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Investigations are focused on the two main diseases of cacao, Black Pod and Witches’ Broom, caused by the pathogens, Phytophthora spp. (Black Pod) and Moniliophtora perniciosa (Witches' Broom).
Our major objectives have been:
1. to create rapid and consistent methods to screen for these diseases.
2. to use these screening methods to identify sources of resistance, which can be use as parents in pre-breeding studies.
3. to add to the knowledge of host/pathogen relationships,
Some of the major achievements of the team include:
· Two leaf tests (penetration and post-penetration) developed for screening cocoa germplasm. (Iwaro et al., 1997)
· Stem canker identification test developed.
· Pod test developed.
· Successful screening of nine hundred and sixty accessions of the ICGT for Black Pod resistance using spray inoculation on pods.
· Rapid screening method modified for screening germplasm for the disease (Umaharan, R., et al 1999).
· Confirmatory test developed by Sreenivasan et al and fine-tuned by Surujdeo-Maharaj et al.
· A total of 773 clones have been screened for resistance to Witches’ Broom disease using spray inoculation techniques. Results obtained from screening have shown that there is considerable variation for resistance to WB (ranging from highly resistant to highly susceptible) within the collection of cacao held at the ICGT and confirmed that sources of resistant germplasm can be sourced from within the collection. We are pleased to collaborate with the World Cocoa Foundation (formerly the American Cocoa Research Institute) who have funded the screening for witches’ broom.
Measuring disease symptoms in infected cocoa (Witches Broom)
Thévenin, J.M., Umaharan, R., Surujdeo-Maharaj, S., Latchman, B., Cilas, C., and Butler, D.R. 2005. Relationships between black pod and witches’ broom diseases in Theobroma cacao. Phytopathology 95: 1301-1307.
Cilas, C., Lanaud, C., Paulin, D., Nyassé, S., N'Goran , J.A. Kébé, B.I., Ducamp, M., Flament, M.H., Risterucci, A,M., Pieretti, I., Sounigo, O., Thévenin, J-M., and Despréaux, D. (1998) Resistance to pod rot caused by Phytophthora spp., the search for resistance components. Plantations, recherché, développment 5(6): 447-449
Iwaro, A.D., Sreenivasan, T.N., and Umaharan, P. (1998). Cacao resistance to Phythophthora: effect of pathogen species; inoculation depths and pod maturity. European Journal of Plant Pathology 104: 11-15
Iwaro, A.D., Sreenivasan, T.N. and Umaharan, P. (1997) Phytophthora resistance in cacao (Theobroma cacao). Influence of pod morphological characteristics, Plant Pathology 46: 557-565