Wild sunflower (Helianthus annuus) as a potential source of phytopathogenic fungi associated with sorghum diseases

Background/Objective. Weeds can act as alternate hosts for pathogens and promote their persistence in crops. In northern Tamaulipas, Helianthus annuus is an annual weed of agronomic importance that coexists with sorghum and could promote the exchange of phytopathogenic microorganisms between both hosts. The objective was to identify and evaluate the pathogenicity of the fungal microbiota associated with its seeds. Materials and Methods. Seeds of H. annuus were collected from 19 sites in northern Tamaulipas during 2023. Seeds were surface-disinfected and plated on PDA to isolate fungi, which were purified through monosporic cultures and identified by morphology and molecular analysis. The pathogenicity of Fusarium and Alternaria was evaluated in seeds and seedlings under laboratory conditions, as well as in sorghum plants of the Pioneer® 83G19 hybrid in a nursery, using a completely randomized design. Germination, damage severity using a visual scale, plant height, panicle length, and biomass were recorded. Data were analyzed using analysis of variance. Results. A total of 25 pure isolates were obtained, corresponding to Fusarium (92%) and Alternaria (8%). Molecular identification confirmed F. oxysporum (98.35% identity) and A. alternata (99.30%). They had no significant effect on germination (88–97% in inoculated vs. 98% in the control); however, root lesions with an incidence of up to 90% were recorded in seedlings with F. oxysporum isolates. In the nursery, both fungi reduced sorghum growth and biomass compared to the control: A. alternata decreased plant height by 16.2%, whereas F. oxysporum reduced total dry weight and panicle weight by up to 24.6 % and 20.0%, respectively. Likewise, A. alternata (16.6%) and F. oxysporum strain 33 (27.7%) recorded the highest levels of visual damage. Conclusion. Fusarium oxysporum (92%) and Alternaria alternata (8%) were identified morphologically and molecularly in seeds of wild H. annuus. The isolates showed pathogenic capacity on sorghum under controlled conditions. Pathogenic variability depended on the isolate, with epidemiological implications of the weed in inoculum dynamics within the sorghum crop. Integrated weed management can reduce phytosanitary risks in sorghum production systems of northern Mexico.