Trichothecene production and pathogenicity of Fusaria isolated from symptomatic soybean roots in Ethiopia and Ghana

Authors: Hartman, Glen; McCormick, Susan; O Donnell, Kerry

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2019
Publication Date: 3/25/2019
Citation: Hartman, G.L., McCormick, S.P., O'Donnell, K. 2019. Trichothecene production and pathogenicity of Fusaria isolated from symptomatic soybean roots in Ethiopia and Ghana. Plant Disease. https://doi.org/10.1094/PDIS-12-18-2286-RE.
DOI: https://doi.org/10.1094/PDIS-12-18-2286-RE

Interpretive Summary: Soybeans is one of the most important crops worldwide. There are a number of pathogens that infect soybean including Fusarium species that often invade soybean roots. Most of the important Fusarium species are known in the United States; however, little research has been conducted to characterize fusarial pathogens in Sub-Saharan Africa. Therefore, in this study we isolated Fusarium species from root segments of symptomatic soybeans grown in Ethiopia and Ghana. Isolates were identified using DNA sequence data, assayed for trichothecene mycotoxin production in the laboratory and tested for pathogenicity on soybean. Molecular phylogenetic analyses revealed the trichothecene mycotoxin-producing isolates comprised three undescribed species within two species complexes. Mycotoxin analyses demonstrated that 18 of the 21 isolates tested possessed the ability to produce trichothecene mycotoxins. Of the 13 isolates tested for their impact on seed germination, five comprising three undescribed species completely inhibited germination, whereas four caused no reduction in germination. Root lesions induced by all 13 isolates were greater than the non-inoculated negative control. Additional variation among the isolates was reflected in differences in percentage of lesion lengths per total root length, which ranged from 34 to 67%. This is the first report characterizing the genetic diversity and mycotoxigenic potential of fusaria isolated from soybean roots in Ghana and Ethiopia. This report will be of interest to soybean pathologists and mycologists that are interested in Fusarium species causing plant disease and producing mycotoxins.

Technical Abstract: Numerous pathogen surveys have revealed diverse Fusarium species threaten soybean production in North and South America. However, little research has been conducted to characterize fusarial pathogens of this crop in Sub-Saharan Africa. Therefore, in this study we isolated Fusarium species from root segments of symptomatic soybeans grown in Ethiopia and Ghana. Isolates were identified using DNA sequence data, assayed for trichothecene mycotoxin production in vitro and tested for pathogenicity on soybean. Molecular phylogenetic analyses revealed the trichothecene mycotoxin-producing isolates comprised three undescribed species within the F. incarnatum-equiseti (FIESC) and F. sambucinum species complexes (FSAMSC). Mycotoxin analyses demonstrated that 18 of the 21 isolates tested possessed the ability to produce the type B trichothecene 4,15-diacetylnivalenol (4,15-diANIV) or T-2 toxin and related type A neosolaniol trichothecenes when grown in agmatine broth or on a solid rice culture. Of the 13 isolates tested for their impact on seed germination, five comprising three undescribed phylospecies (i.e., Fusarium sp. #3, Fusarium sp. FIESC 2 and Fusarium sp. FIESC 29) completely inhibited germination, whereas four caused no reduction in germination. Root lesions induced by all 13 isolates were greater than the uninoculated negative control. Additional variation among the isolates was reflected in differences (' = 0.05) in percentage of lesion lengths per total root length, which ranged from 34 to 67%. This is the first report characterizing the genetic diversity and mycotoxigenic potential of fusaria isolated from soybean roots in Ghana and Ethiopia.