Host plant resistance is the most economic and effective strategy for Fusarium wilt control. To implement steps to develop resistant germplasm to this pathogen, existing commercial Acala, non-Acala Upland (Gossypium hirsutum L.) and Pima (G. barbadense) cultivars, as well as improved germplasm were subjected to FOV race 1 (R1) with root-knot nematodes and race 4 (R4) field disease pressures, and non-infested field. All cotton entries tested were infected by R1 and R4, and variability in symptoms forFOV R1 and R4 occurred in both G. hirsutum and G. barbadense cottons. Significant differences were observed for plant survival within each race and between races of FOVs. Disease severity was significantly greater for FOV R4 than for FOV R1 as expressedby foliar symptoms and vascular root staining ratings. Plants infected by FOV tended to be smaller with a larger number of nodes than those grown in non-infested soils. In host plant resistance in Pima cottons, known resistant (Phy-800) and susceptible (DP-744) commercial cultivars under R4 pressure were observed to respond significantly different under R1 pressure. DP7-44 was more resistant than Phy-800 under R1 pressure based on plant survival and vascular staining. The host plant resistance observations may suggest that two independent genes and/or an additional gene may control the R1 and/or R4 resistance. Additional research is needed to address host plant interactions between races. Certain forms of this pathogen can survive for a long time in soils even if the host plant is not present. This research is providing information about the susceptibility of commercial and improved germplasm cottons, allowing growers to make informed decisions regarding the choice of cotton cultivar to plant in fields infested with FOV R1 and/or R4. In addition, this research identified potentially improved resistant germplasm and raises the need to breed cotton in California with resistance to existing FOV races.
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