|Schnell ii, Raymond|
|De souza filho, Goncalo|
Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/6/2005
Publication Date: 5/20/2006
Citation: Faleiro, F.G., Queiroz, V.T., Lopes, U.V., Guimaraes, C.T., Pires, J.L., Yamada, M.M., Araujo, I.S., Pereira, M.G., Schnell Ii, R.J., De Souza Filho, G.A. 2006. Mapping QTLs for Witches'Broom (Crinipellis perniciosa) Resistance in cacao (Theobroma cacao L.). Euphytica. 149:227-235 Interpretive Summary: The efficiency of phenotypic selection in tree crops is low. Molecular markers associated with Quantitative Trait Loci (QTL) for disease resistance can be used to greatly increase the efficiency of selection. In cacao, a major disease known as witches' broom causes severe crop loss in South America. In order to identify QTL for witches' broom resistance, a specific population was used and evaluated for disease resistance. This population was screened using 342 molecular markers and a genetic linkage map produced. With this information it was possible to identify a major QTL providing resistance to this disease. This major QTL explained over 40% of the variation for this trait and is now being used to increase the efficiency of the selection program.
Technical Abstract: Molecular markers (RAPD, AFLP and microsatellites) were used to generate a linkage map and to identify QTLs associated with witches' broom (Crinipellis perniciosa) resistance in cacao (Theobroma cacao), using 82 individuals of an F2 population derived from the clones ICS-1 (susceptible) and SCA-6 (resistant). Fifteen evaluations of the number of brooms have been carried out in six years (1997-2002). In order to increase the precision and accuracy in the measures of resistance, each F2 plant was cloned in three replications in a randomized block design with single-tree plots and evaluated over 2 years. Three hundred and forty-two markers were obtained, being 33 microsatellites, 77 AFLPs and 232 RAPDs. The distribution of the number of brooms in the F2 population was skewed to resistance, suggesting the involvement of major genes controlling resistance and the repeatability estimated for resistance was 44%. A strong putative QTL was detected as being related to witches' broom resistance. Associated to this QTL, the microsatellite mTcCIR35 explained 35.5% of the phenotypic variation in resistance. This marker is being used for marker-assisted selection in SCA-6 progenies, including those selected in private plantations, as an auxiliary tool to the phenotypic selection.