3.1. AMMI analysis
The combined AMMI showed highly significant differences (P<00.1) across environments for environment, genotypes, genotype by environment, and genotype by environment interaction (Table 4). AMMI revealed that there was a significant G x E for grain yields. This highlights the importance of thoroughly testing these cultivars in a multi-environment before recommending them to farmers. This result strongly supports the findings reported by other authors, which have important implications for the grain yield of maize grown in multiple environments [5, 14,15 and 16]. The test environment accounted for 55.78 percent of total variation in grain yield, with genotype accounting for 7.88 percent and G x E accounting for 14.55 percent, indicating that environmental main effects outweighed genotypic main effects. The magnitude sum of squares of G x E is greater than that of genotype effects, indicating that there are more differences in genotypic response across environments. Many researchers [5, 11, 15 and 17] have reported that the environment has a significant impact on yield stability. The multiplicative effects analysis (Table 4) revealed that the AMMI model with test environment contributed 55.78 percent of the total variation of sum square for grain yield, while G and G x E sources of variation accounted for 7.88 percent and 14.55 percent, respectively. Other research has found that in multi-environment trials, location accounts for the vast majority of total variation, with genotype and G x E accounting for only a minor portion [4,5, 15].
Table 3 AMMI analysis for grain yield. After “Table 3”
Source of Variation
|
df
|
Sum of squares
|
Mean Squeres
|
Total variation explained %
|
G x E explained%
|
Probability
|
ENV
|
4
|
767.45
|
191.86**
|
55.78
|
-
|
0.0001
|
GEN
|
14
|
108.45
|
7.74**
|
7.88
|
-
|
0.00001
|
G x E
|
56
|
200.19
|
3.57**
|
14.55
|
-
|
0.01
|
IPCA1
|
17
|
137.01
|
8.06**
|
-
|
68.4
|
0.00001
|
IPCA2
|
15
|
31.70
|
2.11ns
|
-
|
15.8
|
0.34
|
IPCA3
|
13
|
22.63
|
1.74ns
|
-
|
11.3
|
0.530
|
IPCA4
|
11
|
8.85
|
0.80ns
|
-
|
4.40
|
0.94
|
IPCA5
|
9
|
0
|
0ns
|
-
|
-
|
1
|
Residuals
|
150
|
299.76
|
1.99
|
21.79
|
-
|
NA
|
df=‘degree of freedom’, ns ‘non-significant’ (P> 0.05), IPCA ‘Interaction Principal Components’ ** Significant at P < 0.01
3.2 Performance of genotype in specific environment and mult-enviromnent
In Table 4, AMMI revealed that the first two hybrids (G11, G12) were the best performers in each environment, while CK1 was the worst performer. The genotype by environment interactions explains the differences in grain yields t-ha-1 (t-ha-1 = tons per hectare) between selected genotypes in five environments. This is also referred to as crossover genotype by environment interaction [4, 5, 15=18, 16=19, 13=17 and 17=20]. Bako 10.63 t-ha-1 (MABK181259), A/ Negele 9.04 t-ha-1 (MABK181255), Pawe 6.62 t-ha-1 (MABK181261), F/selam10.3 t-ha-1 (MABK181262), and Haromaya 7.43 t-ha-1 (MABK181259) were the highest yielders for each individual location. However, BH660 (check1) produced the lowest yielder for five individual locations: Bako (5.52 t-ha-1), A/Nagel (4.41 t-ha-1), Pawe (3.51 t-ha-1), F/Selam (4.87 t-ha-1) and Haromaya (3.6 t-ha-1). The average grain yield for all genotypes evaluated in multi-environment was higher than the best commercial check (BH661), with the exception of MABK181254. This implies possibility of fast releasing and overtake of new maize hybrids for transitional high land agroecology of Ethiopia to exploits available of maize inbred line germplasm to maximize production and productivity. Wender [21] also reported similar result that grain yield of some hybrids evaluated over location was higher than grain yield of commercial check. From total studied genotypes, seven genotypes had more than grand mean (6.55 t-ha-1) of grain yield. This study approves Legesse [14] which the grain yield of maize genotype varied based on the interactions of genotypes x environments within across test environments. Based on IPCA1 scores, genotype MABK181251, MABK181252, MABK181257, MABK181259, MABK181260 and MABK181262 had negative interaction with the environment, in opposite direction genotype MABK181250, MABK181253, MABK181254, MABK181255, MABK181256, BH660 and BH661 had positive interaction with environment in Table 5. Genotype MABK181255 (0.66) had highest positive interaction with environment whereas, genotype MABK181261 (0.13) had the lowest positive interaction. Relatively, the lowest and the highest negative interaction with environment expressed from MABK181259 (-1) and MABK181257 (-0.05) respectively. Genotype MABK181257, MABK181258, MABK181259 and MABK181262 had negative interaction with environment for both IPCA1 and IPCA2. However, genotype MABK181250, MABK181254, MABK181256, BH660 and BH661 had positive interaction with for IPCA and IPCA2. In AMMI analysis, positive interactions of IPCA scores of genotypes indicate environmental stability. These genotypes that exhibit a high degree of positive interaction with the environment can make use of the specific agro-ecological conditions of the environment to better adapt to these environments [18-19].
Table 4 Grain yield mean Performance for Individual location and all studied traits multi-environment
Genotype name
|
Individual location for GY t-h1
|
Across locations for all traits
|
BAKO
|
ARSI NEGELE
|
PAWE
|
F/SELAM
|
HARAMAYA
|
GY t-h1
|
AD
|
SD
|
PH
|
EH
|
EA
|
PA
|
MABK181250
|
8.18
|
6.49
|
5.96
|
5.68
|
6.55
|
6.57
|
89.07
|
93.64
|
276
|
155.4
|
2.17
|
2.56
|
MABK181251
|
9.04
|
5.3
|
5.38
|
7.44
|
4.71
|
6.37
|
89.65
|
93.87
|
280.5
|
155.6
|
2.42
|
2.41
|
MABK181252
|
7.77
|
5.35
|
5.14
|
8.14
|
5.11
|
6.3
|
90.07
|
93.89
|
275.4
|
161.3
|
2.5
|
2.53
|
MABK181253
|
7.56
|
7.11
|
3.77
|
6.72
|
6.25
|
6.28
|
90.03
|
93.99
|
266.2
|
151.4
|
2.25
|
2.48
|
MABK181254
|
4.77
|
5.47
|
5.03
|
6.19
|
4.57
|
5.21
|
90.07
|
94.1
|
271.9
|
155.6
|
2.38
|
2.46
|
MABK181255
|
7.34
|
9.04
|
4.07
|
6.53
|
4.37
|
6.27
|
89.41
|
93.67
|
280.7
|
175.2
|
2.58
|
2.61
|
MABK181256
|
7.39
|
7.71
|
5.34
|
7.34
|
6.81
|
6.92
|
88.98
|
93.53
|
266.9
|
159.5
|
2.5
|
2.51
|
MABK181257
|
8.82
|
6.75
|
3.83
|
7.29
|
5.39
|
6.42
|
89.17
|
93.43
|
275.5
|
161
|
2.38
|
2.56
|
MABK181258
|
9.2
|
5.84
|
5.21
|
8.11
|
6.43
|
6.96
|
89.41
|
93.69
|
269.1
|
165
|
2.5
|
2.38
|
MABK181259
|
10.63
|
4.41
|
4.61
|
9.42
|
7.43
|
7.3
|
89.93
|
93.89
|
270.7
|
151.1
|
2.17
|
2.38
|
MABK181260
|
9.18
|
5.61
|
5.31
|
8.4
|
7.34
|
7.17
|
89.6
|
93.64
|
275.4
|
153.9
|
2.46
|
2.41
|
MABK181261
|
9.44
|
8.22
|
6.62
|
7.99
|
6.65
|
7.78
|
89.65
|
93.57
|
273.3
|
160
|
2.54
|
2.51
|
MABK181262
|
9.09
|
6.98
|
5.57
|
10.3
|
6.93
|
7.77
|
89.26
|
93.5
|
267
|
154.7
|
2.13
|
2.48
|
BH660 (S Check)
|
5.57
|
7.07
|
3.51
|
4.86
|
3.6
|
4.92
|
90.79
|
94.08
|
265
|
158.1
|
2.42
|
2.75
|
BH661 (S check)
|
6.94
|
7.88
|
4.15
|
5.41
|
5.51
|
5.98
|
89.36
|
93.67
|
274.8
|
155.4
|
2.46
|
2.73
|
MEAN
|
8.06
|
6.62
|
4.9
|
7.32
|
5.84
|
6.55
|
89.63
|
93.74
|
272.5
|
158.2
|
2.39
|
2.51
|
MAX
|
10.63
|
9.04
|
6.62
|
10.3
|
7.43
|
7.78
|
90.79
|
94.08
|
|
|
2.42
|
2.75
|
MIN
|
5.57
|
4.41
|
3.51
|
4.86
|
3.6
|
4.92
|
88.98
|
93.53
|
266.9
|
5
|
2.5
|
2.51
|
LSD 0.05
|
3.05
|
1.63
|
2.13
|
1.8
|
0.92
|
0.88
|
|
|
|
|
|
|
CV (%)
|
33.24
|
14.58
|
20.9
|
22.19
|
13.54
|
22.32
|
|
|
|
|
|
|
GY =grain yield, AD= anthesis date, SD= silking date, PH= plant height, EH= ear height EA= ear aspect PA= plant aspect
Table 5 AMMI adjusted mean grain yield (t-ha1) IPCA score of genotypes and ASV of 15 genotypes tested across five environments in Ethiopia. After “Table 5”.
Genotype name
|
Mean GY
(t-ha1)
|
IPCA1
|
IPCA2
|
ASV
|
MABK181250
|
5.92
|
0.18
|
0.30
|
-0.71
|
MABK181251
|
5.90
|
-0.40
|
0.07
|
-0.31
|
MABK181252
|
5.79
|
-0.33
|
0.29
|
0.21
|
MABK181253
|
5.66
|
0.22
|
-0.27
|
0.09
|
MABK181254
|
4.75
|
0.27
|
0.85
|
0.29
|
MABK181255
|
5.83
|
0.66
|
-0.47
|
0.23
|
MABK181256
|
6.24
|
0.32
|
0.15
|
0.16
|
MABK181257
|
5.88
|
-0.08
|
-0.49
|
-0.02
|
MABK181258
|
6.31
|
-0.38
|
-0.02
|
-0.11
|
MABK181259
|
6.56
|
-1.00
|
-0.25
|
-0.06
|
MABK181260
|
6.43
|
-0.45
|
0.07
|
-0.06
|
MABK181261
|
7.12
|
0.13
|
-0.01
|
-0.21
|
MABK181262
|
7.08
|
-0.38
|
-0.02
|
0.64
|
BH660 (S Check)
|
4.56
|
0.64
|
-0.01
|
0.03
|
BH661 (S check)
|
5.43
|
0.61
|
-0.17
|
-0.16
|
1(Bako)
|
8.06
|
-0.55
|
-0.50
|
-0.43
|
3(Arsi Negele)
|
6.61
|
1.00
|
-0.32
|
0.14
|
4(Pawe)
|
4.89
|
0.08
|
0.64
|
-0.25
|
5(F/Selam)
|
7.32
|
-0.57
|
0.02
|
0.62
|
6(Haramaya)
|
2.92
|
0.05
|
0.15
|
-0.08
|
3.3 GGE Biplot analysis
The GGE biplot can be thought of as a graphical representation of matrix multiplication. As a result, fifteen hybrids, including two commercial checks, were evaluated at the five sites shown in Figures 2, 3, 4, and 5. GGE biplot analysis gathered a lot of useful information from various biplot graphs [4, 5 and 15]. The x-axis was the first principal component (PC1) scores, and the y-axis was the second principal component (PC2) scores. Biplot's total variation in relation to G and GEI explained 80.1 percent of the variance (Figure 2).
PC1 explained 65.4 percent of genotype by GGE from total variation, while PC2 explained 14.7 percent. Two principal components (PC1 & PC2) explained more than half of the G x E interpretation. Therefore, the first two PCs can be used to predict the best AMMI model to explain the two interpretable modes which supported finding of Yan & Tinker [20] and Yan [21]. The GGE biplot is shown in Figure 4, in which the environments are connected to the biplot origin vs the vectors. This perspective aids in comprehending the environment's interrelationships. According to Yan [22], the vector length close to the standard deviation in each test environment is a measure of the environment's ability to distinguish genotypes. As a result, the F/Selam’s vector is abnormally short in comparison to the plot size. Therefore, predicted genotype differences based on vectors from such environments may not be reliable and only reflect noise. The polygon view of the GGE biplot is useful for visualizing the multi-environment trial dataset's "which-won-where" pattern. PC1 accounted for 62.7 percent of variation, while PC2 accounted for 17.5 percent (Figure 5). Demisew [15], Hortense [23] and Legesse [14] also reported the variation of PC1 was much greater than PC2 in their studies of maize hybrids. Grain yield was explained by 80.4 percent of total variation on both axes. Draw vertical lines on each side of the polygon starting at the biplot origin. As shown in Figure 5, the rays of the two-line graphs divide the graph into six parts, with five environments appearing in one sector and the remaining environments appearing in another. The sectors had different high yielding vertex genotypes, such as MABK181261, MABK181255, MABK181253, MABK181254, MABK181259, and MABK181262, which are located at the polygon's corner and have the longest vectors. In comparison to other hybrids, these genotypes were among the most responsive to the environments in their respective directions. When a test environment is divided into mega Environments, it means that different environments have different high yielding genotypes for those sectors, indicating crossover G x E [24]. Based on this, the polygon views divided the test environment into three mega environments, with Bako, Pawe and Haromaya in best genotype MABK181262 group I, F/Selam MABK181259 group II and A/Negele in best genotype 6 (group III). Eliyas [16] also used GGE-biplot models and classified eight environments into two mega-environments for sugar cane genotypes evaluation for yield. To avoid random GEI, genotype evaluation in mega environment should be based on both mean performance and stability [25]. As a result, the genotypes MABK181261 and MABK181262 were identified as high yielders in the AMMI analysis. However, MABK181261 was identified as stable. only MABK181261 was chosen as the ideal genotype because it met both of the criteria. Demissew [15] also selected three maize hybrids for high land mid altitude of Ethiopia using the same criteria. Genotype MABK181262 is the highest yielding vertex hybrid in all the test environments that share the sector with it. Whereas MABK181259 was the highest yielding found in separate sector at F/selam site.
The environment -vector view of the GGE biplot with the average -environment axis was shown in Figure 3. A test environment with a smaller angle with average environmental axis is the most representative of the others. Thus, Pawe's vector is very short, ensuring that all genotypes perform similarly. Consequently, it no information or gave little information about genotype difference [4 and 14]. According to Yan [22] the biplot's concentric circles aid in visualizing the length of the environment vectors. This is a measure of the environments' discriminating ability and representativeness that is proportional to the standard deviation of each environment Bako has long vectors and small angles, and when combined with absicca, which is more discriminating genotypes and representative of test environments, the result is ideal for genotype selection. Through discriminating and representativeness by GGE biplot analysis, testing environments were used to distinguish environments that select high yielder genotypes in sets of environments. A/NEGEL has a long vector with a large angle as the result it cannot be used to select genotype.
performing genotypes, but it can provide information on genotypes that are unstable [24]. The discriminating test environments of A/NEGEL and F/SELAM are not representative, but they are useful for selecting specific adapted genotypes and discarding unstable genotypes. The performance of genotypes can be easily identified in a test environment with high representativeness and discriminating ability [21]. Only one test environment (Bako) is both representative and discriminating, making it a good place to find genotypes that are generally adapted. Similar results as many authors Y Matana [4]; SALEEM [26], Dagnechew [27], Ndlala [28], Dao [29] and Moges [30], who used GGE biplot to identify high representativeness and discriminating for different crops.
3.4 Stability of genotype
The stability of maize genotypes and average grain yield in all environments should be assessed within a single mega environment. Figure 4 shows the stability and average performance of the evaluation genotype. According to Yan [21], the AEC abscissa is a single arrowed line that points to higher mean yield cross environments. Thus, the maximum grain yield was MABK181262, followed by MABK181261, MABK181259, and so on. The acute angle between MABK181262 and MABK181259 indicates that these two genotypes respond similarly in all environments, and the difference between them is proportional. Whereas, an obsute angle (e.g., MABK181261 vs BH660) indicates that the genotypes reacted inversely, with the MABK181261 outperforming the BH660 and vice versa. The difference in performance between genotypes MABK181261 and MABK181262, MABK181253 and MABK181251, and MABK181254 and BH660 in the respond environment was due to G x E, where the genotypes were presented at right angles. AEC ordinate is the double arrowed line. It indicates a higher level of variability (poor stability in both directions). As a result, G1 was extremely stable, whereas MABK181259 was extremely unstable.