Relative Values of Three Different Testers in Evaluating Combining Ability
of New Maize Inbred Lines
Fifteen inbred lines and three testers of maize were crossed in line x tester
scheme to study the combining ability effects for earliness, grain yield and
yield components. A yield trial included the 45 top crosses, 15 inbred lines,
3 testers and two check hybrids S.C. Pioneer 3084 and T.W.C Giza 352. The experiment
was conducted for three years at the Agricultural Research Station of the Faculty
of Agriculture, Moshtohor, Benha University. The experimental design was randomized
complete blocks with three replications. Mean squares due to crosses (C) inbred
lines (L), testers (T) and line x tester (LxT) were significant for most studied
traits for the combined analysis over two evaluation seasons. Significance of
interaction variance for C, L, T and LxT with seasons on most studied traits
was detected. δ2SCA played the major role in determining
inheritance of all traits, revealing that the largest part of the total genetic
variability associated with these traits was a result of non- additive gene
action. The magnitude of the interaction of δ2SCAxyears
(SY) was generally higher than for δ2GCA x SY.
This indicates that non-additive type of gene action is more affected by SY
than additive and additive x additive types of gene action. Inbred lines M L4,
8, 9, 10, 11 and L12 were reliable general combiners for earliness and M L3,
4, 5, 6 and L13 for grain yield plant-1. For earliness the top-cross
M 212D x SC (M 201xM 204) gave the best Sij effects. Regarding grain yield plant-1,
five SC between M L 204 and each of inbred lines M 232A, M 202C, M 242A, M 212D
and M 236B as well as the two TWC M 202cxSC (201x204) and M 236BxSC (201x204)
showed significantly and out yielded than check hybrid SC Pioneer 3084 by 18.99%, 12.67%, 15.71%, 11.29%, 14.11%, 10.55% and 6.56% in the combined analysis,
Received: November 18, 2013;
Accepted: February 18, 2014;
Published: April 15, 2014
The practical phase of maize breeding is based upon searching for elite inbred
lines that possess higher combining ability to be used as parents for new superior
hybrids or replace the currently used ones. The top cross method using broad
and narrow base testers is the most common procedure for the evaluating process.
A desirable tester may be defined as one that combines the greatest simplicity
in use with the maximum information on the performance expected from the tested
lines when used in other combinations or grown in other environments. No single
tester can completely fulfill these requirements. The nature of testers to be
used in the line x tester model for evaluating inbred lines is still unsolved
problem. Therefore, the choice of a suitable tester is an important decision.
Matzinger (1953) showed that a narrow genetic base
tester contributes more to linextester interaction than does a heterogeneous
one. Grogan and Zuber (1957) concluded that some single
crosses were as equally effective as double crosses for measuring general combining
ability. Davis (1927), Jenkins (1935)
and Sprague (1939) suggested the method of early testing
that is greatly affected by the nature of testers needed for efficient evaluation
of inbred lines. The magnitude of genetic components for a certain trait would
depend mainly upon the environmental fluctuations under which the breeding populations
are tested. Therefore, much effort has been devoted by maize breeders to estimate
the interactions between genetic components and environments.
The main objectives of the current study were to identify and assess superior
inbred lines of maize, compare different testers for evaluating inbred lines,
determined superior top crosses relative to check hybrid and estimate the combining
ability of the testers and lines.
MATERIALS AND METHODS
Fifteen new inbred lines in S7 of yellow maize i.e. (Moshtohor)
M. 233A (L1), M. 207B (L2), M 254A (L3), M 232A (L4), M 220A (L5), M 202C (L6),
M 262A (L7), M 242A (L8), M 212D (L9), M 208A (L10), M 217D (L11), M 222C (L12),
M 236B (L13), M 228A (L14) and M 250V (L15), all of which varied considerably
in their characteristics, were used in this study. These inbred lines were crossed
in the 2011 summer season with three different testers as follows: Moshtohor
population openpollination variety (M pop.), a promising high yield single
cross M 201xM 204 and an elite of combining abilities inbred line M 204 generate
45 top crosses combinations in line x tester mating design. The top crosses
with parents and two check hybrids single cross Pioneer 3084 and three way cross
(TWC) Giza 352 were evaluated at the Agricultural Research Station of the Faculty
of Agriculture, Moshtohor, Benha University in a randomized complete block design
with three replications. The planing dates were 2nd June and 18th
May in 2012 and 2013 seasons, respectively. Each plot consisted of one ridge
6-m long with a 70x25 cm plant density. The plots were irrigated eight times
during the growing season and fertilized at rate of 286 kg N ha-1.
The other cultural practices of maize growing were practiced. The following
traits were noted on a random sample of 15 guarded plants in each plot; days
to 50% tasseling, ear length, ear diameter, number of rows ear-1,
number of kernels row-1, 100-kernel weight, grain yield plant-1
(adjusted to 15.5% moisture content) and shelling%. Analysis of variance was
made for each of the two seasons then across both seasons after testing the
homogeneity of error variances. Combining ability analysis was performed based
on the procedure developed by Kempthorne (1957) over the
RESULTS AND DISCUSSION
The analyses of variance for the studied traits are presented in Table
1. Mean squares due to years were highly significant for all traits, indicating
overall differences between the two seasons. Highly significant crosses and
their partitioning into inbred lines (L), testers (T) and linex tester (LxT)
were significant for all studied traits of each season and across the two seasons
except LxT for shelling%, revealing a wide range of variability among parental
tester (males), lines (females) and that the lines performed differently according
to the tester which they crossed. Significant interactions between crosses and
year as well as between line and years were obtained for all traits except for
the traits of days to 50% tasseling and ear diameter. This indicates that the
crosses and lines behaved somewhat differently from one year to another. Mean
squares for line x tester x years were significant for yield and yield components.
This indicates that the studied top crosses responded differently to the summer
seasons. These results are in accordance with those obtained by Sofi
and Rather (2006), Abd El-Aal (2012) and El-Hosary
and El-Gammal (2013). However, Amer and El-Shenawy
(2007) who obtained significant interactions between environment, lines
and testers regarding flowering and grain yield plant-1.
|| Mean squares from ordinary analysis of variance and combining
ability for the studied traits
|*, **: Significance at 0.05 and 0.01 levels of probability,
El-Morshidy et al. (2003) reported that testers
were affected much more by environmental conditions than by line.
The estimates of the variance due to the general combining ability (δ2GCA)
and the specific combining ability (δ2SCA) and their
interactions with years (δ2GCAx year and δ2SCAx
year), presented in Table 1, show that the δ2SCA
played a major contribution in inheritance for total genetic variability associated
with these attributes and was a result of non-additive action types. The results
for grain yield plant-1 supports the findings by Sadek
et al. (2002) who reported that δ2SCA was
more important in the inheritance of grain yield plant-1. The magnitude
of the interaction of δ2GCAx year was higher than
that of δ2SCAx year for all of the studied traits.
Consequently, additive gene effects seemed greatly affected by environment.
These results are in agreement with the findings reported by Hefny
(2010) and El-Badawy (2013) who noted that δ2SCA
is more sensitive to environmental changes than δ2GCA.
Test of homogeneity revealed the validity of the combined analysis for the
data of the two years. General combining ability effects (gi) calculated
for each female and male (combined over two seasons) are presented in Table
2. High positive values would be of interest under all traits in question
except that of days to 50% tasseling where high negative values would be useful
from the breeder's point of view. The effects of gi for testers (males)
showed that the inbred line M204 behaved as a good combiner for all traits.
Earliness and high yielding if found in maize, would expand the opportunity
for intensive cropping. Therefore, the male parent M204 could be an excellent
parent in breeding programs towards releasing early and high yield potentiality
of hybrid maize. On the other hand, the parental tester SC (201x204) expressed
a highly significant negative results for days to 50% tasseling. The male parents
Moshtohor pop. and SC(201x204) had undesirable gi effects for the
remaining traits. Therefore, both male parents were of greatest interest and
should be used as testers for evaluating the new inbred lines for these traits.
|| General combining ability effects for testers and inbred
lines for all studied traits in the combined analysis
|*,** :Significance at 0.05 and 0.01 levels of probability,
The parental females (inbred lines) M 232A (L4), M 242A (L8), M 212D (L9),
M 208A (L10), M 217D (L11) and M 222C (L12) showed significant negative gi efects
for days to 50% tesseling, M 233A (L1), M 202C (L6) and M 242A (L8) for ear
length, M 262A (L7), M 242A (L8) for ear diameter, M 220A (L5), M 202C (L6),
M 262A (L7), M 242A (L8), M 212D (L9) and M 217D (L11) for No. of kernels row-1,
M 254A (L3), M 232A (L4), M 220A (L5), M 262A (L7), M 208A (L10) and M 250V
(L15) for number of rows ear-1, M 233A (L1), M 202C (L6), M 222C
(L12) and M 228A (L14) for 100-kernel weight, M 254A (L3), M 232A (L4), M 220A
(L5), M 202C (L6) and M 236B (L13) for grain yield plant-1 and M
242A (L8) for shelling percentage had significant positive gi effects.
Specific Combining Ability effects (SCA) of 45 top cross are presented in Table
3. The greatest inter-and intra-allelic interaction as deduced from SCA
effects were observed in top crosses: M 232AxM pop., M 217DxSC(201x204), M 207BxL
M 204 and M 212DxL M 204 for ear length; M pop. with each of M 254A, M202c,
M 228A and M250v; SC (201x204) with each of M 207B and M 236B; and M 204 with
each of M 262A, M 242A and M 208A for the number of kernels row-1;
M pop with each of M 242A, M 228A and M 250V; SC (201x204) with each of M 208A
and M 236B; and M 204xM 236B for number of kernels row-1; M pop with
each of M 233A and M 262A; SC (201x204)xM 202C; and L M 204 and each of M 232A
and M 212D for the 100-kernel weight; and M pop and each of M 254A, M 202C,
M 208A, M 217D, M 236B and M 250V; SC (201x204) and each of M 220A and M 236B
and L M 204 with each of M 232 A, M 242A, M 212D, M 208A and M 236B for grain
yield plant-1. These top-crosses might be of interest in breeding
programs as most of them involved at least one good combiner for the concerned
traits. These top crosses could be of interest to obtain synthetic varieties
or produced inbred lines.
It could be concluded that testers of broad genetic base are more efficient
than those of the narrow genetic base for evaluation of GCA inbred lines of
maize. Among the material evaluated, the line Moshtohor 202A and M 232A gave
the highest GCA effects for high yielding ability and that the top crosses M
242AxL M 204, M 236BxSC (201x204), M 250CxM pop. and M 236BxL M 204 appeared
efficient and promising in improving grain yield.
Mean performance of 45 top crosses and two checks for days to 50% tasseling
and grain yield plant-1 are presented in Table 4.
For days to 50% tasseling, results showed that the most top crosses were earlier
than the two check hybrids. The best top crosses for earliness were obtained
by combinations between each of inbred lines; M. 208A, M. 232A, M. 222C, M.
242A, M. 228A and M. 202A with the three testers in both seasons and the combined
Mean grain yield plant-1 of 45 top crosses ranged from 138.5 (M.
222CxM pop.) to 234.6 (M. 236B x M 204) in the first season, 163 (M236BxM Pop.)
to 275.50 (M232xM204) in the second season and 154.7 (242AxM Pop.) to 246.55
(M. 232xM 204) in the combined analysis. The five SC between M L 204 and each
of inbred lines M 232A, M 202C, M 242A, M 212D and M 236B as well as the two
TWC M 202cxSC (201x204) and M 236Bx SC (201x204) showed significantly and out
yielded than check hybrid SC Pioneer 3084 by 18.99%, 12.67%, 15.71%, 11.29%,
14.11%, 10.55% and 6.56% in the combined analysis, respectively. All top crosses
surpassed or insignificant differ than TW cross Giza 352. While, twenty seven
crosses out yielded or insignificant than check hybrid Pioneer 3084. Hence,
it could be concluded that these crosses offer possibility for improving grain
yield of maize. These hybrids exhibited significant increase of one or more
of traits contributing to grain yield. The fluctuation of hybrids from seasons
to another was detected for grain yield plant-1.
|| Specific combining ability, effects over both seasons (years)
for all studied traits
|*,**: Significance at 0.05 and 0.01 levels of probability,
||Mean performance of the top crosses and check varieties in
both seasons as well as the combined analysis for days to 50% tasseling
and grain yield plant-1
From the above results it could be clear that non-additive genetic variance
is considered to be the major source of total genetic variance responsible for
the inheritance of all studied traits. The tester inbred line M 204 behaved
as an excellent combiner for all traits. The Inbred lines M 242A, 232A, M. 212D
and M. 236B had desirable and exhibited good general combiners for earliness
and grain yield. The single cross M 204x242 A exhibited the highest SCA effects
and suitable combinations for grain yield plant-1.
The five SC between ML 204 and each of inbred lines M 232A M 202C, M 242A,
M 212D and M 236B as well as the two TWC M202CxSC (201x204) and M 236BxSC (201x204)
showed significantly and out yielded than check hybrid SC Pioneer 3084 in the
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