1. EVALUATION OF HIGH BETA CAROTENE CASSAVA (Manihot esculenta crantz) VARIETIES IN SOUTH EASTERN NIGERIA
Ogbuekiri, H., C.N. Egesi, B. Olasanmi, W. Nwakor, A.S. Nwaogu, I. Chimaobi and E. Okogbenin
National Root Crops Research Institute (NRCRI), Umudike, PMB 7006, Umuahia, Nigeria.
ABSTRACT
Vitamin A deficiency is more common in developing countries where impoverished populations lack adequate resources to diversify diets and purchase foodstuffs or supplements. A typical adult-sized cassava meal (500g) can provide adequate calories but is an insufficient source of iron, zinc, vitamin A and protein. To improve the vitamin A content of cassava meals eaten by the populace, 18 high beta-carotene cassava varieties and 2 check varieties (TMS and TME 419) were evaluated for agronomic parameters, resistance to major pests and diseases of cassava, dry matter and total carotene contents at Umudike in two seasons. Collected data were subjected to analysis of variance (ANOVA) and Genotype plus Genotype x Environment (GGE) biplot analysis. There were significant differences among the genotypes for fresh root yield and harvest index over the two seasons. Genotype 05/1570 had fresh and dry root yields of 47.1 t/ha and 21.5 t/ha respectively. Genotype 05/1601 had the highest total carotene content of 6.8 μg/g. The check varieties had approximate carotene contents of 1.0 μg/g on fresh weight basis. The GGE biplot analysis showed a significant correlation between total carotene contents and colour chart scores among the genotypes. Breeders can therefore select for carotene content in cassava as well as high agronomic performance in order to enhance adoptability of new pro-vitamin A cassava varieties by farmers.
Keywords: total carotene, dry matter, fresh root yield, harvest index, colour chart,
Table 2: Combined Analysis of Variance (ANOVA) for fresh root yield of 18 high beta carotene cassava genotypes and two checks evaluated in two seasons at Umudike, Nigeria
Source DF
Sum of Squares
Mean Square
F. Value
Pr>F
Genotype 20
266.29
0.86
0.6340
Rep 2
730.47
2.35
0.1090
Seas 1
16.11
0.0003
Rep*Genotype 38
436.17
1.41
0.1511
Seas*Genotype 19
441.99
1.42
0.1745
Seas*rep
522.97
261.48
0.84
0.4385
Error 37
310.19 R2
0.76
CV (%)
57.21
Table 3: Combined Analysis of Variance (ANOVA) for harvest index of 18 high beta carotene cassava genotypes and two checks evaluated in two seasons at Umudike, Nigeria
Source DF Sum of Squares Mean Square F Value Pr>F
Genotype
Rep
Seas
Rep*Genotype
Seas*Genotype
Seas*rep
Error R
CV (%)
INTRODUCTION
Cassava (Manihot esculenta Crantz) is a major food crop in the tropics (Cock,1985 ), the third largest calories source for human and animals after rice and maize in the tropical and sub-tropical regions (Huang et al.,2001). The crop ranks as the second most important source of calories after maize in sub-Saharan Africa (Nweke et al., 2001). It is the staple food of the poorer people in many tropical countries and one of the most useful plants around the equator with a crop area of about 14 million hectares (Lothar et al., 1991). Although cassava is highly regarded in many developing countries as a food security crop, it has a number of major liabilities. Most of the cassava varieties grown and consumed in Africa are nutritionally poor and diets that solely depend on them put such populations at high risks of nutritional deficiencies (Gegios et al., 2010). A typical adult-sized meal (500g) can provide adequate calories but is an insufficient source of iron, zinc, vitamin A, and protein (Chaves et al., 2000). Vitamin A deficiency is more common in developing countries where impoverished populations lack adequate resources to diversify diets and purchase foodstuffs or supplements. The objective of this study was therefore to evaluate some cassava genotypes for agronomic parameters and carotene content at harvest in order to identify genotypes with high carotene content and good agronomic attributes to improve the nutritional quality of cassava grown by farmers in Nigeria.
MATERIALS AND METHODS
A set of 18 high carotene cassava genotypes and two check varieties (TMS and TME 419) were evaluated at Umudike in two seasons (2009/10 and 2010/11) for resistance to major pests and diseases of cassava, agronomic parameters, carotene and dry matter content. The experimental design used in each season was randomized complete block design (RBCD) with three replicates. Twenty stem cuttings of each genotype were planted in a 4 x 5 m plot at a spacing of 1m along ridges made 1m apart. NPK fertilizer was applied 6 weeks after planting at the recommended rate of 600kg/ha and weeding was carried out at regular intervals. The genotypes were assessed for response to major pests and diseases of cassava at 1, 3, 6, and 9 months after planting (MAP) and shortly before harvesting. Shortly before harvesting at 12 MAP, 2 mature roots were sampled in each plot from 2 replicates to determine the total carotene (TC) and dry matter (dm) contents of the genotypes. At harvesting, the inner 6 plants were harvested to assess the genotypes for fresh shoot weight, fresh root yield (FRY) and number of roots per plot. The dry root yield (DRY) was estimated from the FRY and dm of each genotype.
Figure 1: Genotype x trait (GT) biplot of 18 high beta-carotene cassava genotypes and 2 checks grown at Umudike, Nigeria in two seasons for total carotene content (TC), fresh root yield (FRY), dry root yield (DRY), harvest index (HI), dry matter content (DM) and Colour Chart scores (COLOUR).
RESULTS AND DISCUSSION
The evaluated cassava genotypes were highly or moderately resistant to major pests and diseases of cassava (data not shown). The FRY ranged between 14.4 and 47.1 t/ha while the DRY ranged between 5.1 and 21.5 t/ha over the two seasons (Table 1). Genotype TMS 05/1570 had an average dm content of 45.7% and high fresh root yield of 47.1 t/ha, hence the highest DRY of 21.5 t/ha. There is need to evaluate this genotype further for root yield at different locations to ascertain its stability. Genotype TMS 05/1601 had the highest TC content of 6.8µg/g among the genotypes evaluated in this trial which is lower than the carotene content of each of the 3 newly released high beta-carotene cassava varieties in Nigeria (Egesi et al, 2011). It is noteworthy that among all the variables, only seasonal variation had significant effect on the FRY and harvest index (HI) of the cassava genotypes evaluated (Tables 2 and 3). This therefore corroborates further the need for multi-environment evaluation of new genotypes in breeding programmes (Edwards and McCouch, 2007; Baiyeri et al., 2008). Genotypes TMS 05/1601 showed more stability for total carotene (TC) content over the two seasons (Fig. 1). There was significant correlation between TC content and color chart scores (Color) among the genotypes as shown by the angle between the vertices of the two variables (Fig. 1).
CONCLUSION AND PERSPECTIVES
Each of the 3 newly released high carotene cassava varieties in Nigeria has higher TC content than the genotype with highest carotene content among the genotypes evaluated in this study. It is good to promote genotypes with better performance than the existing varieties in a breeding programme, hence, there is no need for further evaluation of these genotypes with the objective of improving cassava for carotene content. However, some of the genotypes can be used in breeding programmes for high root yield and high dm content. The significant correlation observed between TC and Colour chart score in this study suggests that breeders can select for high carotene content in cassava using the color chart score most especially at early stages of a breeding programme when many genotypes are evaluated. This will enable the breeder to easily handle many genotype always involved at early stage of a breeding programme at a reduced cost.
ACKNOWLEDGEMENT
This study was conducted with funding support from Harvest Plus and National Root Crops Research Institute (NRCRI), Umudike, Nigeria. The fund for attending this conference was provided by Bill and Melinda Gates Foundation through the organizers of GCP21.
Table 1: Carotene content and other attributes of high beta carotene cassava varieties (TMS 05 series) at Umudike in two seasons
Genotype
FRY (t/ha)
%DM
DRY (t/ha) HI
Colour
TC (µg/g)
TMS 05/1601
18.7
30.8
5.7
0.38
5.3
6.8
TMS 05/0741
25.0
44.6
11.4
0.42
4.5
6.4
TMS 05/0311
40.1
33.8
13.4
0.52
4.3
5.5
TMS 05/1570
47.1
45.7
21.5
0.65
2.3
TMS 05/0099
19.4
27.4
5.1
0.40
4.0
4.9
TMS 05/0303
24.4
45.6
11.1
TMS 05/0127
44.4
34.7
15.0
0.56
3.8
4.1
TMS 05/0998
37.7
39.4
15.1
0.51
2.5
3.7
TMS 05/0128
21.0
8.0
0.50
3.0
3.6
TMS 05/1740
36.4
32.5
11.6
TMS 05/1553
30.3
46.2
15.4
0.44
3.5
TMS 05/0125
23.8
33.4
3.4
TMS 05/0231
39.2
33.5
13.1
3.3
TMS 05/1814
21.1
38.8
8.2
0.39
2.0
2.9
TMS 05/0327
7.9
0.45
TMS 05/0024
19.6
36.2
0.36
2.8
TMS 05/1274
14.4
44.5
6.3
TMS 05/0286
32.9
29.6
9.8
0.59
TMS 30572
31.1
0.46
1.8
TME 419
33.9
48.1
17.1
0.57
1.3
1.2
Average
29.4
36.9
10.8
0.49
3.1
Maximum
Minimum
CV (%)
33.7
18.9
41.2
18.2
32.1
39.1
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