
The majority of resource-poor families in sub-Saharan Africa (SSA) consume conventional maize that were deficient in major nutrients such as provitamin A (PVA) carotenoids and amino acids (lysine and tryptophan) (Oyekale
Tryptophan and lysine amino acids are major protein building blocks needed by monogastric animals and humans (Oyekale
Maize streak virus transmitted by leafhopper (Cicadulina spp.) is a major biotic vector of maize in Africa, including Nigeria by reducing the quantity and quality of maize products (Sime
The development of resistance host-plant maize varieties is reported as an environmentally friendly, consistent, efficient, and viable strategy for governing foliar infections (Muiru
Breeding of PVA-QPM hybrids with resistance to MSV by incorporating suitable genes from resistant donors requires adequate knowledge of MSV resistance genetics because the major genes conferring resistance varied among maize accessions (Lameck
Five improved PVA-QPM inbred lines (TZEIORQ 13, TZEIORQ 24, TZEIORQ 29, TZEIORQ 59, and TZEQI 82) were obtained at the International Institute of Tropical Agriculture (IITA) Ibadan. Five promising open-pollinated MSV resistance cultivars (Pop 28 SR, Acr. 91 Suwan-1-Sr C1, IK.91 TZL Comp 3-Y C1, Ikenne 88 TZSR-Y-1 and TZB-SR SGY TZB-SR) were also collected from the Insti-tute and used as testers. The cultivars were identified as superior in grain yield, disease resistance, and adaptation to tropical Africa. Two yellow commercial hybrids of maize (Oba Super 2 and Oba Super 4) varietal checks were served as controls (Table 1). All the MSV resistance cultivars and PVA-QPM inbreds were crossed in a half-diallel fashion without reciprocals [n(n-1)/2] (parent numbers). Fifty-seven genotypes consisting of 45 F1 testcross hybrids, 10 parents, and the two commercial hybrids were assessed in Nigeria, at the Lower Niger River Basin Development Authority, Oke-Oyi (80°30’N and 8°36’E) during 2019 and 2020 rain-fed regimes.
Table 1 . Description of five early maturing PVA-QPM inbreds, five MSV resistance cultivars, and two commercial hybrid checks.
Genotypes | Pedigree |
---|---|
PVA-QPM inbreds | |
TZEIORQ 13 | 2009-TZE OR2 DT STR-QPM S6 inb 7-1/3-1/2-2/2-3/3-1/1 |
TZEIORQ 24 | 2009-TZE OR2 DT STR-QPM S6 inb 26-1/1-1/2-4/6-2/3-1/1 |
TZEIORQ 29 | 2009-TZE OR2 DT STR QPM S6 inb 28-1/1-2/2-1/2-1/2-1/1 |
TZEIORQ 59 | 2009-TZE OR2 DT STR QPM S6 inb 50-2/2-1/3-2/3-2/2-1/1 |
TZEQI 82 | TZE-COMP5-Y C6S6 Inb 25 × Pool 18 SR QPM BC1S6 2-3-1-1-6-6 |
MSV resistance cultivars | |
AK-9528-DMRSR Pop 28 SR | Pop 28 SR |
Acr. 91 Suwan-1-Sr C1 | Suwan-1 |
IK.91 TZL Comp 3-Y C1 TZL Comp 3 | TZL Comp 3 |
Ikenne 88 TZSR-Y-1 TZSR-Y-1 | TZSR-Y-1 |
TZB-SR SGY TZB-SR | TZB-SR |
Commercial maize hybrid checks | |
Oba super 2 | Commercial yellow maize hybrid |
Oba super 4 | Commercial yellow maize hybrid |
The maize cross-pollination was done by staggering seed sowing twice at seven days intervals. This is to capture the niche of different flowering dates. Before cross-polli-nation commenced, extruded ear shoot and shedding of pollen grains were observed on a day-to-day basis. Before silks protrusion of ears from the plants, cutting of ear shoots was done and enclosed with translucent shoot bags to control unwanted cross-pollination. The shoot bags were then covered carefully with the maize stalks of the testers (female). This was carried out to attain uniform protrusions of silks and prevent dislodging by wind and/or rainfall droplets. To achieve appropriate silks development, appro-priate spacing was allowed for clamping the shoot bags. Subsequently, the tassel bag was fastened with paper clips to the tassels to obtain pure pollen from a specific male inbred. As the silks emerged and were receptive to pollen fertilization, the plants were pollinated utilizing preferred genotype pollens. To pollinate, it is necessary to shake the stapled tassel bags lightly and dispensed the pollens on the silks of the desired ear. After that, they were unclamped and dislodged the grains against the silks. Finally, the shoots were fastened using tassel bags until the period of har-vesting to prevent unwanted pollens. Hybrids maize grains produced were stored distinctly in sacks for advanced evaluation.
The trial site was prepared by ploughing, harrowing, and ridging with a planting space of 0.75 m between ridges. Each entry contained a four-row 5 m plot, 50 cm within the row of about 53,333 plants ha‒1. About 170 g/l Atrazine ha‒1 and 3 kg/l Metolachlor active ingredients were sprayed as pre-emergence herbicides to control weed infestations after land preparation. The inbred parents, their 45 F1 hybrids, with the 2 commercial checks were tested on 18th and 12th June 2019 and 2020, respectively. The leafhoppers’ resis-tance s were applied artificially and arranged to exploit the randomized complete block design of 4 replicates. About 3 seeds were planted in each hole and retained 2 at two weeks after sowing (WAS). Complimentary roguing was done at four WAS preceding fertilization. Fertilizers were supplied at a proportion of 40kg of P2O5 ha‒1 (single superphos-phate), 80kg of N ha‒1 (urea), and 40kg K2O ha‒1 (muriate of potash).
The leafhoppers (
The infection severity was rated at an interval of 8 days from 2 weeks when the plants germinated till the flowering period. This is rated on an average of ten plants at the middle of the plot with an ordinal scale of one to five. The scoring includes 1 showing high resistance of below 10% with slight green streaks on the leaves, 2 = mild symptoms of 10 to 25% comprising shattered slight green with small yellow streaks on the leaves, 3 = reasonable streaking with 26 to 50% yellow-green streaks on the leaves, 4 = susceptibility with stern streaking with 51 to 75% of yellow streaks on the leaves with resultant plant premature death and little cobs, 5 = high susceptibility with 76 to 100% of severe stunting and streaking on the leaves with subsequent plant premature death and very small cobs (Bello 2017).
When the maize matured, harvesting and weighing of cobs were carried out per plot independently while the following formula was used to determine grain yield in kilograms per hectare:
The 12.5% reveals grain moisture content standard, 10,000 m2 denotes the plot ha‒1, 7.5 m2 connotes the plot area harvested (5 m × 0.75 × 9 2) and fresh weight indicates the cobs weight per plot during harvest, Based on the cob weight plot‒1 measurement, grain yield was computed assuming a shelling percentage of an 80%. The grain yield was later converted to tonnes ha‒1 (Bello
Kjeldahl apparatus was used in grinding and defat of grain samples for each maize genotype. A single approach of papain hydrolysis was used for protein solubilization. Acetic acid was oxidized by iron ions to glyoxylic acid by applying sulphuric acid. Glyoxylic acid reacted with free tryptophan indole ring of bound dissolved proteins to generate the violet-purple reactants. The violet-purple colouration was assessed using the spectrophotometer at 560 nm. As described by Teklewold
% Tryptophan
= Factor × Corrected optical density at 560 nm
The optical density
= Optical density 560-nm sample − Optical density 560-nm papain blanks mean
Two readings were recorded for each genotype. Only tryptophan was analyzed in maize grain endosperm because lysine was greatly correlated with tryptophan (r > .9) (Nurit
Carotenoid was analyzed with high-performance liquid chromatography according to the protocol extraction method for dried maize kernels analysis (Howe and Tanumihardjo 2006; Obeng-Bio
Method 2 (and hybrids and parents without reciprocal crosses) and Model I (Fixed model) diallel analysis were exploited as described by Griffing (1956). Specific combin-ing ability (SCA) and general combining ability (GCA) mean squares and individual error variances were evalu-ated with the SAS program (SAS 2018) from ANOVA. Following tests for homogeneity, independence, and nor-mality of variance, the combined analysis of the PVA- QPM inbreds, as well as testcrosses for the two years of evaluation with nine analyzed features was as follows:
The m is the average total, genotype i is the ith effect of genotype, year j is the jth effect of year, genotype × year ij is the jth year, and ith genotype interactive effect. Also, rep(year)jk is the effect of kth replication in the jth year, block(rep × y) jkl is the effect of incomplete block lth within the jth year, and the kth replicates while ꜫijkl is the variance error. For untransformed data, standard residuals for all the effects of heritable traits were explored with mean squares error from the testcrosses. The least signi-ficant difference test was utilized to calculate the dif-ferences in the trait averages. The percentage coefficient of variation (PCV) was employed to measure the variation sum.
Grain yield decidedly differed among the parents in the two growing seasons of the field trials (Table 2). Among the five QPM-PVA inbreds used as parents, four (TZEIORQ 24, TZEQI 82, TZEIORQ 59, and TZEIORQ 13) had higher grain yield with a mean yield of 5.86 t ha‒1 com-parable with commercial hybrid checks (5.44 t ha‒1) with a 7.2% yield advantage. The AK-9528-DMRSR POP 28 SR (5.32 t ha‒1) was very prolific among MSV-resistant cultivars but with a yield increase of 2% over the commercial checks. All the topcrosses varied strikingly with superior yield compared with corresponding parents and checks. The PVA-QPM × PVA-QPM hybrids were higher in yield potential while MSV-resistant × PVA-QPM was next, then MSV × MSV-resistant cultivars
Table 2 . Means of PVA-QPM lines, MSV resistance cultivars, selected testcrosses and commercial checks for grain yield, MSV disease rating, carotenoids, and tryptophan contents assessed in two years of cropping seasons.
Genotypes | Tryptopha n (%) | Grain yield (t ha‒1) | MSV (no.) | PVA µg g‒1 | βC µg g‒1 | ZEA µg g‒1 | αC µg g‒1 | LUT µg g‒1 | βCX µg g‒1 |
---|---|---|---|---|---|---|---|---|---|
TZEIORQ 13 | 3.97 | 5.83 | 3.52 | 4.01 | 2.02 | 7.63 | 0.47 | 11.24 | 2.98 |
TZEIORQ 24 | 3.98 | 5.91 | 2.21 | 3.87 | 2.45 | 7.77 | 0.49 | 12.25 | 2.81 |
TZEIORQ 29 | 3.91 | 5.24 | 3.01 | 3.76 | 2.23 | 7.81 | 0.51 | 12.33 | 2.85 |
TZEIORQ 59 | 3.93 | 5.84 | 2.34 | 3.84 | 2.41 | 7.67 | 0.56 | 12.67 | 2.91 |
TZEQI 82 | 3.95 | 5.86 | 3.11 | 3.76 | 2.52 | 7.98 | 0.51 | 12.66 | 2.96 |
AK-9528-DMRSR POP 28 SR | 2.34 | 5.32 | 1.02 | 0.11 | 0.12 | 2.62 | 0.01 | 1.67 | 0.12 |
ACR. 91 SUWAN-1-SR C1 | 2.21 | 5.01 | 1.51 | 0.15 | 0.08 | 1.81 | 0.06 | 2.64 | 0.04 |
IK.91 TZL COMP 3-Y C1 | 2.33 | 5.22 | 1.43 | 0.02 | 0.04 | 2.53 | 0.08 | 2.77 | 0.03 |
IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 2.48 | 5.15 | 1.72 | 0.06 | 0.03 | 2.68 | 0.04 | 2.11 | 0.01 |
TZB-SR SGY TZB-SR | 2.12 | 5.11 | 1.65 | 0.12 | 0.02 | 2.63 | 0.02 | 2.47 | 0.02 |
Selected testcrosses | |||||||||
TZEIORQ 13 × TZEIORQ 24 | 4.06 | 6.12 | 3.56 | 4.25 | 2.81 | 8.6 | 0.69 | 14.22 | 2.81 |
TZEIORQ 13 × TZEIORQ 29 | 4.34 | 6.34 | 3.54 | 4.34 | 2.77 | 7.99 | 0.61 | 15.1 | 2.77 |
TZEIORQ 24 × TZEIORQ 29 | 4.09 | 6.32 | 2.96 | 4.25 | 2.69 | 8.55 | 0.72 | 14.34 | 2.69 |
TZEIORQ 29 × TZEIORQ 59 | 4.13 | 6.11 | 3.61 | 4.39 | 2.75 | 8.63 | 0.68 | 14.43 | 2.75 |
TZEIORQ 29 × TZEQI 82 | 3.97 | 6.18 | 3.88 | 4.28 | 2.98 | 8.69 | 0.59 | 15.29 | 2.98 |
TZEIORQ 59 × TZEQI 82 | 4.24 | 6.44 | 3.49 | 4.15 | 2.11 | 8.48 | 0.57 | 15.31 | 2.81 |
TZEIORQ 13 × AK-9528-DMRSR POP 28 SR | 3.79 | 5.82 | 2.16 | 3.87 | 2.32 | 7.99 | 0.76 | 13.29 | 2.77 |
TZEIORQ 24 × AK-9528-DMRSR POP 28 SR | 3.65 | 5.5 | 2.18 | 3.76 | 2.29 | 7.73 | 0.72 | 12.27 | 2.69 |
TZEIORQ 29 × AK-9528-DMRSR POP 28 SR | 3.78 | 5.86 | 2.17 | 3.84 | 2.32 | 7.57 | 0.49 | 12.39 | 2.75 |
TZEIORQ 59 × AK-9528-DMRSR POP 28 SR | 3.81 | 5.54 | 2.11 | 3.76 | 2.54 | 7.79 | 0.53 | 13.26 | 2.98 |
TZEQI 82 × AK-9528-DMRSR POP 28 SR | 3.89 | 5.98 | 2 | 3.87 | 2.33 | 7.83 | 0.74 | 11.29 | 2.81 |
TZEIORQ 13 × ACR. 91 SUWAN-1-SR C1 | 3.61 | 5.83 | 2.66 | 3.76 | 2.51 | 7.77 | 0.53 | 13.44 | 2.77 |
TZEIORQ 29 × ACR. 91 SUWAN-1-SR C1 | 3.6 | 5.89 | 2.58 | 3.84 | 2.68 | 7.99 | 0.61 | 13.56 | 2.69 |
TZEQI 82 × ACR. 91 SUWAN-1-SR C1 | 3.87 | 5.97 | 2.64 | 3.79 | 2.11 | 7.78 | 0.59 | 12.52 | 2.75 |
TZEIORQ 24 × IK.91 TZL COMP 3-Y C1 | 3.68 | 5.87 | 2.56 | 3.87 | 2.45 | 7.57 | 0.63 | 12.76 | 2.98 |
TZEQI 82 × IK.91 TZL COMP 3-Y C1 | 3.88 | 5.96 | 2.68 | 3.76 | 2.32 | 7.7 | 0.71 | 13.89 | 2.81 |
TZEIORQ 24 × IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 3.67 | 5.88 | 2.69 | 3.84 | 2.61 | 7.83 | 0.53 | 11.36 | 2.77 |
TZEIORQ 59 × IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 3.69 | 5.75 | 2.56 | 3.76 | 2.45 | 7.75 | 0.64 | 13.51 | 2.69 |
TZEQI 82 × IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 3.56 | 5.99 | 2.65 | 3.87 | 2.38 | 7.99 | 0.81 | 13.46 | 2.75 |
TZEIORQ 24 × TZB-SR SGY TZB-SR | 3.64 | 5.76 | 2.66 | 3.79 | 2.29 | 7.72 | 0.67 | 12.73 | 2.94 |
TZEIORQ 59 × TZB-SR SGY TZB-SR | 3.69 | 5.78 | 2.73 | 3.84 | 2.87 | 7.57 | 0.54 | 12.68 | 2.75 |
TZEQI 82 × TZB-SR SGY TZB-SR | 2.59 | 5.96 | 2.71 | 3.77 | 2.44 | 7.71 | 0.49 | 13.72 | 2.91 |
AK-9528-DMRSR POP 28 SR × ACR. 91 SUWAN-1-SR C1 | 2.91 | 5.88 | 1 | 3.99 | 2.44 | 7.68 | 0.51 | 12.31 | 2.98 |
IK.91 TZL COMP 3-Y C1 × TZB-SR SGY TZB-SR | 2.78 | 5.33 | 2.32 | 3.83 | 2.53 | 7.83 | 0.54 | 13.11 | 2.57 |
IKENNE 88 TZSR-Y-1 TZSR-Y-1 × TZB-SR SGY TZB-SR | 2.59 | 5.56 | 2.43 | 3.91 | 2.5 | 7.72 | 0.5 | 12.28 | 2.93 |
Varietal checks | |||||||||
Oba Super 2 | 3.98 | 5.4 | 2.86 | 0.22 | 0.02 | 2.13 | 0.05 | 3.21 | 0.02 |
Oba Super 4 | 3.97 | 5.48 | 2.88 | 0.24 | 0.05 | 2.24 | 0.03 | 4.09 | 0.04 |
SE | 0.074 | 0.029 | 0.055 | 0.011 | 0.047 | 0.023 | 0.031 | 0.051 | 0.011 |
CV (%) | 5.34 | 5.91 | 10.11 | 7.93 | 9.63 | 11.34 | 8.93 | 10.44 | 7.32 |
LSD (0.05) | 0.91 | 0.87 | 0.68 | 0.65 | 0.73 | 0.89 | 0.99 | 0.72 | 0.45 |
MSV: maize streak virus, PVA: total provitamin A, βCX: β-cryptoxanthin, ZEA: zeaxanthin, LUT: lutein, βC: β-carotene, αC: α-caro.
Grain yield decidedly differed among the parents in the two growing seasons of the field trials (Table 2). Among the five QPM-PVA inbreds used as parents, four (TZEIORQ 24, TZEQI 82, TZEIORQ 59, and TZEIORQ 13) had higher grain yield with a mean yield of 5.86 t ha‒1 comparable with commercial hybrid checks (5.44 t ha‒1) with a 7.2% yield advantage. The AK-9528-DMRSR POP 28 SR (5.32 t ha‒1) was very prolific among MSV-resistant cultivars but with a yield increase of 2% over the com-mercial checks. All the topcrosses varied strikingly with superior yield compared with corresponding parents and checks. The PVA-QPM × PVA-QPM hybrids were higher in yield potential while MSV-resistant × PVA-QPM was next, then MSV × MSV-resistant cultivars.
The AK-9528-DMRSR POP 28 SR combined well for high Tryptophan in some PVA-QPM testcrosses and MSV-resistant cultivars (Table 2).
Concerning PVA, two hybrids (TZEIORQ 13 × TZEIORQ 29 and TZEIORQ 59 × TZEQI 82) and four testcrosses (TZEQI 82 × IKENNE 88 TZSR-Y-1, TZEQI 82 × ACR. 91 SUWAN-1-SR C1, TZEQI 82 × AK-9528-DMRSR POP 28 SR, and TZEQI 82 × TZB-SR SGY TZB-SR) were of topmost performance among PVA-QPM hybrids. They also had high and comparable values among the selected testcrosses for other carotenoids (ZEA, LUT aC, bCX, and bC).
The MSV-resistant cultivars and PVA-QPM inbreds pooled analysis of variance for the virus resistance scoring, carotenoids, grain quality protein, and yield were assessed in the two cropping seasons (Table 3). Crosses mean squares vastly differed among the ten traits studied.
Table 3 . Pooled analysis of variance of PVA-QPM lines and their hybrids and MSV-resistant testcrosses for grain yield, MSV disease scoring, carotenoids, and tryptophan contents assessed in two years of cropping seasons.
Source of variation | Df | Grain yield (t ha‒1) | MSV (no.) | Tryptophan (%) | PVA | ZEA | LUT | aC | bC | bCX |
---|---|---|---|---|---|---|---|---|---|---|
Year | 1 | 4.67 | 3.81 | 5.31 | 6.56 | 8.22 | 4.87 | 7.93 | 10.52 | 9.38 |
Rep (year) | 6 | 7.24 | 5.78 | 12.78 | 10.63 | 14.72 | 11.43 | 13.65 | 11.57 | 12.11 |
Crosses | 45 | 99.83** | 87.69** | 92.13** | 78.89** | 95.37** | 92.19** | 87.44** | 91.72** | 89.55** |
Crosses × Year | 45 | 10.67 | 12.83 | 11.87 | 13.11 | 12.89 | 10.09 | 13.65 | 11.23 | 9.11 |
GCA | 9 | 87.32* | 95.55** | 88.78** | 97.21** | 95.34** | 87.71** | 99.67** | 67.58** | 78.79** |
SCA | 35 | 34.01* | 43.21* | 51.32* | 48.67* | 53.34* | 41.89* | 54.22* | 49.46* | 53.32* |
Year × GCA | 6 | 13.37 | 15.11 | 8.70 | 11.13 | 9.73 | 12.25 | 13.11 | 10.79 | 12.22 |
Year × SCA | 35 | 21.12 | 10.99 | 11.22 | 12.67 | 9.28 | 10.54 | 13.27 | 10.44 | 11.56 |
Pool error | 329 | 12.52 | 9.88 | 7.04 | 10.22 | 8.01 | 11.56 | 8.07 | 7.04 | 10.76 |
GCA/SCA (Baker ratio) % | 1.45 | 0.78 | 0.56 | 0.82 | 0.74 | 0.31 | 0.75 | 0.38 | 0.50 | |
CV% | 9.8 | 11.2 | 7.55 | 10.82 | 11.78 | 9.54 | 10.59 | 12.66 | 11.83 |
** and * significant at 0.01 and probability levels, respectively.
MSV: maize streak virus, PVA: total provitamin A, bCX: b-cryptoxanthin, ZEA: zeaxanthin, LUT: lutein, bC: b-carotene, aC: a-caro.
All traits studies, excluding MSV, are suitable for meaningful positive GCA effects since the aim is for improved disease resistance, carotenoids, grain quality protein, and yield (Table 4). The whole genotypes were positive and significant for GCA, suggesting better combinations for outstanding grain-yielding development, corresponding to Nyaligwa
Table 4 . Estimates of GCA for PVA-QPM lines and their hybrids and MSV-resistant testcrosses for grain yield, MSV disease scoring, carotenoids, and tryptophan contents assessed in two years of cropping seasons.
Genotypes | Tryptophan (%) | Grain yield (t ha‒1) | MSV (no.) | PVA | ZEA | LUT | aC | bC | bCX |
---|---|---|---|---|---|---|---|---|---|
TZEIORQ 13 | 80.35** | 1.97** | 0.26 | 89.96** | 87.22** | 111.10** | 92.33** | 53.91* | 97.55** |
TZEIORQ 24 | 91.97** | 0.74** | 0.34 | 91.74** | 98.76** | 91.88** | 88.54** | 92.93** | 81.99** |
TZEIORQ 29 | 100.44** | 1.87** | 0.23 | 84.87** | 82.11** | 87.74** | 76.97** | 47.25* | 92.77** |
TZEIORQ 59 | 98.98** | 1.92** | 0.14 | 98.31** | 89.32** | 76.81** | 99.25** | 89.88** | 79.12** |
TZEQI 82 | 86.87** | 0.86** | 0.35 | 87.88** | 78.87** | 92.93** | 71.11** | 45.74* | 88.94** |
AK-9528-DMRSR POP 28 SR | 0.07 | 1.09** | ‒1.99** | 1.29 | 2.11 | 2.03 | 2.04 | 1.06 | 2.07 |
ACR. 91 SUWAN-1-SR C1 | 1.01 | 0.82** | ‒0.71** | 1.54 | 1.65 | 1.99 | 3.11 | 2.09 | 1.87 |
IK.91 TZL COMP 3-Y C1 | 0.08 | 1.88** | ‒0.88** | 1.19 | 1.09 | 1.86 | 0.04 | 1.05 | 2.07 |
IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 1.05 | 0.91** | ‒1.76** | 1.09 | 1.42 | 2.54 | 1.73 | 1.11 | 3.05 |
TZB-SR SGY TZB-SR | 0.09 | 1.93** | ‒0.93** | 0.11 | 0.77 | 1.39 | 0.67 | 0.68 | 2.01 |
** and * significant at 0.01 and 0.05 probability levels, respectively.
MSV: maize streak virus, PVA: total provitamin A, bCX: b-cryptoxanthin, ZEA: zeaxanthin, LUT: lutein, bC: b-carotene, aC: a-caro.
Distinctly positive GCA effects are suitable for all traits studied, excluding MSV resistance since the aim is for improved carotenoids, grain quality protein, and yield (Table 4). The whole genotypes were positive and signi-ficant for GCA.
It appears that the remarkable yield expressed by PVA-QPM × PVA-QPM crosses could be credited to suita-ble allelic interactions among the PVA-QPM combined. The TZEQI 82 was a common parental inbred with superior grain yield among the selected topcrosses. The TZEIORQ 59 × TZEQI 82 (6.44 t ha‒1) was the foremost yielding topcross with a yield gain of 2% above the checks. Besides, AK-9528-DMRSR POP 28 SR produced topcrosses of elevated yield with some PVA-QPM inbreds. Testcros-sed TZEQI 82 × AK-9528-DMRSR POP 28 SR, TZEQI 82 × ACR. 91 SUWAN-1-SR C1 and TZEQI 82 × IK.91 TZL COMP 3-Y C1 produced an average of 5.97 t ha‒1, representing 8%, 10%, and 11% above the superior check, inbred, and MSV-resistant cultivar, respectively. These results corroborated with that of Bello (2017; Oluwaseun
That MSV × MSV-resistant testcrosses were utmost resistant genotypes. MSV-resistant × PVA-QPM were next, while MSV × MSV-resistant topcrosses were most susceptible. These findings were earlier reported by Bello, (2017). AK-9528-DMRSR POP 28 SR was the best MSV- resistant cultivar with a 1.01 score and favourably com-bined with many QPM inbred lines in producing resistant topcrosses with increased yield. This indicates that AK-9528-DMRSR POP 28 SR was commonly resistant to the virus, containing great occurrences of desirable bene-factor genes than the rest parents. TZEQI 82 × AK- 9528-DMRSR POP 28 SR with the greatest yield among MSV-resistant × PVA-QPM testcrosses was also prominent with 30% exceedingly resistance over the checks. The two vulnerable checks scores signify the degree of the disease virulence and that the inoculation procedures used were effective.
The highest Tryptophan (3.98) expressed by TZEQI 82 × AK-9528-DMRSR POP 28 SR in the MSV-resistant × PVA-QPM testcrosses was comparable to the checks. It seems that AK-9528-DMRSR POP 28 SR not only possessed MSV-resistant alleles suitable for introgression with other maize genotypes but a favourable resource for quality protein and grain yield genes. The PVA-QPM inbreds derived from TZEIORQ 13, TZEIORQ 29, and TZEQI 82 that were crossed with MSV-resistant AK- 9528-DMRSR POP 28 SR appeared exceedingly promising for high virus resistance, grain quality protein, carotenoids, and yield.
Concerning PVA, two hybrids (TZEIORQ 13 × TZEIORQ 29 and TZEIORQ 59 × TZEQI 82) and four testcrosses (TZEQI 82 × IKENNE 88 TZSR-Y-1, TZEQI 82 × ACR. 91 SUWAN-1-SR C1, TZEQI 82 × AK-9528-DMRSR POP 28 SR, and TZEQI 82 × TZB-SR SGY TZB-SR) were of topmost performance among PVA-QPM hybrids. They also had high and comparable values among the selected testcrosses for other carotenoids (ZEA, LUT aC, bCX, and bC). This indicates that PVA-QPM inbreds of different pedigrees transformed to high grain yielding MSV-resistant attributes with justifiable quality protein are feasible to be adapted in savanna agroecology (Oluwaseun
Crosses mean squares vastly differed among the ten traits studied, indicating broadly diverse parents were used and the genotypes contributed differently among the top-crosses. It also shows that genetic diversity is apparent in the improvement scheme. SCA mean squares of GCA were greatly significant for all the traits in the trials, denoting that the genetic variations governing these traits were primarily influenced by additive effects. Varied genetic frequency distribution in the genotypes was also obtained in this study. These findings not only accentuated the possibility of evolving divergent parents for hybrids improvement but assisted as unique sources of alleles in modifying the genic base of adapted genotypes for genetic gain sustainability in the hybridization schemes. Additive gene action governing maize grain yield was reported by many workers (Bello and Olawuyi, 2015). However, the mean squares results showed non-significant interaction between years and both SCA and GCA, highlighting that both gene actions (non-additive and additive) were comparable across the two years. Baker (1978) reported that the predominant additive genetic effects (GCA) and non-additive genetic effects (SCA) for grain yield and other traits showed the type of genetic effects in diallel crosses. In this study, the worth of the GCA/SCA fraction revealing above one for grain yield and below one for rest traits implied that additive inheritance components conditioning the grain yielding and non-additive inheritance components governing the carotenoids, MSV resistance, and quality protein grain.
All traits studies, excluding MSV, are suitable for mean-ingful positive GCA effects since the aim is for improved disease resistance, carotenoids, grain quality protein, and yield (Table 4). The whole genotypes were positive and significant for GCA, suggesting better combinations for outstanding grain-yielding development, corresponding to Nyaligwa
Distinctly positive GCA effects are suitable for all traits studied, excluding MSV resistance since the aim is for improved carotenoids, grain quality protein, and yield. The whole genotypes were positive and significant for GCA, similar to Nyaligwa
Table 5 . SCA effects of selected MSV-resistant testcrosses for grain yield, MSV disease scoring, carotenoids, and tryptophan contents assessed in two years of cropping seasons.
Crosses | Grain yield (t ha‒1) | MSV (no.) | Tryptophan (%) | PVA | ZEA | LUT | αC | βC | βCX |
---|---|---|---|---|---|---|---|---|---|
TZEIORQ 13 × TZEIORQ 24 | 0.99** | 0.84 | 99.92** | 78.61** | 73.11** | 79.45** | 87.56** | 78.51** | 86.34** |
TZEIORQ 13 × TZEIORQ 29 | 1.22** | 0.56 | 111.74** | 92.55** | 98.22** | 98.23** | 88.12** | 98.12** | 89.56** |
TZEIORQ 24 × TZEIORQ 29 | 3.45** | 0.72 | 76.87** | 77.52** | 84.23** | 87.34** | 87.35** | 88.47** | 84.94** |
TZEIORQ 29 × TZEIORQ 59 | 2.12** | 0.89 | 87.44** | 91.53** | 91.56** | 91.57** | 99.12** | 92.02** | 91.23** |
TZEIORQ 29 × TZEQI 82 | 1.98** | 0.75 | 98.82** | 104.76** | 100.03** | 99.83** | 111.05** | 112.60** | 96.67** |
TZEIORQ 59 × TZEQI 82 | 3.43** | 0.96 | 81.91** | 78.44** | 92.04** | 100.42** | 93.48** | 98.63** | 104.25** |
TZEIORQ 13 × AK-9528-DMRSR POP 28 SR | 2.77** | ‒1.76** | 66.91** | 51.67** | 56.22** | 61.34** | 54.66** | 51.43** | 56.33** |
TZEIORQ 24 × AK-9528-DMRSR POP 28 SR | 1.01** | ‒0.88** | 70.42** | 56.54** | 67.53** | 49.51** | 65.11** | 56.54** | 60.98** |
TZEIORQ 29 × AK-9528-DMRSR POP 28 SR | 2.22** | ‒0.91** | 67.22** | 61.33** | 54.98** | 21.98* | 22.56* | 6356** | 61.54** |
TZEIORQ 59 × AK-9528-DMRSR POP 28 SR | 0.97** | ‒1.83** | 30.43* | 56.11** | 64.69** | 67.54** | 63.11** | 67.56** | 50.66** |
TZEQI 82 × IK.91 TZL COMP 3-Y C1 | 0.88** | ‒0.75** | 67.78** | 27.54* | 24.11** | 52.22** | 67.78** | 49.22** | 69.33** |
TZEIORQ 13 × ACR. 91 SUWAN-1-SR C1 | 0.75** | ‒1.32** | 56.11** | 51.33** | 61.34** | 59.54** | 59.23** | 59.89** | 59.78** |
TZEIORQ 24 × ACR. 91 SUWAN-1-SR C1 | 1.11** | ‒0.44** | 49.78** | 47.12** | 56.67** | 43.66** | 25.99* | 51.66** | 51.32** |
TZEIORQ 29 × TZB-SR SGY TZB-SR | 1.56** | ‒0.97** | 51.11** | 56.45** | 49.76** | 24.78* | 53.65** | 29.23* | 48.76** |
TZEIORQ 59 × IK.91 TZL COMP 3-Y C1 | 0.88** | ‒1.43** | 33.24* | 61.41** | 54.78** | 63.11** | 63.78** | 48.11** | 66.31** |
TZEQI 82 × IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 0.75** | ‒0.89** | 61.81** | 28.56* | 26.09** | 54.99** | 64.33** | 56.89** | 57.22** |
TZEQI 82 × TZB-SR SGY TZB-SR | 1.91** | ‒0.94** | 56.91** | 23.56* | 21.24** | 53.22** | 61.56** | 61.24** | 62.56** |
AK-9528-DMRSR POP 28 SR × TZB-SR SGY TZB-SR | 1.34** | ‒1.41** | 1.4 | 0.78 | 0.98 | 1.22 | 1.77 | 1.78 | 1.66 |
ACR. 91 SUWAN-1-SR C1 × IKENNE 88 TZSR-Y-1 TZSR-Y-1 | 2.54** | ‒0.93** | 1.83 | 1.11 | 1.22 | 1.75 | 1.56 | 1.01 | 1.4383 |
IK.91 TZL COMP 3-Y C1 × TZB-SR SGY TZB-SR | 0.99** | ‒1.86** | 2.11 | 0.23 | 0.66 | 0.84 | 1.78 | 0.67 | 0.97 |
IKENNE 88 TZSR-Y-1 TZSR-Y-1 × TZB-SR SGY TZB-SR | 1.76** | ‒0.72** | 0.81 | 0.87 | 0.98 | 0.93 | 0.77 | 0.91 | 0.11 |
TZB-SR SGY TZB-SR × TZB-SR SGY TZB-SR | 1.55** | ‒0.89** | 1.94 | 0.11 | 1.32 | 0.77 | 0.89 | 1.55 | 1.67 |
** and * significant at 0.01 and 0.05 probability levels, respectively.
MSV: maize streak virus, PVA: total provitamin A, βCX: β-cryptoxanthin, ZEA: zeaxanthin, LUT: lutein, βC: β-carotene, αC: α-caro.
The authors appreciate the Anonymous Reviewers and Editor whose contributions have significantly enhanced the manuscript quality.
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