Detection and Genotyping of Fov4 (Race 4, VCG0114), the Fusarium Wilt Pathogen of Cotton.

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), is an important disease of cotton. More than 14 different genotypes as determined by VCG and sequence analyses are known to occur in the United States. Fov4 (race 4, VCG0114), originally found in India, was first detected in the United States in 2001 in California and recently in 2017 and 2019 in Texas and New Mexico, respectively. Four sub-genotypes of Fov4 have been identified, with Fov4 N, T, and MiT genotypes occurring in California, and Fov4 T and MT genotypes occurring in Texas. Unlike other genotypes of Fov in the United States, Fov4 does not require the presence of root-knot nematodes (Meloidogyne incognita) to cause severe wilt in cotton and is a major concern to US cotton growers. Fov4 can be spread through a variety of mechanisms including through infected seed. Once a field is infested, the fungus becomes endemic since there are no economically viable means to eradicate the pathogen from infested fields. Therefore, a rapid and accurate detection method is essential for early identification of infested fields and seed lots to prevent further spread of Fov4. This chapter describes multiplex and singleplex PCR diagnostics for detection of Fov4, and for detection and genotyping N, T, MiT, and MT genotypes of Fov4 from wilted cotton plants.