Biochemical and molecular studies on the interaction between Theobroma cacao, L., and their fungal pathogens in vitro

In Malaysia, Theobroma cacao, L., (cocoa) plants of Sterculiasae family are commonly dealt with several endemic diseases such as vascular streak dieback(VSD) and black pod (BP) diseases causing by the fungal Oncobasidium theobromae TALBOT and KEANE and Phytophthora palmivora respectively. Biotechnology and molecular biology studies were used to investigate the biochemical and molecular biology markers of resistant and susceptible cocoa clones. Crude culture filtrates of the particular fungal pathogen were bioassayed in vitro with cocoa leaf disks, callus portions and cell-suspension cultures. The resistant clones were found highly produced polyphenols compared with the susceptible clones. When dual-culture technigue (an isolated fungal pathogen, O. theobromae grew together with the cocoa tissues) was applied, the tissue resistant clones(ICS95, KKM25) resulting in less hyphae compared to those susceptible clones (NA32, PA 7). However, electron miscroscopic(EM) studies showed that the infected tissues of susceptible cocoa clones showed some damage symptoms such cell shrinkage and plasmolysed cells compared to less in the resistant clones. The finding of AFLP technique was markedly able to differentiate between cocoa clones that are resistant and susceptible to a VSD disease using selected primer combinations and this showed polymorphism among the cocoa clones.