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Isolate by clone interaction as assessed with the leaf disc test in Montpellier

Paulin D., Ducamp M., Vezian-Bonnemayre K., Eskes A.. 2006. In : Eskes Albertus (ed.), Efron Yoel (ed.). 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). Amsterdam : CFC, p. 124-131. (CFC Technical paper, 50).

Multi-site clone trials were planted by each of the CFC/ICCO/IPGRI project partners. For this, 32 clones, 20 of which were common, were delivered to ten countries in 1998 and 1999 by the quarantine centres at CIRAD in Montpellier and at the University of Reading. CIRAD in Montpellier evaluated the level of resistance to black pod disease (Phytophthora pod rot or Ppr) in 30 of those clones by the leaf inoculation test with 30 different isolates of P. palmivora, P. megakarya, P. capsici and P. parasitica originating from the ten cocoa-producing countries taking part in the project. There were four series of inoculations for each clone/isolate combination, with 10 leaf discs per series. The different isolates and species used were characterized by molecular markers and by in vitro observations, which showed that the degree of isolate aggressiveness was affected by the culturing and inoculum preparation conditions. The subsequent inoculation results revealed significant isolate and clone effects. Classification of isolates according to their degree of aggressiveness and of clones according to their resistance level is given in detail. The most resistant clones were IMC47, PAl20, GU255V, GU307V, NA33, SCA6, AMAZ15-15, MAN15-2 and P7. The most susceptible clones were LAF1, N38, EET59, VENC22-6, BE10, LCTEEN46, MXC67 and EQX3360-3. For the species P. palmivora, the isolates from Trinidad and an isolate from Côte d'Ivoire were more aggressive than the isolates from Papua New Guinea, Ecuador, Ghana and Malaysia. For the species P. megakarya, the isolates from Nigeria were more aggressive than those from Cameroon and Ghana. For the species P. capsici the isolates from Trinidad were more aggressive than those from Malaysia. The effects of interaction between clones and isolates were generally less than the clone and isolate effects. The classification of clone resistance was significantly correlated for 85% of the comparisons between isolates. This relative stability of resistance in relation to the different species and isolates of Phytophthora meant that varieties with a wide spectrum of resistance could be selected using only one isolate in resistance tests.

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