Moniliophthora roreri (frosty pod rot).

The invasive basidiomycete pathogen M. roreri originated in Western Colombia/Ecuador. In recent years it has expanded its range in South America (Peru, Venezuela and Bolivia) and throughout Mesoamerica as far as Mexico. Africa, Asia and insular Caribbean are still free of this pathogen. M. roreri causes the devastating frosty pod rot of cocoa (Theobroma cacao), a disease that commonly reduces yields by over 80% within a few years of pathogen establishment. The severe losses, and occassionally complete crop failure, frequently render cocoa production economically unfeasible. The results are loss of livelihoods and abandonment and conversion of the affected agroforests to less environmentally sustainable uses, with secondary effects ranging from habitat loss for wildlife, fragmentation of forested landscapes and soil erosion. It is therefore imperative that the introduction of the pathogen to additional cocoa-producing regions is prevented. These include the insular Caribbean, the Guyanas and Brazil in the Americas, as well as the bulk-cocoa producing continents, Africa and Asia (Krauss, 2010).

SNP markers associated with resistance to frosty pod and black pod rot diseases in an F1 population of Theobroma cacao L.

Economically, cacao (Theobroma cacao L.) is a major tropical commodity for the Americas; however, severe losses due to Moniliophthora roreri (Cif. and Par.), which causes frosty pod rot (FPR), and Phytophthora spp., which causes black pod rot (BPR), have reduced cacao production in the Americas. The objectives of this study are to (i) re-confirm the QTL using different marker set; (ii) discover new QTL associated with FPR and BPR resistance using SNP markers; and (iii) find genes in the candidate QTL regions. At CATIE in Turrialba, Costa Rica, an F1 mapping population of cacao was obtained by crossing “POUND 7,” a clone moderately susceptible to FPR and resistant to BPR, with “UF 273,” resistant to FPR and highly susceptible to BPR. A total of 179 F1 progeny were fingerprinted with 5149 SNP markers and a dense linkage map composed of 10 linkage groups was developed using 2910 polymorphic SNP markers. Also segregating F1 trees were screened for resistance to FPR and BPR diseases. Seven QTL previously reported on chromosomes 2, 7, and 8 for FPR resistance and on chromosomes 4, 8, and 10 for BPR resistance were confirmed. Additionally, eight QTL were identified for FPR resistance (chromosomes 4, 9, and 10) and BPR resistance (chromosome 2). The expression of genes commonly associated with plant defense and disease resistance that are located within the identified QTL was confirmed.

Pathogenicity of Moniliophthora roreri isolates from selected morphology groups in harvested cacao pods and in vitro sensitivity to compost tea.

Moniliopthora roreri is the frosty pod rot disease (FPD) and one of the most devastating cacao pathogens worldwide. However, M. roreri pathogenicity on harvested cacao pods and sensitivity to compost tea have not been fully described. Monosporic cultures of M. roreri from different morphology groups were obtained. The isolates’ pathogenicity was tested by inoculation onto harvested cacao pods, and symptoms were evaluated at 3-day intervals during 16 days before estimating the area under the disease progress curve (AUDPC). The sensitivity of M. roreri to compost tea was evaluated on potato dextrose agar (PDA) amended with 1 to 5 % compost tea. All morphology groups could infect harvested cacao pods during the 16 days with a disease severity index abode 75 %. Compost tea completely inhibited the growth of M. roreri when used at 4.5 % or higher. Results suggest a shortened biotrophic phase during the infection in harvested pods and a medium to high sensitivity of M. roreri to compost tea.

Chocolate Crisis

Chocolate is the center of a massive global industry worth billions of dollars annually, yet its future in our modern world is currently under threat. Here, Dale Walters discusses the problems posed by plant diseases, pests, and climate change, looking at what these mean for the survival of the cacao tree. Walters takes readers to the origins of the cacao tree in the Amazon basin of South America, describing how ancient cultures used the beans produced by the plant, and follows the rise of chocolate as an international commodity over many centuries. He explains that most cacao is now grown on small family farms in Latin America, West Africa, and Indonesia, and that the crop is not easy to make a living from. Diseases such as frosty pod rot, witches’ broom, and swollen shoot, along with pests such as sap-sucking capsids, cocoa pod borers, and termites, cause substantial losses every year. Most alarmingly, cacao growers are beginning to experience the accelerating effects of global warming and deforestation. Projections suggest that cultivation in many of the world’s traditional cacao-growing regions might soon become impossible. Providing an up-to-date picture of the state of the cacao bean today, this book also includes a look at complex issues such as farmer poverty and child labor, and examines options for sustainable production amid a changing climate. Walters shows that the industry must tackle these problems in order to save this global cultural staple and to protect the people who make their livelihoods from producing it.

Witches’ Broom

In this chapter, the deadly witches’ broom disease is unmasked. Its true identity took considerable time to unravel, but the perseverance of researchers paid off and it turned out that the agent responsible is Moniliophthora perniciosa, a close relative of the frosty pod rot pathogen. The pathogen spread across the northern areas of South America and into the Caribbean, causing devastation from which cacao production in some countries never fully recovered. The major cacao-growing region of Bahia in Brazil remained free of the disease for a long time, but all that changed in the late 1980s. The discovery of witches’ broom there had far-reaching consequences for cacao production in Brazil, effects which are still felt today. This chapter looks at the efforts made to understand the pathogen and the disease it causes, and how this research informs work aimed at tackling the disease.

Frosty Pod Rot

Chapter 7 follows the journey of frosty pod rot from the first report of the disease in 1895 in western Ecuador to the present day, where it has spread to much of South and Central America, and several Caribbean countries. To date, it has not been reported in Brazil, and considerable effort is being expended to ensure it does not spread to other cacao-growing regions. The chapter explores the fascinating biology of the causal agent, Moniliophthora roreri, which turns out to be related to the witches’ broom pathogen. Efforts to control the pathogen, reduce its impact, and contain its spread, are discussed.