Diversidade genética, morfológica e patogênica de isolados de Fusarium Oxysporum associados à murcha em feijão-caupi

Abstract

The cowpea (Vigna unguiculata) is grown predominantly in the North and Northeast of brazil, with low yields due to a variety of factors, including the fusarium wilt, caused by Fusarium oxysporum f. sp. tracheiphilum. The present study aimed to characterize isolates of F. oxysporum associated with wilt in cowpea through observations of morphological characters, pathogenicity test and analysis of sequences of the translation elongation factor 1-α (tef1) gene. The colony color of the isolates varied from white to violet with dense aerial mycelium. The microconidia were oval to ellipsoid, slightly curved and unicelular, arranged in false heads formed on short monophyalides. The macroconidiaformed on sporodochia were falcate, slightly curved with three to five septa. Of the 27 isolates of F. oxysporum analyzed 20 were pathogenic to cowpea, causing disease with severity ranging from 1 to 99%. The neighbor-joining analysis based on tef1 grouped the isolates into six haplotypes that were not correlated with pathogenicity.. It is suggested from the results of the present study that f. sp. tracheiphilum represents at least three phylogenetic lineages behaving as polyphyletic and paraphyletic, indicating they have independent evolutionary origins.