Cacao phylloplane: The first battlefield against Moniliophthora perniciosa, which causes witches' broom disease
The phylloplane is the first contact surface between Theobroma cacao and the fungus Moniliophthora perniciosa, which causes witches' broom disease (WBD). We evaluated the index of short glandular trichomes (SGTs) in the cacao phylloplane and the effect of irrigation on the disease index of cacao genotypes with/without resistance to WBD, and identified proteins present in the phylloplane. The resistant and susceptible genotype CCN51 and Catongo presented a mean index of 1600 and 700 SGTs·cm-219 , respectively. The disease index in plants under drip irrigation was reduced by approximately 30% compared with plants under sprinkler irrigation prior to inoculation. Leaf water wash (LWW) of the cacao inhibited the germination of spores by up to 98%. Proteins from the LWW of CCN51 were analyzed by 2D SDS-PAGE followed by ms/ms. The gel showed 71 spots and identified a total of 42 proteins; 28 from the plant and 14 from bacteria. Proteins related to defense, to synthesis of defense metabolites and involved in nucleic acid metabolism were identified. The results support the hypothesis that the proteins and water-soluble compounds secreted to the cacao phylloplane participate in the defense against pathogens. They also suggest that SGTs can contribute to the resistance of cacao.