Detection and Characterization of Fusarium oxysporum f. sp. vasinfectum VCG0114 (Race 4) Isolates of Diverse Geographic Origins

Abstract

A highly virulent cotton wilt pathogen, Fusarium oxysporum f. sp. vasinfectum VCG0114 (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, and during 2001 to 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 of these isolates, except one isolate from China, caused disease in a soil-infestation assay without nematodes. Thus, they belong to the nematode-independent pathotype. Texas isolates were significantly more virulent than were isolates from China or California on Gossypium barbadense ‘Pima S-7’. Four different genotypes (N, T, MT, and MiT) were identified based on the transposable element Tfo1 insertion into the PHO gene and independent MULE or MITE insertions into the Tfo1 transposon. Some significant differences in virulence were detected among the genotypes in some locations. No differences in pathogenicity were observed between the California and China collection isolates on Pima S-7, and the virulence of the major genotypes was similar on the Gossypium hirsutum cultivar ‘Stoneville 474’ or the Barbren 713 germplasm line. Simple polymerase chain reaction (PCR) methods were developed to specifically determine and detect the four genotypes within VCG0114. A specific PCR method to detect all VCG0114 isolates was also developed. These methods will facilitate the timely identification of infested fields and seed lots and the elucidation of evolutionary relationships among the isolates. This should help to closely monitor the movement of the pathogen and reduce dissemination of these devastating pathogens.

Soil-free pathogenicity assay of Fusarium oxysporum f.sp. vasinfectum race 4 on Pima cotton (Gossypium barbadense) seedlings

“…Significantly, a highly virulent race 4 (Fov4), originating in India, was identified in the California San Joaquin Valley in 2004 (Kim et al 2005), west Texas in 2017 (Bell et al 2019) and New Mexico in 2020 (Zhu et al 2020). Fov4 was determined as the pathogen responsible for dead seedlings and black streaks inside tap roots of wilting Pima cotton plants.…”

“…Geographically, Texas is also unique as this location is where western Pima production transitions to upland cotton production to the east. Though upland cotton was once thought to be less susceptible to Fov4, we are now learning that Fov4 may be an inoculum density-dependent disease and can pose serious threat to upland cotton production as well (Bell et al 2019).…”

“…Since the emergence of Fov4 in the US, a number of studies were performed to improve pathogen detection, population diversity, and distribution surveys (Bell et al 2019;Cianchetta et al 2015;Doan 2014;Ortiz et al 2017). In addition, several disease assay methods were described to test Fov4 virulence against cotton varieties (Cianchetta et al 2015;Ortiz et al 2017;Wang et al 2018).…”

Registration of upland cotton cultivar ‘Acala 1517‐20’ resistant to Fusarium wilt race 4

“…Therefore, screening and use of FW‐resistant parental lines in cotton breeding is the first step in transferring FW resistance into high‐yielding US upland cultivars. It is recognized that FOV4 is closely related to FW race 7 (FOV7), which was identified in China (Bell et al., ). Scientists in China have developed several hundreds of cultivars resistant to FOV7 since the 1950s (Zhang, Sanogo, Ma, & Qu, ).…”

“…Race 4 (FOV4) was originally identified in India and cultivars. It is recognized that FOV4 is closely related to FW race 7 (FOV7), which was identified in China (Bell et al, 2019). Scientists in China have developed several hundreds of cultivars resistant to FOV7 since the 1950s (Zhang, Sanogo, Ma, & Qu, 2015).…”