Patogenicidade, Transmissão de Fungos Associados a Sementes de Amendoim, Caracterização Morfológica e Molecular de Colletotrichum fructicola

Abstract

Peanut (Arachis hypogaea L.) is an important economic and social crop in several regions of Brazil,and is widely cultivated in agricultural systems ranging from traditional to technologically advanced. However, the productivity and health quality of this oilseed are frequently compromised by fungal diseases, many of which are directly associated with the seeds used for sowing. The presence of pathogenic microorganisms in seeds can compromise not only germination and seedling vigor, but also act as a primary source of inoculum for the establishment and spread of diseases in the field. In this context, seed health analysis plays a fundamental role in identifying phytopathogenic fungi and assessing their transmission capacity and pathogenicity. Assessing these aspects is essential for developing effective control strategies and ensuring the health of the propagation material used by farmers. Chapter I determined the incidence of fungi associated with the seeds of peanut cultivars (Tatu Vermelho, BR-1, BRS 151 L-7 and Caiapó), where it is influenced by both the cultivar and the presence of the pod and the tegument. It was found that the incidence was higher in the treatment with the presence of the pod (CDCV). Among the genera identified, Fusarium sp. and Colletotrichum stand out, with the highest incidence. Transmissibility via seed-plant of Fusarium sp., Colletotrichum sp., Rhizoctonia sp., Phoma sp. and Lasiodiplodia sp. was found, being also identified in abnormal seedlings, dead seeds and normal plants. The pathogenicity analysis demonstrated that all isolates of Fusarium sp., as well as Colletotrichum sp., Rhizoctonia sp., Macrophomina sp. and Lasiodiplodia sp., were pathogenic to peanut plants. In Chapter II, a new species of Colletotrichum was identified, causing anthracnose in peanut crops, in the municipality of Conceição do Araguaia/Pará. The initial symptoms of the disease were characterized by small brown spots, which over time, increased in size, with rounded and oval shapes, with lesions located on the adaxial and abaxial surfaces of peanut leaves. Microscopic Analytics of the morphological characteristics of colonies and spores grown in PDA medium were consistent with the genus Colletotrichum. Molecular identification of the fungal isolates was performed with PCR amplification and sequencing of the ITS region and the genes GAPDH, APMAT, glutamine synthetase (GS) and β-tubulin (TUB2). BLAST analysis of these four genes showed 88-100% identity with the corresponding sequences in GenBank, of Colletotrichum fructicola. The result of the phylogenetic analysis also indicated that the pathogen was identified as C. fructicola. Koch's Postulates were fulfilled, with the inoculated plants reproducing the typical symptoms of anthracnose and the reisolation of the pathogen, with the same characteristics as C. fructicola. Thus, this dissertation work was able to prove two interconnected research axes: the sanitary analysis of peanut seeds, focusing on the transmission and pathogenicity of associated fungi, and the unprecedented record of C. fructicola as an etiological agent of anthracnose in the crop, thus contributing to the advancement of knowledge about the dissemination of pathogens by emerging seeds in peanut and their impacts on plant health.