Alpha Y. Kamara

The influence of drought stress on growth, yield and yield components of selected maize genotypes

The risk of drought is high in the Sudan savannah zone of West and Central Africa because rainfall in this area is unpredictable in quantity and distribution. Thus, improved maize genotypes tolerant to drought could stabilize maize grain yield in this zone, where recurrent drought threatens grain production. Six maize genotypes, two each of hybrids, open-pollinated varieties (OPVs) and landraces, were evaluated for tolerance to terminal water deficit before flowering. Water deficit significantly reduced growth, grain yield and yield components of the maize genotypes. Significant differences were observed among genotypes for all the traits measured. One hybrid, 9011-30, and two improved OPVs, STR-EV-IWD and IYFD-C0, that showed tolerance to water stress recorded higher grain yield, and accumulated and partitioned more assimilates to the grain than the drought-susceptible genotypes. Also the drought-tolerant genotypes, 9011-30, STR-EV-IWD and IYFD-C0 had more ears/plant and greater numbers of kernels/ear. These genotypes could serve as sources of drought tolerance for the development and improvement of new drought-tolerant maize genotypes.

Agronomic performance of maize cultivars representing three decades of breeding in the Guinea Savannas of West and Central Africa

Maize improvement at the International Institute of Tropical Agriculture (IITA), which began in the 1970s, built on the germplasm and experience of earlier years. The main breeding emphasis was to develop maize cultivars and hybrids with high yield potential and durable resistance to diseases and pests with specific adaptation to the different agro-ecological zones of West and Central Africa. Over the years, open-pollinated cultivars have been developed with different levels of resistance to biotic and abiotic stresses. Identification of the factors that contributed to improvements in the maize cultivars developed during the past decades may be useful to sustain the genetic gain from selection in the future. A study was conducted to quantify genetic gains in yield and associated traits of open pollinated maize cultivars released from 1970 to 1999 in the West African savannas. The genetic gain in grain yield was 0.41 % per year and seems to be associated with increases in total biomass and kernel weight, and reductions in plant height and days to flowering (anthesis and silking). There was no significant change in harvest index of the cultivars.

Field performance of improved cowpea varieties under conditions of natural infestation by the parasitic weed Striga gesnerioides

Cowpea is an important food crop in the dry savannas of West and Central Africa because of its high protein content. Yields are, however, considerably reduced by the parasitic angiosperm Striga gesnerioides. Field trials over 2 years in two localities in northeast Nigeria evaluated the performance of diverse cowpea varieties under conditions of natural infestation by Striga. Grain yield was higher in Tilla than in Damboa where the higher Striga infestation may be caused by the lower rainfall and the sandy nature of the soils. Two varieties (IT97K-499-35 and IT90K-82-2) were confirmed to be resistant to Striga. Yield gain from IT97K-499-35 over the local variety ranged from 30% in Tilla in the northern Guinea savanna to 126% in Damboa in the Sudan savanna. The local variety Borno Brown and two improved varieties were found to be as susceptible to Striga as the susceptible control, TVX-3236, and therefore may not be recommended for cultivation in areas where Striga infestation is a problem. One variety, reported previously to be resistant to one or two races of Striga supported moderate levels of emerged Striga, suggesting that it is not totally resistant to the Striga race in the two localities. However, it produced grain yields that were comparable to the resistant varieties in the locality that was most infested, suggesting that it is tolerant to Striga. There are concerns about the adoption potential of the Striga-resistant variety IT97K-499-35 because of its medium-sized white seeds. Farmers in this zone prefer large-seeded brown cowpea. We recommend that efforts be made to develop Striga-resistant varieties that satisfy end-user preferences.

A PARTICIPATORY APPROACH TO INCREASING PRODUCTIVITY OF MAIZE THROUGH STRIGA HERMONTHICA CONTROL IN NORTHEAST NIGERIA

SUMMARY Striga hermonthica is a parasitic weed that attacks maize, sorghum and other staple cereal crops and has long been considered one of the greatest biotic constraints to cereal production in Africa. Use of resistant or tolerant maize varieties, a maize–legume rotation using trap crops that stimulate suicidal germination of Striga and the application of nitrogen fertilizer are all effective in reducing infestation and damage. This paper reports on the use of a participatory research and extension approach in assessing the performance and scaling-up of integrated Striga control packages in three agro-ecological zones in Borno State, Nigeria. The participatory process which encourages close interaction between research, extension and farmers, involved 30 local communities and 228 farmers representing 193 farmer groups in identifying their own problems and seeking solutions to them. Results showed not only effective Striga control but productivity increases of over 200%. The involvement of local farmers and groups in the evaluation process, firstly, helped to confirm that Striga control can best be achieved using soyabean followed by Striga-resistant maize together with productivity-increasing management practices and, secondly, promoted farmer-to-farmer extension. A participatory adoption assessment exercise indicated widespread adoption of new varieties and management practices, despite the need for increased labour. Great potential exists to scale out the results to similar areas of Guinea and Sudan savannas in the West Africa region.

Response of Corn Genotypes to Weed Interference and Nitrogen in Nigeria

Abstract The effects of nitrogen (N) rate and weed interference on the grain yield of four corn genotypes were investigated in 2002 and 2003 at Ikenne (7°38′N, 3°42′E), Shika (11°11′N, 7°38′E), and Samaru (10°24′N, 7°42′E) in Nigeria. Nitrogen (N) at 0, 30, 60, and 90 kg N ha−1 were the main plot treatments. Weed-free (weeded weekly), low (intrarow weeds only), and high (zero weeding) weed pressure were the subplot treatments. Four corn genotypes (ACR8328 BN C7, Low-N-Pool C2, Oba Super II, TZB-SR) were the sub-subplot treatments. Weed density was higher at Shika and Samaru than at Ikenne, and the order of average weed biomass 8 to 10 weeks after planting was Samaru (271 g m−2) > Ikenne (236 g m−2) > Shika (161 g m−2). Corn genotype and N rate had no effect on weed biomass except at Samaru where fertilized treatments had higher weed biomass than the unfertilized treatments. Corn leaf area (LA) increased with increasing N rate at all locations regardless of weed pressure and genotype, except at Shika where ACR8328 BN C7, Oba Super II, and TZB-SR did not show any clear N response; LA was highest in the weed-free and lowest in the unfertilized treatments for all genotypes and locations, and weed pressure treatments. Low-N-Pool C2 had the highest LA, which was 1.3 times larger than in Oba Super II, which had the lowest LA. Nitrogen rate, weed pressure, and genotypes significantly affected corn leaf chlorophyll content. Chlorophyll content was higher in the fertilized treatments than the unfertilized treatments, and higher in the weed-free treatments than the low or high weed pressure treatments. ACR8328 BN C7 and Oba Super II had significantly more chlorophyll than the other genotypes. Low-N-Pool C2 showed a linear grain yield response with the increase in N rates. ACR8328 BN C7 did not respond to N application. Compared with the results in the weed-free treatment, high weed pressure reduced grain yield in all genotypes by more than 65% at Samaru, 50% at Shika, and 35% at Ikenne.

Using CERES-Maize and ENSO as Decision Support Tools to Evaluate Climate-Sensitive Farm Management Practices for Maize Production in the Northern Regions of Ghana

Maize (Zea mays) has traditionally been a major cereal staple in southern Ghana. Through breeding and other crop improvement efforts, the zone of cultivation of maize has now extended to the northern regions of Ghana which, hitherto, were the home to sorghum and millet as the major cereals. Maize yield in the northern Ghana is hampered by three major biophysical constraints, namely, poor soil fertility, low soil water storage capacity and climate variability. In this study we used the DSSAT crop model to assess integrated water and soil management strategies that combined the pre-season El-Niño-Southern Oscillation (ENSO)-based weather forecasting in selecting optimal planting time, at four locations in the northern regions of Ghana. It could be shown that the optimum planting date for a given year was predictable based on February-to-April (FMA) Sea Surface Temperature (SST) anomaly for the locations with R2 ranging from 0.52 to 0.71. For three out of four locations, the ENSO-predicted optimum planting dates resulted in significantly higher maize yields than the conventional farmer selected planting dates. In Wa for instance, early optimum planting dates were associated with La Nina and El Niño (Julian Days 130-150; early May to late May) whereas late planting (mid June to early July) was associated with the Neutral ENSO phase. It was also observed that the addition of manure and fertilizer improved soil water and nitrogen use efficiency, respectively, and minimized yield variability, especially when combined with weather forecast. The use of ENSO-based targeted planting date choice together with modest fertilizer and manure application has the potential to improve maize yields and also ensure sustainable maize production in parts of northern Ghana.

Integrating planting date with insecticide spraying regimes to manage insect pests of cowpea in north-eastern Nigeria.

We sought to establish the most effective combination of planting dates with insecticide spraying regimes for the management of insect pests of cowpea in the savannas of northeast Nigeria. The results after 3 sprays, made once each at the bud initiation, flowering, and podding stages, did not differ significantly from those after 2 sprays, made once each at flowering and podding, in terms of reducing insect pest population and increasing grain yield. Despite the reduction in insect infestation, delaying planting beyond mid-August reduced cowpea grain yield by 12.3%, on average. The yield of the medium-maturing variety IT89KD-391 was significantly higher when planted in mid-August and sprayed twice than when planted on the earlier or later dates. The yield of the indeterminate late-maturing variety ITKD89-288 was higher when planted in early August and sprayed thrice. Early- and medium-maturing cowpea varieties should therefore be planted in mid-August and sprayed twice. Late-maturing indeterminate varieties should be planted in early August and sprayed thrice.

Influence of phosphorus application on growth and yield of soybean genotypes in the tropical savannas of northeast Nigeria

Abstract The cultivation of soybean is increasing in the savannas of Nigeria due to its widespread use in the food and feed industry. Production is, however, constrained by low soil phosphorus (P) levels in northeast Nigeria. This study evaluated four soybean varieties for their response to three rates of P in two agro-ecozones in 2004 and 2005. Experimental design was a split-plot arrangement of treatments with three replications. The main plots were assigned the P treatments and subplots were soybean cultivars randomised within the main plots. The studies found that soybean responds to P application but differences between 20 and 40 kg P/ha were not significant, despite low test P levels. This may be due to limitations in other nutrients. More studies are needed to determine the synergistic effect of P and other nutrients on soybean growth and yield. Soybean growth and seed yield were lower in 2004 than in 2005 because trials were established comparatively late in 2004 and crops were therefore affected by late season moisture stress. There is, therefore, a need to establish the appropriate time for planting soybean in these zones. Late maturing varieties produced higher yields than early maturing varieties in 2005 probably due to early planting which allowed full use of the growing season.

Assessment of nitrogen uptake and utilization in drought tolerant and Striga resistant tropical maize varieties

Maize (Zea mays L.) is an important food crop in the Guinea savannas of Nigeria. Despite its high production potential, drought, Striga hermonthica parasitsim, and poor soil fertility particularly nitrogen deficiency limit maize production in the savannas. Breeders at IITA have developed drought- and Striga-tolerant cultivars for testing, dissemination, and deployment in the region. Information on the response of these cultivars to N fertilization is, however, not available. This study evaluated grain yield, total N uptake (TNU), N uptake (NUPE), N utilization (NUTE), and N use efficiency (NUE) of selected maize cultivars along with a widely grown improved maize cultivar at two locations in the Guinea savannas of northern Nigeria. Maize grain yield increased with N application. The average grain yield of the maize cultivars was 76% higher at 30, 156% higher at 60, and 203% higher at 120 kg N ha−1 than at 0 kg N ha−1. This suggests that N is a limiting nutrient in the Nigerian savannas. Five drought-tolerant cultivars produced consistently higher yields when N was added at all levels. These cultivars had either high NUPE or NUTE confirming earlier reports that high N uptake or NUTE improves maize grain yield. The study also confirms earlier reports that maize cultivars that are selected for tolerance to drought are also efficient in uptake and use of N fertilizer. This means that these cultivars can be grown with application of less N fertilizer thereby reducing investment on fertilizers and reduction in environmental pollution.

Influence of nitrogen fertilization on the performance of early and late maturing maize varieties under natural infestation with Striga hermonthica (Del.) Benth

Field studies were conducted in northeast Nigeria to evaluate the response of early and late-maturing maize varieties infested with natural populations of Striga to different rates of nitrogen (N) fertilizer. There were significant reductions in the number of emerged Striga at 120 kg N ha−1 for the early varieties and at 60 and 120 kg N ha−1 for the late varieties. The number of emerged Striga only significantly differed among the late varieties. Averaged across varieties, grain yield of the early varieties was 144% higher at 60 kg N ha−1 and 192% higher at 120 kg N ha−1 than without added N. For the late varieties the increase in grain yield was 85% higher at 60 kg N ha−1 and 144% higher at 120 kg N ha−1 than without added N. Among the early varieties, TZE COMP4 C3 had significantly lower grain yield than the other varieties. Among the late varieties, grain yields of 8338-1-1 and TZB-SR were significantly lower than in the other varieties. Our results show that the application of 60–120 kg N/ha to Striga resistant or tolerant varieties may reduce damage and increase grain yield. Higher economic rates of return was obtained at N rates of 60–120 kg N/ha than the other rates.