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a IITA, c/o L.W. Lambourn & Co, Carolyn House, 26 Dingwall Road, Croydon CR9 3EE, UK
b CIMMYT-Nairobi, Addis Ababa, Ethiopia
c Maize and Wheat Improvement Programs, Institut des Sciences Agronomiques du Rwanda (ISAR), Ruhengeri, Rwanda
d SG 2000, C.P. 4247, Maputo, Mozambique
e CRI, Box 3785, Kumasi, Ghana
f CRI, Box 3785, Kumasi, Ghana
g CRI, Box 3785, Kumasi, Ghana
h SG 2000, Kumasi, Ghana
* Corresponding author (b.badu-apraku{at}cgiar.org)
‘Obatanpa GH’ (Reg. no. CV-1, PI 641711), a tropically adapted, intermediate maturing, open-pollinated maize (Zea mays L.) cultivar was developed by the Crops Research Institute (CRI), Kumasi, Ghana in collaboration with the International Institute of Tropical Agriculture (IITA), Ibadan; the International Maize and Wheat Improvement Center (CIMMYT), Mexico; and the Sasakawa Global 2000 (SG 2000). Obatanpa GH is a white dent and flint endosperm Quality Protein Maize (QPM) with elevated levels of lysine and tryptophan and was first released by CRI, Ghana in 1992 as Obatanpa to help improve the protein nutritional status and the health of a large population of low-income groups in sub-Saharan Africa who depend on maize as a major component of their dietary protein intake.
Maize has such a critical nutritional role to play because it is the most important staple food crop across sub-Saharan Africa. Traditionally, maize is consumed as a starchy base in a variety of forms such as gruels, porridge, and pastes. It is also widely fed as porridge to weaning children (2 to 3 mo, until the children are completely weaned at the age of 15 to 24 mo) and preschool children (3 to 5 yr) without protein supplements. The normal maize has a major nutritional constraint as human food because even though it has about 10% protein, the protein is deficient in two essential amino acids, lysine and tryptophan. The result is that, infants fed on normal maize without any balanced protein supplements suffer from malnutrition and develop diseases such as kwashiorkor, a fatal syndrome characterized by initial growth failure, irritability, skin lesions, edema, and fatty liver. The high lysine content of QPM improves the absorption of Zn and Fe in the human digestive system and may thus contribute to improved micronutrient status.
Obatanpa GH has been widely adopted by farmers and consumers in Ghana. Presently, it covers more than 50% of the maize hectarage (650 000 ha) in Ghana (Dankyi et al., 2005). It has also been released formally or informally in several other African countries including Bénin (as Faaba), Togo, Mali (as Debunyuman), Guinea, Burkina Faso, Côte d'Ivoire, Senegal, Cameroon, Nigeria (as SAMMAZ 14), Mozambique (Susuma), Uganda, Ethiopia, Zimbabwe, Swaziland, Malawi, and South Africa (Badu-Apraku et al., 2004). The cultivar is also serving as a source of inbred lines for the development of QPM hybrids and synthetic varieties in several maize breeding programs in Africa. Obatanpa GH has good levels of resistance to the Maize streak virus (MSV), lowland rust (incited by Puccinia polysora Underw.), and moderate levels of resistance to blight [caused by Bipolaris maydis (Nisikado & Miyake) Shoemaker].
Obatanpa GH was derived from Population 63 SR, a white dent QPM, adapted to the lowland tropics. Population 63 SR is a composite of intermediate maturing tropical maize germplasm originally developed by CIMMYT, Mexico. IITA incorporated resistance to MSV into the population. Following multilocation testing of Pop 63 SR in Ghana between 1987 and 1989, the population was identified as a promising source for new QPM varieties. At that time the major defect of the population as a source of QPM was the low level of streak resistance, poor husk cover, the presence of high percentage of kernels with soft chalky endosperm, and low grain yield potential. While a visiting scientist in IITA-Ibadan in 1989, the senior author initiated a breeding program to extract a streak resistant, high yielding QPM variety with improved husk cover, appropriate hard endosperm modification as well as elevated levels of lysine and tryptophan.
A bulk of Pop 63 SR was planted at IITA, Ibadan (7°38' N, 3°93' E), Nigeria and S0 plants were infested with viruliferous leaf hoppers (Cicadulina spp.) about 9 d after planting. Two weeks after streak infestation, the streak susceptible plants were rogued out and the streak resistant S0 plants were selfed. At harvest, about 500 ears from agronomically desirable S1 plants with good husk cover were selected and screened under a light box for kernels with the desirable endosperm modification. Kernels with good endosperm modification selected from 250 ears were planted ear-to-row in a recombination block in the field at Ibadan. The S1 plants were advanced to the second cycle of recombination under artificial infestation with viruliferous leaf hoppers. This was followed by screening of the selected ears for desirable kernel modification under the light box. The selected kernels of each ear were planted ear-to-row and advanced to the S1 stage by selfing under artificial MSV infection. At harvest, about 250 S1 ears selected from plants with good husk cover and other desirable agronomic traits were planted ear-to-row in a recombination block at Fumesua (1°36' W, 6°45' N) in Ghana. In addition, about 30 kernels from each S1 ear were sent to CIMMYT, Mexico for tryptophan and lysine analyses.
Based on the results from laboratory analyses, 80 S1 lines with high levels of the two essential amino acids were advanced to two cycles of recombination with selection for improved husk cover, grain yield, and desirable kernel characteristics. The resulting variety was designated Obatanpa which in Ghanaian language means "good nursing mother." Results of multilocation field tests showed that Obatanpa was superior or comparable in grain yield and other agronomic characters to the top improved intermediate and late maturing normal endosperm maize varieties in Ghana (Twumasi-Afriyie et al., 1997; Sallah et al., 1997). Furthermore, results of feeding trials with piglets and chicken showed that Obatanpa had higher nutritional value and could be used as a replacement for normal endosperm maize in animal feeds with economic advantage (Okai et al., 1994; Osei et al., 1994). Because of its superior performance and the elevated levels of lysine and tryptophan, Obatanpa was released for production by farmers in Ghana in 1992.
As an open-pollinated cultivar, it has been necessary to upgrade the genetic purity of Obatanpa periodically since its release in 1992. For instance, in 2001 the lysine and tryptophan levels of the grains of Obatanpa were found to be low and some plants were observed to be susceptible to the MSV. In an effort to upgrade the lysine and tryptophan content of the variety, 277 half-sib families selected from Obatanpa were analyzed for the two essential amino acids in the QPM laboratory at CIMMYT, Mexico. Based on the results of the laboratory analysis, 40 families with high levels of lysine and tryptophan were selected and recombined to reconstitute the variety during the off-season of 2001 in Ghana. Furthermore, a program was initiated during the major season of 2002 to upgrade the level of streak resistance of the reconstituted variety. More than 500 families selected from the reconstituted Obatanpa were planted under artificial infestation with viruliferous leaf hoppers at Ferkessedougou (9°3' N, 5°10' W), Côte d'Ivoire. The streak susceptible plants were rogued out at 3 wk after planting. At flowering, the streak resistant plants with agronomically desirable characteristics were selfed. At harvest, the selected S1 ears were recombined under artificial streak infestation in Ibadan during the off-season of 2003 to reconstitute the new version of Obatanpa, Obatanpa GH being proposed for registration.
Evaluation trials involving five QPM hybrids, six open-pollinated QPM varieties including the new and old versions of Obatanpa, and three normal endosperm varieties were conducted at seven locations in the forest and forest–savanna ecologies of Ghana during the major and minor planting seasons of 2004 (Table 1). The results showed that Obatanpa GH was the highest yielding open-pollinated variety with a grain yield of 4.96 Mg ha–1 compared to 3.56 Mg ha–1 for the normal endosperm local check. Obatanpa GH silked at 55 d after planting with a plant height of 205 cm. In 19 on-farm trials conducted in the northern Guinea savanna zone of the Republic of Benin in 2004, Obatanpa GH had an average grain yield of 3.67 Mg ha–1, which was comparable to that of the popular Striga and drought tolerant normal endosperm variety, EV 97 IWDT STR (3.37 Mg ha–1). However, Obatanpa GH out-yielded the released normal endosperm local check (2.66 Mg ha–1). Results of laboratory analyses of Obatanpa GH for total protein and tryptophan at IITA in 2005 showed that it contains 10.0% total protein in the grain with 0.88% tryptophan in the protein. In contrast, the normal endosperm check had 9.6% total protein with 0.49% tryptophan in the protein of the grain.
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ACKNOWLEDGMENTS
The authors are grateful to the Canadian International Development Agency, SG 2000, the United States International Development Agency, and the Nippon Foundation for financial support, and CRI, IITA, and CIMMYT for technical support. Appreciation is also expressed to the scientists of the national programs of West and Central Africa who have been involved in the testing and release of Obatanpa in the various countries, especially Ghana and Bénin, and the staff of IITA for technical assistance.
NOTES
Received for publication November 1, 2005.
REFERENCES
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