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Soil constraints for sustainable upland crop production in humid and subhumid West Africa
(1991)Major upland soils in the humid and sub humid zones of West Africa consist of low activity clays (LAC) Alfisols, Ultisols and Oxisols. Alfisols which are less leached and have a high base saturation are more dominant in the sub-humid zone. Chemically they are more fertile, but they have a low structural stability. The Ultisols/Oxisols which are more prevalent in the humid zone, are less fertile, with major nutrient and acidity constraints. The major constraints on sustainable crop production on ... -
Preliminary results at IITA in breeding plantain for black sigatoka resistance in Africa
(1991)Africa accounts for 50 of all plantain produced in the world. These plantains are overwhelmingly import as a food crop for local consumption. Black sigatoka has now invaded Africa, thereby endangering this important food source. The long term solution lies in the creation of black sigatoka resistant plantains. The available Musa germplasm at IITA was screened for female fertility with AA black sigatoka resistant diploids. Sixteen `French' plantains and seven `False Horn' plantains produced seed. ... -
Representativeness of farmers and sites in onfarm trials
(1991)In the farming systems approach to technology development, trials are carried out on a limited number of farmers’ fields. Results of these trials are extrapolated to the entire target area and used either to identify directions for further research or to develop recommendations for farmers. Extrapolation is obviously not valid if farmers and fields are not representatives of the target area. In practice however, it is difficult to select a sample of farmers according to predetermined criteria. ... -
Framework for orientation of Striga research at IITA
(1991)Striga research at IITA is conducted by multidisciplinary team. To coordinate and focus the activities of the team, two models have been developed that attempt to provide a framework for research. One model addresses the agro biological aspects of Striga seed population dynamics. This model shows the combination of, and the necessary impact of, each of various technological inputs to stop or decrease Striga seed population growth. The second model has been adapted to assess the likelihood of ... -
Aerial release of acarine biological control agents on carrier materials
(1991)Laboratory and field experiments were performed to test several materials on their suitability as carrier for the aerial release of phyroseiid mites. Relatively few mites adhered to the materials. Nevertheless, mites were rettieved in cassava fields after a mass release, using oat flakes as carrier material. This method can be suitable when large areas are to be supplied with low mite densities. -
Host plant resistance of cassava green spider mite (CGM) (Mononychellus tanajoa Bondar) at IITA
(1991)Major upland soils in the humid and sub humid zones of West Africa consist of low activity clays (LAC) Alfisols, Ultisols and Oxisols. Alfisols which are less leached and have a high base saturation are more dominant in the sub-humid zone. Chemically they are more fertile, but they have a low structural stability. The Ultisols/Oxisols which are more prevalent in the humid zone, are less fertile, with major nutrient and acidity constraints. The major constraints on sustainable crop production on ... -
Breeding for resistance to Striga and Alectra in cowpea
(1991)An outline is given of the progress made in a systematic breeding programme set up in Nigeria to develop improved cowpea cultivars with combined resistance to Striga gesnerioides and Alectra vogelii along with multiple disease and insect resistance. Several sources of resistance to both parasitic weeds have been identified. Of these, B301, a land race from Botswana has shown complete resistance to S. gesnerioides and A. vogelii. This was crossed with a susceptible cultivar, IT84S-2246-4, which is ... -
Progress in breeding maize for Striga tolerance/resistance at IITA
(1991)IITA has been breeding maize for Striga tolerance/resistance (STR) since 1982. Populations of Striga hermonthica from Nigeria have been used to challenge maize germplasm. Initially (1982-1984), field screening was done under natural infestation, but variability both within sites and across years was high. Since 1985, fields have been infested artificially. Artificial infestations have been improved with experience, and variability has now declined to an acceptable level. The most important ... -
Root crops for food security in subSaharan Africa
(1994)Food production in sub-Saharan Africa has not kept up with population growth and the increasing pressure of population on the land has decreased the resource base and caused the farming environment to become vulnerable to unpredictable climatic changes. Thus, there will be more acute food deficits in the future unless the productivity of food crops, including root crops, is increased by at least 3% per annum. Root crops are capable of efficient production of low cost calories under marginal soil ... -
Screening cassava cultivars for resistance to the cassava anthracnose disease (CAD)
(1994)Forty-seven cultivars of cassava in IITA's trials were screened for their reaction to infection by Colletotrichum gloesporiodes f. sp. manihotis in the field. The following parameters were observed: (a) distance of first canker from the soil, (b) total number of cankers per plant, (c) size of cankers on young stem and shoot, (d) size of canker on material stem, and (e) size of cankers mature stems. Cultivars Isunikankiyan, 81/00110, 82/00142, and 84751 had cankers developing at the lowest level ... -
Productivity of cassava intercrop as influenced by cassava variety and time of introducingrice into cassava
(1994)The study was carried out to determine the most appropriate time of introducing rice into cassava with the aim of improving the total productivity of the intercrop. The rice variety Rok 16 was introduced into cassava at four different times—planted at the same time with cassava, and then at 2, 4, and 6 wk after cassava. The cassava varieties used were 80/40, an improved clone, and the local Cocoa. Both variety and time of introducing rice into cassava affected tuberous root yield of cassava. Variety ... -
Cyanide and cassava breeding
(1994)Cassava (Manihot esculenta Crantz) contains cyanogenic glucosides which lead to the release of hydrogen cyanide (HCN) after hydrolysis. A study carried out using six cassava populations revealed that the broad-sense heritability for HCN was relatively low at 34.58 and 32.18 percent in roots and leaves respectively. Relationships between HCN in roots and leaves and twenty other cassava characters were examined. None of the characters was found significantly related to cyanide content in either leaf ... -
Can biological control resolve the larger grai borer crisis?
(1994)The accidental introduction of the lager grain borer, Prostephanus truncates, in the early 1980s result in destructive pest outbreaks in small-farm maize stores in both East and West Africa. Studies comparing the situation in rural maize stores in Costa Rica (in the pest's neotropical area of origin) with that control of natural enemies in Central America and that classical biological control of the pest in Africa might be feasible. The search for appropriate natural enemies is reviewed, with ... -
The cassava biotechnology network and African agriculture research and development programmes
(1994)In modern biological research, cassava has been an orphan crop, because most advances have taken place in developed countries where cassava is not grown. In order for cassava to profit from biotechnology, efforts around the world must be pooled, integrating developing countries into the process. The Cassava Biotechnology Network fosters developments which are environmentally acceptable and promote the well being of small-scale farmers within sustainable cassava production systems. The network will ... -
Interspecific hybridization in the genus Manihot progress and prospects
(1994)Most cassava (Manihot esculenta Crantz) improvement programs depend on the range of variability available within the cultigen for breeding varieties adapted to target environments. Efforts by some programs to introduce additional variability from wild Manihot species into cassava have led to improved diseases and pest resistance as well as higher ploidy levels. They have also provided insights into the evolution of the genus. Much remains to be investigated. This paper reviews the progress from ... -
Genotype environment interaction studies with cassava
(1994)Multilocational trials were conducted in several agroecological zones in West Africa to assess the magnitude of genotype x environment (G x E) interaction and to identify stable varieties which could be used in breeding programs in the region. The reaction of the varieties to major cassava diseases and pests was also assessed. Ten clones, including 7 IITA improved cassava clones, were used in the study. Results from 22 trials conducted in a randomized complete block design revealed a highly ... -
Production and distribution of virusfree yam (Dioscorea rotundata Poir.)
(1994)The international distribution of vegetative plant parts is restricted by the risks of introducing diseases and pests to non-infected areas. Methods used at IITA to produce and distribute virus-free yams to requesting national programs and collaborators are described. The selected yam clones are cleaned from virus disease infection through thermotherapy and meristem culture. The regenerated plants are virus indexed. The negatively indexed plants are then multiplied in vitro for international ...
