Poster: Plant Pathogen/Symbiont Interactions

Abs # 722: Scanning Electron Microscopy of Witches’ Broom Disease in Theobroma Cacao

Presenter:	Kilaru, Aruna , kilaru@louisiana.edu
Authors	Kilaru, Aruna  (A)   Hasenstein, Karl H (A)
Affiliations:	(A): University of Louisiana at Lafayette

Young detached leaves and callus of Theobroma cacao were incubated with primary mycelium of Crinipellis perniciosa to investigate host-pathogen interaction leading to witches' broom disease. SEM studies after 3, 5 and 10 days fungal incubation showed that the biotrophic primary mycelium was capable of penetrating leaf and callus tissue. Prior to invasion, the hyphal tips were club-shaped with adhesive, filamentous structures, suggesting involvement of mechanical mode of recognition and/or breaching of the host barrier. Later the hyphae penetrated through the cuticle and randomly invaded leaf tissue. Cuticular disintegration was observed at the site of penetration. Initial stages of infection showed penetrations were more prolific on the adaxial than the abaxial surface of the leaf. Further incubation for 10 days resulted in complete digestion of tissue and accumulation of fibrous debris. Only at this stage, hyphae showed clamp connections, indicative of a change from primary to necrotrophic secondary mycelial stage. This is in concurrence with the assumption that necrosis causes phase transition in C. perniciosa. Neither the presence of open wounds nor stomata is prerequisite for infection with primary mycelium. Furthermore, penetration and tissue degeneration by C. perniciosa suggests involvement of hydrolytic enzymes. This is in accord with our previous report that secreted hydrolytic fungal enzymes were capable of digesting cellulose, xylan and pectin. Future studies will focus on gene activation during the host-pathogen interaction.