Characterization of soybean seedborne Fusarium spp. in the state of Kansas, USA.

Abstract

Fusarium spp. are among the most important pathogen groups on soybeans. However, information regarding this genus on soybean seeds in the state of Kansas remains underexplored. Therefore, the goal of this study was to characterize the identity, frequency, and pathogenicity of soybean seedborne Fusarium spp. in the state of Kansas. For the identification and frequency of seedborne Fusarium spp., culture-dependent (i.e. semi-selective medium) and -independent (i.e. DNA metabarcoding) approaches were used. Also, information regarding the pathogenicity of the most common seedborne Fusarium spp. from soybeans was assessed to better understand their role as soybean pathogens. Overall, eleven Fusarium spp. were identified in this study. Semi-selective media showed that approximately 33% of soybean seed samples were infected with Fusarium spp. Moreover, Fusarium spp. were isolated from seed sampled from 80% of the locations in Kansas. Furthermore, a low incidence of Fusarium spp. was observed within infected seed samples and averaged 2%. Nine Fusarium spp. were found in soybean seeds using the culture-dependent approach. Fusarium semitectum was the most frequent, followed by F. proliferatum and F. verticillioides. Fusarium acuminatum, F. equiseti, F. fujikuroi, F. graminearum, F. oxysporum, and F. thapsinum were found in lower frequencies among naturally infected seeds. DNA metabarcoding experiments showed that Fusarium spp. are more frequent in soybean seeds than previously known. All asymptomatic soybean seeds analyzed, using Illumina MiSeq platform, showed the presence of the genus Fusarium including two pathogenic species, F. proliferatum and F. thapsinum. Fusarium acuminatum, F. merismoides, F. solani, F. semitectum, and Fusarium sp. were also identified using the culture-independent approach. Preliminary results also showed that F. proliferatum and F. thapsinum were observed in all three major soybean seed tissues: seed coat, cotyledons, and the embryo axis. Depending on the soybean genotype, inoculum potential and aggressiveness, F. proliferatum, F. graminearum, F. fujikuroi, F. oxysporum, F. semitectum, F. thapsinum, and F. verticillioides were pathogenic to soybean and negatively affect soybean seed quality, at different levels, in controlled conditions. Moreover, F. equiseti and F. acuminatum did not cause significant damage to soybean seeds and seedlings. Understanding seedborne Fusarium spp. and their influence on soybean seed and seedling diseases is critical for the development of effective disease control strategies, especially regarding early detection of pathogenic strains in seeds (i.e., seed health testing), ensuring the crop productivity, quality, and safety.