5.3. Results
5.3.1 Relative grain yield performance of maize hybrids under high and low nitrogen
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Standard heterosis or relative grain yield under both low N (LN) and high (HN) conditions was estimated as follows:
Trial mean heterosis = [(F1 hybrid - trial mean)/trial mean]*100 Local check heterosis = [(F1 hybrid - local check)/local check]*100 Best check heterosis = [(F1 hybrid - best check)/best check]*100
Mean check heterosis = [(F1 hybrid - mean of checks)/mean of checks]*100
Relative performance across N regimes and standard heterosis could also be a measure of N-use efficiency (NUE) of a genotype.
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Table 5.2: Summary statistics for grain yield (tons ha-1) of 54 maize hybrids across environments Environment R2
(%)
CV (%)
Grain yield
(ton ha-1)
Error mean
square LSD Genotypes
(Pr>F)
Mean Min Max Differe
nce
HNDS08 80.9 17.2 8.74 3.66 13.58 9.92 2.258 3.05 *
LNDS08 85.2 13.7 5.99 2.91 8.72 5.81 0.673 1.66 **
% Mean diff. 31.46
HN WS09 86.1 13.7 5.66 2.10 9.18 7.08 0.602 1.57 **
LN WS09 93.7 13.5 4.10 1.27 8.77 7.50 0.308 1.12 **
% Mean diff. 27.56
HN DS09 91.8 13.0 7.60 2.90 12.00 9.10 0.970 2.00 **
LN DS09 90.5 14.9 6.02 1.97 10.60 8.63 0.802 1.82 **
% Mean diff. 20.79
**, * = statistically significant at p≤0.0001, and p≤0.05. HNDS08 = high nitrogen fertiliser application rate at 120kg N ha-1 for dry season year 2008, HNDS09 = high nitrogen fertiliser application rate at 120kg N ha-1 during dry season year 2009, HNWS09 = high nitrogen fertiliser application rate at 120kg N ha-1 during wet season year 2009, LNDS09 = low nitrogen fertiliser application rate at 60 kg N ha-1 during dry season year 2008, LNDS09 = low nitrogen fertiliser application rate at 60kg N ha-1 , LNWS09 = low nitrogen fertiliser application rate at 60kg N ha-1 , R2 = coefficient of determination, CV = coefficient of variation, LSD ((α=0.05, 37df,critical value of t = 0.02619)
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Table 5.3: Summary statistics for maturity related characters of 54 maize hybrids across environments Environment R2 (%) CV (%) Error mean square LSD (α=0.05) Pr>F
50 % anthesis date Genotype
HNDS08 96.2 1.71 2.25 3.11 **
HNDS09 94.9 1.76 2.75 3.36 **
HNWS09 96.2 1.96 2.33 2.96 **
LNDS08 96.4 1.74 2.49 3.20 **
LNDS09 88.5 2.53 6.36 5.11 **
LNWS09 94.6 2.53 3.80 3.95 **
50% silking date
HNDS08 96.5 1.56 2.02 2.88 **
HNDS09 94.6 1.85 3.11 3.57 **
HNWS09 96.1 2.03 2.33 3.09 **
LNDS08 96.1 1.81 2.83 3.41 **
LNDS09 93.7 2.16 4.78 4.43 **
LNWS09 85.4 4.56 12.80 7.25 **
Leaf chlorophyll concentration
HNDS08 95.9 2.88 1.97 2.85 **
HNDS09 88.2 6.28 7.52 5.56 **
HNWS09 94.1 5.34 5.04 4.55 **
LNDS08 96.0 4.31 3-00 3.51 **
LNDS09 89.7 7.26 6.23 5.06 **
LNWS09 92.1 9.35 9.25 6.62 **
Kernel dry-down index
HNDS08 91.6 8.77 0.004 0.13 **
HNDS09 79.7 19.5 0.010 0.20 *
HNWS09 87.7 12.01 0.005 0.15 **
LNDS08 91.2 9.75 0.005 0.14 **
LNDS09 85.2 10.21 0.003 0.11 **
LNWS09 91.0 12.64 0.006 0.16 **
Kernel moisture content
HNDS08 87.2 3.63 0.66 1.65 **
HNDS09 84.0 4.74 0.97 2.00 *
HNWS09 92.7 5.07 0.97 2.00 **
LNDS08 91.7 3.23 0.51 1.45 **
LNDS09 91.1 2.92 0.42 1.32 **
LNWS09 92.2 5.92 1.26 2.28 **
Effective grain filling duration
HNDS08 88.4 4.22 3.94 4.02 **
HNDS09 65.6 1.75 84.58 18.63 ns
HNWS09 85.3 5.18 4.68 4.38 **
LNDS08 88.1 4.53 4.54 4.32 **
LNDS09 90.7 5.05 5.53 4.76 **
LNWS09 82.8 9.08 12.37 7.13 *
Calendar physiological maturity
HNDS08 85.6 1.04 2.07 2.91 **
HNDS09 84.0 1.24 3.29 3.68 *
HNWS09 92.4 1.36 2.53 3.23 **
LNDS08 92.1 0.92 1.64 2.60 **
LNDS09 90.9 0.84 1.56 2.53 **
LNWS09 92.4 1.36 2.53 3.23 **
**, * = statistically significant at p≤0.0001, and p≤0.05; ns = statistically non-significant. HN and LN = high and low N; DS and WS = dry and wet seasons; 08 and 09 = 2008 and 2009
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Figure 5.1 indicates the seasonal average of yield loss for hybrids ranging from 30-40% in DS08, 25-35% in WS09, and 25-40% in DS09. Relative yield loss of about -80% was observed at a frequency of one in dry season year 2009. Frequency distributions of hybrids for relative yield loss tended to normal curves in DS08 and WS09. However, DS09 had bimodal distribution, although the trend of the normal frequency curve was clear on the right- hand side of the bimodal curve. Generally, all the three frequency curves had the mean centred around 30% yield loss due to application of low N.
Figure 5.1: Frequency distributions of relative grain yield loss indices (%) for 54 hybrids due to application of low rate of N in different seasons
Table 5.4 shows mean and relative yield loss due to the application of low N. High N had a site mean of 7.46, with ranges from 3.88 to 9.45 t ha-1. The range for low N was from 2.69 to 7.56, with a site mean of 5.44 t ha-1. An average of 26.7% yield loss, due to low N application, was evident with a range from 6.1 to 43.2%. The results regarding the best and worst ten hybrids, due the response of high and low N, are also demonstrated in Table 5.4.
Six and eight out of the best 10 hybrids involved local inbred lines under high and low N, respectively. Hybrids NG2 x T3, T20 x T15, T5xT17, T6 x T13 and commercial check SC513 were consistent for both regimes of N. For the relative yield loss, hybrids C60 x T5, NG18 x C4, NG3 x T5, and T17 x C4 were consistent with low N with five out of 10 hybrids involving local inbred lines. There was no consistency between yield loss and high N.
For poor performance of hybrids in high N, except T3 x T5, all hybrids involved exotic crosses. Under low N, two hybrids involving local inbreds, including local check, were also
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observed for poor performance. Six out of 10 hybrids involving inbreds from IITA Nigeria were consistently poor yielders under both conditions of N. Considering the relative yield loss on the poor end, checks PAN77 and PAN67, and four out of 10 hybrids involving local inbreds performed poorly. Whereas only NG2 x NG1 was consistently poor yielder under both N regimes, hybrids NG18 x NG7, T15 x T12, T13 x T15 and NG18 x T12 matched relative yield loss and low N.
Hybrids NG18 x T12 and C58 x C4, which were among the best 10 yielders under high N, were poor in the relative yield loss under low N. Hybrids C60 x C68, C49 x C3, and T3 x T5, grown in high N on the poor side, were consistent with high relative yield loss on the list of the best end. Under low N the best 10 hybrids were not consistent for both yield performance and relative yield loss.
Entries T5 x T17, T20 x T15, T17 x T7, C58 x C38, C60 x T5, T17 x C4, NG2 x T3, NG3 x T5, and T15 x NG7 were above the grand mean for both and individual regimes of N. In terms of individual sets, the local x local and West Africa x local sets were above average for both, and individual N regimes, but they were only slightly above the mean for tolerance to low N.
However, southern Africa x local set and check SC513 were above the mean for both and individual regimes of N. Southern Africa x southern Africa, West Africa x West Africa sets were below the grand average for HN and LN, however, southern Africa x southern Africa had low tolerance to low N, which is advantageous in breeding for a wide adaptation across N regimes. By looking at means of sets, west Africa x local (8.23), check (7.96), local x local (7.89), and southern Africa x local (7.85) were above average for HN; southern Africa x local (6.26), west Africa x local (5.98), local x local (5.74), West Africa x southern Africa (5.46) were above average for LN; West Africa x local (7.13), southern Africa x local (7.05), local x local (6.82) and check (6.68 t ha-1) were above grand mean across N regimes; for tolerance to LN, southern Africa x local (20.03%), West Africa x southern Africa (25.73%) and southern Africa x southern Africa (26.31%) were superior. Overall, best hybrid combinations were found between local and exotic inbred lines. Low N conditions gave lower yields than high N.
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Table 5.4: Mean grain yield and relative yield loss of maize hybrids under high and low N conditions evaluated for three seasons
High N Low N Across N regimes Low N tolerance
Entry# Pedigree Hybrid Set t ha-1 rank t ha-1 rank t ha-1 Rank % yield loss rank
1 T3 x T5 L x L 5.52 44.00 4.92 36.00 5.22 40.00 10.90 2.00
2 T15 x T12 L x L 6.79 33.00 4.26 42.00 5.53 37.50 37.20 43.00
3 T5 x T17 L x L 9.06 5.00 6.76 5.00 7.91 5.00 25.30 17.00
4 T7 x T20 L x L 8.17 16.00 5.37 25.00 6.77 20.50 34.20 38.00
5 T20 x T15 L x L 9.13 4.00 7.32 2.00 8.23 3.00 19.80 12.00
6 T17 x T7 L x L 8.01 18.00 5.90 15.00 6.96 16.50 26.30 20.00
7 T13 x T15 L x L 7.43 27.00 4.60 38.00 6.02 32.50 38.10 44.00
8 T6 x T13 L x L 8.99 6.00 6.82 3.00 7.91 4.50 24.20 15.00
Set mean (n=8) 7.89 19.13 5.74 20.75 6.82 19.94 27.00 23.88
9 C56 x C58 S x S 7.54 24.00 5.13 31.00 6.34 27.50 32.00 32.00
10 C58 x C38 S x S 7.48 26.00 5.55 19.00 6.52 22.50 25.80 19.00
11 C4 x C56 S x S 7.96 20.00 5.15 30.00 6.56 25.00 35.30 40.00
12 C49 x C3 S x S 6.13 39.00 4.95 35.00 5.54 37.00 19.40 9.00
13 C14 x C58 S x S 6.74 34.00 5.45 22.00 6.10 28.00 19.10 8.00
14 C58 x C4 S x S 9.14 3.00 5.35 27.00 7.25 15.00 41.50 45.00
15 C60 x C68 S x S 6.16 38.00 5.48 21.00 5.82 29.50 11.10 3.00
Set mean (n=7) 7.31 26.29 5.29 26.43 6.30 26.36 26.31 22.29
16 NG18 x NG7 W x W 7.20 28.00 4.69 37.00 5.95 32.50 34.90 39.00
17 NG2 x NG1 W x W 5.74 42.00 3.71 45.00 4.73 43.50 35.40 41.00
18 NG2 x NG18 W x W 6.00 40.00 4.51 40.00 5.26 40.00 24.90 16.00
19 NG18 NG3 W x W 5.64 43.00 4.52 39.00 5.08 41.00 19.80 11.00
20 NG2 x NG3 W x W 3.88 46.00 2.69 46.00 3.29 46.00 30.80 30.00
21 NG15 x NG8 W x W 5.35 45.00 3.71 44.00 4.53 44.50 30.60 28.00
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High N Low N Across N regimes Low N tolerance
Entry# Pedigree Hybrid Set t ha-1 rank t ha-1 rank t ha-1 Rank % yield loss rank
22 NG7 x NG15 W x W 6.34 37.00 5.02 34.00 5.68 35.50 20.90 13.00
Set mean (n = 7) 5.74 40.14 4.12 40.71 4.93 40.43 28.19 25.43
23 C49 x T7 S x L 7.10 30.00 5.13 32.00 6.12 31.00 27.70 23.00
24 C60 x T5 S x L 8.06 17.00 7.56 1.00 7.81 9.00 6.10 1.00
25 T12 x C38 S x L 6.71 35.00 5.95 14.00 6.33 24.50 11.30 4.00
26 C3 x T3 S x L 8.59 8.00 6.03 13.00 7.31 10.50 29.80 27.00
27 T17 x C4 S x L 8.40 11.00 6.74 6.00 7.57 8.50 19.70 10.00
28 T15 x C14 S x L 8.23 15.00 6.12 11.00 7.18 13.00 25.60 18.00
Set mean (n = 6) 7.85 19.33 6.26 12.83 7.05 16.08 20.03 13.83
29 C49 x NG18 W x S 6.90 32.00 5.74 17.00 6.32 24.50 16.80 7.00
30 NG7 x C56 W x S 7.54 25.00 5.42 24.00 6.48 24.50 28.20 25.00
31 NG18 x C4 W x S 7.15 29.00 6.22 9.00 6.69 19.00 12.90 5.00
32 C3 x NG3 W x S 5.80 41.00 3.90 43.00 4.85 42.00 32.70 36.00
33 C68 x NG2 W x S 8.93 7.00 6.04 12.00 7.49 9.50 32.40 35.00
34 NG1 x C58 W x S 7.93 21.00 5.44 23.00 6.69 22.00 31.40 31.00
Set mean (n =6) 7.38 25.83 5.46 21.33 6.42 23.58 25.73 23.17
35 NG2 x T3 W x L 9.20 2.00 6.77 4.00 7.99 3.00 26.40 21.00
36 NG3 x T5 W x L 7.61 23.00 6.49 8.00 7.05 15.50 14.70 6.00
37 T7 x NG1 W x L 7.07 31.00 5.08 33.00 6.08 32.00 28.10 24.00
38 NG18 x T12 W x L 9.45 1.00 5.37 26.00 7.41 13.50 43.20 46.00
39 NG15 x T10 W x L 7.98 19.00 5.65 18.00 6.82 18.50 29.30 26.00
40 T15 x NG7 W x L 8.37 12.00 6.52 7.00 7.45 9.50 22.10 14.00
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High N Low N Across N regimes Low N tolerance
Entry# Pedigree Hybrid Set t ha-1 rank t ha-1 rank t ha-1 Rank % yield loss rank
Set mean (n = 6) 8.28 14.67 5.98 16.00 7.13 15.33 27.30 22.83
41 SC513 Check 8.43 10.00 6.18 10.00 7.31 10.00 26.60 22.00
42 PAN77 Check 8.37 13.00 5.52 20.00 6.95 16.50 34.00 37.00
43 PAN67 Check 8.26 14.00 5.21 29.00 6.74 21.50 36.90 42.00
44 DKC8033 Check 8.51 9.00 5.79 16.00 7.15 12.50 32.00 33.00
45 SC407 Check 7.77 22.00 5.28 28.00 6.53 25.00 32.10 34.00
46 LOCAL Check 6.40 36.00 4.43 41.00 5.42 38.50 30.80 29.00
Set mean (n =6) 7.96 17.33 5.40 24.00 6.68 20.67 32.07 32.83
Minimum 3.88 2.69 3.29 6.13
Maximum 9.45 7.56 8.23 43.18
Mean 7.46 5.44 6.46 26.70
Key: T = Tanzania, C = CIMMYT Zimbabwe, NG = IITA-Nigeria inbred lines, N = nitrogen, high N = 120 kg N ha-1 fertiliser application rate, Low N= 60 kg N ha-1 fertiliser application rate. L x L = local by local set, S x S = southern Africa by southern Africa set, W x W = West Africa by West Africa set, S x L = southern Africa by local set, W x S = West Africa by southern Africa, W x L = West Africa by local, check = commercial hybrid check
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