Detection and characterization of Fusarium oxysporum f. sp. vasinfectum VCG0114 (Race 4) isolates of diverse geographic origins

Authors: Bell, Alois - Al; GU, AIXING - Xinjiang Agricultural University; OLVEY, JIM - O&a Enterprises; WAGNER, TANYA - Texas A&M University; TASHPULATOV, JAVLON - US Department Of State; PROM, SANDRIA - Texas A&M University; Quintana, Jose; NICHOLS, ROBERT - Cotton, Inc; Liu, Jinggao

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2019
Publication Date: 3/18/2019
Citation: Bell, A.A., Gu, A., Olvey, J., Wagner, T.A., Tashpulatov, J.J., Prom, S., Quintana, J., Nichols, R.L., Liu, J. 2019. Detection and characterization of Fusarium oxysporum f. sp. vasinfectum VCG0114 (Race 4) isolates of diverse geographic origins. Plant Disease. https://doi.org/10.1094/pdis-09-18-1624-re.
DOI: https://doi.org/10.1094/pdis-09-18-1624-re

Interpretive Summary: A highly virulent cotton wilt pathogen Fusarium race 4 was found in West Texas in 2017, after being known in California since 2001. Isolates obtained from wilted plants collected in 2017 from Texas, in 2015 from China (race 7), and during 2001-2014 from California, and isolates from historical collections were characterized by pathogenicity assays, DNA sequence analysis, and genetic analysis. All cotton pathogenic isolates belonged to genotype VCG0114. All field collected isolates except one caused disease without nematodes and thus belong to a nematode-independent pathotype. Texas isolates were more virulent than isolates from China and California on Pima S-7. Four different sub-types, N, T, MT, MiT were identified based on the transposable elements insertion events in a functional gene. Significant differences in virulence were detected among the sub-types in some locations. No differences in pathogenicity were observed between the California and China collections on Pima S-7; and on ST 474 or Barbren 713, the virulence of the major sub-types were similar. They (race 4 and race 7) all should be referred as VCG0114, or simply Fov4. Simple PCR methods were developed to specifically determine and detect Fov4 as well as the 4 sub-types. This will facilitate not only timely identification of infested fields and seed lots, but also elucidation of evolutionary relationships of the isolates and tracing movement directions, and should help reduce dissemination of these devastating pathogens.

Technical Abstract: A highly virulent cotton wilt pathogen, Fusarium oxysporum f. sp. vasinfectum VCG0114 (race 4) was recently found in West Texas in 2017, after being known in California since 2001. Isolates obtained from wilted plants collected in 2017 from Texas, in 2015 from China, and during 2001-2014 from California, and isolates from historical collections including the race 4 reference isolate were characterized by soil-infestation pathogenicity assays, DNA sequence analysis, and vegetative compatibility analysis. All obtained F. oxysporum f. sp. vasinfectum isolates belonged to VCG0114. All these isolates except one isolate from China caused disease in soil-infestation assay without nematodes and thus belong to nematode-independent pathotype, though some virulence variation exits. Texas isolates were significantly more virulent than isolates from China and California on G. barbadense Pima S-7. Four different sub-genotypes, N, T, MT, MiT were identified based on the transposable element Tfo1 insertion event in the PHO gene, and independent MULE or MITE insertion events into the Tfo1 transposon. Some significant differences in virulence were detected among the sub-genotypes in some locations. No differences in pathogenicity were observed between the California and China collections on Pima S-7; and on G. hirsutum ST 474 or Barbren 713, the virulence of the major sub-genotypes were similar. They all should be referred as VCG0114. Simple PCR methods were developed to specifically determine and detect VCG0114 genotype as well as the 4 sub-genotypes. This will facilitate not only timely identification of infested fields and seed lots, but also elucidation of evolutionary relationships of the isolates and tracing movement directions, and should help reduce dissemination of these devastating pathogens.