Mapas de ligação e identificação de Locos Controladores de Características Quantitativas (QTLs) associados à resistência a Crinipellis perniciosa em acessos de cacaueiro (Theobroma cacao) originários da Amazônia Brasileira / Linkage Maps and Identification of Quantitative Trait Loci (QTL) associated with resistance to Crinipellis perniciosa in cacao (Theobroma cacao) acessions from the Brazilian Amazon

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The witches’ broom (Crinipellis perniciosa) is the most important disease of cacao in Brazil. The main method of disease control is the use of resistant cultivars, however due to the narrow genetic basis found in commercial cacao growing areas, the resistance is frequently broken. The objectives of this work were: to select new sources of resistance to C. perniciosa among cacao accessions originally collected in the Brazilian Amazon (CAB series); to identify by genetic mapping, quantitative trait loci (QTLs) associated with resistance in selected genotypes; and to evaluate the genetic relationship between the selected accessions and clones selected by cacao growers from Southern Bahia with traditional resistance sources against C. perniciosa. Based on the proportion of witches’ broom infection, the levels of resistance to C. perniciosa were estimated in 44 cacao families under greenhouse and field conditions. Under greenhouse conditions, the average proportion of infection was compared based on Wald test, and under field conditions using an analysis of repeated measures and contrast. Among the families evaluated under greenhouse and field conditions, the ones with least incidence of witches’ broom symptoms derived from ‘CAB 0169’, ‘CAB 0208’, ‘CAB 0214’, ‘CAB 0270’, ‘CAB 0371’, ‘CAB 0388’, ‘CAB 0392’ and ‘CAB 0410’. Two linkage maps were developed for populations derived from crosses between contrasting accessions selected as the most resistant to C. perniciosa (‘CAB 0208’ and ‘CAB 0214’) and a susceptible accession ‘ICS 39’. The linkage maps were developed using 65 microsatellite loci, applying the software JoinMap 3.0®. The identification and localization of QTLs associated with resistance to C. perniciosa were performed using MAPQTLTM 4.0. For the family derived from ‘ICS 39 x CAB 0208’, 11 linkage groups were formed, with total coverage of 541 cM and 14 cM average distance between markers. The linkage map from ‘ICS 39 x CAB 0214’ presented a total coverage of 501 cM in 10 linkage groups formed with an average distance between markers of 11.4 cM. Three QTLs associadted with resistance to C. perniciosa were detected, with one at linkage group VIII of ‘ICS 39 x CAB 0208’, and two for the ‘ICS 39 x CAB 0214’ family, with one located at linkage group IV and another at group IX. The genetic relationship between these two CAB accessions and 81 genotypes used as source of resistance to C. perniciosa were determined using genetic dissimilarity and co-ancestry based on allele frequencies of 20 microsatellite loci. The dissimilarity analyses among the accessions generated two distinct groups. ‘CAB 0208’ and ‘CAB 0214’ did not belong to any of the two groups. The co-ancestry between the two accesions were high, close to full-sib, but without any relationship with any of the other genotypes. The clones selected by growers derived mostly from ‘Scavina 6’, a commonly used source of resistance to C. perniciosa.

ASSUNTO(S)

mapeamento genético witches’ broom genetic mapping cacau molecular marker marcador molecular qtl resistance theobroma cacao cacao resistência genética vegetal ssr vassoura-de-bruxa crinipellis perniciosa cocoa

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