Resistance of cacao tree to witches’ broom disease – A study of inheritance

Abstract

Over a 10-year period, the number of vegetative brooms and floral cushion brooms was evaluated in each plant of progenies from a North Carolina II mating design with the clones: Ca 5, CAB 5003, Chuao 120, ICS 1, Moq 216, Scavina 12, Scavina 6 and SPA 5 as group 1 of progenitors, and CC 10, CCN 34, Cepec 90, CSul 3, Ma 16, RB 36, SGu 26 and SIAL 70 as group 2. Highly significant effects were found for progenitors and interactions among progenitors, indicating that the species Theobroma cacao has a high level of genetic diversity for resistance to witches’ broom. Results demonstrated the presence of different genes, alleles or gene combinations among progenitors; the association of various genes, alleles or gene combinations in the progenies, and the presence of additive and dominant effects on the inheritance of these factors. There was also significant loss of inheritance of Scavina 6, the most traditional source of resistance, when it was used alone but not when it was combined with other clones bearing resistance genes or alleles. This demonstrated that gene association increases resistance durability in that source.