Mancha de Cercospora em Toona ciliata no Brasil

Abstract

This work aimed at reporting the occurrence of the Cercospora spot on Australian cedar in Brazil, as well as evaluating the penetrating process of the host and favorable temperatures to the mycelial growth and the production of the cercosporin toxin in vitro. Koch postulates were performed to confirm the causing agent. The fungus was identified, by means of morphological and molecular traits, using the ITS and actin genic regions. Subsequently, the study of the penetration process of the isolates in cedar leaves was performed under scan electronic microscopy. The four isolates presented Cercospora meliicola morphological traits. However, by means of phylogeny, they were grouped with the C. alchemiliicola, forming a bootstrap supporting class of 85%. The isolates did not penetrate the host through the stomata. The penetration occurred through lesions on the cedar leaves, 12 hours after inoculation. The contribution of the Phyllachora balansae fungus over the development of lesions on the leaf surface was also observed, thus favoring, the penetration of the Cercospora isolates of the cedar. To evaluate the best temperatures for mycelial growth and production of cercosporin, the isolates were incubated under temperatures ranging from 15 to 30oC. The highest mycelial growth was observed under the temperature of 24.8oC. The best range of temperature to produce cercosporin, considering the four isolates, ranged from 21.6 to 23oC, with cercosporin production peaks of up to 4.84 μmol.disk-1.