Resumo

The ascomycete Fusarium decemcellulare is a common saprophyte found in tropical and subtropical regions associated to plant material. It is also an important pathogen of tropical fruit trees, causing flower galls on cacao or stem dieback on mango. Its sexual form is known as Albonectria rigidiuscula, but is rarely found in nature. In order to determine sexual behavior of this species and characterize it by means of the biological species concept and morphology, isolates were obtained from different cocoa production areas in the states of Bahia and Espírito Santo, Brazil, from mango trees in Colima, Mexico, and a few other plants in Brazil. Monosporic cultures were prepared from 60 isolates and tested for homothallism. Cultures were inoculated on carrot agar (CA) and synthetic nutrient-poor agar (SNA) and checked for formation of perithecia during eight weeks. The mating type of the isolates was determined by PCR using primers published in literature. Isolates of opposite mating types were then crossed using each isolate as female and also as male partner. An isolate or crossing was considered fertile when perithecia exsudated ascospores. Of all evaluated isolates, eight showed to be homothallic, producing perithecia after five weeks. No fragments were amplified from homothallic isolates with primers used for the determination of the mating type. Out of 52 supposedly heterothallic isolates, only the MAT 2 idiomorph could be amplified from 32 isolates. These isolates were then crossed with the remaining 21 isolates which were considered as MAT 1. Up to now, 11 crossings produced fertile perithecia after three weeks. Two isolates from Mexico formed fertile perithecia when crossed with three of the Brazilian isolates, showing that there is no reproductive barrier between these populations. Assessment of morphological markers evidenced that homothallic isolates consistently produce four ascospores, while heterothallic isolates were characterized by the production of eight ascospores. All other markers of the anamorph and teleomorph are typical of the species. Results show that it is possible to induce the teleomorphic stage of F. decemcellulare and that the number of ascospores is a marker for homothallic and heterothallic isolates. We are now investigating if these characteristics influence on pathogenicity or aggressiveness.