Identificação e caracterização de Fusarium spp. e Pestalotiopsis spp. associados a Carya illinoinensis no Rio Grande do Sul

Abstract

Cultivation of Walnut-pecan (Carya illinoinensis [Wangenh.] K. Koch) has intensified in recent years in the state of Rio Grande do Sul. However, the research related to plant pathology has not developed to the same degree, so producing pecan nuts have faced many unknown diseases in the state. The main objective of this study was: a) identify and characterize causal agents of new diseases on Walnut-pecan in Rio Grande do Sul, and as specific objectives: b) to collect and to identify pathogens in different locations in Rio Grande do Sul, c) evaluate the pathogenicity of isolates collected in plantations of Walnut-pecan from different locations in Rio Grande do Sul, d) perform the isolates morphological characterization collected from diseased plants of Walnut-pecan, and e) to identify the isolates species. For this purpose, samples were taken in seven cities in the state for isolating potentially pathogenic fungi which were also collected and analyzed soil samples to characterize the area and georeferencing. Pathogens, Fusarium spp. and Pestalotiopsis spp. which were not yet reported were tested for their pathogenicity. The first genus was tested by inoculation on substrate, and the second by leaf inoculation with spore suspension. The pathogenic isolates were characterized by mycelial growth, sporulation, conidial dimensions, colony pigmentation and formation of specific structures to each genus. The same isolates were also identified by molecular sequencing of the ITS and TEF-1α genes for Fusarium spp. and ITS and β-tubulin genes for Pestalotiopsis spp. Twelve pathogenic isolates of Fusarium spp. and eleven of Pestalotiopsis spp. were identified. The variables used on morphological characterization were able to differentiate the isolates, especially the width of conidia for Fusarium spp. and diameter of the colonies for Pestalotiopsis spp. The sequencing of the ITS regions and TEF-1α to Fusarium spp. confirmed the separation of isolates through morphological characteristics and identified five species: F. chlamydosporum, F. oxysporum, F. equiseti, Giberella fujikuroi species complex and F. graminearum species complex and for Pestalotiopsis spp. sequencing of the ITS regions and β-tubulin could identify some species, such as P. clavisora and P. cocculi, and other isolates remained without precise identification of the species, since the phylogeny of the genus is still poorly known.