Chrysanthemum wilt caused by Fusarium incarnatum: Etiology unveiled through polyphasic taxonomic methods

During the 2019 and 2020 planting seasons, an unexpected and rapid wilting disease affected chrysanthemum fields, impacting both the Pusa Centenary and Karnal Pink cultivars. Affected plants displayed initial signs of lower leaf yellowing, progressing to leaf browning and defoliation, followed by partial wilting. This disease eventually led to complete plant collapse, marked by vascular browning and eventual death. Upon isolation, the fungus linked to this wilt displayed whitish mycelium initially, evolving into light yellow aerial mycelium and brown pigments as it matured. Detailed examination of the purified fungus from these chrysanthemum cultivars identified it as Fusarium incarnatum-Equiseti species complex (FIESC). Pathogenicity tests confirmed its ability to induce wilt symptoms in six-week-old chrysanthemum seedlings within 6-12 days post-inoculation using a soilinoculation method. To validate the identity of the isolates, sequencing was performed using multi-gene regions (ITS, Tef-1 alpha, RPB1, and RPB2), and analysis through Fusarium-ID and Fusarium-MLST databases definitively categorized the pathogen as Fusarium incarnatum. Moreover, molecular phylogenetic analysis placed the Fusarium isolates within the Incarnatum group. This study establishes the association of Fusarium incarnatum (FIESC) with chrysanthemum wilt, backed by a comprehensive range of pathological, symptomatic, cultural, microscopic, and molecular-taxonomic tools. The findings are expected to significantly aid in pathogen detection, accurate species identification, and highlight the need for specific marker genes to understand pathogen diversity, ultimately assisting in the development of effective disease management strategies in the future.