Investigating the population dynamics of <i>Fusarium oxysporum</i> f. sp. <i>eustomae</i> causing stem rot in lisianthus with the PCR-based markers and virulence

Lisianthus is an economically important cut flower in Taiwan. Fusarium oxysporum f. sp. eustomae (Foe) was identified as major pathogen and were separated into Group Ib and II in Taiwan. This study assessed virulence of Group Ib and Group II on four commercial lisianthus cultivars, and designed specific PCR markers based on secreted in xylem (SIX) genes, validated for detecting Foe groups, and used to investigate Foe population dynamic in fields. Results showed that Foe elicited varying degrees of disease severity in four commercial lisianthus cultivars. Group Ib was more aggressive in Arena III Pink Flash, and Group II was more aggressive in Voyage II First Love, while Reina III Pink Flash showed most resistant overall. For SIX genes profile analysis, Group Ib carried SIX6 and Group II carried SIX1 and SIX13. The primer pairs, SIX6-220628-F/R and SIX1-220813-F/R, were developed to detect Group Ib and Group II, respectively, based on multiplex touchdown PCR assay. These two primer pairs could detect and differentiate Foe groups in infected plant tissues without interference from host DNA. Field surveys indicate that Foe was the dominant pathogen from winter to spring, and Group Ib and II coexisted in different greenhouses with varying prevalence. Group Ib and Group II isolates co-infected the same lisianthus plant. These findings highlight cultivar-pathogen interactions in the field and the potential challenges of disease management. Our new PCR protocols provide practical tools for Foe detection and monitoring, supporting integrated pest management.