Five species of the Fusarium solani species complex cause sudden death syndrome and root rot of soybean in Brazil

Sudden death syndrome (SDS) and red root rot (RRR) are important diseases of soybean and have different members of the Fusarium solani species complex (FSSC) as causal agents. Brazil is the world’s greatest soybean producer; however, knowledge about occurrence and etiology of those diseases in the country is still limited. The objectives in this work were (i) to define the FSSC species that are associated with soybean in Brazil through molecular phylogeny; (ii) to confirm their pathogenicity to soybean; (iii) to identify through PCR the presence of FvTox1 and FvNIS1, phytotoxin coding genes, in the genomes of different FSSC species; and (iv) to evaluate whether the disease symptomatology induced by species of Clade 2 and 3 can be distinguished. We obtained 54 isolates from different soybean producing regions in Brazil. Molecular phylogeny analysis based on the second largest subunit of RNA polymerase (RPB2) and intergenic region of anonymous loci 44 (L44) gene fragments identified the isolates as F. paranaense ( n = 28), F. solani ( n = 11), F. brasiliense ( n = 2), F. crassistipitatum ( n = 3), F. tucumaniae ( n = 4), and Fusarium sp. ( n = 6). All representative isolates used in the pathogenicity tests induced typical disease symptoms characterized as interveinal foliar chlorosis, necrosis and root rot 35 days after inoculation to soybean plants. No statistical difference in disease severity was observed among Fusarium species from different FSSC Clades. We also designed primers and identified the presence of the FvTox1 and FvNIS1 genes in the genome of FSSC species present in Brazil. Species of Clade 2 and Clade 3 of the FSSC carry phytotoxin encoding genes and induce symptoms of SDS and RRR. Our results confirm the diversity of SDS causal agents in Brazil which should raise the attention of the community to expand their research of SDS genetic resistance and disease control focusing on the interaction of soybean with the different F. solani species present in Brazil.