Detection, genotyping and virulence characterization of Fusarium wilt race 4 (VCG0114) causing cotton wilt in three Texas fields

Fusarium wilt of cotton, caused by the soilborne fungus Fusarium oxysporum f.sp. vasinfectum race 4 (Fov4, VCG0114), is a serious disease that has adversely affected cotton production in California since 2001 and in the Upper Rio Grande Region near El Paso in the border areas between Texas and New Mexico since 2017. Fov4 was isolated from cotton stem samples collected from wilted or asymptomatic plants adjacent to the wilting plants from the El Paso area. The MT genotype was the only Fov4 genotype found in two fields in the Lower Valley of El Paso and the T genotype was the only Fov4 genotype found in one field in the Upper Valley Region of El Paso. No N, MiT or mixed genotypes of Fov4 were detected in any of these fields. Furthermore, the F. oxysporum f.sp. vasinfectum isolates were exclusively Fov4. The results support the observation that the MT genotype of Fov4 is mainly distributed in the Lower Valley of El Paso and the T genotype of Fov4 is mainly distributed in the Upper Valley Region of El Paso. Virulence of the MT genotype of Fov4 was higher than that of the T genotype. PCR methods previously developed for Fov4 specific PCR detection and multiplex Fov4 genotyping were validated by VCG analyses of the newly obtained isolates. These PCR methods were adapted for the in planta detection of Fov4, but Fov4 genotyping was limited to the detection of T, MT and MiT genotypes. It is important to continue to monitor dynamic population structure of Fov4 genotypes to prevent the spread of Fov4 and optimize disease control.