Biologia reprodutiva, filogenia e patogenicidade de Fusarium decemcellulare

Abstract

Fusarium decemcellulare is a fungal species commonly found in tropical and subtropical regions, known as saprobe and also parasite tot many woody plants, inducing the formation of galls, oversprouting and cancers. The objective of this work was to characterize F. decemcellulare isolates obtained from different hosts and substrates, by evaluating morphological markers, laboratory crossings aiming at inducing the sexual phase, phylogenetic analysis and pathogenicity test. Single spore cultures were submitted to homothallism test in order to verify the spontaneous formation of fertile perithecia. Of the heterothallic isolates, the mating type was determined by PCR using specific primers and opposite type isolates were then crossed in carrot-agar medium. The phylogenetic analysis was performed with partial sequences of the genes tef-1α, rpb2, acl1 and of the ITS-28S rDNA region, including sequences of reference isolates and of other species. Selected F. decemcellulare isolates were inoculated into cocoa plant seeds for the conduction of pathogenicity tests in greenhouse. All 67 evaluated isolates presented morphological markers typical of F. decemcellulare, according to literature. Among the evaluated isolates, nine were homothallic. Among the heterothallic, 21 belonged to the MAT-1 and 33 to the MAT-2.Approximately 1590 crossings were performed and, in 54 crossings we observed the formation of fertile perithecia, exuding ascospores. The presence of four ascospores per asci in homothallic isolates and eight ascospores per asci in heterothallic isolates was observed. In the phylogenetic analysis, all individual trees presented similar topology, grouping the heterothallic isolates obtained from cocoa plant, mango tree and guarana plant in a distinct clad. Distinct groups were formed by homothallic isolates, isolates from other substrates or hosts and F. decemcellulare reference isolates. In the pathogenicity test, only the heterothallic isolates induced gall symptoms. The results showed that isolates associated with galls and oversprouting on the evaluated hosts belong to a distinct phylogenetic and biological species, different from F. decemcellulare. The results confirm the number of ascospores as marker in separating the homothallic and heterothallic forms.