Distribution, Detection, Evolutionary Relationship, and Pathogenicity of the Four Sub-Genotypes of Race 4 (VCG0114) of Fusarium Wilt Pathogen of Cotton

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. From wilted plants, we isolated 66 race 4 and 19 putative race 7 isolates from West Texas in 2017 and from China in 2015, respectively. Pathogenicity tests on three cotton hosts, DNA sequence analyses, and VCG analyses of these isolates compared to that of California isolates showed that race 4 and 7 were not different. Texas isolates were significantly more virulent than China and California isolates on Pima S-7. Virulence of China and California isolates was similar. All isolates belonged to the nematode-independent pathotype and VCG0114. Four sub-genotypes within VCG0114 were identified based on transposable element (Tfo1, MULE, and MITE) insertion patterns within the PHO gene and their evolutionary relationship was established. Texas isolates were comprised of two sub-genotypes of which one was the major sub-genotype of California and the other the minor sub-genotype of China. Simple PCR methods were developed to specifically determine and detect the VCG0114 genotype as well as the four sub-genotypes. This will greatly facilitate monitoring and tracing the movement of these sub-genotypes of VCG0114.