Skip to main content
ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Mycotoxin Prevention and Applied Microbiology Research » Research » Publications at this Location » Publication #328555

Title: Races of the celery pathogen Fusarium oxysporum f. sp. apii are polyphyletic

item O Donnell, Kerry

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2016
Publication Date: 2/27/2017
Citation: Epstein, L., Kaur, S., Chang, P.L., Carrasquilla-Garcia, N., Lyu, G., Cook, D.R., Subbarao, K.V., O'Donnell, K. 2017. Races of the celery pathogen Fusarium oxysporum f. sp. apii are polyphyletic. Phytopathology. 107(4):463-473.

Interpretive Summary: Celery is a major vegetable crop within the U.S. with an annual cash value estimated at close to one-half a billion dollars. Fusarium yellows, caused by the wilt pathogen Fusarium oxysporum f. sp. apii (Foa), poses a significant threat to celery production within the U.S. and other countries where it is cultivated. Therefore, this study was initiated to determine the genetic diversity and pathogenic potential of 174 Foa isolates recovered from celery exhibiting symptoms of Fusarium yellows within the U.S. Standard greenhouse pathogenicity experiments were conducted on different celery cultivars to determine what races were present. In addition, comparative genomic data was collected and analyzed to determine the genetic diversity of Foa races and putatively non-pathogenic F. oxysporum isolates recovered from celery crown and root tissues exhibiting symptoms of Fusarium yellows. Results of this study indicated that four Foa races are responsible for Fusarium yellows within this U.S. and that Foa race 2 evolved independently of races 1, 3, and 4. To help prevent the spread of Foa races into new celery production areas, the DNA data was used to develop a robust molecular diagnostic test for the rapid detection and identification of Foa races in celery. This study will be of interest to quarantine officials and plant pathologists because it contains novel information on the current distribution, genetic diversity, and novel molecular diagnostics for the rapid detection and identification of Foa races within the U.S. In addition, knowledge that Foa races evolved independently will benefit plant breeders interested in developing celery cultivars with broad based resistance to Fusarium yellows.

Technical Abstract: Fusarium oxysporum species complex (FOSC) isolates were obtained from celery with symptoms of Fusarium yellows between 1993 and 2013 primarily in California. Virulence tests and a two-gene dataset from 174 isolates indicated that virulent isolates collected before 2013 were a highly clonal population of F. oxysporum f. sp. apii (Foa) race 2. In 2013, new highly clonal isolates, designated race 4, were discovered in production fields in Camarillo, California. Long-read Illumina data were used to analyze 16 isolates: six race 2, one of each from races 1, 3, and 4, and seven genetically diverse FOSC that were isolated from symptomatic celery but are nonpathogenic on this host. Analyses of a 10-gene dataset comprising 38 kb indicated that F. oxysporum f. sp. apii is polyphyletic; race 2 is nested within clade 3, whereas the evolutionary origins of races 1, 3, and 4 are within clade 2. Based on 6,898 single nucleotide polymorphisms from the core FOSC genome, race 3 and the new highly virulent race 4 are highly similar with Nei’s Da = 0.0019, suggesting that F. oxysporum f. sp. apii (Foa) race 4 evolved from race 3. Next generation sequences were used to develop PCR primers that allow rapid diagnosis of races 2 and 4 in planta.