Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/5/2007
Publication Date: 9/1/2007
Citation: Elmer, W.H., Covert, S.F., O Donnell, K. 2007. Investigation of an outbreak of Fusarium foot and fruit rot of pumpkins within the United States. Plant Disease. 92:1142-1146. Interpretive Summary: We investigated an outbreak of Fusarium foot and fruit rot of pumpkin that occurred during 2001-2003 in multiple states within the United States. Isolates collected from diseased fruit and nearby soil were assayed for pathogenicity on pumpkin seedlings and mature fruits. Results of the pathogenicity assay indicated that 82 isolates might be Fusarium solani f. sp. cucurbitae. To confirm this identification, phylogenetic analysis of a subset of these isolates indicated that 42 of the 53 isolates genotyped were the so-called race 1 of Fusarium solani f. sp. cucurbitae (Fsc-1), also known as mating population I of Nectria haematococca. A PCR assay for mating-type revealed that all of the Fsc-1 isolates belonged to just one of the two mating-types, suggesting that the pathogen may be strictly clonal or asexual in the affected fields. These findings provide convincing evidence that the Fusarium foot and fruit rot outbreaks were incited by Fsc-1. This research should help plant breeders develop cultivars of pumpkin with greater resistance to Fsc-1 and benefit plant pathologists by providing molecular tools for the early detection and identification of the pathogen.
Technical Abstract: Isolates of two biologically and phylogenetically distinct species, referred to as Fusarium solani f. sp. cucurbitae race 1 (Fsc-1 = Nectria haematococca mating population I [MPI]) and F. solani f. sp. cucurbitae race 2 (Fsc-2 = N. haematococca mating population V [MPV]), were suspected of causing an outbreak of Fusarium foot and fruit rot of pumpkin during 2001-2003 in Connecticut, New York, Ohio, and Missouri. Both species affect the fruit, but Fsc-1 also affects the crown and causes a stem rot. In this study, 156 isolates from affected plants and from soil under diseased fruits that were tentatively identified morphologically as members of the F. solani species complex (FSSC) were assayed for pathogenicity on pumpkin seedlings and mature fruits. Results of the pathogenicity assay indicated that 82 of the isolates were Fsc-1. The remaining 74 isolates were either nonpathogenic or only weakly pathogenic on the fruit. A subset of 53 test isolates from soil and plants, plus reference isolates of Fsc-1 and Fsc-2, and an isolate from wheat reported to cause a seedling rot on cucurbits, were characterized phylogenetically by sequencing a portion of the translation elongation factor 1-' gene. A BLAST query of the FUSARIUM-ID database at Pennsylvania State University indicated that 42 of the 53 test isolates were Fsc-1, whereas none were typed as Fsc-2. A PCR assay for mating-type (MAT) idiomorph revealed that all of the Fsc-1 isolates were MAT-1-2, suggesting that the pathogen may be strictly clonal in the affected fields. These findings provide convincing evidence that the Fusarium foot and fruit rot outbreaks were incited by Fsc-1.