RESUMO
PREMISE OF THE STUDY: Phytophthora megakarya is the agent of black pod disease of cacao and is the main pathogen of this crop in Africa. Population genetic studies are required to investigate how this pathogen emerged. To this end, we developed 12 novel polymorphic microsatellite markers for P. megakarya. METHODS AND RESULTS: Microsatellite sequences were obtained by pyrosequencing of multiplex-enriched libraries. Candidate loci with di- or trinucleotide motifs were selected, and primer pairs were tested with nine P. megakarya isolates. The 12 most polymorphic and unambiguous loci were selected to develop three multiplex PCR pools. The total number of alleles varied from two to nine, depending on loci, and higher than expected heterozygosity was observed. CONCLUSIONS: These markers were used for population genetic studies of P. megakarya in Cameroon and for comparison with reference strains from West Africa. This is the first time that microsatellite markers have been developed for P. megakarya.
Assuntos
Cacau/microbiologia , Repetições de Microssatélites/genética , Phytophthora/genética , África Ocidental , DNA Fúngico/genética , DNA Fúngico/isolamento & purificação , Loci Gênicos/genética , Variação Genética , Genética Populacional , Dados de Sequência MolecularRESUMO
This study aimed to compare the genetic control of cacao resistance to three species of Phytophthora: Phytophthora palmivora, Phytophthora megakarya and Phytophthora capsici. The study was conducted on 151 hybrid progenies created in Côte d'Ivoire and grown in a green-house in Montpellier. Phytophthora resistance was screened by leaf-test inoculation with two different strains per species. Selection of the best individuals for resistance to P. palmivora at a 10% selection rate, would lead to a genetic progress of 47% in the disease evaluation for this species and a genetic progress of 42% and 21% for the two other species. A genetic map with a total length of 682 cM was built with 213 markers, 190 AFLPs and 23 microsatellites. QTLs were identified using composite interval mapping. QTLs were found located in six genomic regions. One of these was detected with five strains belonging to the three Phytophthora species. Two other regions were detected with two or three strains of two different species. Three additional QTLs were detected for only one species of Phytophthora. Each QTL explained between 8 to 12% of the phenotypic variation. For each strain, between 11.5% to 27.5% of the total phenotypic variation could be explained by the QTLs identified. The identification of multiple QTLs involved in resistance to Phytophthora offers the possibility to improve durability of resistance in cocoa by a possible cumulation of many different resistance genes located in different chromosome regions using marker-aided selection.