Resistance gradient of black pod disease in cocoa and selection by leaf disk assay

Abstract

To characterize the gradient of resistance to black pod disease experimentally, the leaf disk assay was applied to 217cocoa genotypes. The parameters time interval, number of leaves evaluated per genotype and distribution of experimental treatmentswere evaluated. Significant differences between genotypes were found, resulting in the grouping in five homogenous groups(p < 0.01). In the assessments with the leaf disk test, five and seven days after inoculation, the F value was highest after seven days,clearly separating the resistant from susceptible genotypes. There was no difference between the clones behavior and the use of morethan one box to group the genotypes (p = 0.56) and the use of different leaves of the same genotype (p = 0.08). The resistancegradient observed indicates variability enough for mapping and cocoa breeding in the population.

Keywords

• genetic mapping
• breeding
• disease index
• Phytophthora palmivora
• Theobroma cacao.