Title : Beyond Fusarium oxysporum: Multilocus phylogeny reveals hidden Fusarium diversity in cultivated Passiflora species in Colombia
Abstract:
Passiflora fruit crops are economically important in Colombia, especially in the Andean departments of Boyacá and Cundinamarca, but production is limited by diseases commonly attributed to Fusarium oxysporum and Fusarium solani sensu lato. Because morphological traits and the internal transcribed spacer region alone provide insufficient resolution within Fusarium species complexes, the diversity associated with diseased Passiflora plants may be underestimated. This study isolated and characterized Fusarium from purple passion fruit (Passiflora edulis f. edulis), yellow passion fruit (P. edulis), and granadilla (P. ligularis) crops showing vascular wilt, collar rot, or foliar symptoms. Targeted surveys were conducted in commercial fields in Boyacá and Cundinamarca. Vascular wilt was the predominant syndrome, while collar rot was observed at only one site. Fourteen isolates were recovered from internal stem tissues with vascular discoloration and from foliar tissues, then characterized using colony and microscopic features. Most isolates displayed morphology compatible with F. oxysporum. Molecular identification was then performed using concatenated phylogenetic analyses of ITS, translation elongation factor 1-alpha (TEF1), and beta-tubulin (TUB2). Multilocus analysis revealed substantial taxonomic diversity across the F. oxysporum, F. incarnatum-equiseti, F. sambucinum, and F. graminearum species complexes. Five isolates were identified as F. triseptatum, two as F. nirenbergiae, one as F. incarnatum, one as F. weifangense, one as F. sambucinum, and three as F. venenatum. One isolate remained unresolved at species level but was assigned to the F. graminearum species complex. Although several isolates belonged to the F. oxysporum species complex, none corresponded to F. oxysporum sensu stricto. No isolates belonged to Neocosmospora, formerly considered the F. solani species complex, despite the occurrence of collar-rot symptoms. Therefore, the predominance of F. oxysporum-like morphology concealed considerable species-level diversity, including cryptic lineages that could only be resolved by multilocus phylogenetic analysis. Since recovery from symptomatic tissue does not establish disease causality, pathogenicity tests focused on F. triseptatum 3141, F. nirenbergiae 2141, and F. venenatum 3241-1, isolated directly from vascular tissues of plants with representative wilt symptoms. The isolates were inoculated into two-month-old purple passion fruit plants under greenhouse conditions, and disease development was assessed using a severity scale. Isolates 3141 and 3241-1 induced symptoms consistent with vascular wilt and were reisolated from symptomatic inoculated plants, fulfilling Koch’s postulates. One pathogenic isolate originated from granadilla, indicating that pathogenic potential was not restricted to the original host. These results challenge the routine attribution of Passiflora vascular wilt to F. oxysporum based mainly on morphology and demonstrate the importance of multilocus identification for resolving etiologically relevant Fusarium diversity. This evidence supports disease diagnosis, epidemiological surveillance, and development of sustainable management strategies for Passiflora crops. The resulting collection provides a taxonomically informed basis for selecting representative isolates in future pathogenicity studies and evaluating Piper spp. extracts as potential sources of biofungicidal compounds within the SGR-funded project BPIN 2023000100058. Research activities were conducted under Genetic Resource Access Contract No. 121 of January 22, 2016, and its Amendment (Otrosí) No. 21, executed between Ministerio de Ambiente y Desarrollo Sostenible and the Universidad Nacional de Colombia.
