Annals of Botany

Bioinformatics for chocolate lovers: getting a tag on cocoa

One of the recurring themes in surveys of global agricultural research is the comparative lack of effort expended on tropical crops. This is even true of crops of major economic importance, as is illustrated for Theobroma cacao (cocoa) by the work of Gesteira et al., a Franco–Brazilian research group (pp. 129–140). The authors indicate that more than 20 million people, many of them in very poor countries, depend directly on cocoa for their livelihood: the importance of the crop extends far beyond the needs of chocolate lovers. Despite this, knowledge of interactions between T. cacao and its various pests and pathogens is very limited; thus the authors’ work on witches broom disease of cocoa, caused by the fungus Moniliophthora pernicosa, is very welcome. They have selected T. cacao cultivars that are resistant or susceptible to M. pernicosa. Apical meristems of 4-week-old plantlets in both groups were inoculated with spores of M. pernicosa; control plants were mock-inoculated. Apical meristems were harvested and rapidly frozen 24, 48 and 72 h after inoculation, and thereafter every 5 d until day 90. Disease development was monitored over the same period. RNA extracted from the harvested meristems was used to construct cDNA libraries. From these libraries clones were randomly selected and partially sequenced to give expressed sequence tags (ESTs), the first EST analysis of the T. cacao–M. pernicosa interaction. From a total of 6884 ESTs, 2926 individual sequences were identified, of which 54 % could be allocated to genes of known function. Comparison of the ESTs revealed differences that included the greater representation in the ESTs from resistant plants of ‘genes involved in the resistance process’ and in the ESTs of susceptible plants of genes involved in the oxidative burst and in programmed cell death. Thus, as the authors themselves state, this work will lead to the development of strategies to control witches broom disease in this very important crop.