Fred Kanampiu

Imazapyr seed dressings for Striga control on acetolactate synthase target-site resistant maize

Abstract High herbicide levels can be localized on or near seed of acetolactate synthase (ALS) resistant maize ( Zea mays ). The magnesium salt of imazapyr was optimal for seed dressings (drenching, priming, and coating), for preventing field damage from parasitic Striga hermonthica (witchweed) in three seasons. Striga emerged on untreated maize from 6 to 12 weeks after planting. There was almost no Striga emergence for 3 months on imazapyr-dressed homozygous ALS-R 3245IR maize seeds. Occasional Striga that emerged and flowered formed no seed by harvest. Dust or polyvinylpyrrolidone adhesive coatings were safer in maize and as effective in Striga control as priming. Seed dressing coupled with pulling Striga escapes reduces infestation and can be used to deplete the Striga seed bank until genetic crop resistance becomes available.

Appropriateness of biotechnology to African agriculture: Striga and maize as paradigms

This paper focuses on the impact of Striga spp. on maize production and the use of biotechnology (e.g. transgenics, tissue culture, Bt genes, and transposon-transmitted suicide (inducible) genes) to control the damage caused by Striga spp. The use of biocontrol measures to Striga control is briefly discussed.

Herbicide Applied to Imidazolinone Resistant-Maize Seed as a Striga Control Option for Small-Scale African Farmers

Abstract Striga is a major constraint to food production in Africa. Most technologies developed for the eradication of Striga asiatica from the United States are not adaptable to Africa. Imazapyr and pyrithiobac coated imidazolinone-resistant (IR)-resistant maize seed prior to planting at rates of 30 to 45 g ha−1 provide near season long control of Striga and can increase maize yields three- to fourfold if supplied with fertilizer. Slow release seed coatings reduce maize injury when post-planting rains are sparse and improve Striga control when there is excessive rainfall early in the season. Models suggest that herbicide resistance may not be a significant threat in short season maize, but vigilance in removing flowering Striga plants that are not controlled is recommended due to the known risk of evolution of resistance to these herbicides. Stacking the IR gene with glyphosate resistance and using imazapyr treated seed and applying glyphosate mid-season would provide season long Striga control and delay the evolution of resistance to both herbicides. To date, adoption of this technology has been limited by a number of factors. However, it should be included as one component of a multi-factor approach to increasing maize productivity in areas of Africa where Striga is problematic. Nomenclature: imazapyr; pyrithiobac; Striga, Striga hermonthica (Del.) Benth. STRHE; Zea mays L.

Effect of intercropping maize and soybeans on Striga hermonthica parasitism and yield of maize

Striga hermonthica a major biotic constraint to cereal production can be controlled by trap crops. Soybean cultivars vary in ability to stimulate suicidal germination of the weed. An experiment was conducted to select soybean (Glycine max) varieties with the ability to stimulate germination of S. hermonthica seeds. Experiments were conducted with strigol Nijmegen 1® (GR 24), a synthetic stimulant, as a check. In the pot and field experiments, maize (variety WH507) was intercropped with soybeans. Variation occurred among soybean varieties in inducing germination of S. hermonthica. The relative germination induction by soybean varieties ranged from 8% to 66% compared to 70% for synthetic stimulant check. Varieties TGX1448-2E, Tgm 1576, TGX1876-4E and Tgm 1039 had the highest relative germination. Soybean varieties TGX 1831-32E, Tgm944, Tgm 1419 and Namsoy4m had high stimulation but low attachment. Intercropping maize with soybeans in the field led to a low S. hermonthica count and high maize yield.

A new approach to Striga control

Fred Kanampiu (e-mail: f.kanampiu@africaonline.co.ke) and Dennis Friesen (email: d.friesen@cgiar.org) of the International Maize and Wheat Improvement Center (CIMMYT), based in Nairobi in Kenya, and Jonathan Gressel (e-mail: Jonathan.Gressel@weizmann.ac.il) of the Weizmann Institute of Science in Rehovot, Israel, outline new herbicide maize seed coating technology and new IR varieties for Striga control.

From best fit technologies to best fit scaling: incorporating and evaluating factors affecting the adoption of grain legumes in Sub-Saharan Africa

The success of scaling out depends on a clear understanding of the factors that affect adoption of grain legumes and account for the dynamism of those factors across heterogeneous contexts of sub-Saharan Africa. We reviewed literature on adoption of grain legumes and other technologies in sub-Saharan Africa and other developing countries. Our review enabled us to define broad factors affecting different components of the scaling out programme of N2Africa and the scales at which those factors were important. We identified three strategies for managing those factors in the N2Africa scaling out programme: (i) testing different technologies and practices; (ii) evaluating the performance of different technologies in different contexts; and (iii) monitoring factors that are difficult to predict. We incorporated the review lessons in a design to appropriately target and evaluate technologies in multiple contexts across scales from that of the farm to whole countries. Our implementation of this design has only been partially successful because of competing reasons for selecting activity sites. Nevertheless, we observe that grain legume species have been successfully targeted for multiple biophysical environments across sub-Saharan Africa, and to social and economic contexts within countries. Rhizobium inoculant and legume specific fertiliser blends have also been targeted to specific contexts, although not in all countries. Relatively fewer input and output marketing models have been tested due to public–private partnerships, which are a key mechanism for dissemination in the N2Africa project.

ON-FARM EXPERIMENTATION ON CONSERVATION AGRICULTURE IN MAIZE-LEGUME BASED CROPPING SYSTEMS IN KENYA: WATER USE EFFICIENCY AND ECONOMIC IMPACTS

Conservation agriculture (CA) is a promising technology for controlling soil degradation, mitigating drought, increasing crop yield and reducing production costs. We hypothesized that adopting CA system would improve system productivity and efficiency, hence resulting in higher profits. To test the hypothesis, we designed a study to evaluate water use efficiency (WUE) and the economic benefits (yield and gross margins) of CA in the upper and lower midlands agro-ecological zones of eastern Kenya. Four tillage treatments, including farmers’ practice (residues removed), conventional tillage (residues removed) and two CA practices with residue retention (zero tillage and furrow–ridge), were laid out in 22 farmers’ fields where each farm was treated as a replicate. The results are based on four consecutive seasons farmer–researcher managed trials during the period 2010 and 2012. CA significantly improved crop yields after the first season of experimentation. Joint use of zero tillage and furrow–ridge provided higher WUE and yield advantage (25–34%) in the third and fourth seasons compared to the conventional practices. The lower midlands zone gave higher WUE values, which can be explained by the effects of water harvesting and retention for longer period on CA treatments. CA practices have increased income on average by 12% resulted from labour cost reduction and yield increment. Weeding costs for conventional tillage were USD 88 ha −1 compared to USD 24 ha −1 for herbicide application under CA. Practicing CA will certainly increase crop yields, WUE, generate more revenue and diversify risks during poor seasons. However, these benefits may not necessarily be earned in the first season, but will accrue in subsequent seasons.

Assessment of management options on striga infestation and maize grain yield in Kenya

Abstract The parasitic purple witchweed [Striga hermonthica (Del.) Benth.] is a serious constraint to maize production in sub-Saharan Africa, especially in poor soils. Various Striga spp. control measures have been developed, but these have not been assessed in an integrated system. This study was conducted to evaluate a set of promising technologies for S. hermonthica management in western Kenya. We evaluated three maize genotypes either intercropped with peanut (Arachis hypogaea L.), soybean [Glycine max (L.) Merr.], or silverleaf desmodium [Desmodium uncinatum (Jacq.) DC] or as a sole crop at two locations under artificial S. hermonthica infestation and at three locations under natural S. hermonthica infestation between 2011 and 2013. Combined ANOVA showed significant (P<0.05) cropping system and cropping system by environment interactions for most traits measured. Grain yield was highest for maize grown in soybean rotation (3,672 kg ha-1) under artificial infestation and in D. uncinatum and peanut cropping systems (3,203 kg ha-1 and 3,193 kg ha-1) under natural infestation. Grain yield was highest for the Striga spp.-resistant hybrid under both methods of infestation. A lower number of emerged S. hermonthica plants per square meter were recorded at 10 and 12 wk after planting on maize grown under D. uncinatum in the artificial S. hermonthica infestation. A combination of herbicide-resistant maize varieties intercropped with legumes was a more effective method for S. hermonthica control than individualcomponent technologies. Herbicide-resistant and Striga spp.-resistant maize integrated with legumes would help reduce the Striga spp. seedbank in the soil. Farmers should be encouraged to adopt an integrated approach to control Striga spp. for better maize yields.

In Vitro Selection of Soybean Accessions for Induction of Germination of Striga hermonthica (Del.) Benth Seeds and Their Effect on Striga hermonthica Attachment on Associated Maize

Production of maize in western Kenya is adversely affected by Striga hermonthica. Integrating legumes as intercrops is one way of reducing the density of S. hermonthica in the soil and improving the livelihood of subsistence farming communities. Legume species and varieties, however, vary in the ability to stimulate suicidal germination of S. hermonthica seeds. A study was conducted to select soybean (Glycine max) accessions with ability to stimulate germination of S. hermonthica seeds from western Kenya. The cut-root technique was used to screen 32 soybean accessions with Desmodium, Mucuna and maize varieties Nyamula, KSTP92 and WH502 as checks. Fourteen soybean accessions (selected from the cut-root experiment), Desmodium and Mucuna were grown in association with maize variety WH502 in pots inoculated with Striga seeds. There was a significant variation among soybean accessions in inducing germination of Striga. The relative germination of Striga seed by soybean accessions ranged from 8 to 66% compared to 70% for synthetic germination stimulant Nijmegen 1®. Accessions TGx1448-2E, Tgm1576, TGx1876-4E and Tgm1039 had the highest relative germination percent. Most accessions that stimulated high germination of Striga seeds increased Striga attachment by 6–95%. There was a negative correlation (R 2 = 0.7) between maize shoot dry weight and intercrop shoot dry weight. Accessions TGx1831-32E, Tgm944, Tgm1419 and Namsoy 4m had high stimulation but low attachment, hence making them potentially important trap crops.