Design and Implementation of a Robust Metric to Quantify Soilborne Fusarium Oxysporum f. Sp. Vasinfectum Race 4 Inoculum Density

Fusarium oxysporum f. sp. vasinfectum (FOV) is a soilborne fungal pathogen of cotton (Gossypium spp.) and the causal agent of Fusarium wilt. For most races of FOV, a disease complex is formed with the root knot nematode (Meloidogyne incognita) which leads to the infection of cotton plants. Race 4 (FOV4), however, is the exception to this rule because it can infest cotton without the co-infection of the root knot nematode. As a result, FOV4 can invade cotton planted in soil types that are inhospitable for the root knot nematode.

Since its introduction to West Texas, FOV4 has spread rapidly within and between cotton fields. The extent of the spread cannot be determined unless, or until, cotton is planted in the field and the symptoms of Fusarium wilt present. Symptomology is not consistent because symptom expression and severity are dependent on the cotton variety. Moreover, symptomology is dependent upon soilborne inoculum density, which is variable even within a single field. Characterization of the epidemiology of FOV4 in Texas is required to mitigate future spread into other, larger cotton growing regions. We designed and implemented a quantitative real-time polymerase chain reaction (qPCR) based assay to evaluate soilborne inoculum in FOV4 infested fields. Results underscore that soilborne FOV4 inoculum density is highly variable throughout a single field.