Resistance Gene Mapping for Witches' Broom Disease in Theobroma cacao L. in an F2 Population using SSR Markers and Candidate Genes

Abstract

<jats:p>A genetic linkage map was created from 146 cacao trees (<jats:italic>Theobroma cacao</jats:italic>), using an F<jats:sub>2</jats:sub> population produced by selfing an F<jats:sub>1</jats:sub> progeny of the cross Sca6 and ICS1. Simple sequence repeat (SSR) markers (170) were used principally for this map, with 12 candidate genes [eight resistance gene homologues (RGH) and four stress related WRKY genes], for a total of 182 markers. Joinmap software was used to create the map, and 10 linkage groups were clearly obtained, corresponding to the 10 known chromosomes of cacao. Our map encompassed 671.9 cM, approximately 100 cM less than most previously reported cacao maps, and 213.5 cM less than the one reported high-density map. Approximately 27% of the markers showed significant segregation distortion, mapping together in six genomic areas, four of which also showed distortion in other cacao maps. Two quantitative trait loci (QTL) for resistance to witches' broom disease were found, one producing a major effect and one a minor effect, both showing important dominance effects. One QTL for trunk diameter was found at a point 10.2 cM away from the stronger resistance gene. One RGH flanked the minor QTL for witches' broom resistance, implying possible association. QTLs mapped in F<jats:sub>2</jats:sub> populations produce estimates of additive and dominance effects, not obtainable in F<jats:sub>1</jats:sub> crosses. As dominance was clearly shown in the QTL found in this study, this population merits further study for evaluation of dominance effects for other traits. This F<jats:sub>2</jats:sub> cacao population constitutes a useful link for genomic studies between cacao and cotton, its only widely grown agronomic relative.</jats:p>

Novel sources of witches’ broom resistance (causal agent Moniliophthora perniciosa) from natural populations of Theobroma cacao from the Brazilian Amazon

“…The resistance from 'Scavina 6' was initially considered to be dominant and predominantly monogenic (Bartley 1986). Indeed, a major dominant quantitative resistance locus (QRL) was identified in 'Scavina 6' by molecular mapping, at linkage group 9 of the consensual map, responsible for up to 51% of the phenotypic variance for resistance (Brown et al 2005;Faleiro et al 2006). However, another minor QRL was detected on linkage group 1, accounting for 6.7% of the variance, with dominance for the susceptible parent 'ICS1' (Brown et al 2005).…”

“…Indeed, a major dominant quantitative resistance locus (QRL) was identified in 'Scavina 6' by molecular mapping, at linkage group 9 of the consensual map, responsible for up to 51% of the phenotypic variance for resistance (Brown et al 2005;Faleiro et al 2006). However, another minor QRL was detected on linkage group 1, accounting for 6.7% of the variance, with dominance for the susceptible parent 'ICS1' (Brown et al 2005). Our results indicated a clear distinction for witches' broom resistance in the field between 'Scavina 6' and the hybrid family 'Theobahia', derived from a cross with 'ICS 1', which maintained a limited disease incidence, at levels similar to the most resistant CAB families during the nine year evaluation (Fig.…”

“…1). Therefore, it appears that the performance of 'Theobahia' may originate from the presence of additional resistance gene(s) derived from the susceptible 'ICS 1', including the one identified by Brown et al (2005), in addition to the major gene inherited from 'Scavina 6', resulting in a complete distinct infection behavior from the Euphytica (2010) 172:125-138 135 resistant parent under field condition. Our own results from genome mapping of two families derived from crosses between 'CAB 0214' or 'CAB 0208' with the highly susceptible 'ICS 39' indicated that, besides a major QRL, additional QRLs were identified at distinct linkage groups and loci (Paulo Albuquerque and Antonio Figueira, unpublished).…”

“…By genetic mapping, a major resistance locus was identified at linkage group nine of the cacao consensual map (Brown et al 2005;Faleiro et al 2006). 'Scavina 6' has been the only recognized source of resistance widely used in cacao breeding programs; however, this resistance was overcome in Ecuador, Peru and the Brazilian Amazon after few years of deployment (Bartley 1986;Wheeler and Suarez 1993).…”

Analysis of clonal germplasm from five Saccharum species: S. barberi, S. robustum, S. officinarum, S. sinense and S. spontaneum. A study of inter- and intra species relationships using microsatellite markers

“…Irregularities in genotypic profiles produced by markers are not uncommon, especially in polyploidy species, as seen for some markers in this experiment. Brown et al (2005) experienced the failure of SSR markers to be strictly inherited as actual genes even in a simpler, diploid species such as cacao (Theobroma cacao L.).…”