 
other hybrids provide greater heterosis. The traits grain yield and ear insertion height were those who more and less 
contributed, respectively, for genetic divergence among hybrids. 

 

KEYWORDS: Dissimilarity. Hybrid development. Genetic breeding. Zea mays L. 
 
INTRODUCTION 

 
Knowledge of the genetic diversity in 

available germplasms is fundamental for the optimal 
designing of breeding programs, the efficiency of 
which can be increased if superior crossings are pre-
established. In the last five decades, a big number of 
maize (Zea mays L.) hybrids have been developed 
from genotypes with a restricted genetic base. This 
causes the risk of loss of genetic diversity and 
restricts the possibility of crossings among 
genetically divergent genotypes. Knowledge of the 
genetic relationships among breeding materials 
could help to prevent the great risk of increasing 
uniformity in the elite germplasm and could ensure 
long-term selection gains (OLIVEIRA et al. 2004). 

The adequate choice of genotypes as 
sources of lines extraction can determine the success 
or economic return of a breeding program to 
develop maize hybrids. The trends are in order to 
use F2 populations originated from crossings of 
single hybrids, synthetic elite lineages and even 
commercial hybrids, as it the inappropriate choice of 
population will result in losses of time and resources 
destined for breeding (OLIVEIRA et al. 2004). 

 
Front of numerous genitors frequently used 

in the maize breeding programs, hundreds of new 
lines are generated each year. Thus, the difficulty 
arises in relation to combination capacity studies for 
determination of heterotic groups, which are highly 
correlated with genetic divergence between the 
genitors. The determination of genetic dissimilarity 
among genitors contributes in the extraction of 
endogamic lines with considerable specific 
combination ability and thus allows exploiting the 
phenomenon of heterosis in hybrid crossings, 
increasing the chances to obtain segregating 
generations (PEJIC et al. 1998). These estimates are 
of great use in breeding programs and in the choice 
of genitors for mapping of genes. 

In the genetic diversity study of a 
population, quantitative morphological traits are 
subjected to multivariate biometric techniques, 
allowing unify multiple information of a trait set 
(TORES et al., 2015). Given the above, the aim of 
this study was to estimate the genetic divergence 
measured for nine quantitative morphological traits 
in eleven single-cross hybrids of maize cultivated in 
the Cerrado-Pantanal ecotone. 

Received: 11/04/14 
Accepted: 20/01/15 



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MATERIAL AND METHODS 
 

The experiment was installed at 
Universidade Estadual de Mato Grosso do Sul – 
Aquidauana Unit (UEMS/UUA), in the municipality 
of Aquidauana (MS), located in the 
Cerrado/Pantanal ecotone, comprising the 
coordinates 20º27'S and 55º40'W, with an average 
elevation of 170 m. 

The soil was classified as Ultisol sandy 
loam texture, with the following chemical features 
in the layer 0 – 0.20 m: pH (H2O) = 6.2; Al 
exchangeable (cmolc dm

-3) = 0.0; Ca+Mg (cmolc 
dm-3) = 4.31; P (mg dm-3) = 41.3; K (cmolc dm

-3) = 
0.2; Organic matter (g dm-3) = 19.7; V (%) = 45.0; 

m (%) = 0.0; Sum of bases (cmolc dm
-3) = 2.3; 

cation exchange capacity (or CEC) (cmolc dm
-3) = 

5.1. The climate according to the Köppen 
classification is Aw with humid and hot summers 
and dry winters (TEODORO et al, 2015). The 
cumulative rainfall during the experiment 450 mm 
and maximum and minimum temperatures of 91.4 
and 66.2 º F, respectively. 

The experimental design was a randomized 
block with four replications. The area was split into 
four blocks with a total of seventy-four plots, each 
with 15.75 m² (3.15 x 5.0 m) and two meters 
spacing between blocks. The treatments consisted of 
eleven single-cross hybrids of maize (Table 1). 

 
Table 1. Features of eleven single-cross hybrids of maize grown in Aquidauana, MS, Brazil, 2012. 
Commercial Name Business Cycle 
AG 9010 Agroceres Very early 
FÓRMULA TL Syngenta Very early 
MAXIMUS Syngenta Early 
P30F53 Pioneer Early 
P3340 Pioneer Early 
STATUS TL Syngenta Early 
XB 6010 Semeali Very early 
XB 6012 Semeali Early 
2B587 Dow Agrosciences Early 
30A30 Agromen Hyper early 
30A37 Agromen Very early 
 

In preparation of the experimental area was 
used glyphosate herbicide for desiccation, in doses 
of 1 kg ha-1. After drying and complete death of the 
plants, the furrows were opened using a seeder, 
performing manually the seeding under no-tillage 
system, on 2012-02, ten days after desiccation, 
which were distributed six seeds per meter in the 
rows, spaced 0.45 m. With about fifteen days after 
emergence of the plants were carried thinning 
keeping four plants per linear meter for 
establishment of 88,889 plants ha-1. 

The fertilization at sowing time consisted of 
300 kg ha-1 formulation 4-20-20. In topdressing 
nitrogen was used urea as a source of N, applying 
100 kg ha-1 on the surface when the plants had five 
to eight fully expanded leaves. It was made the 
control of fall armyworm (Spodoptera frugiperda 
Smith) 30 days after sowing using Triflumuron 
insecticide at a rate of 75 mL ha-1. For control of 
pre-emergence weeds, it was used 1,125 g ha-1 of 
active ingredient atrazine and subsequently 
weeding. 

At harvest time, when the grain had about 
18% humidity, measurements were made of plant 
height and ear insertion height, being carried out 

with a ruler graduated in five plants per plot. In each 
plot it were randomly harvested five ears, which it 
were numbered according to the plants evaluated for 
determining ear diameter, ear length, stem diameter, 
number of kernels per rows and number of rows per 
ear. 

The harvesting and threshing of maize ears 
were performed manually in three central rows of 
five meters length, according to the cycle of each 
hybrid. We determined the weight of hundred grains 
by manual counting, weighing and correction of 
moisture to 13%. We estimated the grain yield by 
extrapolation of production harvested in the area 
useful for one hectare, correcting for a 13% wet 
basis. 

In the application of clustering technique of 
hybrids, we adopted the Mahalanobis’s generalized 
distance (1930) as dissimilarity measure, 
considering the degree of dependence among the 
nine traits evaluated. In relation to the establishment 
of similar groups was applied the hierarchical 
agglomerative optimization method proposed by 
Tocher (RAO, 1952), whose calculations were 
equally grounded in Mahalanobis’s generalized 
distance (D²) and Unweighted Pair Group Method 



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with Arithmetic Mean (UPGMA), proposed by 
Sneath and Sokal (1973). We applied the criterion 
of Singh (1981) to quantify the contribution of each 
trait in the dissimilarity among hybrids. All analyzes 
were carried using the statistical software SAS (SAS 
INSTITUTE, 1999). 

 
RESULTS AND DISCUSSION 
 

There was genetic variability among corn 
hybrids for all traits, confirming the results obtained 
in other studies conducted in this region (TORRES 

et al., 2013; TEODORO et al, 2014a, b) The 
dissimilarity measures estimated from the 
Mahalanobis’s distance matrix (D²), based on nine 
quantitative traits are delineated in Table 2. The 
magnitude of the observed distances (0.03<D²<4.20) 
evidences the existence of large genetic divergence 
among the hybrids, allowing the choice of 
contrasting genitors for the extraction of endogamic 
lines. Simon et al. (2012) obtained similar results, 
which evaluating nineteen single-cross hybrids of 
maize in the Brazilian Cerrado found high genetic 
variability. 

 
Table 2. Estimates of genetic dissimilarity of eleven maize hybrids from the Mahalanobis’s distance matrix 

(D²) based on nine quantitative traits.  
Hybrid 30A37HX AG9010 MAXIMUS P30F53 FÓRMULA P3340 XB6010 STATUS 30A30HX 2B587HX 

XB6012 2.19 3.31 4.20 2.17 1.77 2.11 2.16 2.46 1.48 4.06 
30A37HX  1.12 1.75 2.03 1.65 1.72 2.14 1.37 1.01 1.90 
AG9010   0.87 1.88 2.80 2.44 2.18 3.06 1.89 2.60 
MAXIMUS    2.81 3.24 2.73 2.97 3.28 1.58 1.87 
P30F53     0.80 0.52 0.03 3.12 2.06 1.98 
FÓRMULA      0.19 0.79 1.83 1.16 1.60 
P3340       0.53 2.27 1.16 1.30 
XB6010        3.20 2.13 2.00 
STATUS         1.38 1.76 
30A30HX          1.96 
 

Cluster analysis aims to gather the genitors 
(or any other type of sample unit) through 
classification criterion in several groups, so that 
there is homogeneity within the group and 
heterogeneity between groups. This way, in a 
dendrogram, large level change indicates the union 
of heterogeneous hybrids. Using 60% similarity as a 
criterion for defining groups based on the UPGMA 
method from nine quantitative traits evaluated, it 

were formed five groups (Figure 1). Four hybrids 
are containing in the group I (P30F53, XB6010, 
FÓRMULA and P3340), one in the group II 
(2B587HX), three in the group III (30A37HX, 
30A30HX and STATUS), one in the group IV 
(XB6012) and two in the group V (AG9010 and 
MAXIMUS). 
 

 
Figure 1. Illustrative dendrodram of dissimilarity pattern established by Unweighted Pair Group Method with 

Arithmetic Mean (UPGMA) for eleven maize hybrids through nine morphological traits.  



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Cluster analysis by Tocher's optimization 
method provided the formation of five distinct 
groups of hybrids (Table 3). Tocher's optimization 
method (RAO, 1952) allows establishing mutually 
exclusive clusters of objects according to an 
objective function that adopts the criterion of 
optimization, which minimizes the average distance 
intra-cluster and maximizes the average distance 
inter-cluster. The dissimilarity among hybrids 
established by UPGMA method based on the 

arithmetical mean of dissimilarity measures is a tool 
that associated with Tocher's optimization method 
provides greater safety in discriminating different 
genotypes to genetic divergence. Both cluster 
methods similarly have hybrids allocated in groups 
with greater genetic similarity, a fact that has also 
been observed by other authors (SMITH et al. 1997; 
OLIVEIRA et al., 2010; ROTILI et al. 2012; 
SIMON et al. 2012; PREISIGKE et al. 2013 and 
GOMES JÚNIOR et al. 2014). 

 
Table 3. Cluster analysis of maize hybrids by Tocher’s method, based on the dissimilarity expressed by 

Mahalanobis’s generalized distance. 
Groups Hybrids 
I P30F53, XB6010, P3340 and FÓRMULA 
II AG9010, MAXIMUS and 30A37 
III STATUS and 30A30HX 
IV 2B587HX 
V XB6012 
 

The most divergent hybrids according to 
Mahalanobis’s distance (D²=4.20) were XB6012 
and MAXIMUS, which were also allocated into 
different groups (groups V and II) by Tocher’s 
method. These results suggest the possibility of 
lineages extracted from hybrids of these groups had 

distinct genetic divergence and consequently 
heterosis in hybrid combinations. Another point that 
reinforces this hypothesis is that these hybrids 
constituted the groups with the highest amplitude 
between them (3:23) also obtained by Tocher's 
optimization method (Table 4). 

 
Table 4. Intergroup estimated average distances by Tocher's optimization method, involving eleven maize 

hybrids. 
Groups II III IV V 
I 2.38 2.12 1.72 2.05 
II  2.03 2.12 4.06 
III   1.86 1.97 
IV    3.23 
 

Groups formed by just one individual 
suggest that these individuals are more divergent 
compared to the other. This facilitates the projection 
of breeding works, finding distinct genotypes for 
future crosses. In this sense, there is interest in 
obtaining distinct populations in maize breeding 
program, increasing the chances of crossings. 
Therefore, the extraction of lines of hybrids 
2B587HX and XB6012 for crosses with lines 
belonging to other genotypes may result contrasting 
genitors and, concomitantly, heterotic gains.  

In order to reduce efforts and perform the 
most efficient and economical breeding program is 

possible to select some of the hybrids that were 
considered less divergent as is the case of P30F53 
and XB6010, which showed D²=0.03, in addition to 
belonging to the same group formed by UPGMA 
and Tocher’s optimization methods. 

The Singh’s method (1981), based on the 
Mahalanobis’s D², considers of lesser importance 
characteristics that express less variability. It is 
suggested, therefore let it be discarded in this case, 
the traits number of rows per ear, plant height, ear 
insertion height and ear length (Table 5), that 
showed minor contribution to the divergence. 

 
Table 5. Relative contribution of the traits evaluated to genetic divergence by Singh’s method (1981), based on 

Mahalanobis’s generalized distance (D²). 
Trait Percentage value 
Ear lenght 1.56 
Ear diameter 7.10 
Number of rows per ear 0.46 



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Number of kernels per rows 4.98 
Stem diameter 9.75 
Ear insertion height 0.11 
Plant height 13.68 
Weight of hundred grains 18.33 
Yield grains 44.12 
 

 
The traits that most contributed to the 

genetic divergence among the hybrids were grain 
yield and weight of hundred grains, corroborating 
the results obtained by Rotili et al. (2012). 
According to Hallauer et al. (1988), the great 
interest in evaluating the relative importance of the 
traits refers to possibility of discarding of the 
features that contribute little to the discrimination of 
the evaluated material, reducing workforce, time 
and cost spent by experimentation. Moreover, the 
identification of traits that most contributed to the 
dissimilarity justifies its use in evaluation of genetic 
divergence among maize hybrids. 

 
CONCLUSIONS 

  
There is genetic variability among tested 

hybrids. The higher genetic divergence was 
observed among MAXIMUS and XB6012, implying 
in heterotic gains.  

Crossings of lines extracted from hybrids 
2B587HX and XB6012 with lines extracted from 
other hybrids provide higher heterosis.  

The traits grain yield and ear height were 
that most and least contributed, respectively, to the 
genetic divergence among hybrids. 

 
 
RESUMO: Em programas de melhoramento em milho podem surgir dificuldades quanto a estudos de 

capacidade de combinação para determinação de grupos heretóticos, que estão altamente correlacionados com a 
divergência genética entre os genitores. O objetivo deste trabalho foi estimar a divergência genética mensurada para nove 
descritores morfológicos quantitativos em onze híbridos simples de milho cultivado no ecótono Cerrado-Pantanal. O 
experimento foi conduzido na área experimental da Universidade Estadual de Mato Grosso do Sul, Aquidauana (MS). O 
delineamento experimental utilizado foi o de blocos casualizados com quatro repetições. No momento da colheita, foram 
mensurados os seguintes descritores: altura de planta, altura de inserção da primeira espiga, diâmetro da espiga, diâmetro 
do colmo, número de grãos por fileira, número de fileiras por espiga, massa de cem grãos e rendimento de grãos. Na 
aplicação da técnica de agrupamento de híbridos foi adotada a distância generalizada de Mahalanobis como medida de 
dissimilaridade, e para o estabelecimento de grupos similares foi aplicado o método de Tocher. Os resultados indicaram a 
existência de variabilidade genética entre os híbridos testados. A maior divergência genética foi observada entre os pares 
MAXIMUS e XB6012, implicando em ganho heterótico. Cruzamentos de linhagens extraídas dos híbridos 2B587HX e 
XB6012 com linhagens obtidas a partir dos demais híbridos proporcionaram maior heterose. Os descritores rendimento de 
grãos e altura de inserção da espiga foram os que mais e menos contribuíram, respectivamente, para a divergência genética 
entre os híbridos.  

 
PALAVRAS-CHAVE: Dissimilaridade. Desenvolvimento de híbridos. Melhoramento genético. Zea mays L.  

 
 
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