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On-line version ISSN 1678-4677
DANTAS NETO, Alfredo et al. Characterization of a cocoa population for mapping of genes of resistance to Witches' Broom and Phytophthora pod rot. Fitopatol. bras. [online]. 2005, vol.30, n.4, pp. 380-386. ISSN 1678-4677. http://dx.doi.org/10.1590/S0100-41582005000400007.
Cocoa (Theobroma cacao) is a target for several diseases, the main one being black-pod, caused by Phytophthora spp. However, witches' broom caused by Crinipellis perniciosa is the most devastating cocoa disease in Brazil. The search for sources of disease resistance is the first step in breeding programs. To this end, this study aimed to quantitatively characterize a progeny from the cross between the cocoa clones SIC-864 and CCN-51, two contrastant genotypes for several traits, including resistance to witches' broom and black pod. The progeny was assessed under field conditions for the average number of pods per tree per year, the percentage of healthy pods, the percentage of pods with witches' broom, the percentage of pods with black pod, the average number of vegetative brooms per tree per year and the average number of cushion brooms per tree per year, for a period of four years. The descriptive statistics for productivity and resistance to diseases were computed considering the maximum, the mean and the minimum values, the standard deviation, the coefficient of variation and the distribution of frequency. The repeatability coefficient was computed to estimate the accuracy of the phenotypic measurements through the methods variance analysis, principal components and structural analysis. It was shown that this progeny segregates for resistance to witches' broom, black pod and other traits, thus illustrating its usefulness for studies of genetic mapping using molecular markers, aiming to identify genes of resistance and quantitative trait loci (QTLs) different from those found in the Scavina-6 clone, traditionally used in cocoa breeding programs.
Keywords : Crinipellis perniciosa; Phytophthora spp; Theobroma cacao; breeding programs.