Etiology and variability of the causal agent of soybean anthracnose in Brazil

Author(s)

Flávia Rogério

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2015-04-13

Examining board members

Nelson Sidnei Massola Júnior; Maísa Ciampi Guillardi; Claudine Dinali Santos Seixas

• Advisor: Nelson Sidnei Massola Júnior

Abstract

Diseases are among the main factors that limit high yields in soybean crops. Anthracnose is a major disease of the culture, caused, according to the literature, by Colletotrichum truncatum. In Brazil, there are no detailed studies on the real etiology of the disease. Identification and distribution of Colletotrichum species in different soybean producing regions of Brazil is critical to understand the epidemiology and develop effective control of these diseases. The polyphasic approach was used to characterize 51 isolates from different soybean producing regions in Brazil, using molecular, cultural, morphological and pathogenic analyses. Genomic DNA extraction was performed and polymerase chain reaction (PCR) of GAPDH, HIS3 genes and the ITS region. Phylogenetic analyses were carried for each gene isolated and in the concatenated form. A phylogenetic tree was constructed according to the Bayesian inference, using concatenated genes. We also analyzed the intraspecific genetic diversity of the isolates by building a network of haplotypes in the collection. The remaining characterizations were performed with 10 strains selected based on the molecular characterization. The cultural characterization was performed in PDA and SNA media and sporulation, mycelial growth rate, colonies color, morphology and topography were evaluated. The morphological characterization was also performed in the same culture media by measuring 50 conidia per isolate in addition to observation of acervuli, setae and appressoria. The pathogenic characterization was performed using the variety BMX Potencia inoculated with toothpicks colonized with the fungus as well as by seed inoculations using the water restriction technique followed by sowing in sterilized soil. The evaluation of the pathogenicity was based on disease incidence and severity. The molecular analysis of Colletotrichum isolates showed only occurrence of C. truncatum species associated with soybean in the collection studied. However, the intraspecific analysis showed a high variability degree, with the presence of 27 haplotypes in the collection, many of them genetically identical to strains of C. truncatum elsewhere in the world. There was high cultural, morphological and pathogenic variability among the isolates. Pathogenic characterization showed, in both methods, high variation in aggressiveness of isolates. Isolates CMES 1075 and CMES 1080 were more aggressive due to their ability to cause bigger lesions on soybean stem and affect more severely the development of inoculated seeds. It was not possible to correlate intraspecific variability observed in the isolates with their respective geographical origin. (AU)

• FAPESP's process: 13/03726-2 - Etiology and variability of the causal agent of soybean anthracnose in Brazil
• Grantee: Flávia Rogério
• Support Opportunities: Scholarships in Brazil - Master