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The parasitic weed, Striga gesnerioides, is a major threat to cowpea productivity throughout the savannas of West and Central Africa. The identification of sources of S. gesnerioides resistance and their incorporation into breeding programs would be a beneficial strategy to combat the devastation caused by the parasite in cowpea fields. In this study we examined one hundred and ninety-four (194) accessions, four commercial varieties and two controls collected from a mini core collection of cowpea held at the International Institute of Tropical Agriculture genebank for resistance to S. gesnerioides race 3 (SG3), the most prevalent race in Nigeria, using phenotypic screening and molecular marker analysis. Our studies identified two cowpea accessions, Tvu-1272 and Tvu-16514, that are resistant to S. gesnerioides SG3. Resistance in these lines is associated with the molecular marker SSR1, known to segregate with the gene conferring resistance to SG3 in the cultivar B301. Phenotypically, resistance in Tvu-1272 and Tvu-16514 is expressed as a hypersensitive response at the site of infection on the roots. Allelism tests indicated that the gene that conferring SG3 resistance in Tvu-1272 is independent of that conferring resistance in B301. Tvu-1272 and Tvu-16514 will provide additional new sources of resistance to Striga and races prevalent in Nigeria.

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This study was conduced to determine optimal concentrations of sucrose and combinations of growth regulators required for callus initiation and plant regeneration from immature embryos of 'Councill' and other triticales (X Triticosecale Wittmack) and to make histological observations of triticale callus during differentiation and organogenesis. Immature triticale embryos were cultured on a basal medium containing the salts of Murashige and Skoog and vitamins plus selected concentrations of sucrose and different auxins or cytokinins, alone or in combination. The optimal concentration of sucrose for increasing fresh weight of callus derived from hexaploid embryos was 20 g/liter. The addition of 2, 4‐D [(2, 4 dichlorophenoxy) acetic acid] to the basal medium was superior to the addition of IAA (indoleacetic acid), kinetin (6‐furfurylaminopurine) and auxin/cytokinin combinations for both callus initiation and growth. higher concentrations of 2, 4‐D (6 mg/liter) promoted callus initiation and growth, but prevented plant regeneration on callus subsequently subcultured to a medium without growth regulators. Histological observations gave evidence of formation of active growth centers or meristemoids in callus. These subsequently led to differentiated root primordia. Our study showed that triticale embryos behaved similar to other cereals in their callus initiation and plant regeneration traits.

Striga gesnerioides (Willd) Vatke, is a major destructive parasitic weed of cowpea (Vigna unguiculata (L.) Walp.) which causes substantial yield reduction in West and Central Africa. The presence of different virulent races within the parasite population contributes to significant genotype 9 environment interaction, and complicates breeding for durable resistance to Striga. A 3-year study was conducted at three locations in the dry savanna agro-ecology of Nigeria, where Striga gesnerioides is endemic. The primary objective of the study was to identify cowpea genotypes with high yield under Striga infestation and yield stability across test environments and to access suitability of the test environment. Data collected on grain yield and yield components were subjected to analysis of variance (ANOVA). Means from ANOVA were subjected to the genotype main effect plus genotype 9 environment (GGE) biplot analysis to examine the multi-environment trial data and rank genotypes according to the environments. Genotypes, environment, and genotypes 9 environment interaction mean squares were significant for grain yield and yield components, and number of emerged Striga plants. The environment accounted for 35.01%, whereas the genotype 9 environment interaction accounted for 9.10% of the variation in grain yield. The GGE biplot identified UAM09 1046-6-1 (V7), and UAM09 1046-6-2 (V8), as ideal genotypes suggesting that these genotypes performed relatively well in all study environments and could be regarded as adapted to a wide range of locations. Tilla was the most repeatable and ideal location for selecting widely adapted genotypes for resistance to S. gesnerioides.

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Genotype-by-environment TGX 1904-6F, TGX 1935-3F, TGX 1440-1E and TGX 1984-22F falling into them. TGX 1448-2E and TGX 1895 appeared to be overall best genotypes combining high stability and yield though they did not fall into mega-environment could be recommended for use in breeding programmes.