Infection by Uromyces euphorbiae : a trigger for the sporulation of endophytic Colletotrichum truncatum on the common host Euphorbia hirta

Abstract

The common weed Euphorbia hirta (Euphorbiaceae) grows widely across tropical and subtropical regions. In this study, plants infected by an Uromyces species displayed characteristic rust pustules delimited by a necrotic band with a reddish-brown border. Observation of leaf tissues revealed 74% of lesions encircled by a row of dark brown setose acervuli, present exclusively within the necrotic area. Acervuli were never observed in the absence of Uromyces pustules. Isolation from healthy leaf tissues revealed the fungus to be endophytic. Morphological and molecular characterization confirmed Uromyces euphorbiae as the pathogen and revealed both the endophyte and the pustule-associated fungus to be members of the Colletotrichum trucatum complex, representing the first record of this fungus on E. hirta. As understanding of the interaction between host plants, endophytes and phytopathogens is currently limited, this system constitutes a model for investigation of the physiological processes involved in this endophyte-biotrophic pathogen interaction.

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