Fusarium solani f. sp. cucurbitae race 2: An opportunistic pathogen of plants and people

In two recent studies, clinical and hospital environmental isolates in the Fusarium solani species complex (FSSC) were sequenced; one of the most common lineages was FSSC Group 1, a phylogenetic species conspecific with F. solani f. sp. cucurbitae race 2 (Fsc2), a plant pathogen that causes fruit rot of cucurbits. The first objective of this work was to study Fsc2 and the related but distinct species Fsc race 1 (Fsc1) as plant pathogens; because clean seed is critical for disease control, experiments were conducted to determine if visual inspection of fruits could predict whether seeds would be infected. Since Fsc1 and Fsc2 are not easily distinguished morphologically, taxon-specific primers were designed from translation elongation factor 1-alpha sequences. Isolates from pumpkin fruits and seeds were identified as Fsc1 based on PCR; Fsc2 was not isolated. No infected seeds were recovered from lesion-free fruit, so visual inspection and exclusion of symptomatic fruit is sufficient to obtain uninfected seed.;The second objective was to determine if clinical, hospital environmental, and sewage isolates conspecific with Fsc2 are plant pathogenic and members of the same biological species as Fsc2 from cucurbits, and to determine if these isolates can tolerate 37°C. Isolates from the different sources did not differ in virulence on zucchini fruits and all were sexually compatible with plant isolates. All isolates germinated, grew, and sporulated equally well at 37°C. FSSC Group 1 and Fsc2 are apparently synonyms.;Environmental sources of FSSC Group 1(=Fsc2) are important to the epidemiology of both human and plant diseases caused by this organism. The third objective was to further identify and quantify FSSC Group 1 in the environment. FSSC Group 1 was detected in five and six of 14 community shower drains by culturing and PCR, respectively. F. solani was detected from all drains, and, based on quantification with real-time PCR, was a major component of the total Fusarium. FSSC Group 1 was detected from sewage but did not survive the wastewater treatment process. FSSC Group 1 was rarely isolated from post-harvest cucurbit fruits and was not found in cucurbit fields in California.