|ORTIZ, CARLOS - Texas A&M University|
|Bell, Alois - Al|
|MAGILL, CLINT - Texas A&M University|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2016
Publication Date: 10/14/2016
Citation: Ortiz, C.S., Bell, A.A., Magill, C.W., Liu, J. 2016. Specific PCR detection of Fusarium oxysporum f. sp. vasinfectum California Race 4 based on a unique Tfo1 insertion event in the PHO gene. Plant Disease. 101(1):34-44.
Interpretive Summary: Fusarium oxysporum f. sp. vasinfectum (Fov) race 4 causes severe wilt of cotton and has become an increasingly important problem in the cotton producing areas in California. The pathogen is still confined within California, but it can spread into new areas by movement of seed, soil, and plat debris. A reliable detection method is imperative for early identification of infested fields and seed lots in order to prevent further movement. Available race 4 detection assays including a PCR method and a commercial kit cross react with race 3 and race 7. Herein, a method was developed to discern the highly virulent Fov race 4 from other Fov races, including the race 3 and race 7, and other Fusarium species and soilborne fungi. The method was reliable in detecting California race 4 with no cross reactivity found to date. Therefore, the assay will improve the specificity for detecting California race 4.
Technical Abstract: A highly virulent race 4 (Cal race 4) of Fusarium oxysporum f. sp. vasinfectum (Fov) was identified in California cotton fields in 2001, and has since been found in increasing numbers of fields. Cal race 4 isolates contain a unique Tfo1 transposon insertion in the PHO gene that was not found in other Fov genotypes. Based on this insertion, a multiplex PCR method was developed to detect the Cal race 4 pathogen. A panel of Fov isolates representing different vegetative compatibility groups (VCG) and DNA sequence types was assembled to test the specificity of the detection method. Sixteen of 17 Cal race 4 isolates produced a 583 bp amplicon; the other isolate produced a 396 bp amplicon reflecting the absence of the Tfo1 insertion. This isolate was a moderately virulent pathogen among Cal race 4 isolates. Eighty other F. oxysporum isolates associated with cotton and 11 other formae speciales of F. oxysporum produced only the 396 bp amplicon. The method also distinguished Cal race 4 isolates from India race 4 isolates and China race 7 isolates, which did not possess the unique Tfo1 insertion but otherwise had identical DNA sequences and all belong to VCG0114. The method provides an effective tool for timely identification of infested fields and seed lots, and should help reduce dissemination of Cal race 4 in the US Cotton Belt.