Browsing by Author "N'Goran, J.A.K."

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    Levels of resistance to Phytophthora pod rot in cocoa accessions
    (2008) Pokou, N.D.; N'Goran, J.A.K.; Kebe, I.; Eskes, A.; Tahi, M.; Sangare, A.
    Resistance to Phytophthora pod rot (Ppr) is becoming an increasingly important criterion for selection of new cocoa cultivars in Cote dlvoire. The predominant speues of the pathogen, Phytophthora palmivora, causes pod losses of !0 15% but the more aggressive Phytophthora ntegakarya present in the eastern part of the country causes losses of 40-60%. The latter species is expected to continue its spread to the main cocoa belt in Cote dlvoire over the next decade. Since 2000, the Centre National de Recherche Agronomique has been selecting new cocoa cultivars with direct involvement of fanners. More than 250 farmers were visited and their knowledge is being used to collect accessions with high yield potential, with low pest (mirids) infestation or with low Ppr incidence. Farmers were capable of identifying mother trees with low Ppr incidence only in regions with high disease pressure (Abengourou and Aboisso). Open-pollinated seedling progenies obtained from 226 promising trees in farmers fields were screened for resistance to Ppr by inoculating leaf discs from nursery plants with spores of a P. palmivora isolate. Three clones (SCA6. PA 150 and NA79) and three recommended hybrids were used as control cultivars. The results of the leaf disc test confirmed the known variation ot" resistance of the control cultivars. The relative level of resistance of the farm accessions varied mainly between moderately resistant and susceptible, but several accessions could be considered as resistant, in relation to the control cultivars. The major part of the 15% most resistant farm accessions came from the Abengourou and Aboisso regions in the eastern part of the country. Progenies from mother trees that fanners had selected as showing low Ppr incidence in their fields also appeared to be more resistant in the leaf disc test. This suggests that the resistance identified to P. palmivora in the leaf disc test may be efficient in the field in areas infected with P. ntegakarya. It is recommended that the genetic diversity identified through participatory selection of promising mother treeslin farmers fields be further exploited in breeding to obtain new hybrid or clonal cocoa cultivars with low incidence of Ppr, good yield and low mirid damage.
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    Levels of resistance to Phytophthora pod rot in cocoa accessions selected on-farm in Cote d' Ivoire
    (Elsevier, 2008) Pokou, N.D.; N'Goran, J.A.K.; Kebe, I.; Eskes, A.; Tahi, M.; Sangare, A.
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    Resistance to Phytophthorapalmivora (Butler) Butler Assessed on Leaf Discs of Cacao (Theobroma cacao L.) Hybrid Trees
    (2009) N'Guetta, S-P.A.; N'Goran, J.A.K.; Akaza, M.J.; Kebe, B.I.; Tahi, G.M.; Sangare, A.
    To select resistant cacao genotypes to Phytophthora palmivora and better understand the genetic determinism of resistance to this pathogen, the individual resistance of 133 and 105 two ways cocoa hybrids trees of two related progenies, Fl andF7, respectively, was evaluated by leaf discs test. The Fl andF7 derived from crosses (P7 x ICS100) x Cl (P7 x ICS95) x Cl, respectively. P7 is a resistant heterozygous Upper Amazon Forastero clone; ICS100 and ICS95 are less susceptible genetically close Tnnitario clones. The common male parent, Cl, is a completely homozygous susceptible Lower Amazon Forastero clone Amelonado type. Three series of inoculations were conducted per family and one-hundred and twenty leaf discs taken from each tree were inoculated. The results showed additivity of transmission of resistance to P. palmivora, the presence of a transgression for this character and the involvement of several recessive alleles in resistance to Phytophthora. Significant differences in levels of resistance were observed between the genotypes of each progeny. The average levels of resistance of Fl and F7 are intermediate between those of both resistant controls SCA6 and PA150 and that of NA79, the susceptible control. In the Fl and F7, respectively, 24 and 05 cocoa trees were more resistant than SCA6 and PA150. These trees may be selected and may serve as potential new genitor clones in Phytophthora sp., genetic resistance breeding programs. They may also provide budwoods for replacements in fields.