Breeding for disease resistance in cacao

Abstract

Cacao production must increase in order to meet the projected rise in the demand for chocolate. Approximately one-third of global production is lost annually to diseases and insects. Four diseases account for the greatest losses worldwide: black pod, caused by four Phytophthora spp.; witches’ broom, caused by Moniliophthora perniciosa; cacao swollen shoot virus, caused by a member of the genus Badnavirus; and frosty pod, caused by Moniliophthora roreri. At the present time, only 30 % of material currently under cultivation is of improved varieties, therefore, there is an urgent need for the development of new, high-yielding, disease-resistant varieties. Sustainable production increases could be achieved if improved varieties were used by the farmers. Cacao breeding was started in Trinidad in the 1930s by F. J. Pound and within a few decades cacao research centers had been established in all the major cacao producing areas worldwide including West Africa and Southeast Asia. Pound and other researchers have made several expeditions to the Amazon to collect wild cacao germplasm. In addition to using the germplasm collected from the wild and farmers’ fields to find new sources of resistance genes, researchers have developed breeding programs that cross and select cacao genotypes in order to accumulate desirable genes for resistance, as well as good horticultural and quality traits. Recently, numerous molecular tools, including the genome sequences of two varieties of cacao, have been developed and/or made available to accelerate the breeding process. International private/public collaborations are in progress to identify candidate resistance genes, map these in the sequenced genomes, and develop molecular markers associated with these genes. Researchers will use these markers in genomics-assisted breeding programs to screen young cacao plants and select those with desirable traits.