Find the information such as human life, natural resource,agriculture,forestry, biotechnology, biodiversity, wood and non-wood materials.
Blog List
Friday, 17 March 2017
Generation mean analysis in wheat (Triticum aestivum L.) under drought stress conditions
Published Date
Annals of Agricultural Sciences December 2014, Vol.59(2):177–184,doi:10.1016/j.aoas.2014.11.003 Open Access, Creative Commons license,Funding information
Author
Ali Said,
Agronomy of Dep., Faculty of Agric., Sohag Univ., Egypt
Received 22 June 2014. Accepted 20 August 2014. Available online 12 December 2014.
Abstract The six populations (parents, F1, backcrosses and F2) of the two wheat crosses, Gemmeiza 9 × IL1 (C1) and Sids 1 × IL2 (C2) were grown under normal irrigation (N) and drought stress (D) at the farm of Faculty of Agriculture, Sohag University, Egypt to study the genetic background of drought stress tolerance. Genetic variation was found for No. of spikes/plant (NS), 100-seed weight (SW), grain yield (GY), biological yield (BY), relative water content (RWC) and chlorophyll content (CC) under normal and drought stress environments in the two crosses. High heterosis was observed for all studied characters under both water treatments in the two crosses except RWC and CC in the first cross. Genetic analysis showed dominance in the inheritance of all studied characters under both water treatments in two crosses except BY, RWC and CC under normal irrigation in cross 1 and RWC under drought in cross 2 were controlled by the additive type of gene action. Narrow-sense heritability in the two crosses ranged from 0.20 for GY (D) to 0.57 for CC (N) in C1. The genetic advance in the two crosses was high (more than 40%) for GY (N&D), while NS, BY, RWC and CC (N&D) were moderate (14–40%), indicating the importance of direct selection for these characters. The genetic models fitted for NS, SW, BY, GY, RWC (D) and CC (D) in C1 and NS, BY (N), GY, RWC and CC in C2 indicated dominance and additive × additive gene effects. Both additive × additive [i] and dominance × dominance [1] effects were significant for NS, BY, GY, RWC (D) and CC (D) in C1 and NS, BY (N), GY, RWC and CC in C2, supporting the presence of duplicate type of epistasis. Since several important characters are influenced by dominance and non-allelic gene interaction, it is advisable to delay selection to later generation with increased homozygosity. Keywords
Wheat (T. aestivum L.)
Drought stress
Gene action
Scaling test
Introduction
Egyptian wheat production is not sufficient to meet the demands of growing population. Egypt is one of the countries that suffer severe drought and high temperature problems, especially in Upper Egypt. The development of well adapted cultivars to a wide range of environmental stresses is the ultimate goal of plant breeders in wheat. Among the environmental stresses drought is the second contributor to yield reduction after disease losses (Farshadfar et al., 2001 and Farshadfar et al., 2003 and Farshadfar et al., 2008a). Improving drought resistance is, therefore a major objective in plant breeding programs for rainfed agriculture (Ehdaie et al., 1991 and Ehdaie and Waines, 1993).
The plant breeder is interested in the estimation of gene effects in order to formulate the most advantageous breeding procedures for improvement of the attribute in question. Therefore, breeders need information about nature of gene action, heterosis, inbreeding depression, heritability and predicted genetic gain from selection for yield and yield components. Sprague (1963) listed three major factors that must be considered and which may limit progress in the analysis of quantitative genetic variation: the number of genes involved, the type of gene action, and the genotype–environment interaction.
The variation observed between the genotypes for the characters investigated indicates that selection may be effective for the improvement of drought tolerance (Umarahan et al., 1997, Farshadfar et al., 2001 and Farshadfar et al., 2008a). However, the selection efficiency is related to the magnitude of heritability and genetic advance (Johnson et al., 1955 and Singh and Narayanan, 1993). Heritability estimates along with genetic advance are important selection parameters and normally more helpful in predicting the gain under selection than heritability estimates alone. However, heritability estimates are influenced by the type of genetic material, sample size, method of sampling, type of experiment, method of calculation and effect of linkage. Genetic advance which refers to the improvement in the mean genotypic value of selected individuals over the parental population is influenced by the genetic variability, heritability and selection intensity (Alza and Martinez, 1997 and Sharma, 2003).
Many workers developed genetic models for the estimation of different genetic effects (Gamil and Saheal, 1986 and Kearsey and Pooni, 2004). However, the majority of these genetic models are basically additive–dominance models or simply additive models. The epistatic or non-allelic interactions are largely ignored so as to have a simplified interpretation of genetic variation. But, it has now been established that such inter-allelic interaction is of frequent occurrence in the control of trait-expression for continuous variation.
Generation mean analysis (Mather and Jinks, 1982) provides information on the relative importance of average effects of the genes (additive effects), dominance deviations and effects due to nonallelic genetic interactions in determining genotypic values of the individuals and consequently, mean genotypic values of families and generations., Generation mean analysis is a simple but useful technique for estimating gene effects for a polygenic trait, its greatest merit lying in the ability to estimate epistatic gene effects such as additive × additive, dominance × dominance and additive × dominance effects.
This study was carried out to determine the potential of morphological and physiological traits for drought tolerance in terms of heritability, genetic advance and type of gene action prevailing in wheat using six generation model i.e. P1, P2, F1, F2, Bc1, and Bc2 in two wheat crosses. It is hoped that results obtained herein would be of value for Egyptian wheat breeders.
Material and methods
The experimental material consisted of the six populations (P1, P2, F1, F2, Bc1, and Bc2) derived from two crosses between the two local cultivars, Gemmeiza 9 and Sids 1 which were more adapted and proved high yielding and the two breeding lines (IL1 and 2) which are characterized as drought tolerant (Table 1). The study was carried out at the experimental farm of Faculty of Agriculture, Sohag University, Egypt during the successive growing seasons of 2010/2011, 2011/2012 and 2012/2013. In 2010/2011 season, the two crosses were made among the parents to produce F1hybrid seeds and designated as follows:
Table 1. Pedigree and origin of the genotypes used in two bread wheat crosses.
In 2011/2012 season, F1 plants were selfed to produce F2 seeds and backcrossed to the parents to produce BC1 and BC2 seeds.
In 2012/2013, the six populations of the two crosses were grown in two separate experiments in a randomized complete blocks design with two replicates for each one. Each replicate consisted of 20 plants in one row for each of the parents and F1, 40 plants in two rows each of back cross and 80 plants in four rows for the F2population. Rows were 2.0 m long and 30 cm apart and 10 cm between plants. The first experiment was under normal irrigation (N) (irrigated when ever required), the second experiment was under drought stress (D) (where water stress was started from booting stage till milk ripe stage). The soil was fertilized at the rate of 20 kg/fed (15% P2O5) and 80 kg/fed (33.5% ammonium nitrate) and weeds were controlled by hand.
Data were recorded on 5 competitive individual plants for non-segregate populations (P1, P2 and F1) and 10 plants for BC1 and BC2 and 60 plants for F2 population for each replicate for the following:
1.
No. of spikes/plant (NS).
2.
100-grain weight (SW) in grams.
3.
Grain yield/plant (GY) in grams.
4.
Biological yield/plant (BY) in grams.
5.
Relative water content (RWC): RWC of flag leaves was determined by the standard method (Barr and Weatherley, 1962). Leaves were cut, and collected at anthesis stage of plant growth to determine fresh weight (FW). Then the leaf segments were placed in distilled water for 4 h and reweighed to obtain turgor weight (TW). Thereafter the leaf segments were oven dried and weighed (dried weight = DW). The RWC is determined as follows: RWC% = [(FW − DW)/(TW − DW)] × 100.
6.
Chlorophyll content (CC). Chlorophyll content was measured at anthesis stage of plant growth using a SPAD-502 chlorophyll meter (Minolta, Japan). For this measurement the average of three leaves per plant per replication per treatment was taken.
Statistical analysis
Analysis of variance and mean comparison of the characters were done using SAS Software. Generation mean analysis was performed using Mather and Jinks method (1982). In this method the mean of each character is indicated as follows:
Where:
Y = the mean of one generation.
m = the mean of all generation.
d = the sum of additive effects.
h = the sum of dominance effects.
i = the sum of additive × additive interaction (complementary).
1 = the sum of dominance × dominance interaction (duplicate).
j = sum of additive × dominance and α, 2α β and β2 are the coefficients of genetic parameters.
The genetic para meters (m, [d], [h], [I], [j], [1]) were tested for significance using a t-test.
To estimate the parameters and to select the most suitable model the least squares method and the joint scaling test of Mather and Jinks (1982) were employed.
Potence ratio, was estimated by using the formula of Smith (1952).
Stress Tolerance index (STI) for grain yield was computed as described by Farshadfar et al. (2001),
where GYN is grain yield/plant under normal irrigation and GYD is grain yield/plant under drought.
Broad-sense (Hb2) and narrow-sense (Hn2) heritability were estimated by Warner (1952) formulas:
Genetic advance was calculated according to (Johnson et al. (1955) with a selection intensity of i = 5% for all the characters as follows: GA = i.Hb.√VF2
The components of variation in six populations were calculated by the formulae of F2variance were obtained by the following formula of Mather and Jinks (1982) as:
Where:
D – additive genetic variance.
H – dominance variance.
E – environmental component of variance.
F – correlation between D and H over all loci.
Results and discussion
Analysis of variance (Table 2) revealed significant differences for the two environments and populations for all characters in the two crosses, except environments for NS in Cross 1 indicating the existence of genetic variation and possibility of selection for drought tolerance. The genotypes × environments interaction was also significant except for NS and GY in cross 1, displaying their similar response and different responses of other traits. Genetic variation was found in wheat for NS, SW, BY and GY by Tammam, 2005, Farshadfar et al., 2008a and Amin, 2013 and for RWC by Manette et al., 1988 and Farshadfar et al., 2001.
Table 2. Analysis of variance for various characters investigated.
Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively.
⁎
Significant at 5% levels of probability, respectively,
⁎⁎
Significant at 1% levels of probability, respectively.
In fact the development of any plant breeding program is dependent upon the existence of genetic variability. The efficiency of selection and expression of heterosis also largely depend upon the magnitude of genetic variability present in the plant population (Singh and Narayanan, 1993, Singh and Chaudhary, 1999, Farshadfar et al., 2001, Farshadfar et al., 2008a and Amin, 2013). The potence ratio presented in Table 3, its values ranged from less than one (−0.17) for RWC (D in C1) to more than one (17.67) for CC under drought in C2, indicating the presence of over dominance for all studied characters in the two crosses under normal and drought stress except RWC and CC under both water treatments in C1 were partial dominance. These results are in line with those obtained by Ketata et al., 1976, Moshref, 1996, Tammam, 2005 and Amin, 2013.
Data of means of six generations (Table 3) showed that Gemmeiza 9, in Cross 1, which had the highest GY under both water treatments, showed a significant difference from IL1 and BC2, while IL2, in Cross 2, had the highest GY significant difference from Sids 1, BC1 and BC2. The F1 hybrids were higher than best parent in all studied characters for the two crosses except RWC and CC (N&D for C1). These results showed the presence of heterotic effects for these characters.
Table 3. Mean comparison of the characters studied under normal irrigation and drought stress.
Generations
Characters
NS
SW
BY
GY
RWC
CC
N
D
N
D
N
D
N
D
N
D
N
D
Cross 1
Gemeiza 9 (P1)
10.67
8.97
6.19
4.94
95.67
46.91
37.99
26.96
74.97
50.96
48.10
34.16
Line 1 (P2)
14.67
12.27
5.55
4.20
86.82
40.83
33.38
25.63
85.76
58.04
57.25
43.95
F1 (P1 × P2)
15.47
14.47
6.66
5.44
99.87
48.79
41.29
34.01
81.84
55.11
53.55
41.85
F2
13.67
12.67
4.87
4.63
79.74
38.34
34.16
24.01
75.88
48.48
50.00
39.27
P1 × F1(BC1)
14.67
12.17
5.82
4.82
99.23
52.42
39.62
29.87
70.40
49.68
47.57
31.88
P2 × F1(BC2)
15.17
13.67
5.37
4.45
81.63
42.71
35.71
26.09
80.20
58.89
53.74
36.16
LSD0.05
0.62
0.53
0.35
0.48
1.25
1.19
1.31
2.22
1.08
0.76
1.14
1.04
Potence ratio
1.40
2.33
2.47
2.35
2.40
1.62
2.43
4.08
−0.27
−0.17
−0.19
−0.58
Cross 2
Sids 1 (P1)
11.67
9.27
5.57
4.80
72.64
48.96
36.62
24.98
64.61
42.53
46.25
36.88
Line 2 (P2)
13.17
10.97
6.20
5.19
65.03
37.71
38.34
27.46
69.79
48.60
49.15
37.70
F1 (P1 × P2)
15.67
11.67
6.54
5.73
76.28
51.40
43.09
35.09
77.45
54.76
57.35
45.25
F2
13.17
8.17
6.00
5.05
70.45
41.56
28.18
20.86
60.17
43.63
45.15
32.40
P1 × F1(BC1)
13.16
9.17
6.05
4.76
80.66
45.00
31.39
21.74
69.85
39.96
54.55
39.15
P2 × F1(BC2)
15.07
10.17
6.64
5.53
72.94
38.57
36.25
23.87
82.16
59.28
58.80
40.20
LSD0.05
1.45
0.90
0.50
0.36
2.96
2.53
2.22
2.37
1.39
1.99
2.83
2.63
Potence ratio
4.33
1.82
2.08
3.77
1.96
1.43
6.52
3.12
3.96
3.02
6.79
17.67
N and D denote; normal irrigation and drought stress, respectively. Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively.
The highest stress tolerance index (Table 4) was revealed by the F1 hybrid (STI = 0.82 in C1 and 0.81 in C2), displaying the presence of heterobeltiosis for drought resistance in the F1 hybrid, followed by P2 (0.77) and BC1 (0.75) in C1 and P2 (0.72) and F2 (0.74) in C2.
Table 4. Grain yield/plant under normal (GYN) and drought stress (GYD), and stress tolerance index (STI) for each generation.
Generations
GYN
GYD
STI
Cross 1
Gemmeiza 9 (P1)
37.99
26.96
0.71
Line 1 (P2)
33.38
25.63
0.77
F1 (P1 × P2)
41.29
34.01
0.82
F2
34.16
24.01
0.70
P1 × F1 (BC1)
39.62
29.87
0.75
P2 × F1 (BC2)
35.71
26.09
0.73
Cross 2
Sids 1 (P1)
36.62
24.98
0.68
Line 2 (P2)
38.34
27.46
0.72
F1 (P1 × P2)
43.09
35.09
0.81
F2
28.18
20.86
0.74
P1 × F1 (BC1)
31.39
21.74
0.69
P2 × F1 (BC2)
36.25
23.87
0.69
The degree of dominance (h/d), broad-sense (Hb) and narrow-sense (Hn) heritabilities, genetic advance (GA) and genetic components of variation is presented in Table 5 and Table 6, which shows that the degree of dominance (h/d) for all studied characters was greater than one in the two crosses under both water treatments except RWC (N in C1), indicating the presence of the over dominance type of gene action in the inheritance of these traits. Selection of these characters must therefore be delayed until the F3 or F4 generation. This delay permits a loss of non-additive genetic variances through inbreeding, so that the additive genetic variances can be more clearly evaluated. RWC (N in C1) was controlled by the additive type of gene action, the pedigree method of selection can be used for improved of this trait, while for characters under control of the non-additive type of gene action, biparental mating offers good prospects for increasing the frequency of genetic recombination, hastening the rate of genetic improvement, through it may be necessary to resort to heterosis breeding (Gill et al., 1972, Sharma and Singh, 1976, Srivastava et al., 1992, Farshadfar et al., 2001, Tammam, 2005 and Amin, 2013).
Table 5. Genetic parameters and components of variation for all studied characters in Gemmeiza 9 × IL1 (cross 1) under normal (N) and drought stress (D) conditions.
Chara.
h/d
Hb
Hn
GA
D
H
F
Ew
√H/D
F/√H × D
NS
N
−15.60
0.75
0.33
24.51
21.09
5.01
−1.95
4.08
0.49
−0.19
D
−3.23
0.65
0.32
22.87
21.70
0.36
+2.15
6.03
0.13
0.77
SW
N
+8.20
0.83
0.34
12.60
9.94
4.46
−1.01
1.22
0.67
0.15
D
+2.41
0.82
0.35
13.84
11.52
3.66
+0.95
1.52
0.56
0.15
BY
N
+2.93
0.73
0.34
27.96
25.59
1.49
+0.67
6.81
0.24
−0.16
D
+4.31
0.75
0.35
18.94
16.98
1.98
+1.14
2.95
0.34
0.11
GY
N
+5.02
0.73
0.27
57.56
41.46
24.72
+1.77
10.42
0.77
0.06
D
+4.92
0.58
0.20
40.10
27.16
19.86
+5.38
14.09
0.86
0.23
RWC
N
+0.08
0.83
0.34
19.36
15.50
6.43
−1.39
1.86
0.64
−0.14
D
−2.59
0.82
0.37
18.24
15.86
3.27
+0.63
2.01
0.45
0.09
CC
N
−1.69
0.81
0.57
15.62
21.13
−12.21
+0.78
1.76
0.76
0.05
D
+4.21
0.80
0.51
13.65
16.76
−7.28
−0.20
1.63
0.66
0.02
Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively. h/d, Hb, Hn, GA, D, H, Ew and F denote; the degree of dominance, broad-sense, narrow-sense heritabilities, genetic advance, additive, dominance, environmental components and an indicator of correlation between D and H over all loci, respectively.
Table 6. Genetic parameters and components of variation for all studied characters in Sids 1 × IL2 (cross 2) under normal (N) and drought stress (D) conditions.
Chara.
h/d
Hb
Hn
GA
D
H
F
Ew
√H/D
F/√H × D
NS
N
−3.68
0.67
0.35
6.94
21.98
−1.96
+2.99
5.08
0.30
0.46
D
−7.55
0.61
0.30
9.55
21.20
0.40
−0.60
6.88
0.14
−0.21
SW
N
−3.46
0.72
0.54
21.68
3.90
−2.60
+0.05
0.50
0.82
0.02
D
−1.46
0.72
0.42
20.17
4.44
−1.36
−0.30
0.72
0.56
−0.12
BY
N
+2.93
0.82
0.51
3.21
34.00
−13.37
−0.32
2.91
0.63
−0.02
D
+4.26
0.70
0.41
3.85
25.51
−7.53
+1.44
4.74
0.55
0.10
GY
N
−5.86
0.75
0.24
3.82
34.36
38.07
+3.14
8.82
1.05
0.09
D
−1.71
0.71
0.30
4.06
41.56
15.17
−2.04
9.69
0.61
−0.08
RWC
N
−5.98
0.76
0.51
2.63
30.54
−15.05
−0.93
3.47
0.70
−0.04
D
−1.71
0.71
0.47
2.76
31.61
−15.35
+2.13
5.02
0.70
0.10
CC
N
−13.13
0.78
0.54
4.12
19.82
−10.93
−2.53
2.09
0.74
−0.17
D
−35.29
0.80
0.47
12.23
27.93
−7.75
+1.08
2.93
0.53
0.07
Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively. h/d, Hb, Hn, GA, D, H, Ew and F denote; the degree of dominance, broad-sense, narrow-sense heritabilities, genetic advance, additive, dominance, environmental components and an indicator of correlation between D and H over all loci, respectively.
Heritability estimates indicate the progress from selection for plant characters is relatively easy or difficult to make in breeding program. Plant breeders, through experience, can perhaps rate a series of their response to selection. Heritability gave a numerical description of this concept. Assessment of heritability of various traits is of considerable important in crop improvement program, for example, to predict response to selection, Nyguist (1991). High broad-sense heritability estimates for all studied characters in the two Crosses under both environments (Table 5 and Table 6) showed that effective progress can be made through selection. Moderate narrow-sense heritability (0.2–0.5) was shown for all studied characters in two crosses except CC (N&D) in Cross 1 and SW, BY, RWC and CC under normal condition (N) in Cross 2 where heritability estimate was greater than 0.5 (Tefra and Peat, 1997). The difference between Hn and Hb exhibits the involvement of the dominance effect in the genetic constitution of these characters.
The variation observed between the genotypes for the characters investigated indicate that selection maybe effective for the improvement of drought tolerance.(Umarahan et al., 1997, Farshadfar et al., 2001 and Farshadfar et al., 2008b), however, the selection efficiency is related to the magnitude of heritability and genetic advance (Johnson et al., 1955 and Singh and Narayanan, 1993). Heritability estimates along with genetic advance are important selection parameters and normally more helpful in predicting the gain under selection than heritability estimates alone. However, heritability estimates are influenced by the type of genetic material, sample size, method of sampling, conduct of experiment, method of calculation and effect of linkage. Genetic advance which refers to the improvement in the mean genotypic value of selected individuals over the parental population is influenced by the genetic variability, heritability and selection intensity (Alza and Martinez, 1997 and Sharma, 2003).
The rate of genetic advance is connected with heritability (Mather and Jinks, 1982). The genetic advance (Table 5 and Table 6) was high (more than 40%) for GY under both water treatments in the two crosses, while NS, BY, RWC and CC in the two crosses were moderate (14–40%), indicating the importance of direct selection for these characters and the significance of indirect selection for SW (N&D) in the two crosses with low genetic advance (less than 14%) through correlated response with characters having high heritability and genetic advance (Sharma et al., 1991 and Farshadfar et al., 2001 and Farshadfar et al., 2008b).
Degree of dominance and variance components is presented in Table 5 and Table 6. Ew, D and H are environmental, additive and dominance components, respectively. Fis an indicator of correlation between D and H over all loci. If F is zero it means that dominant genes are in the parent with high performance, while negative F denotes that dominant genes are in the low performance parent. If the ratio of F/√D × H is equal to or near one confirms that the magnitude and sign of dominance for all the genes monitoring the character is equal, therefore, the ratio √H/D is a good estimator of dominance. If F/√D × H is equal to zero or close to zero, the magnitude and sign of the genes controlling the character is not equal and hence √H/D explains average dominance. The h/d ratio estimates the degree of dominance (Singh and Chaudhary, 1999, Kearsey and Pooni, 2004 and Farshadfar et al., 2001 and Farshadfar et al., 2008b). The ratio of √H/D for all studied characters (N&D) in two crosses showed average dominance.
The estimates of heterosis and inbreeding depression together provide information about type of gene action involved in the expression of various quantitative traits. The percentage of heterosis with regard to high Parent (HP) and mid-Parent (MP) and Inbreeding Depression (ID) (Figs. 1 and 2 and Figs. 3 and 4) illustrate that mid-parent and high parent heterosis were positive for NS, SW, BY, GY, RWC and CC in the two crosses under the two environments except RWC and CC (N&D) in Cross 1 which were negative compared with high parent. Inbreeding depression was positive for all studied characters.
Figs. 1 and 2. Percentage of heterosis and inbreeding depression under two environments in Gemmeiza 9 × IL1 (Cross 1) for characters investigated.
Figs. 3 and 4. Percentage of heterosis and inbreeding depression under two environments in Sids 1 × IL2 (Cross 2) for characters investigated.
The joint scaling test (Mather and Jinks, 1982) was employed to estimate the mean (m), additive effect (d), dominance effect (h), additive × additive (i), additive × dominance (j) and dominance × dominance (1) values (Table 7 and Table 8). The results of A, B, C and D scaling test for the two wheat crosses under both environments, revealed that significance of any of these tests indicates the presence of non-allelic gene interactions or epistasis on the scale of measurement used. Results of scaling test, showed that additive–dominance model is inadequate for explaining the inheritance of all studied characters, indicating the present of non-allelic gene interaction in two crosses under the two environments.
Table 7. Estimates of scaling test and types of gene action using generation means for all studied Characters in Gemmeiza 9 × IL1 (cross 1) under normal (N) and drought stress (D) conditions.
Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively. m, [d], [h], [i], [j] and [1] denote; mean, additive effect, dominance effect, additive × additive, additive × dominance and dominance × dominance, respectively.
∗ Significant at 5% levels of probability, respectively.
⁎⁎
Significant at 1% levels of probability, respectively.
Table 8. Estimates of scaling test and types of gene action using generation means for all studied characters in Sids 1 × IL2 (cross 2) under normal (N) and drought stress (D) conditions.
Where NS, SW, BY, GY, RWC and CC denote; number of spikes/plant, 100-grain weight, biological yield/plant, grain yield/plant, relative water content and chlorophyll content, respectively. m, [d], [h], [i], [j] and [1] denote; mean, additive effect, dominance effect, additive × additive, additive × dominance and dominance × dominance, respectively.
⁎
Significant at 5% levels of probability, respectively,
⁎⁎
Significant at 1% levels of probability, respectively.
The mean parameters (m) for all studied attributes of the two crosses and environments (Table 7 and Table 8) indicate that the contribution due to the overall mean plus the locus effects and interaction of the fixed loci was significant. Additive gene effect (d) was significant for BY, RWC and CC (N in C1) and RWC (D in C2), indicating potentiality of improving the performance of these characters using the pedigree selection program may be more effective, on the other hand, the estimated of dominance gene action (h) was significant for the rest characters (N&D) in two crosses, indicating the importance gene effects in inheritance of these characters. The significant [d] and [h] in the inheritance BY (N in C1) and RWC (D in C2) revealed that both types of additive and dominance effects are involved in the genetics of BY and RWC (Farshadfar et al., 2001, Farshadfar et al., 2008b, Tammam, 2005 and Amin, 2013).
The genetic models fitted (Table 7 and Table 8) for NS, SW, BY, GY, RWC (D) and CC (D) in Cross 1 and NS, BY (N), GY, RWC and CC in Cross 2 indicated dominance and additive × additive gene effects (Table 3 and Table 5). It is therefore suggested that selection should be carried out in late generation and the interaction should be fixed by selection under selfing conditions. The epistatic effect (dominance × dominance [1]) was significant for all studied characters (N&D) in the two crosses except SW (N in C1), which confirm the important role of dominance × dominance gene interaction in the genetic system. These results were reported by Srivastava et al., 1992, Tammam, 2005 and Amin, 2013. Both additive × additive [i] and dominance × dominance [1] effects were significant for NS, BY, GY, RWC (D) and CC (D) in Cross 1 and NS, BY (N), GY, RWC and CC in Cross 2, supporting the presence of duplicate type of epistasis. This complementary interaction increases the variation between the generation and in the segregating population. Where; the crosses, which showed most promising in terms of narrow sense heritability and genetic gain, also showed highest means in both conditions, chance to find stress tolerant breeding material in segregating populations of these crosses is promising.
No comments:
Post a Comment