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Mapping of quantitative trait loci for resistance to Phytophthora to Theobroma cacao

Risterucci A.M., Paulin D., N'Goran J.A.K., Pieretti I., Ducamp M., Glaszmann J.C., Lanaud C.. 1999. In : Shearago International. The international conference on the status of plant and animal genome research : Workshop abstracts. New York : Scherago International, p. 126-126. numero_rapport: P192. Plant and Animal Genomes Conference. 7, 1999-01-17/1999-01-21, San Diego (Etats-Unis).

Black pod disease on cocoa can be caused by different species of Phytophthora. Our study includes three species found in producing countries: P. palmivora, worldwide, P. megakarya so far only present in Africa and P. capsici present in Latin America.The two parents of the mapping population are Scavina 6, an Upper Amazon Forestaro clone, and C1, an amelonado clone. Scavina 6 is highly resistant to Phytophthora. The cross was made in Cote d'Ivoire. BC 1 population of 151 individuals was in green house in Montpellier (France) and used for genetic linkage and QTL analyses. Resistance evaluation was made by artificial inoculation on leaf discs. Two strains of each species were used. The segregation of 202 markers was analysed using a LOD score of 4.0 to identify the linkage groups. All the markers were assigned to ten linkage groups that putatively correspond to the ten gametic chromosomes of Theobroma cacao. These loci include 191 AFLPs and 11 simple sequence repeats as anchor markers.The total length of the map is 724 cM, the average distance between markers is 3.6 cM.The interval mapping method was used for the QTL analyses (MapQTL 3.0 software). The theoretical significance threshold for the LOD score was 2.4.Three QTLs were detected, two on chromosome 5 and one on chromosome 6. These three QTLs explain 31% of the variation of the character.Two of them were common to two Phytophthora species. The significance and potential use of these QTLs in cocoa breeding programs will be discussed.This work was supported by CIRAD and CAOBISCO (Chocolate and biscuit industry association). (Texte intégral)

Mots-clés : theobroma cacao; phytophthora palmivora; phytophthora capsici; résistance aux maladies; gène; carte génétique; phytophthora megakarya; qtl

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