Caracterização morfológica e molecular de isolados de fusarium associados a grãos de milho

Abstract

Fusarium species cause important diseases on maize such as stalk-rot and ear-rot. Fungi in the Gibberella fujikuroi species complex (GFSC) are among the causal agents of these diseases, such as F. proliferatum, F. subglutinans, F. temperatum and F. verticillioides. The present study aimed to characterize the diversity of Fusarium isolates from different maize growing areas in Brazil. Morphological characters and sequences of fragments of the gene that encodes the translation elongation factor (tef1) were used to characterize the isolates. Fifty isolates obtained from maize kernels in different growing areas in Brazil were used. In the morphological characterization the isolates showed variation regarding the colony color and mycelial growth. The colony color varied from salmon to violet and the average diameter of the colonies at three days varied from 2.83 cm to 4.07 cm. The majority of isolates showed long chains of conidia and monophialides. A few isolates showed short chains, false heads and polyphialides. None of the isolates formed chlamydospore. Considering the morphological characterization the isolates were identified as F. proliferatum (4 isolates) and F. verticillioides (46 isolates). In the molecular characterization a neighbor-joining phylogenetic tree was generated from the sequenced fragments of the tef1 gene. From 50 isolates analyzed, 47 grouped together with reference isolates of F. verticillioides forming a sister group to F. musae. Two isolates grouped close to F. fujikuroi and one isolate grouped close to F. proliferatum. Ten haplotypes were identified within the F. verticillioides isolates from Brazil, with six haplotypes being new to the species. The cultural and morphological characters could not be grouped according with the phylogenetic sub-groups and haplotypes. The phylogenetic groups also did not reflect the geographical localization of isolates. The data collected in this study show that F. verticillioides is the dominant species and is widely distributed in the maize growing regions of Brazil, with high genetic diversity in the population.