International Journal of Agronomy
Volume 2018 (2018), Article ID 3439090, 12 pages
https://doi.org/10.1155/2018/3439090

Research Article

Estimates of Combining Ability and Heterosis for Yield and Its Related Traits in Pearl Millet Inbred Lines under Downy Mildew Prevalent Areas of Senegal

Ghislain Kanfany,1,2,3 Amadou Fofana,³ Pangirayi Tongoona,¹ Agyemang Danquah,¹ Samuel Offei,¹ Eric Danquah,¹ and Ndiaga Cisse²

¹West Africa Centre for Crop Improvement, University of Ghana, PMB LG 30, Legon, Ghana
²Centre d’Etudes Régional pour l’Amélioration de l’Adaptation à la Sècheresse, BP 3320, Thies, Senegal
³Centre National de Recherches Agronomiques de Bambey, BP 211, Bambey, Senegal

Correspondence should be addressed to Ghislain Kanfany; gkanfany@wacci.edu.gh

Received 11 December 2017; Accepted 22 March 2018; Published 2 May 2018

Academic Editor: Iskender Tiryaki

Copyright © 2018 Ghislain Kanfany et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Pearl millet is an important cereal crop for smallholder farmers’ food security in West and Central Africa. However, its production has stagnated due to several factors such as the continuous use of local populations. A set of 17 inbred lines was crossed with Sosat C 88 and Souna 3 following a line × tester mating design. The hybrids, their parents, and a check were evaluated in Bambey and Nioro research stations during the rainy season of 2017. Data on downy mildew incidence, plant height, flowering time, panicle length and diameter, productive tillers, thousand-grain weight, panicle, and grain yield were recorded. GCA and SCA mean squares were significant for most of the traits indicating that both additive and nonadditive gene effects were involved in the control of the inheritance of these traits. However, the contribution of GCA to total mean squares was higher than that of SCA for all the traits, providing that additive gene action was more important in their inheritance. The top-cross hybrid IBL155-2-1 × Sosat C 88 exhibited negative and significant SCA effects for downy mildew incidence, flowering time, and plant height. Lines IBL003-B-1, IBL091-1-1, IBL095-4-1, IBL110-B-1, and IBL 206-1-1 had positive GCA effects for grain yield and negative GCA effects for downy mildew, flowering time, and plant height. These lines can be used as parents to create synthetic varieties or hybrids.

1. Introduction

Pearl millet (Pennisetum glaucum (L.) R. Brown) is the 4th most important tropical cereal after rice, maize, and sorghum [1]. In 2014, global grain pearl millet production was estimated at 28 million tons, harvested from 32 million ha in Asia, Africa, and the Americas. The average yield is about 900 kg ha⁻¹. India and Africa are the most important producers with more than 85% of the total production in 2016 [1]. It is an important dual purpose cereal crop in Africa and Asia where it is considered as a staple food and source of fodder and feed for livestock for smallholders farmers [2]. The grain of pearl millet is a very rich source of protein, vitamins, and minerals in comparison with other cereals and is used for human consumption in diverse ways [3]. The pearl millet stover is used as fuel, material for building and fencing, and also a soil additive to enhance soil fertility [4]. It is also being experimented as a grain and forage crop in the USA, Canada, Mexico, India, and West and North Africa [5].

As the world population is continuously increasing and is projected to reach nine billion by 2050, pearl millet is expected to play an important role for achieving food security in West and Central African countries, which have the highest population growth rates in the world [6]. However, in this part of the world, yields of pearl millet are very low compared to yields in India and yet African farmers, particularly in Senegal, have not adopted improved varieties in a large scale. In pearl millet growing areas in Africa, adoption rate of improved OPVs varied from 5 to 37% [7]. In contrast, most Indian farmers are using improved varieties, particularly hybrids since the 1960s. Indeed, in India hybrids had 25–30% grain yield advantage over OPVs, leading to the rapid adoption of the hybrids whose yield increased from 305 kg ha⁻¹ during 1951–1955 to 998 kg ha⁻¹ during 2008–2012 [5]. Thus, enhancement of pearl millet production and productivity in Africa, which is a high priority, can be achieved through the identification of elite parent materials which can be used as parents to develop hybrid varieties.

ICRISAT has developed pearl millet inbred lines derived from landraces originating from West and Central Africa which can be useful in developing high yielding pearl millet hybrids and synthetic varieties with considerable adaptation to this pearl millet growing environment. These lines were screened for pearl millet downy mildew resistance in Senegal and some of them showed good agronomic traits and resistance to the pearl millet downy mildew. However, the per se performance of these pearl millet inbred lines does not predict the performance of hybrids for disease resistance and agronomic traits [8]. Therefore, to make effective use of these pearl millet inbred lines, their combining abilities need to be elucidated [9]. This genetic information can be obtained by different mating design including line × tester [10]. GCA and SCA estimates of pearl millet inbred parents or landraces for different traits such as micronutrients [11], grain quality [12], and fodder yield [13] were reported to be important. Additive genetic action was also reported to be important in controlling traits such as grain yield, flowering time, and panicle length [14]. There is scanty published information on the combining ability of the pearl millet inbred lines derived from landraces collected in West and Central Africa, known as the origin of the crop, for disease resistance and agronomic traits. The objectives of this study were to estimate combining ability and heterosis of pearl millet inbred lines for downy mildew, yield, and other agronomic traits under downy mildew infested fields and identify superior pearl millet hybrids for yield, yield components, and resistance to downy mildew.

2. Materials and Methods

2.1. Plant Material and Mating Design

Seventeen inbred lines were used as females and crossed each to two OPVs used as males according to the line × tester mating design [10] to generate 34 hybrids. The OPVs varieties were considered as testers and the inbred lines as lines. The two testers named Souna 3 and Sosat C 88 are popular varieties adapted to the groundnut agroecological zone. The pearl millet inbred lines used for the study were selected from a pool of pearl millet landraces from West and Central Africa converted to inbred lines through successive selfing up to S6 [15]. These inbred lines were selected through a downy mildew phenotypic evaluation conducted at Bambey and Nioro research stations during the rainy season 2016. They showed less than 10% DMI and were classified as resistant varieties. The seeds of the male parents were planted in 4 different dates in order to synchronise the flowering time of these male parents with the ones of the female parents. Thus, from January 2017, the sowing of the male parents was done every week and seeds of each of the male parents were sown in 5 rows of 15 hills per row. All the female parents were sown in one time during the second sowing date of the male parents in a one row-plot of 15 hills. At the booting stage, at least plant heads of 4 panicles per plant of the male and female parents were covered in order to avoid undesirable pollination. At flowering, each covered panicle of female plant was pollinated with bulk pollen collected from at least 20 different plants of the male parent.

At maturity stage, panicles of the female parents were harvested and the lower and upper parts of each panicle were cut before threshing to minimize outcrossing from unknown plants or selfing. Indeed, because of the protogynous nature of the crop the stigmata of a plant are receptive before the shedding of pollen and the flowering starts from the upper to the lower part. Then, the upper part of the panicle may be pollinated by unknown plants if not covered on the right time and the lower part of the panicle may be pollinated by the pollen from the same plant.

After threshing, seeds from the same female parent were bulked and used as hybrids. The 34 hybrids along with the 17 inbred lines, the two testers, and an OPV named Thialack II as check, providing 54 genotypes, were used for the evaluation (Table 1).

Table 1: List of parental lines and check used in the study.

Number
Genotype
Source
Role in crosses
Status
Response to downy mildew

IBL 001-4-1
ICRISAT
Line
Inbred line
Resistant

IBL 003-B-1
ICRISAT
Line
Inbred line
Resistant

IBL 011-4-1
ICRISAT
Line
Inbred line
Resistant

IBL 021-3-1
ICRISAT
Line
Inbred line
Resistant

IBL 055-4-1
ICRISAT
Line
Inbred line
Resistant

IBL 091-1-1
ICRISAT
Line
Inbred line
Resistant

IBL 095-4-1
ICRISAT
Line
Inbred line
Resistant

IBL 098-3-1
ICRISAT
Line
Inbred line
Resistant

IBL 106-B-1
ICRISAT
Line
Inbred line
Resistant

IBL 110-B-1
ICRISAT
Line
Inbred line
Resistant

IBL 114-6-1
ICRISAT
Line
Inbred line
Resistant

IBL 119-B-1
ICRISAT
Line
Inbred line
Resistant

IBL 155-2-1
ICRISAT
Line
Inbred line
Resistant

IBL 165-1-1
ICRISAT
Line
Inbred line
Resistant

IBL 179-2-1
ICRISAT
Line
Inbred line
Resistant

IBL 179-3-1
ICRISAT
Line
Inbred line
Resistant

IBL 206-1-1
ICRISAT
Line
Inbred line
Resistant

Souna 3
Senegal
Tester
OPV (improved)
Susceptible

Sosat C 88
Senegal
Tester
OPV (improved)
Resistant

20
Thialack II
Senegal
Check
OPV (improved)
Susceptible

2.2. Study Sites, Experimental Design, and Field Management

The 34 hybrids, together with their parents and the OPV check, were evaluated under rainfed conditions during the rainy season of 2017 at two locations in Senegal. The study sites were Bambey (13°49′12′′ North, 13°55′12′′ West) and Nioro (13°45′0′′ North, 15°48′0′′ West) research stations. Both locations are in the groundnut agroecological zone, the main pearl millet growing area in Senegal, and were characterized as hotspots for downy mildew in the previous study. The genotypes were arranged in 9 × 6 alpha lattice design with three replications at each site. Each block was surrounded by a downy mildew infector row consisting of a downy mildew susceptible line, 7042 S, sown 3 weeks before the tested materials. Each plot consisted of one row of 8.1 m length with a spacing of 0.9 m between rows and between plants within a row. At least 10 seeds were planted per hole and later thinned to two plants two weeks after sowing. The fields were weeded two times after sowing. The trials received the recommended 15N-15P-15K basal fertilizer at a rate of 150 kg ha⁻¹ just before sowing. During the crop development a top dressing using area at a rate of 100 kg ha⁻¹ was done in two fractions: 50 kg ha⁻¹ after thinning and 50 kg ha⁻¹ after the second weeding.

2.3. Data Collection

The recorded data were collected according to the method described by Drabo [14]. Flowering (FWT) was recorded by counting the total number of days from sowing to the time when 50% of plants in a plot flowered. Downy mildew incidence (DMI) was obtained by dividing the total number of infected plants, 30 DAS from a plot, by the total number of plants. Panicles harvested in a plot were weighed to determine panicle yield (PY) and then threshed. Grains obtained in each plot were weighed and used to calculate grain yield (GY) in kg ha⁻¹ using the following formula:

Five random plants were selected in each plot to measure the plant height (PH) from the base of the plant to the upper part of the panicle, number of productive tillers (PT) by counting the number of tillers per plant which produce productive panicles, panicle length (PL), and panicle diameter (PDIA). Five random samples of 1000 grains for each plot were weighed using a sensitive balance to determine the 1000-grain weight (TGW).

2.4. Data Analysis

Analysis of variance for each experimental site as well as for combined data after the homogeneity test of variance across the two experimental sites was performed using the general linear model (GLM) procedure in SAS version 9.4 (SAS Institute, Cary, NC). The following mathematical linear model was used:

where

  is the observed value of the variable for the th entry in the th location within th replication;  is the overall general mean;  is the effect of the th genotype;  is the effect of the th location;  is the interaction effect of the th entry and the th location;  is the effect of the th replication within the th location;  is the effect of the th block of the th replication in the th location;  is the experimental pooled error.

For the combining ability, analysis of variance was performed for traits that showed significant differences among hybrids using SAS software version 9.4 (SAS Institute, Cary, NC). Thus, the sum of squares of hybrids was partitioned into various variations due to lines, testers, and their interactions based on the following statistical model described by Singh and Chaudhary (1977):

where

  is  th observation on the th and th progeny;  is the overall general mean;  is the effect of the th male;  is the effect of the th female;  is interaction effect;  is error associated with each observation.

The values of the general combining ability for both male and female and the specific combining ability effects for all the studied traits were estimated as follows:

where

  is overall mean;  is mean of all the hybrids containing an th line average over all replications, sites, and males;  is mean of all the hybrids containing a th tester average over all replications, sites, and females;  is mean of the cross between th line and th tester across all replications and sites.

The significance of the GCA effects was tested using the formula described by Cox and Frey (1984):

where

 Me is the error mean sum of squares; r, t, l, s are numbers of replications, testers lines, and sites, respectively; SE is standard error.

Standard, mid-parent, and better parent heterosis for grain yield were also calculated for each cross across locations following Hallauer et al. (2010):

where denotes the mean performance of the hybrid averaged over the two locations. The mean value of the OPV check was used to calculate the standard heterosis. The parent with the highest mean value was used as better parent in the calculation of high-parent heterosis while the average between the two parents was used for the mid-parent heterosis.

3. Results

3.1. Performance of Hybrids and Parents across Locations

Combined analysis of variance across locations showed highly significant () genotype effect for all measured traits (Table 2). Site effect was also significant for all the traits, except for DMI and PH. However, interaction genotype × site effect was only significant for FWT, TGW, PY, and GY.

Table 2: Mean squares for studied traits across locations.

Source of variation
d.f.
DMI
FWT
PH
PL
PDIA
PT
TGW
PY
GY

Rep (site)
4
232.4
28.4
746.4
28.5
0.4
2.2
4.9
2499694
1258762

Block (Rep × site)
48
85.5
8.2
359.9
32.9
0.14
1.5
2.3
817310
324630

Site
1
84.6
248.9
0.1
444.1
1.6
29.4
36.2
5279671
3168503

Genotype
53
156.4
82.3
3193.5
278.6
0.46
5.1
10.4
3975982
1157443

Genotype × site
53
72.7
13.62
488.1
45.1
0.19
2.0
2.4
1418904
603031

Error
164
60.04
7.9
474.7
31.6
0.17
1.9
1.6
997156
297217

DMI: downy mildew incidence; FWT: flowering time; PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield; d.f.: degree of freedom; Rep: replication. Significant at 0.05 and 0.01 and 0.001 probability levels, respectively.

All genotypes were resistant to downy mildew with a mean DMI of 4%, except for IBL 155-2-1 and its progeny with Souna 3 which displayed both 22% DMI (Table 3). Days from sowing to 50% flowering (DAS) of genotypes across the two sites ranged from 50 to 69 DAS with an average of 56 DAS. The genotypes were tall with plant height ranging from 2 to 3.2 m. Panicle length of the pearl millet genotypes varied from 27 to 58 cm with an average of 44 cm while their diameter ranged from 1.2 to 2.7 cm with a mean diameter of 2.1 cm. The number of productive tillers ranged from 2 to 6 tillers per plant with a mean value of 4 productive tillers per plant. The 1000 seeds weight varied from 5 to 12 g with a mean of 9 g. The panicle yield of genotypes across the two sites varied from 376 kg ha⁻¹ for IBL 119-B-1 to 4190 kg ha⁻¹ for IBL 110-B-1 × Souna 3 and their grain yield varied from 92 kg ha⁻¹ for IBL 119-B-1 to 2024 kg ha⁻¹ for IBL 206-1-1 × Souna 3.

Table 3: Performance of tested genotypes for studied traits across sites.

Genotype
DMI
FWT
PHIG
PLEN
PDIA
PT
TGW
PY
GY

IBL 001-4-1
2
60
255
34
2.1
2
10
1104
585

IBL 003-B-1
4
51
231
31
2.5
5
11
1872
1340

IBL 011-4-1
14
59
237
44
1.9
3
7
1164
428

IBL 021-3-1
0
63
223
32
2.1
2
8
1178
419

IBL 055-4-1
6
65
210
37
1.6
2
6
517
286

IBL 091-1-1
0
60
246
47
2.2
4
8
2328
1136

IBL 095-4-1
0
50
243
37
1.9
5
10
2015
947

IBL 098-3-1
11
51
239
31
1.8
4
10
1946
1188

IBL 106-B-1
6
54
278
39
1.8
3
10
1340
710

IBL 110-B-1
0
62
240
45
1.6
2
6
997
404

IBL 114-6-1
0
62
199
27
1.8
2
8
750
324

IBL 119-B-1
0
69
260
41
1.2
2
5
376
92

IBL 155-2-1
22
57
200
35
1.3
3
7
1099
466

IBL 165-1-1
2
64
238
39
1.6
4
7
1349
489

IBL 179-2-1
0
60
272
43
1.9
2
8
850
394

IBL 179-3-1
8
54
233
35
2.0
5
8
1497
886

IBL 206-1-1
0
56
228
38
1.8
4
8
2102
1126

IBL 001-4-1 × Souna 3
17
53
273
43
2.0
5
11
3475
1923

IBL 003-B-1 × Souna 3
8
52
259
44
2.1
4
9
3218
1646

IBL 011-4-1 × Souna 3
5
52
255
50
1.8
4
8
2368
942

IBL 021-3-1 × Souna 3
4
57
210
44
1.9
3
7
1772
852

IBL 055-4-1 × Souna 3
0
58
241
38
2.7
3
8
2232
1397

IBL 091-1-1 × Souna 3
0
54
250
54
2.0
4
8
2369
1211

IBL 095-4-1 × Souna 3
0
52
262
58
2.0
4
9
2975
1641

IBL 098-3-1 × Souna 3
19
54
277
46
1.9
4
9
2326
1289

IBL 106-B-1 × Souna 3
6
56
256
52
1.6
3
9
2462
1351

IBL 110-B-1 × Souna 3
0
56
274
52
2.6
5
7
4190
1493

IBL 114-6-1 × Souna 3
4
57
270
47
2.0
3
8
2991
1181

IBL 119-B-1 × Souna 3
0
56
321
49
2.0
5
9
3586
1530

IBL 155-2-1 × Souna 3
22
56
287
46
1.9
5
9
2562
1101

IBL 165-1-1 × Souna 3
0
59
289
45
2.1
4
8
3420
1612

IBL 179-2-1 × Souna 3
0
59
298
44
2.0
3
9
1906
735

IBL 179-3-1 × Souna 3
2
55
275
46
2.2
4
8
2943
1402

IBL 206-1-1 × Souna 3
2
54
245
44
2.1
5
9
3671
2024

IBL 001-4-1 × Sosat C 88
9
56
284
36
2.4
4
9
2997
1579

IBL 003-B-1 × Sosat C 88
2
50
234
28
2.6
4
12
3182
1883

IBL 011-4-1 × Sosat C 88
0
50
257
39
2.1
5
10
2468
1331

IBL 021-3-1 × Sosat C 88
0
54
284
37
2.3
4
10
3053
1654

IBL 055-4-1 × Sosat C 88
0
57
298
40
2.0
3
9
1824
1131

IBL 091-1-1 × Sosat C 88
0
50
260
41
2.3
4
10
2912
2019

IBL 095-4-1 × Sosat C 88
2
55
281
39
2.3
4
10
2426
1368

IBL 098-3-1 × Sosat C 88
6
57
285
43
2.2
3
9
2722
1381

IBL 106-B-1 × Sosat C 88
0
57
255
37
2.2
3
9
1933
949

IBL 110-B-1 × Sosat C 88
2
55
256
38
2.6
4
9
2827
1433

IBL 114-6-1 × Sosat C 88
0
52
264
31
2.4
5
9
2944
1416

IBL 119-B-1 × Sosat C 88
2
60
298
41
2.0
4
8
1993
871

IBL 155-2-1 × Sosat C 88
0
51
260
35
1.9
6
10
2414
1215

IBL 165-1-1 × Sosat C 88
0
60
287
39
2.5
4
10
2785
1114

IBL 179-2-1 × Sosat C 88
0
54
277
32
2.4
6
9
2920
1586

IBL 179-3-1 × Sosat C 88
0
56
260
29
2.4
4
9
2375
1247

IBL 206-1-1 × Sosat C 8
0
53
242
34
2.4
5
9
3325
1988

Souna 3
5
56
273
55
2.0
4
8
2918
1268

Sosat C 88
2
51
251
33
2.3
4
10
2568
1548

Thialack II
7
53
292
54
1.9
4
8
3380
1694

Mean
4
56
259
41
2.1
4
9
2313
1171

Range
0–22
50–69
200–321
27–58
1.2–2.7
2–6
5–12
376–4190
92–2024

Standard deviation
5.6
4.1
25.8
7.3
0.3
0.9
1.4
868.8
483.1

DMI: downy mildew incidence; FWT: flowering, PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield.

As expected, the hybrids were generally more productive compared to the inbred lines and OPVs. The top five genotypes across sites were hybrids IBL 206-1-1 × Souna 3 (2024 kg ha⁻¹); IBL 091-1-1 × Sosat C 88 (2019 kg ha⁻¹); IBL 206-1-1 × Sosat C 88 (1988 kg ha⁻¹); IBL 001-4-1 × Souna 3 (1923 kg ha⁻¹); and IBL 003-B-1 × Sosat C 88 (1883 kg ha⁻¹). Among these top hybrids, two involved the inbred line IBL 206-1-1 as parent. The hybrid IBL 179-2-1 × Souna 3 (735 kg ha⁻¹) was the lowest yielding among the tested hybrids. The check, Thialack II, was the most productive OPV with an average grain yield of 1694 kg ha⁻¹ and ranked among the ten best genotypes. The best inbred line was IBL 003-B-1 (1340 kg ha⁻¹).

Genotypes flowered 2 days earlier in Nioro (55 DAS) compared to Bambey (57 DAS) (Table 4). The average TWG in Nioro was 8 g while in Bambey it was 9 g. The panicle yield of genotypes under Nioro conditions ranged from 461 kg ha⁻¹ for the inbred line IBL 110-B-1 to 4647 kg ha⁻¹ for hybrid IBL 110-B-1 × Souna 3 while under Bambey conditions it varied from 251 kg ha⁻¹ for the inbred IBL 119-B-1 to 4660 kg ha⁻¹ for the hybrid IBL 165-1-1 × Souna 3. Grain yield of genotypes under Bambey environment ranged from 61 kg ha⁻¹ for inbred IBL 119-B-1 to 2162 kg ha⁻¹ for hybrid IBL 165-1-1 × Souna 3. In Nioro, the grain yield varied from 87 kg ha⁻¹ for inbred line IBL 110-B-1 to 2966 kg ha⁻¹ for the hybrid IBL 206-1-1 × Sosat C 88.

Table 4: Mean flowering time, yield, and related traits of genotypes per site.

Genotype
FWT (das)
TGW (g)
PY (kg ha⁻¹)
GY (kg ha⁻¹)

Bambey
Nioro
Bambey
Nioro
Bambey
Nioro
Bambey
Nioro

IBL 001-4-1
60
61
9
10
1284
924
768
402

IBL 003-B-1
51
52
11
12
1856
1888
1512
1168

IBL 011-4-1
63
55
7
7
1195
1132
437
419

IBL 021-3-1
62
63
9
7
1423
933
718
119

IBL 055-4-1
68
63
5
7
321
712
139
432

IBL 091-1-1
63
56
8
8
2557
2099
1140
1132

IBL 095-4-1
49
50
10
11
1658
2372
924
969

IBL 098-3-1
49
53
9
11
1687
2206
1057
1318

IBL 106-B-1
55
54
10
10
780
1900
428
992

IBL 110-B-1
61
62
7
5
1533
461
721
87

IBL 114-6-1
65
58
6
9
628
873
267
382

IBL 119-B-1
73
64
3
6
251
500
61
122

IBL 155-2-1
55
58
7
6
1235
962
649
284

IBL 165-1-1
64
63
7
8
1970
727
792
186

IBL 179-2-1
59
60
8
7
1078
622
559
228

IBL 179-3-1
54
53
8
8
1330
1664
746
1025

IBL 206-1-1
60
52
8
8
920
3283
564
1687

IBL 001-4-1 × Souna 3
54
51
10
12
2625
4325
1223
2624

IBL 003-B-1 × Souna 3
52
51
9
10
2758
3677
1011
2281

IBL 011-4-1 × Souna 3
54
50
9
8
2151
2585
923
961

IBL 021-3-1 × Souna 3
58
56
7
7
1672
1872
1113
591

IBL 055-4-1 × Souna 3
59
57
9
8
2140
2324
1609
1185

IBL 091-1-1 × Souna 3
55
53
8
7
2375
2363
1295
1127

IBL 095-4-1 × Souna 3
53
50
9
8
2847
3102
1513
1768

IBL 098-3-1 × Souna 3
56
53
7
10
1983
2669
1018
1559

IBL 106-B-1 × Souna 3
57
55
8
9
1908
3015
1005
1697

IBL 110-B-1 × Souna 3
59
53
7
7
3733
4647
934
2051

IBL 114-6-1 × Souna 3
57
56
7
10
3154
2828
1436
926

IBL 119-B-1 × Souna 3
59
53
10
8
4175
2996
1829
1231

IBL 155-2-1 × Souna 3
59
54
8
9
1913
3211
907
1294

IBL 165-1-1 × Souna 3
60
57
8
8
4660
2180
2162
1061

IBL 179-2-1 × Souna 3
60
58
9
8
1728
2084
617
854

IBL 179-3-1 × Souna 3
56
54
7
9
2031
3855
822
1982

IBL 206-1-1 × Souna 3
56
53
8
11
3285
4058
1609
2438

IBL 001-4-1 × Sosat C 88
57
54
9
10
2503
3490
1298
1860

IBL 003-B-1 × Sosat C 88
48
51
12
12
3562
2802
1959
1806

IBL 011-4-1 × Sosat C 88
49
51
10
10
2380
2555
1259
1403

IBL 021-3-1 × Sosat C 88
53
55
9
10
2526
3580
1304
2005

IBL 055-4-1 × Sosat C 88
58
56
9
9
1630
2017
1007
1255

IBL 091-1-1 × Sosat C 88
48
51
11
10
2563
3262
1976
2061

IBL 095-4-1 × Sosat C 88
56
53
9
10
1963
2889
1080
1657

IBL 098-3-1 × Sosat C 88
59
55
8
11
1260
4184
404
2357

IBL 106-B-1 × Sosat C 88
59
54
8
11
2133
1733
944
953

IBL 110-B-1 × Sosat C 88
56
53
9
10
2367
3288
1032
1835

IBL 114-6-1 × Sosat C 88
53
51
9
10
2917
2971
1662
1171

IBL 119-B-1 × Sosat C 88
59
60
9
7
2992
994
1261
482

IBL 155-2-1 × Sosat C 88
51
51
9
11
1939
2889
801
1630

IBL 165-1-1 × Sosat C 88
60
59
11
9
3801
1770
1450
778

IBL 179-2-1 × Sosat C 88
53
55
9
10
2449
3390
1103
2070

IBL 179-3-1 × Sosat C 88
58
54
9
10
1644
3107
727
1767

IBL 206-1-1 × Sosat C 88
54
52
8
9
2411
4240
1010
2966

Souna 3
55
56
8
8
3465
2372
1731
805

Sosat C 88
50
52
9
10
2956
2180
1707
1389

Thialack II
54
52
7
8
3716
3044
1659
1729

Mean
57
55
8
9
2186
2441
1072
1270

SD
5
4
2
2
955
1089
476
703

FWT: flowering time; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield.

Based on grain yield, the ten best genotypes in Nioro were only hybrids while in Bambey the three OPVs were among the top ten genotypes. The hybrids IBL 091-1-1 × Sosat C 88 and IBL 206-1-1 × Souna 3 performed well under both locations and were among the best ten genotypes across the two environments.

3.2. Combining Ability Analysis across Locations

The total variation due to crosses was partitioned into line, tester, and line × tester interaction (Table 5). The mean squares due to hybrids were significant for all the traits except for PY and GY. Line mean squares across the two locations were also significant for all the traits except for PDIA while tester mean squares were not significant for PT, PY, and GY. Line × tester mean squares were significant for most traits except PDIA, PY, and GY. The mean squares due to line × site were significant for TGW, PY, and GY whereas the mean squares due to tester × site interaction were significant for FWT and DMI. However, the mean squares due to site × line × tester interaction were not significant for all the traits across the two locations.

Table 5: Mean squares for combining ability for studied traits across locations.

Source of variation
d.f.
DMI
FWT
PH
PLEN
PDIA
PT
TGW
PY
GY

Rep (site)
2
55.5
12.7
300.9
1.2
0.7
3.1
5.0
316965
25012

Site
1
158.8
178.8
711.6
280.0
0.2
12.2
26.1
9629606
6762757

Hybrid
33
188.1
45.7
2852.4
309.4
0.5
4.3
6.2
1962646
688597

Line (GCA)
16
229.6
64.9
3607.8
160.6
0.4
5.4
4.4
2290926
775061

Tester (GCA)
1
776.5
40.5
270.7
6226.1
1.6
0.7
64.8
1998612
123285

Line × tester (SCA)
16
110.0
26.8
2258.6
88.5
0.4
3.4
4.4
1632117
637466

Site × line
16
52.4
7.5
311.4
18.0
0.3
2.3
3.9
3292948
1351732

Site × tester
1
184.4
54.0
79.1
26.1
1.6
0.9
0.04
95074
444360

Site × line × tester
16
64.1
6.0
173.9
28.2
0.3
1.2
1.2
703213
424419

Error
134
39.7
5.3
281.7
25.4
0.3
1.9
1.8
1244846
414329

DMI: downy mildew incidence; FWT: flowering time; PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield; GCA: general combining ability; SCA: specific combining ability; d.f.: degree of freedom; Rep: replication. Significant at 0.05 and 0.01 and 0.001 probability levels, respectively.

3.3. Relative Contributions of Mean Squares to Additive and Nonadditive Effects

Across the two locations, the relative importance of mean squares, for additive effect ( + ), was higher for all the traits compared to the dominance effect (SCA) (Figure 1). GCA effects accounted for most of the variation observed for most of the traits with more than 80% of the total genotypic variation among hybrids except for PH, PT, PY, and GY. The overall contribution of GCA sums of squares to the total mean squares across the two locations varied from 58% for GY to 99% for PLEN while SCA varied from 1% for PLEN to 42% for grain yield. The contribution of was higher than and SCA for DMI, PLEN, PDIA, and TGW while was larger than GCAm and SCA mean square for FWT, PH, PT, PY, and GY. The contribution of (50%) was slightly higher than SCA (42%) to grain yield.

Figure 1: Proportion of total mean squares of studied traits attributable to , , and SCA across locations. DMI: downy mildew incidence; FWT: flowering time; PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield; : general combining ability for male parent; : general combining ability for female parent; SCA: specific combining ability.

3.4. Estimation of General Combining Ability Effects

The contribution of lines and testers to crosses for traits studied across the two locations is presented in Table 6. For female lines, significant GCA effects were observed for most of the traits while for male lines significant GCA effects were recorded only for TGW. For DMI, the GCA effects varied from −3.2 for IBL 091-1-1 to 9.7 for IBL 001-4-1. Positive and significant GCA effects for DMI were observed on parental lines IBL 001-4-1, IBL 098-3-1, and IBL 155-2-1. For FWT, GCA effects ranged from −4.2 for IBL 003-B-1 to 4.2 for IBL 165-1-1 and both positive and negative significant GCA effects were observed. Estimates of GCA effects for PH ranged from −25.2 for IBL 206-1-1 to 19.4 for IBL 179-2-1. Out of the 19 parental lines, six showed negative and significant effects whereas four lines exhibited positive and significant effects for PH. GCA effects for PLEN varied from −5.7 for IBL 003-B-1 to 6.7 for IBL 095-4-1 with both positive and negative significant effects whereas GCA effects for PDIA ranged from −0.3 for IBL 011-4-1 to 0.4 for IBL 110-B-1 with no significant effects. The GCA effects due to parental lines for PT across locations varied from −1.2 to 1.3 for IBL 055-4-1 and IBL 155-2-1, respectively. Significant positive GCA effects for PT were observed in lines IBL 155-2-1 and IBL 206-1-1 while significant negative GCA effects were observed in lines IBL 055-4-1 and IBL 106-B-1. Across research stations, the GCA for TGW ranged from −0.9 for IBL 110-B-1 to 1.7 for IBL 003-B-1. The tester Sosat C 88 and the inbred line IBL 003-B-1 had significant positive GCA effects while the tester Souna 3 showed significant negative GCA effects for TGW. For PY and GY traits, no significant GCA effects were showed. However, among parental lines, inbred lines IBL 206-1-1, IBL 003-B-1, IBL 001-4-1, IBL 091-1-1, IBL 095-4-1, and IBL 110-B-1 manifested desirable positive GCA effects for GY and most other studied traits for the two research stations. In contrast, inbred lines IBL 011-4-1, IBL 106-B-1, IBL 155-2-1, and IBL 179-2-1 ranked among the worst lines for GY with negative GCA effects.

Table 6: Estimates of GCA effects of lines and testers evaluated across the two sites.

Lines
DMI (%)
FWT (das)
PH (cm)
PLEN (cm)
PDIA (cm)
PT
TGW (g)
PY (kg ha⁻¹)
GY (kg ha⁻¹)

IBL 001-4-1
9.7
−0.8
10.1
−2.5
0.1
0.6
1.1
483.9
354.4

IBL 003-B-1
1.6
−4.2
−21.7
−5.7
0.3
0.2
1.7
447.9
367.4

IBL 011-4-1
−0.4
−3.8
−12.0
3.0
−0.3
0.3
0.0
−334.1
−260.4

IBL 021-3-1
−1.1
0.8
−21.3
−1.2
−0.2
−0.8
−0.5
−339.1
−143.8

IBL 055-4-1
−3.2
2.6
0.9
−2.9
0.3
−1.2
−0.4
−724.2
−132.9

IBL 091-1-1
−3.2
−3.0
−13.2
5.5
−0.1
−0.2
0.0
−111.2
217.9

IBL 095-4-1
−2.4
−1.7
3.0
6.7
−0.2
−0.2
0.0
−51.7
107.5

IBL 098-3-1
9.0
0.8
12.5
2.8
0.0
−0.6
−0.1
−227.9
−62.2

IBL 106-B-1
−0.4
1.4
−12.5
2.3
−0.2
−1.1
0.1
−554.6
−247.0

IBL 110-B-1
−2.3
0.6
−3.4
3.0
0.4
0.4
−0.9
756.7
66.2

IBL 114-6-1
−1.4
−0.5
−1.7
−2.7
0.0
−0.2
−0.3
215.7
−98.2

IBL 119-B-1
−2.4
2.9
41.2
3.3
−0.2
0.3
−0.4
37.4
−196.4

IBL 155-2-1
7.6
−1.0
5.3
−1.2
−0.2
1.3
0.2
−263.9
−239.0

IBL 165-1-1
−3.2
4.2
19.8
0.3
0.2
0.0
−0.1
350.7
−34.2

IBL 179-2-1
−3.2
1.6
19.4
−3.7
0.0
0.3
−0.1
−339.1
−236.0

IBL 179-3-1
−2.4
0.9
−1.1
−4.3
0.1
−0.2
−0.3
−92.9
−72.4

IBL 206-1-1
−2.3
−0.9
−25.2
−2.7
0.0
0.9
0.0
746.5
609.0

SE
2.0
0.8
4.9
1.2
0.2
0.4
0.6
508.2
325.6

Testers

Souna 3
2.0
0.4
−1.2
5.5
−0.1
−0.1
−0.6
99.0
−24.6

Sosat C 88
−2.0
−0.4
1.2
−5.5
0.1
0.1
0.6
−99.0
24.6

SE
1.0
0.5
0.6
0.4
0.1
0.1
0.0
21.6
46.7

DMI: downy mildew incidence; FWT: flowering time; PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield. Significant at 0.05 and 0.01 and 0.001 probability levels, respectively.

3.5. Estimation of Specific Combining Ability Effects

Significant positive and negative SCA effects were recorded for all the observed traits (Table 7). The top-cross hybrid IBL 155-2-1 × Sosat C 88 was the only one which exhibited negative and significant SCA effects for DMI. In addition, its SCA effects for FWT and PH were negative and significant while its SCA effects for PT were significant and positive. Among 34 top-cross hybrids, six top-cross hybrids had significant SCA effects, of which three were positive. All the significant and positive SCA effects for PY and GY were recorded in the crosses among Sosat C 88 with the inbred lines IBL 179-2-1, IBL 091-1-1, and IBL 021-3-1.

Table 7: Estimates of SCA effects for hybrids evaluated across the two sites.

Hybrid
DMI (%)
FWT (das)
PH (cm)
PLEN (cm)
PDIA (cm)
PT
TGW (g)
PY (kg ha⁻¹)
GY (kg ha⁻¹)

IBL 001-4-1 × Souna 3
2.5
−1.9
−4.7
−1.8
0
0.6
1.2
140.3
196.8

IBL 003-B-1 × Souna 3
1.1
0.5
13.8
2.6
−0.3
0.2
−0.9
−81.1
−93.6

IBL 011-4-1 × Souna 3
0.8
0.7
0.2
0.2
−0.1
−0.1
−0.1
−148.8
−170.1

IBL 021-3-1 × Souna 3
0.1
1
−35.4
−2.3
−0.1
−0.4
−0.8
−739.7
−376.5

IBL 055-4-1 × Souna 3
−2
0.2
−27.2
−6
0.5
0.4
0.1
105.2
157.6

IBL 091-1-1 × Souna 3
−2
1.8
−3.7
0.9
0
−0.4
−0.9
−370.6
−379.3

IBL 095-4-1 × Souna 3
−2.8
−2
−8.3
4.2
0.1
0.4
0.1
175.4
160.8

IBL 098-3-1 × Souna 3
4.4
−1.7
−2.9
−4
−0.1
0.5
0.3
−296.6
−21.5

IBL 106-B-1 × Souna 3
0.9
−0.8
1.4
2.1
−0.1
−0.2
0.1
165.6
226

IBL 110-B-1 × Souna 3
−2.9
0.3
10.3
1.9
0.2
0.6
−0.5
582.3
54.2

IBL 114-6-1 × Souna 3
−0.2
1.8
4.2
2.2
−0.1
−0.6
0
−75.6
−92.9

IBL 119-B-1 × Souna 3
−2.8
−2.3
12.4
−1
0.1
0.4
0.9
697.4
354.1

IBL 155-2-1 × Souna 3
8.8
2.1
14.5
0.3
0.1
−0.8
0
−25
−32.8

IBL 165-1-1 × Souna 3
−2
−0.9
2.3
−2.6
−0.2
0.4
−0.5
218.4
273.5

IBL 179-2-1 × Souna 3
−2
2.1
11.8
0.5
0.1
−1.2
0.3
−605.7
−400.8

IBL 179-3-1 × Souna 3
−1.1
−0.9
8.5
3.2
−0.2
0.3
0
184.9
102.3

IBL 206-1-1 × Souna 3
−1
0.1
2.7
−0.4
0.1
−0.2
0.7
73.9
42.3

IBL 001-4-1 × Sosat C 88
−2.5
1.9
4.7
1.8
0
−0.6
−1.2
−140.3
−196.8

IBL 003-B-1 × Sosat C 88
−1.1
−0.5
−13.8
−2.6
0.3
−0.2
0.9
81.1
93.6

IBL 011-4-1 × Sosat C 88
−0.8
−0.7
−0.2
−0.2
0.1
0.1
0.1
148.8
170.1

IBL 021-3-1 × Sosat C 88
−0.1
−1
35.4
2.3
0.1
0.4
0.8
739.7
376.5

IBL 055-4-1 × Sosat C 88
2
−0.2
27.2
6
−0.5
−0.4
−0.1
−105.2
−157.6

IBL 091-1-1 × Sosat C 88
2
−1.8
3.7
−0.9
0
0.4
0.9
370.6
379.3

IBL 095-4-1 × Sosat C 88
2.8
2
8.3
−4.2
−0.1
−0.4
−0.1
−175.4
−160.8

IBL 098-3-1 × Sosat C 88
−4.4
1.7
2.9
4
0.1
−0.5
−0.3
296.6
21.5

IBL 106-B-1 × Sosat C 88
−0.9
0.8
−1.4
−2.1
0.1
0.2
−0.1
−165.6
−226

IBL 110-B-1 × Sosat C 88
2.9
−0.3
−10.3
−1.9
−0.2
−0.6
0.5
−582.3
−54.2

IBL 114-6-1 × Sosat C 88
0.2
−1.8
−4.2
−2.2
0.1
0.6
0
75.6
92.9

IBL 119-B-1 × Sosat C 88
2.8
2.3
−12.4
1
−0.1
−0.4
−0.9
−697.4
−354.1

IBL 155-2-1 × Sosat C 88
−8.8
−2.1
−14.5
−0.3
−0.1
0.8
0
25
32.8

IBL 165-1-1 × Sosat C 88
2
0.9
−2.3
2.6
0.2
−0.4
0.5
−218.4
−273.5

IBL 179-2-1 × Sosat C 88
2
−2.1
−11.8
−0.5
−0.1
1.2
−0.3
605.7
400.8

IBL 179-3-1 × Sosat C 88
1.1
0.9
−8.5
−3.2
0.2
−0.3
0
−184.9
−102.3

IBL 206-1-1 × Sosat C 8
1
−0.1
−2.7
0.4
−0.1
0.2
−0.7
−73.9
−42.3

SE
2.2
0.7
3.7
1.5
0.1
0.3
0.3
234.8
182.5

DMI: downy mildew incidence; FWT: flowering time; PH: plant height; PL: panicle length; PDIA: panicle diameter; PT: productive tillers; TGW: 1000-grain weight; PY: panicle yield; GY: grain yield. Significant at 0.05 and 0.01 and 0.001 probability levels, respectively.

3.6. Estimation of Standard, Best, and Mid-Parent Heterosis for Grain Yield across Locations

The estimates of best parent, mid-parent, and standard heterosis for grain yield are summarized in Table 8. The best parent heterosis for grain yield across the two locations varied from −44 to 60% and 17 hybrids displayed positive best parent heterosis. IBL 206-1-1 × Souna 3, followed by IBL 001-4-1 × Souna 3, had the largest best parent heterosis for grain yield and was among the best five hybrids while IBL 119-B-1 × Sosat C 88 had the least best parent heterosis value. The mid-parent heterosis varied from −16% for IBL 106-B-1 × Sosat C 88 to 125% for IBL 119-B-1 × Souna 3 which was not among the ten best hybrids. All the crosses displayed positive mid-parent heterosis for grain yield except IBL 106-B-1 × Sosat C 88 (−16%) and IBL 179-2-1 × Souna 3 (−12%). The standard heterosis values for grain yield across the experimental sites varied from −57% for IBL 179-2-1 × Souna 3 to 20% for IBL 206-1-1 × Souna 3. The crosses IBL 206-1-1 × Souna 3, IBL 091-1-1 × Sosat C 88, IBL 206-1-1 × Sosat C 88, IBL 001-4-1 × Souna 3, and IBL 003-B-1 × Sosat C 88 exhibited positive standard heterosis for grain yield. These hybrids were the top best five and displayed also both positive better and mid-parent heterosis values for grain yield.

Table 8: Mean grain yield and best and mid-parent heterosis of pearl millet hybrid across locations.

Cross
GY (kg ha⁻¹)
BPH
MPH
SH

IBL 001-4-1 × Souna 3
1923
52
108
14

IBL 003-B-1 × Souna 3
1646
23
26
−3

IBL 011-4-1 × Souna 3
942
−26
11
−44

IBL 021-3-1 × Souna 3
852
−33
1
−50

IBL 055-4-1 × Souna 3
1397
10
80
−18

IBL 091-1-1 × Souna 3
1211
−4
1
−29

IBL 095-4-1 × Souna 3
1641
29
48
−3

IBL 098-3-1 × Souna 3
1289
2
5
−24

IBL 106-B-1 × Souna 3
1351
7
37
−20

IBL 110-B-1 × Souna 3
1493
18
79
−12

IBL 114-6-1 × Souna 3
1181
−7
48
−30

IBL 119-B-1 × Souna 3
1530
21
125
−10

IBL 155-2-1 × Souna 3
1101
−13
27
−35

IBL 165-1-1 × Souna 3
1612
27
83
−5

IBL 179-2-1 × Souna 3
735
−42
−12
−57

IBL 179-3-1 × Souna 3
1402
11
30
−17

IBL 206-1-1 × Souna 3
2024
60
69
20

IBL 001-4-1 × Sosat C 88
1579
2
48
−7

IBL 003-B-1 × Sosat C 88
1883
22
30
11

IBL 011-4-1 × Sosat C 88
1331
−14
35
−21

IBL 021-3-1 × Sosat C 88
1654
7
68
−2

IBL 055-4-1 × Sosat C 88
1131
−27
23
−33

IBL 091-1-1 × Sosat C 88
2019
30
50
19

IBL 095-4-1 × Sosat C 88
1368
−12
10
−19

IBL 098-3-1 × Sosat C 88
1381
−11
1
−18

IBL 106-B-1 × Sosat C 88
949
−39
−16
−44

IBL 110-B-1 × Sosat C 88
1433
−7
47
−15

IBL 114-6-1 × Sosat C 88
1416
−9
51
−16

IBL 119-B-1 × Sosat C 88
871
−44
6
−49

IBL 155-2-1 × Sosat C 88
1215
−22
21
−28

IBL 165-1-1 × Sosat C 88
1114
−28
9
−34

IBL 179-2-1 × Sosat C 88
1586
2
63
−6

IBL 179-3-1 × Sosat C 88
1247
−19
2
−26

IBL 206-1-1 × Sosat C 8
1988
28
49
17

GY: grain yield; BPH: best parent heterosis; MPH: mid-parent heterosis; SH: standard heterosis.

4. Discussion

The significant differences observed among the genotypes for all the characters studied indicated the presence of large amount of genetic variability among the inbred lines, the OPVs, and their crosses, which is a prerequisite in the establishment of a successful breeding programme. Genetic variability for downy mildew disease and several agronomic traits has been also reported in many studies conducted in West and Central Africa [14, 16–19]. The results indicated also the influence of the environment on the performance of the genotypes for FWT, TGW, PY, and GY traits as their genotype × location interaction effect was significant. The environment effect in the performance of genotypes for flowering time was also reported in Burkina Faso [14]. The mean grain yield at Nioro research station was higher compared to Bambey research station. This could be explained by rainfall pattern and soil texture variability existing between the two locations where the experiments were established. Bambey research station is located in the northern part of the groundnut basin in the Sudano-Sahelian area and the soil texture is sandy while Nioro research station, located in the southern part of the groundnut basin in the Sudanese zone, has sandy-clay soil texture. However, despite the site effect on grain yield and yield related traits, some of the genotypes such as IBL 091-1-1, IBL 091-1-1 × Sosat C 88, and Thialack II have performed well under the two environments.

Besides the existence of useful variability, the establishment of a successful breeding programme depends on a deep understanding of the underlying gene action of the traits of interest. Indeed, this genetic information will guide breeders on which breeding methods and lines to use for the development of improved varieties [9]. In this study, GCA and SCA mean squares were significant for all the traits studied except for the SCA of PDIA, PY, and GY traits indicating that both additive and nonadditive gene actions were important for the inheritance of these traits across the two locations. This result is contrary to the findings of [16, 17] that reported only significant GCA effects for agronomic traits such as flowering time, downy mildew incidence, plant height, and panicle length. However, in the present study, the larger proportion of GCA over SCA mean squares for most of the traits such as DMI, FWT, PL, PDIA, and TGW indicated the preponderance of additive gene action over nonadditive gene action. This would imply that recurrent selection could be effectively used for improvement of these traits. The result of this study is consistent with that of [14] that reported additive gene action to be more important that nonadditive gene action in controlling agronomic traits such as grain yield, flowering time, and panicle length. Similarly, [20] reported the importance of additive gene action over nonadditive gene action in the expression of panicle length and diameter. The additive gene action was also reported for other traits in pearl millet such as Fe and Zn densities [11]. For grain yield, the significance of and the lack of significance for SCA suggest that grain yield is controlled by additive gene effects as reported by several authors [14, 16]. However, the slight difference of their mean squares suggests that nonadditive gene action is also important in the inheritance of grain yield trait. This study has also provided information on parental effects in controlling the traits studied. The larger mean squares over mean squares for DMI, PL, PDIA, and TGW display the role of paternal effects in the control of these traits while the larger mean squares over GCAm mean squares for FWT, PH, PT, and GY suggest the role of maternal effects in the control of these traits across the two locations. Similarly, [14] found a paternal effect in controlling PDIA and a maternal effect for FWT and PH under different locations in Burkina Faso. The best performing cross for high grain yield and resistance to downy mildew disease may be produced by crossing the male parents resistant to the disease with female parents having good yield potential.

Inbred lines IBL 001-4-1, IBL 003-B-1, IBL 091-1-1, IBL 095-4-1, IBL 110-B-1, and IBL 206-1-1 had positive GCA effects for grain yield indicating that these lines contributed favorable alleles for grain yield. They produced hybrids that were among the best 15 across the two locations. Thus, such lines could be used as parents to create high yielding synthetic or hybrid varieties. However, IBL 001-4-1 unlike the other five inbred lines had positive and significant GCA effect for downy mildew and produced hybrids with a certain level of disease incidence. The other lines showed negative GCA effects and would be good sources of resistance for downy mildew under Senegalese growing conditions. In addition, they had negative GCA effects for flowering time and plant height. Thus, their cross is expected to produce a medium plant height and early maturing synthetic pearl millet varieties, tolerant to the downy mildew disease with improved grain yield.

In this study, the top-cross hybrids performed better than the inbred lines and OPVs. The top five genotypes across the two locations were hybrids, showing evidence of heterosis for grain yield in pearl millet which has been also reported previously [5, 14, 16]. Grain yield showed a mid-parent heterosis ranging from −16% to 125% and most of the hybrids except IBL 106-B-1 × Sosat C 88 and IBL 179-2-1 × Souna 3 exceeded the parental lines. This finding is consistent with [18] that reported mid-parent heterosis ranging from 1.9 to 98% for top-crosses evaluated under low P conditions. Information about the performance of hybrids compared to the standard check is needed for the farmer to determine the benefit of growing hybrid. In this study, a maximum standard heterosis of 20% for grain yield was observed providing advantage of growing hybrids compared to the local cultivars. Similar standard heterosis for grain yield was also reported in Burkina Faso [14]. The higher mean performance of the crosses compared to their parents and the control check indicate great potential for hybrid pearl millet breeding. Therefore, this technology can be a good strategy to increase pearl millet production like in India where more than 70% of the pearl millet cultivated area is sown with hybrids [5]. However, a strong hybrid pearl millet breeding programme needs to be established.

5. Conclusion

The present study revealed that the crosses IBL 206-1-1 × Souna 3, IBL 091-1-1 × Sosat C 88, IBL 206-1-1 × Sosat C 88, IBL 001-4-1 × Souna 3, and IBL 003-B-1 × Sosat C 88 were the top five hybrids and exhibited positive best parent, mid-parent, and standard heterosis for grain yield. Furthermore, both additive and nonadditive gene action were involved in the inheritance of almost all the traits studied. However, the contribution of the additive gene action was higher than that of nonadditive gene action for all the traits. Inbred lines IBL 003-B-1, IBL 091-1-1, IBL 095-4-1, IBL 110-B-1, and IBL 206-1-1 exhibited positive GCA effects for grain yield and negative GCA effects for flowering time, downy mildew disease, and plant height. These lines can be used as parents for breeding high yielding synthetic varieties or hybrids adapted to West and Central African countries.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

Acknowledgments

The authors are thankful to the West Africa Agricultural Productivity Program (WAAPP). This work could not have been done without the funding received from the WAAPP.

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