Efficiency of methods to evaluate cocoa resistance to Phytophthora pod rot in studies carried out in Côte d'Ivoire

Kébé Boubacar Ismaël, Tahi G.Mathias, Eskes Albertus. 2006. Efficiency of methods to evaluate cocoa resistance to Phytophthora pod rot in studies carried out in Côte d'Ivoire. In : Global approaches to cocoa germplasm utilization and conservation : Final report of the CDC/CCO/IPGRI project on "Cocoa germplasm utilization and conservation: A global approach" (1998-2004). Eskes Albertus (ed.), Efron Yoel (ed.). CFC, ICCO, IPGRI. Amsterdam : CFC, 99-107. (CFC Technical paper, 50) ISBN 978-92-9043-734-5

Résumé : The objective of this paper is to analyze the repeatability and reliability of two screening methods recommended in the CFC/ICCO/IPGRI project to evaluate resistance to Phytophthora pod rot (Ppr). The results presented here correspond to the application of the leaf disc and the detached pod tests (carried out without wounding) on cocoa genotypes with known levels of field resistance to Ppr. Broad-sense heritability for the leaf disc test varied between individual inoculation series from 0.17 to 0.58, and average heritability increased from 0.37 to 0.64 with one to four replications of the test carried out over time. Significant correlations were obtained in several trials between disease scores observed in the leaf disc test and natural level of Ppr infection of cocoa seedling progenies as well as for clones in the field (r=0.74-0.95). Correlations were higher when field data were based on weekly observations on the percentage of rotten pods and cherelles carried out during the epidemic period than on the percentage of rotten pods counted monthly at harvesting time over the entire year. Similar levels of significant positive linear correlations (r=0.84 to 0.95) were also observed for the detached pod tests and field results. The linear correlation between the detached pod and leaf disc test was also highly significant (r=0.86). The repeatability for the detached pod test was very good, with coefficients of rank correlation varying from 0.77 to 0.94. One replicate with five pods can therefore already provide reliable results. The repeatability for the leaf disc test was high for averages of seedling or adult tree progenies, with coefficients of rank correlations between series varying from 0.74 to 0.90. For individual seedlings in the nursery and individual field trees, the coefficients of rank correlations between inoculation series were lower (0.36-0.63 and 0.20-0.49, respectively), but still highly significant. With such levels of repeatability, it is recommended to use two inoculation series for the evaluation of the average resistance of progenies or clones, if these are represented by many plants. For selection of individual plants, at least three replicates should be used for nursery seedlings and four for individual field plants. The results suggest that routine application of the leaf disc test and of the detached pod test, if carried out under uniform conditions and in a standardized manner, should both be efficient in selection of new varieties with high levels of field resistance. The leaf disc test is recommended for early resistance screening, whereas the detached pod test is recommended for screening of resistance of adult trees.

Classification Agris : F30 - Génétique et amélioration des plantes
H20 - Maladies des plantes
U30 - Méthodes de recherche

Champ stratégique Cirad : Axe 1 (2005-2013) - Intensification écologique

Auteurs et affiliations

• Kébé Boubacar Ismaël, CNRA (CIV)
• Tahi G.Mathias, CNRA (CIV)
• Eskes Albertus, CIRAD-CP-UPR Bioagresseurs de pérennes (FRA)

Source : Cirad - Agritrop (https://agritrop.cirad.fr/537702/)

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