Gezira Journal of Agricultural Science
University Of Gezira
Journals Of University Of Gezira
ISSN 9556-1728
Vol7 No2
Heterosis for grain yield and its components in pearl millet topcrosses Yahia D. Eldie1, Abu Elhassan S. Ibrahim2 and Adam M. Ali 3 1
Faculty of Education, University of Alfashir, Alfashir, Sudan. Faculty of Agricultural Sciences, University of Gezira, Wad Medani, Sudan. 3 Agricultural Research Corporation, El Obied, Sudan. 2
ABSTRACT Pearl millet (Pennisetum glaucum (L.) R. Br.) cultivars for marginal, arid environments need to combine adaptation to stress conditions with relatively high grain yields. The experiments were carried out in Sudan during the rainy season of 2006 at two locations (Wad Medani and Elgedarif) in a randomized complete block design following line x tester arrangement. The traits measured were days to 50% flowering, plant height, stover, panicle, biomass and grain yields. The highest grain yield was recorded by SADC togo x ICMA96222 (3234 kg/ha) at Wad Medani and ICMV155 x ICMA99111 (3734 kg/ha) at Elgedarif. Average over the two locations, the highest mean grain yield (3086 kg/ha) was obtained by the hybrid Dembi yellow x ICMA97333 which exceeded the overall mean best parent by 1227 kg/ha. The hybrids showing highly positive heterosis for grain yield were Dembi yellow x ICMA96222 and Baladi white x ICMA97333, at Wad Medani, whereas Topcross x ICMA99111 and ICMV155 x ICMA99111 showed the highest heterosis at Elgedarif. In combined analysis Baladi yellow x ICMA97333 showed the highest heterosis followed by Dembi yellow x ICMA97333 and SADC togo x ICMA96222. However, these crosses had high performance per se for grain yield and other characters. Significant amount of heterosis observed in landrace-based topcross hybrids for grain yield and other related traits suggested that pearl millet high grain yield production can be obtained by topcrossing locally adapted landraces on suitable male-sterile lines.
INTRODUCTION
The 20th century has witnessed significant advances in the productivity of many major food crops, particularly the cereal grains. This improvement was mainly achieved through breeding of high yielding cultivars coupled with improved agronomic practices192(CSSA, 1984). One of the remarkable successful breeding stories is the development of commercial single-cross hybrids in pearl millet (Burton and Powell, 1968; Dave, 1987) following the discovery of cytoplsamic male sterility (Burton, 1965). Crop hybrids have had a dual role in increasing the productivity over the past three decades in India from 339 kg/ha in 1960-1965 to 636 kg/ha in 1990-1995 (Harinaryana et al., 1999). The greater yield potential of hybrids, compared to old open pollinated cultivars (AICPMIP, 1988) has encouraged farmers to increase the level of input use on the crop allowing them to exploit the synergism inherent in the combination of higher inputs. Population hybrids of pearl millet among West African landraces outyielded the mean yields of their parents; however, the hybrids did not outyield the local genotypes, indicating a need to produce hybrids among locally adapted types (Quendeba et al., 1995). Topcross hybrids (open pollinated variety x male-sterile seed parent) exploit heterosis to increase productivity (Mahalakshmi et al., 1992; Yadav et al., 2000) as do single cross hybrids, but breeding topcross hybrids is far simpler and quicker and seed production is easier and more profitable. Cytoplasmic-genetic male sterility has been extensively exploited in commercial hybrids of pearl millet (Burton, 1965). Topcrossing adapted landraces on high yielding male-steriles provide an opportunity to increase disease resistance and/ or fodder yields with no apparent loss of adaptation to the marginal environments in which the landraces have evolved. The effect of heterosis in individual components of growth or yield on grain yield in pearl millet topcross combinations will depend not on the genotype of the pollinator, but on its phenotype in a particular environment. Simply, grain yield heterosis in relation to individual trait heterosis is subject to genotype x environment interaction in crosses. This suggests that the exploitation of heterosis for a given topcross pollinator will be location specific. Different male- sterile lines will have to be used in different environments to maximize heterosis for grain yield for a given topcross pollinator (ICRISAT, 1990). The more effective and rapid way to improve biomass yield in pearl millet is likely to be by exploiting heterosis hybrids (Hanna and Gupta, 1999). Bidinger et a1. (1994) and Yadav et al. (2000) suggested that it may be possible to meet farmers need for increased grain and stover production while retaining critical adaptation to arid zone environments, by exploiting heterosis between locally adapted landraces and male-sterile seed parents
that partition the extra dry matter to both grain and stover. Top crosses appear to be a viable cultivar type in pearl millet, and have various advantages over conventional single cross-hybrids in the form of easier hybrid seed production and likely greater stability of both yield and resistance (Talukdar et al., 1996). The present study describes the extent and nature of heterosis in hybrids for higher grain yields under two environmental locations and compare the grain yield of adapted landraces and the hybrids made by topcrossing on inbred male-sterile lines in different environments.
MATERIALS AND METHODS Four lines of pearl millet (ICMA 91222, ICMA 96222, ICMA 97333, and ICMA 99111) were introduced from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India, and used as female parents in a hybridization process to produce topcross hybrids using line x tester arrangement. The pollinators consisted of 15 open-pollinated varieties (SADC long, SADC togo, MCNELC, MCSRC, Topcross P1, Sudan Đż, ICMV 155, Bayouda, Baladi white, Baladi yellow, Dembi yellow, Omgarfa, Ugandi, ICMV 221 and Ashana). The 60 topcross hybrids together with their19 parents were evaluated during 2006 rainy season at two environmentally different locations in Sudan, viz., Wad Medani (Gezira Research Station Farm, Agricultural Research Corporation) located in the central clay plains of the Sudan (14 o 24/ N, 33o 29/ E) with soil characterized by cracking heavy clay vertisols, very low permeability, pH of 8.5, organic matter (0.4%), nitrogen (380 ppm), and phosphorus (ESP, 4 ppm) and Elgedarif Research Station located in the south east clay plains of Sudan (14o 13/ N, 35o 13/E) with heavy clay soil, low permeability, pH of 8.1, nitrogen (310 ppm) and the available phosphorus was 3.3 ppm. . Sowing dates were the 28th of July at Wad Medani and 17th of July at Elgedarif. In both locations, experiments were carried out in a randomized complete block design, with three replications. The total plot size was 5m x 4rows x 0.8m which is equal to 16 m2. At full maturity, the central two rows of each plot (excluding the boarders and 0.5 m from each end), with a net area of 6.4 m2, was hand harvested in both experiments for trait measurements. In both locations, data were recorded on days to 50% flowering, plant height, stover, panicle, biomass and grain yields. Data for stover yield and panicle yield were further used to calculate biomass production.
The amount of heterosis as mid-parent (MP) was computed for all studied traits. Mid-parent heterosis (MP) = {(F1-MP) x 100}/MP Where, MP = (P1+P2)/2 Where P1 and P2 are parents 1 and 2, respectively. The standard error for the above estimate was calculated as follows SE of heterosis = (1.5 x Me x 1/r) 1/2 Where Me is error mean square obtained from analysis of variance. If the difference between the F1 value and MP was greater than the values obtained from the formulae above, the heterosis estimates were considered significant.
RESULTS AND DISCUSSION The analysis of variance procedure showed highly significant differences (P >0.01) for all traits studied among entries (parents and F1, s) in each location as well as across locations. Mean performance Differences observed in means for most of the traits studied were high across the two locations. However, within parents and crosses specific relationships were observed in mean performance of some parent and hybrids. Mean days to flowering for parents across the two locations, Wad Medani and Elgedarif, ranged from 56 d (ICMA91222) to 75 d (Bayouda) with general mean being 63 d, whereas for crosses ranged from 53 d (ICMV221 x ICMA96222) to 67 d (Sudan Π x ICMA96222). The earliest flowering parents were ICMA91222, MCNELC, Sudan Π, SADC long and ICMA96222. Early flowering in hybrids was noticed across locations and in combined analysis. Among the hybrids ICMV221 x ICMA96222, Baladi yellow x ICMA99111, Sudan Π x ICMA91222, Ugandi x ICMA91222 and ICMV221 x ICMA97333 were the earliest crosses. Contrarily, Bidinger et al. (2005) showed that ICMV221 x ICMA97333 as the best combination for earliness as well as for grain yield heterosis across locations. There were considerable variations in days to flowering of parents in the two locations. Wad Medani on average was earlier (55d) than Elgedarif (71d). Wad Medani had a small gap (15 days) in flowering time between parents whereas; Elgdarif had a big gap (31 days). At Elgedarif the top five grain yield topcrosses were earlier than the top five grain yielding parents (Table 1). Breeding for earliness is of vital importance in hybrids with good agronomic traits to suit the semi-arid tropics such as Sudan. The mean days to 50% flowering were different in the two locations, indicating the
diversity between locations. Early flowering in hybrids was noticed across locations. However, days to 50% flowering are an important character, and are a useful criterion for prediction of inbreds and hybrids performance for use in different agro ecological zones. The mean days to 50% flowering were different in the two locations, indicating the diversity between locations. Early flowering in hybrids was noticed across locations (Table 1). Similar results were obtained by Quendeba et al. (1993), Lynch et al. (1995) and Ali (2002) in pearl millet population diallel crosses; however, they found that the crosses were earlier than their latest parent. However, days to 50% flowering is an important character and a useful criterion for prediction of inbreds and hybrids performance for use in different agro-ecological zones. In the current study, unlikely hybrids tended to be taller than their parents (Table 1). However, previous studies revealed strong association between late flowering and tall plant type (Ali, 1996; Eldie, 2000). Mean plant height for the parents across the two environments varied from 97 cm (ICMA91222) to 189 cm (Baladi white) general mean being 146 cm, the mean for crosses varied from 133 cm (Ashana x ICMA91222) to 177 cm (Baladi white x ICMA96222).The shortest parents were ICMA91222, ICMV221, ICMA99111, Dembi yellow and ICMV155 and the tallest parents were SADC long, Baladi white and Topcross P1. Where, crop environments in sub-Saharan Africa are often characterized by strong winds, tall parents are not appropriate for breeding cultivars for drier areas with high wind velocity, because tall plants were subjected to lodging. However, in the current study most of the crosses were unlikely tended to be taller than their parents. These results are in line with the results obtained by Quendeba et al. (1993) who reported that most of the crosses had mean height slightly higher than the shorter parents, indicating unfavorable highheterotic responses. Pearl millet grain and stover yields are both economic products in remote areas of the arid tropics particularly Sudan, where millet is grown under dry areas, under such conditions the association of earliness with tall plant type is important. Parents having per se mean biomass yield significantly higher than the general mean were Ashana 7820 kg/ha, Omgarfa 7727 kg/ha , MCNELC 7602 kg/ha , Bayouda 7165 kg/ha and Sudan Î 7165 kg/ha. The highest mean biomass yield performance per se for parents and crosses were obtained at Elgedarif location. The mean biomass yield for crosses across the two locations ranged from 5430 kg/ha for Ashana x ICMA91222 to 9375 kg/ha for Baladi yellow x ICMA97333. Crosses having per se mean biomass yield significantly higher than the general mean were, Baladi
yellow x ICMA97333, Topcross P1 x ICMA99111, Baladi white x ICMA96222, ICMV155 x ICMA99111 and Ugandi x ICMA96222. The best yielding crosses involve at least one elite parent. Crosses combined short plant type , earliness, high biomass and grain yields were ICMV155 x ICMA99111, Baladi yellow x ICMA97333, and Topcross P1 x ICMA99111(Table 1). It is of interest to mention that five parents had high grain yield namely MENCLC, MCSRC, SADC long, Bayouda and Ugandi. Therefore, it might be possible to use these parents for grain as well as for biomass especially in vast areas of subtropics like Sudan. However, the former five parents showed high biomass yield coupled with medium plant height and relatively late in maturity. Best grain yielding crosses across the two locations were Dembi yellow x ICMA97333, SADC togo x ICMA96222, Baladi yellow x ICMA97333, ICMV155 x ICMA99111 and Bayouda x ICMA99111 giving high biomass yield, tending to be taller than their parents and with medium maturity, whereas none of the top-yielding parents involved in the former first ranking crosses. However, these crosses gave yields significantly higher than the highest yielding parent, while the combinations of the line ICMA91222 gave grain yields significantly lower than their high yielding parents across locations and in combined analysis. Current study showed considerable differences in maturity and plant height in the two locations which might refers to environmental differences. However, crosses behaved differently across locations, ICMV155 x ICMA99111 was ranked first at Elgedarif, whereas, SADC Togo x ICMA96222 was the best performing hybrid at Wad Medani. The results suggests that rapid improvement in the yielding ability of pearl millet landraces may be, therefore, achieved by topcrossing them on selected male sterile lines. Table1. Mean grain yield of the top five crosses and parents of pearl millet and their mean ranks for the other traits, grown at Wad Medani, Elgedarif and combined over the two locations, 2006. Grain
Biomass yield (kg/ha)
Plant height (cm)
Days to 50% flowering (d)
Wad Medani Crosses SADC togo x ICMA96222 MENCLC x ICMA99111MCSRC x ICMA97333 Topcross P1x ICMA96222
3234
9141 (6)1
180 (77)
55 (61)
3109 3031 3016
8828 (8) 6688 (58) 7969 (21)
155 (46) 147 (22) 163 (62)
50(23) 50 (21) 56 (70)
Baladi white x ICMA97333 Parents Ashana Topcross P1 SADC long Ugandi Omgarfa
3016
8750
10 173 (73)
56 (72)
2375 2188
7609 (31) 7627 (23)
171 (70) 177 (74)
53 (44) 56 (67)
2156 2087 2047
6031 (61) 6766 (55) 8000 (20)
153(33) 157(51) 165 (67)
57 (74) 53 (43) 53 (42)
Elgedarif Crosses ICMV155 x ICMA99111 Baladiyellow x ICMA97333 Dembi yellow x ICMA97333 SADC togo x ICMA97333 Topcross P1x ICMA99111 Parents MENCLC MCSRC Baladi white SADC long ICMV155
3734 3578 3406 3297 3250
9797 (3) 10156 (2) 8547(10) 9016 (7) 10828 (1)
161 (56) 163 (62) 166 (67) 169 (71) 60 (1)
64 (34) 63 (22) 66 (51) 65 (41) 151 (40)
3359 2969
9578 (4) 8641 (9)
145 (22) 153 (42)
63 (16) 76 (74)
2594 2563 2391
9531 (5) 6938 (36) 7078 (34)
187 (78) 175 (76) 152 (41)
84(78) 63 (15) 71 (66)
Table 1. (Continued). Combined Crosses Dembi yellow x ICMA97333 3086 8368 (7) 161(63) SADC togo x ICMA96222 3055 8274 (9) 165 (71) Baladiyellow x ICMA97333 3039 9375 (1) 159 (56) ICMV155 x ICMA99111 3039 8547 (4) 160 (58) Bayouda x ICMA96222 2813 7938 (15) 156 (46) Parents MENCLC 2563 7602 (27) 149 (27) MCSRC 2547 7016(41) 152 (36) SADC long 2360 6735 (52) 164 (69) Bayouda 2250 154 (40) 75 (79) Ugandi 2188 6779 (50) 157 (48) 1 Numbers between parentheses represent the rank among parents and crosses.
59 (46) 57(19) 58 (28) 56 (15) 58 (25) 58 (23) 65 (74) 60 (50) 7165(37) 63 (70)
Heterosis Mid parent heterosis for grain yield averaged over the two locations ranged from 20 to 127% in the favorable direction, while two crosses had undesirable negative heterosis over the mid parent (Table 2). Among hybrids 35 topcrosses showed highly positive heterosis percentage. Crosses manifested the highest positive heterosis were, Baladi yellow x ICMA97333, Dembi yellow x ICMA97333 and SADC togo x ICMA96222 (Table 2). Similar results were obtained by Yadav et al., (2000). The average values for heterosis for grain yield were higher in magnitude than that reported by Quendeba et al. (1993). In the combined analysis for biomass, mid parent heterosis varied from 50 to 101% in the desirable direction, while only one cross showed negative heterosis in the opposed direction. There were 14 hybrids showing positive significant heterosis % (Table 2). The more effective and rapid way to improve biomass yield in pearl millet is likely to be by exploiting heterosis hybrids (Hanna and Gupta, 1999). Similar to grain yield, positive and highly significant heterosis for panicle and stover yields was observed for the topcross hybrids, ranging between 30 to 90% and 26 to 112%, respectively (Table 2). The highest degree of heterosis was given by 15 hybrids for panicle yield (above 40%) and by 21 hybrids for stover yield (above 42%). Heterosis for forage was reported by Burton (1982). Regarding plant height heterosis was significant and positive at Wad Medani, where all crosses exhibited positive heterosis while, at Elgedarif negative heterosis was expressed by SADC long x ICMA99111, Baladi white x ICMA97333 and Bayouda x ICMA91222 (data not shown).
However, in the combined analysis most of crosses showed highly positive heterosis indicating that the hybrids were taller than their parents (Table 2). Therefore, relatively short genotypes are more acceptable in regions characterized with high wind velocity and heavy rainstorms that cause lodging and yield losses of taller plants. Table 2. Average heterosis (%) for the measured traits in pearl millet combined, for the two locations, season 2006. N o. 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 23 2 4
DF1
PH
SY
PY
SADC long x ICMA91222 SADC togo x ICMA91222 MCENLC x ICMA91222 MCSRC x ICMA91222 Topcross x ICMA91222 Sudan Π x ICMA91222 ICMV155 x ICMA91222 Bayouda x ICMA91222 Baladi white x ICMA91222 Baladi yellow x ICMA91222
1.28 -0.14 -2.33 -5.79* -4.26 -3.64 -2.95 -8.38** -7.43** -0.71
11.31 23.28** 12.83 12.46 19.56* 21.51* 25.26** 8.91 12.58 16.31
30.80* 25.48* 26.52* 35.06* 47.77** 32.47* 57.03** 23.88 47.08** 48.31**
12.47 50.50** 48.23 30.46* 61.65** 43.60** 45.76** 3.87 28.15 86.81**
Dembi yellow x ICMA91222
-4.75
21.33*
22.76
Omgarfa x ICMA91222
3.62
11.63
Ugandi x ICMA91222
-6.8**8
Crosses
Ashana x ICMA91222
-5.36*
BY
GY -6.33 65.15** 41.25** 40.30** 66.91** 78.46** 50.00** 12.42 44.95** 111.66**
37.20*
20.19 38.87 38.44 32.40 55.56* 38.56 50.49* 12.75 37.70 69.79* * 30.21
16.67
44.16
25.76
58.80**
15.93
26.88*
12.32
18.47
11.04
-0.63
-13.02
12.92
0.00
17.57
ICMV221 x ICMA91222
-5.04*
29.67**
77.19**
83.07**
SADC long xICMA96222
0.28
22.33*
48.57**
SADC togo xICMA96222
-6.27*
28.19**
MCENLC x ICMA96222
-0.70
MCSRC x ICMA96222
57.14**
87.55**
38.46*
80.62* * 43.01
42.86**
63.88**
54.23*
91.25**
26.63**
-0.27
13.56
7.38
-4.33
-6.27*
25.47**
5.88
13.90
10.50
3.86
Topcross x ICMA96222
-1.79
18.60*
4.96
30.22*
18.67
43.59**
Sudan Π x ICMA96222
13.20**
26.50**
24.44
38.35*
32.04
46.90**
ICMV155 x ICMA96222
-3.54
16.52
19.48
18.96
19.18
16.62
Bayouda x ICMA96222
-14.18**
18.68*
29.03*
33.95*
31.78
45.97**
Baladi white xICMA96222
-4.10
18.46*
26.52*
33.33*
30.28
44.26*
29.11*
Table 2. (Continued). No. 25
Crosses Baladi yellow x ICMA96222
DF1 -2.74
PH 17.51*
SY 58.33**
PY 68.54**
BY 64.23*
26
Dembi yellow x ICMA96222
20.46*
11.11
27.78
19.89
27 28 29 30
Omgarfa x ICMA96222 Ugandi x ICMA96222 Ashana x ICMA96222 ICMV221 x ICMA96222
14.71 18.74* 23.83** 30.45**
17.53 26.89* 8.72 46.43**
40.81* 59.23** 22.64 9.04
29.62 44.92 15.97 24.74
34.10** 35.45** 18.37 13.07
31 32 33 34
SADC long x ICMA97333 SADC togo x ICMA97333 MCENLC x ICMA97333 MCSRC x ICMA97333
15.32 25.59* 20.26 21.10*
47.12** 49.15** -8.41 26.73*
21.09 78.55** 1.22 24.46
32.28 65.26* -2.93 25.59
41.11** 90.88** 2.36 39.84**
35 36 37 38
Topcross x ICMA97333 Sudan Π x ICMA97333 ICMV155 x ICMA97333 Bayouda x ICMA97333
6.40 13.31 24.87** 11.14
12.69 21.76 16.67 16.51
24.41 35.23* -5.05 18.81
19.20 29.28 4.25 17.96
41.77* 51.32** 12.65 17.14
39
Baladi white x ICMA97333
5.32
0.77
19.04
10.06
40 41
Baladi yellow x ICMA97333 Dembi yellow x ICMA97333
23.15** 29.98**
112.7** 42.86**
90.91** 64.86**
101.3** 54.62*
127.7** 98.71**
42 43
Omgarfa x ICMA97333 Ugandi x ICMA97333
20.50* 18.84*
16.30 31.83*
26.21 25.32
21.58 28.39
35.69** 38.78**
44 45
Ashana x ICMA97333 ICMV221 x ICMA973332
3.66 27.79**
22.70 65.38**
37.69* 50.69**
30.64 57.42*
31.65** 37.54**
46
SADC long x ICMA99111
-4.84
31.69*
4.83
15.47
2.73
47
SADC togo x ICMA99111
3.81
72.54**
47.75**
58.75*
52.58**
48
MCENLC x ICMA99111
7.85
11.98
24.29
18.73
25.06*
49
MCSRC x ICMA99111
4.53
11.64
13.68
13.13
14.81
50
Topcross p1x ICMA99111
8.14
103.9**
43.37**
70.17**
66.46**
51
Sudan Π x ICMA99111
9.66
19.76
9.82
14.21
28.39*
52
ICMV155 x ICMA99111
16.65
89.17**
40.05*
59.94*
79.88**
53
Bayouda x ICMA99111
13.72
45.16**
36.87
40.41
50.56**
54
Baladi white x ICMA99111
7.22
8.95
18.78
14.14
16.32
55
Baladi yellow x ICMA99111
7.15
75.10**
37.24*
53.77*
50.92**
56
Dembi yellow x ICMA99111
14.24
33.76*
49.08**
41.99
67.09**
57
Omgarfa x ICMA99111
14.28
43.98**
19.31
30.88
24.92*
58
Ugandi x ICMA99111
13.49
62.00**
31.84*
44.73
30.09
59 60
Ashana x ICMA99111 ICMV221 x ICMA99111
7.11** -1.20 -1.64 1.68 13.16** -2.77 -5.43* 5.79* 6.79** -7.82** -1.13 -2.17 19.31** 8.81** -5.46* 6.57** -1.74 7.32** -1.95 10.15** 13.28** 13.04** 12.06** 12.41** 12.01** 7.11** 13.56** 18.98** 12.81** 16.71** 13.86** 11.75** 14.03** -7.09** -
-1.05 9.53
22.56 34.94*
25.67 5.38
23.96 17.55
10.19 20.12*
GY 64.90** 15.36
52.27**
SEÂą
16.18** 2.17
11.60
12.68
14.80
22.79
9.87
1
DF=days to 50% flowering, PH=plant height, SY=stover yield, PY=panicle yield, BY=biomass yield, GY=grain yield. *,** Siginficant at, 0.05 and 0.01 levels of probability, respectively.
However, crosses that showed highly negative heterosis across locations for days to 50% flowering were Bayouda x ICMA99111, Bayouda x ICMA96222 and Baladi yellow x ICMA99111. The current study generally showed that crosses with the highest heterotic values were not necessarily the best in performance for this trait. However, heterotic hybrids are generally early to flower as a result of rapid initial growth rate, especially in quantitatively photosensitive or photo insensitive crops where flowering starts after the completion of a critical vegetative phase (Banga, 1998). These data, although including too few test locations to draw definitive conclusions, it will be possible to make out crosses with Baladi yellow, Dembi yellow and SADC togo as pollinators on male sterile lines such as ICMA96222 and ICMA97333, with useful level of positive grain yield heterosis. The highest positive heterosis for grain yield at Wad Medani was expressed by Dembi yellow x ICMA96222, Baladi white x ICMA97333, SADC togo x ICMA96222, Dembi yellow x ICMA97333 and Dembi yellow x ICMA99111. At Elgedarif, Topcross P1 x ICMA91222, Sudan Î x ICMA91222, Baladi yellow x ICMA91222, SADC togo x ICMA97333 and ICMV155 x ICMA99111 showed the highest positive heterosis for grain yield. For combined analysis the following crosses manifested the highest positive heterosis, Baladi yellow x ICMA97333, Dembi yellow x ICMA97 333, SADC togo x ICMA96222, Baladi yellow x ICMA91222 and SADC togo x ICMA 97333. Results of the current study indicated that one cross which showed highly significant heterosis at Wad Medani maintained its superiority at Elgedarif (Dembi yellow x ICMA97333) for grain yield. In this study, many hybrids displayed conspicuous heterosis for grain yield. The direction and magnitude of heterosis varied from cross to cross. This indicates that the mechanism of expression of heterosis was different in the various crosses under different environments. Sharma and Shrikant (2006) explained that there was differential behavior of various hybrids in different environments for expression of heterosis. This indicates environmental specificity in the expression of hybrid vigor. The range of heterosis under individual environments as well as over all the two environments indicates wide variability. Pronounced desired heterosis was expressed in the two environments, but more so in Elgedarif environment (data not shown). There was a wide range of heterosis at Elgedarif environment, while high mean heterosis was recorded at Wad Medani. This indicates the
influence of environment on the expression of heterosis. Thus, using only the environmental mean will not be sufficient for proper selection of superior hybrids and the breeder has to consider location/season specific hybrids. The marked heterosis in different locations provides a better chance for selection of desirable location/season specific highly heterotic crosses for grain yield. However, this study was carried out over two environmental locations and it was remarkable that one (Dembi yellow x ICMA97333) out of sixty hybrids maintained its consistently superior performance under both environments. This hybrid can be exploited for possible use over wide areas.
ACKNOWLEDGEMENT The financial support of the German Academic Exchange Service (DAAD) is greatly appreciated.
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