Selection of cocoa progenies for resistance to witches’ broom

Abstract

Witch’s broom (WB) and frost pod rot (FPR) are devastating fungal diseases and responsible for severe losses in cacao trees grown in tropical America. To expand and stabilize the resistance to WB in cacao progenies, as well as to incorporate resistance genes to FPR, 17 genotypes were selected from a structured population. These were used in a second selection cycle, in which four gene donors of FPR resistance were included. All but one of the 59 and 52 progenies differed significantly (P < 0.05) from the susceptible controls Catongo and SIC 23, respectively. Nineteen progenies differed significantly (P < 0.05) from the resistance control SCA 6, suggesting high WB resistance. The direct descendants of cacao genotypes from the Brazilian Amazon and from clones carrying FPR resistance showed lower disease index than the resistant control SCA 6, except for some of the progenies of clone ICS 95, which behaved similarly to the susceptible control. The study highlights nine progenies carrying WB resistance genes from several sources and seven of them from parents carrying frosty pod resistance genes.