Towards The Identification Of Candidate Genes Involved In Witches' Broom Disease Resistance In Theobroma cacao L.

Increasing yield, quality and disease resistance are important objectives for cacao breeding programs. Some of the diseases, such as black pod rot (Phytophtora spp), frosty pod (Moniliophthora roreri) and witches’ broom (M. perniciosa), produce significant losses in all or in some of the various production areas around the world.

We recently identified associations for witches’ broom (WB) resistance (cushion brooms, more specifically) using 185 simple sequence repeat (SSR) markers and a segregating mapping population of 282 trees at the Mars Center for Cocoa Science (Brazil) between ‘TSH-1188’ (WB resistant) and ‘CCN-51’ (WB tolerant). Later, a more extensive set of trees (459) of the same mapping population has been genotyped with 6,000 SNPs. Phenotypic data including vegetative brooms and cushion brooms for this population was collected from 2008 to 2011 and SNP markers were associated with the different traits. The resulting fine map (3,526 SNPs, 852.8 cM) allowed us to identify significant associations for vegetative and cushion brooms, mainly on linkage groups 9, 6 and 4, and some minor associations on linkage groups 7 and 3. Further strategies, such as phasing of the parents and the offspring in order to reduce the size of the associated regions will be presented. The goal is to identify markers for Marker-Assisted-Breeding, and ultimately identify candidate genes involved in witches’ broom resistance.