ABSTRACT Witches' broom, caused by Moniliophthora perniciosa, is the most important cacao disease in Brazil, and the final objective of this study is increasing the level and durability of resistance to this fungus, through the association of different alleles or genes favorable to the character, for the generation of new cocoa varieties. It was conducted, for 10 years, the evaluation of the number of vegetative brooms and cushions brooms per plant, of progenies from a cross breeding scheme in North Carolina II design, with the clones: Be 4, Cepec 89, CSul 7, EEG 29, ICS 98, Oc 67, RB 39 and Scavina 6, as group 1 of progenitors, and CCN 10, CCN 51, Cepec 86, ICS 9, IMC 76, Na 33, P4b, and SGu 54, as group 2. For both groups there were differences in terms of the general combining ability and specific combining ability. Differences among progenitors and among progenies were also found for the tendencies in the evolution of the number of brooms over the evaluation period. And it was possible to increase the level and durability of resistance through the association of alleles or genes favorable to this character, all the three results confirming the original hypothesis.

O retrocruzamento tem sido pouco usado no melhoramento do cacaueiro, particularmente devido ao longo tempo requerido para transferir genes e recuperar o genoma do pai recorrente. O objetivo deste estudo foi selecionar indivíduos resultantes do retrocruzamento de CEPEC-42 x SIC-19, geneticamente relacionado ao pai recorrente SIC 19 por meio do uso de marcador molecular RAPD, dentre aqueles com resistência à vassoura-de-bruxa. Das 31 plantas que agruparam com SIC-19, 18 das replantadas permanecem sem a vassoura-de-bruxa no campo, com bom aspecto vegetativo. Essas 18 plantas podem ser usadas em retrocruzamento para alcançar o objetivo desejado.

Backcrossing has been little used in cacao breeding, particularly due to the long time required to transfer genes and recover the genetic background of the recurrent parent. The objective of this study was to select individuals, resulting from the backcross CEPEC-42 x SIC-19, genetically related to the recurrent parent SIC-19 by using RAPD molecular markers, among those with resistance to witches' broom. Of the 31 plants that clustered with SIC-19, 18 from the replanted material remained free of the disease in the field, with good vegetative aspect and, therefore can be used for backcross to reach the desired objective.