Identification of QTLs related to cocoa resistance to three species of Phytophthora

Abstract

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.

A new cacao linkage map based on codominant markers: development and integration of 201 new microsatellite markers

“…These maps were based on codominant markers such as restriction fragment length polymorphisms (RFLPs), isoenzymes and a small number of simple sequence repeats (SSRs) and, in some of the maps, associated with dominant amplified fragment length polymorphisms (AFLP) and random amplified polymorphic DNA (RAPD) markers. They have been used to locate quantitative trait loci (QTLs) affecting traits of interest, such as disease resistance and yield factors (Crouzillat et al 2000;Flament et al 2001;Clement et al 2003;Queiroz et al 2003;Risterucci et al 2003).…”

Creation of BAC genomic resources for cocoa (Theobroma cacao L.) for physical mapping of RGA containing BAC clones

“…Several regions of the genome involved in yield components and Phytophthora spp. resistance were identified (Crouzillat et al 2000;Flament et al 2001;Lanaud et al 2002;ClØment et al 2003aClØment et al , 2003bRisterucci et al 2003) and confirmed the polygenic nature of this quantitative resistance in cocoa. A region of chromosome 6 appears particularly interesting and gave QTL for yield components and resistance to Phytophthora.…”

“…Recently, both RGAs and defence gene analogues (DGA) were isolated from cocoa genomic DNA using degenerate primers designed from conserved domains of several plant resistance and defence genes including the NBS motif (Kuhn et al 2003, present in a number of resistance genes such as the tobacco N; the STK (serine/threonine kinases) subdomains of plants such as the Pto tomato gene; and conserved domains of two defence gene families, the pathogenesis-related proteins (PR) of classes 2 and 5 ). Most of the RGA and PR2-DGA clones, isolated by Lanaud et al (2004), were mapped in a segregating population and co-localizations were observed between some RGA and DGA, and QTL for resistance to Phytophthora previously identified in several progenies (Crouzillat et al 2000, Lanaud et al 2002, ClØment et al 2003bRisterucci et al 2003).…”

Genetic Improvement in Cocoa

“…Many linkage maps have been developed for cocoa aiming to associate molecular markers to agronomic traits. The major traits mapped are resistance to Phytophthora pod rot caused by Phytophthora spp (Crouzillat et al 2000b;Risterucci et al 2003), yield (Crouzillat et al 2000a) and witches' broom resistance caused by Moniliophthora perniciosa (Queiroz et al 2003).…”

“…The genetic reference map of Theobroma cacao L. has been developed using the progeny UPA402 × UF676 (Lanaud et al 1995;Pugh et al 2004). And, QTLs for resistance to Phytophthora also, for agronomic and quality traits were identified (Lanaud et al 1999;Flament et al 2001;Risterucci et al 2003;Clément et al 2003a,b).…”