Compensatory and susceptive responses of cowpea genotypes to infestation by aphis Craccivora koch.

The aim of the study was to estimate yield loss to10 selected genotypes of cowpea as a result of Aphis craccivora infestation during the vegetative phase of the crop. There were two trials with four replications. The first trial serving as the control was sprayed at the seedling, flowering andpodding stages against insect pests with lambda cyhalothrin (PAWA®). The other trial was sprayed only at flowering and podding stages. The cowpea seedlings of the second trial were infested with five four-day-old aphids per seedling two weeks after planting. The aphids were allowed to form colonies and fed on the seedlings until symptoms of damage were observed. When the susceptible seedlings became stunted with distorted leaves and yellowing of leaves at two weeks after infestation (28 days after planting), aphids were controlled. The results showed that aphids’ infestation delayed flowering and maturity of genotypes of cowpea. With the exception of early flowering genotypes all the medium to late flowering genotypes produced higher dry grain yield in infested plots than the control plots. The trend was not different from the production of dry biomass. The results of the present study implies that control of aphids infestation inearly maturing cowpea genotypes should not be delayed up to two weeks after infestation or 28 days after planting. Aphid’s infestation period for studies in susceptive response in medium to late maturing genotypes should go beyond 28 days after planting probably up to 35 days afterplanting

Yield stability of some groundnut accessions in northern Ghana

Yield stability of 12 groundnut accessions mainly developed by ICRISAT and two check varieties were tested in multilocational trials covering four locations in northern Ghana during the 1994, 1996, and 1997 cropping seasons. The trial for each year was arranged in a randomized complete block design with four replications and analyzed following a factorial design of 14 genotypes W 3 years W 4 locations. Significant differences were obtained (a#0.05) for the main effects of genotypes, years, and locations as well as the first and second order interactions; 33 per cent of the variability in kernel yield was accounted for by genotype W year W location interaction whilst 26 per cent by genotype W location interaction. Proportions of the total variance due to yield differences between genotypes and genotype W year interaction were negligible. Yield stability as indicated by the regression coefficient, among-location variance, and the value of mean yield suggested that JL 24, an early-maturing variety, was the most adapted to marginal environments whereas the check variety, F-mix, maintained its superiority in adapting to favourable environments. : Ghana Jnl agric Sci. Vol.32(2) 1999: 137-14

Selection criteria for early maturing cowpea (Vigna unguiculata L. Walp.) genetypes in northern Ghana

No Abstract. Ghana Journal of Agricultural Science No. 1, 2005: 79-8

Verification of genetic identity of introduced cacao germplasm in Ghana using single nucleotide polymorphism (SNP) markers

Accurate identification of individual genotypes is important for cacao (Theobroma cacao L.) breeding, germplasm conservation and seed propagation. The development of single nucleotide polymorphism (SNP) markers in cacao offers an effective way to use a high-throughput genotyping system for cacao genotype verification. In the present study, high-throughput genotyping with SNP markers was used to fingerprint 160 cacao trees in the germplasm collection at the Cocoa Research Institute of Ghana (CRIG). These accessions had been originally introduced from international germplasm collections. The multilocus SNP profiles, generated by the Sequenom Mass Spectrometry platform, were compared with the SNP profiles of reference trees maintained in the international cacao collections. The comparison unambiguously identified mislabeled trees. For materials introduced as hybrid seeds without an available reference genotype, parentage analysis and model-based assignment were applied to verify their recorded parentage and genetic background. Our study shows that a small set of polymorphic SNP markers can provide a robust and accurate result for cacao genotype identification. This protocol can be applied for large-scale genotyping of cacao as well as for many other crops.Keywords: Cacao, conservation, chocolate, DNA fingerprint, molecular marker, tropical plant, off-type, true-to-type, West Africa.African Journal of Biotechnology, Vol 13(21), 2127-213

New Sources of Resistance in Cowpea to the Cowpea Aphid (Aphis Craccivora Koch) (Homoptera: Aphididae)

Twenty-two advanced breeding genotypes of cowpea were evaluated for their responses to infes-tation by the cowpea aphid, Aphis craccivora Koch. The aim of the study was to identify geno-type(s) of cowpea resistant to A. craccivora to be used as breeding line(s). Seedling screening technique and aphid growth and reproduction on each genotype were used to classify the geno-types into resistant and susceptible groups. The cowpea genotypes SARC 1-57-2 and SARC 1-91-1 were found to be the most resistant genotypes, whereas five of the genotypes namely, Apag-baala, IT 97K-499-35, IT 98K-506-1, IT 95K-193-2 and Marfo-Tuya were highly susceptible. The high susceptibility of the IITA lines must be a cause for concern, particularly the IT 97K-499-35 line which is known to be resistant to A. craccivora in Nigeria. This suggests the exis-tence of cowpea aphid biotype in northern Ghana which is more virulent than the biotypes in Nigeria. The results support earlier findings of the development of aphid biotypes that are more aggressive and are not controlled by the aphid resistance varieties of cowpea developed by IITA for Nigeria