Fusarium oxysporum f. sp. cubense (Foc) causes a vascular wilt that is threatening banana production around the globe. There are several Foc races determined by host pathogenicity. Foc Race 1 (R1) has a global distribution and primarily affects Lady Finger, Gros Michel, Pome, and Silk cultivars. Foc subtropical race 4 (STR4) typically occurs in subtropical regions and causes disease in R1 susceptible varieties but also in Cavendish cultivars under abiotic stress conditions, while Tropical Race 4 can cause disease in Cavendish under irrespective of the growing conditions. In subtropical regions, R1 and STR4 often occur simultaneously. However, Fusarium wilt in these areas with R1 susceptible varieties is frequently attributed to R1 without testing or verification of the causal race, which overlooks the potential involvement of STR4 or TR4.
Although infections caused by different races exhibit varying levels of disease expression, the severity of disease associated with the vegetative compatibility groups (VCGs) within each R1 or STR4 remains unknown. This raises important questions: if multiple races and/or VCGs of the same race coexist in the soil and are capable of infecting a plant, will one be more competitive in establishing infection and driving disease progression? Additionally, does exposure to abiotic stress in the form of low temperature influence the competitive ability and disease severity of VCGs of different races?
To address these questions, we compared the disease severity of different VCGs associated with STR4 and R1 and evaluated intra-race competitiveness after infection of banana plants in a series of glasshouse experiments. The most competitive VCGs within each race were then used in a subsequent glasshouse experiment to determine whether STR4 or R1 is more competitive when both are present in the soil. The effect of low temperature stress on the VCGs and races was also tested on pure cultures, healthy plants, and Foc infected plants in glasshouse experiments.
Preliminary findings suggest that R1 VCGs have a higher level of disease severity only under optimal growing conditions and corresponds to predominant VCGs re-isolated from infected plants. STR4 VCGs predominantly re-isolated from infected plants have been determined and there seems to be no correlation between disease severity and VCG identity.
Ongoing analyses will provide further insights into the relative competitiveness of R1 and STR4 VCGs in mixed infections and their impact on disease progression. Moreover, assessing the influence of low-temperature stress on pathogen competitiveness and disease severity will help refine our understanding of Fusarium wilt epidemiology in subtropical environments. These results will contribute to improving disease management strategies and risk assessments for banana production in regions where multiple Foc races coexist.