QTL Mapping of Ceratocystis Wilt Resistance in Theobroma cacao

Ceratocystis wilt in Theobroma cacao is caused by the ascomycete Ceratocystis cacaofunesta. Infection occurs primarily through wounds caused by common agricultural practices or through insect lesions. The fungus multiplies quickly in the secondary xylem, causing wilting and eventually leads to sudden plant death. Disease control includes removal of infected plants and use of fungicides; however, these practices raise the production costs and have a negative environmental impact. The most effective strategy to control Ceratocystis wilt is the use of genetic resistance. A set of 266 plants derived from a cross between ‘TSH 1188' (resistant) x ‘CCN 51' (susceptible) were previously genotyped using SNP markers and a genetic linkage map was made. For each progeny, six grafted replicates were inoculated with a spore suspension placed in an incision made into the stem. Disease incidence was followed for 52 days. QTL mapping using simple interval mapping (MapQTL) identified a region of 1.2 Mbp on chromosome VI. A genetic association analysis was carried out on the AUDPC by regression method (LASSO) and identified markers associated with resistance also on chromosome VI . The region identified corresponds to a chromosomal fragment containing 10 candidate genes that may be associated with disease resistance. The most important candidate genes within the QTL, based on their annotation, are related to resistance in other economically important species, and are involved in resistance to pathogens, pathogen recognition, hypersensitivity response and recovery from infection after pathogen attack.