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

O Feijão-caupi é uma leguminosa cultivada predominantemente nas regiões Norte e Nordeste do brazil , apresentando baixo rendimento devido a uma diversidade de fatores, dentre eles a murcha-de-fusário, causada pelo fungo Fusarium oxysporum f. sp. tracheiphilum. O presente estudo teve como objetivo caracterizar isolados de F. oxysporum associados à murcha em feijão-caupi por meio de observações de caracteres morfológicos, teste de patogenicidade e análise de sequencias do gene fator de elongação 1-α (tef1). Os isolados apresentaram coloração variando do branco ao violeta com micélio aéreo bastante denso. Os microconídios apresentaram formato oval a elipsóide, ligeiramente curvado e sem septo, dispostos em falsas cabeças produzidos em monofiálides curtas. Os macroconídios formados em esporodóquios apresentaram formato falcado, ligeiramente curvado com três a cinco septos. Dos 27 isolados de F. oxysporum analisados 20 se mostraram patogênicos ao feijão-caupi, causando doença com severidade variando de 1 a 99%. A análise de neighbor-joining baseada na região tef1 agrupou os isolados em seis haplótipos independentemente de serem ou não patogênicos. Pode-se sugerir a partir dos resultados obtidos no presente estudo que a f. sp. tracheiphilum representa pelo menos três linhagens filogenéticas comportando-se como polifilética e parafilética, indicando assim terem origens evolucionárias independentes.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.Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNP

Elucidating the Colletotrichum spp. diversity responsible for papaya anthracnose in Brazil

Papaya (Carica papaya L.) is among the most important tropical fruits produced in Brazil and is grown in nearly every state. However, several diseases can affect papaya production. Anthracnose stands out among these diseases due to high postharvest yield losses. Previous studies identified Colletotrichum magna (invalid name) and Colletotrichum gloeosporioides causing anthracnose of papaya in Brazil, but species identification was inadequate due to reliance on nuclear ribosomal internal transcribed space (nrITS) and glutamine synthetase (GS) sequences. Thus, the diversity of Colletotrichum spp. causing papaya anthracnose in Brazil may be underestimated. The present study aims to identify the Colletotrichum species associated with papaya anthracnose in Brazil based on broad geographical sampling and multilocus phylogenetic analysis, as well as to assess the prevalence and aggressiveness of the species found. Here, we report C. chrysophilum, C. fructicola, C. gloeosporioides, C. karsti, C. okinawense, C. plurivorum, C. queenslandicum, C. siamense, C. theobromicola, Colletotrichum truncatum causing papaya anthracnose in Brazil. We are also synonymizing Colletotrichum corchorum-capsularis under C. truncatum. Colletotrichum okinawense was the most prevalent species in general and in most sampled locations, and with C. truncatum represents the most aggressive species

Optimal markers for the identification of Colletotrichum species

Colletotrichum is among the most important genera of fungal plant pathogens. Molecular phylogenetic studies over the last decade have resulted in a much better understanding of the evolutionary relationships and species boundaries within the genus. There are now approximately 200 species accepted, most of which are distributed among 13 species complexes. Given their prominence on agricultural crops around the world, rapid identification of a large collection of Colletotrichum isolates is routinely needed by plant pathologists, regulatory officials, and fungal biologists. However, there is no agreement on the best molecular markers to discriminate species in each species complex. Here we calculate the barcode gap distance and intra/inter-specific distance overlap to evaluate each of the most commonly applied molecular markers for their utility as a barcode for species identification. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), histone-3 (HIS3), DNA lyase (APN2), intergenic spacer between DNA lyase and the mating-type locus MAT1-2-1 (APN2/MAT-IGS), and intergenic spacer between GAPDH and a hypothetical protein (GAP2-IGS) have the properties of good barcodes, whereas sequences of actin (ACT), chitin synthase (CHS-1) and nuclear rDNA internal transcribed spacers (nrITS) are not able to distinguish most species. Finally, we assessed the utility of these markers for phylogenetic studies using phylogenetic informativeness profiling, the genealogical sorting index (GSI), and Bayesian concordance analyses (BCA). Although GAPDH, HIS3 and β-tubulin (TUB2) were frequently among the best markers, there was not a single set of markers that were best for all species complexes. Eliminating markers with low phylogenetic signal tends to decrease uncertainty in the topology, regardless of species complex, and leads to a larger proportion of markers that support each lineage in the Bayesian concordance analyses. Finally, we reconstruct the phylogeny of each species complex using a minimal set of phylogenetic markers with the strongest phylogenetic signal and find the majority of species are strongly supported as monophyletic

Why species delimitation matters for fungal ecology: Colletotrichum diversity on wild and cultivated cashew in Brazil

Anthracnose is one of the most important plant diseases globally, occurring on a wide range of cultivated and wild host species. This study aimed to identify the Colletotrichum species associated with cashew anthracnose in Brazil, determine their phylogenetic relationships and geographical distribution, and provide some insight into the factors that may be influencing community composition. Colletotrichum isolates collected from symptomatic leaves, stems, inflorescences, and fruit of cultivated and wild cashew, across four Brazilian biomes, were identified as Colletotrichum chrysophilum, Colletotrichum fragariae, Colletotrichum fructicola, Colletotrichum gloeosporioides sensu stricto, Colletotrichum queenslandicum, Colletotrichum siamense and Colletotrichum tropicale. Colletotrichum siamense was the most dominant species. The greatest species richness was associated with cultivated cashew; leaves harbored more species than the other organs; the Atlantic Forest encompassed more species than the other biomes; and Pernambuco was the most species-rich location. However, accounting for the relative abundance of Colletotrichum species and differences in sample size across strata, the interpretation of which community is most diverse depends on how species are delimited. The present study provides valuable information about the Colletotrichum/cashew pathosystem, sheds light on the causal agents identification,and highlights the impact that species delimitation can have on ecological studies of fungi