Spatial Distribution and Bioprospecting of Phytopathogenic Fungi on Amaranthus for Biological Control in Brazil

Abstract

The genus Amaranthus comprises approximately 70 species with a global distribution, particularly in tropical and subtropical regions. In Brazil, Amaranthus hybridus is a highly harmful weed characterised by aggressive ecophysiology, producing more than 250 000 viable seeds per plant and forming extensive soil seed banks. Its resistance to EPSPS‐ and ALS‐inhibiting herbicides exacerbates the problem, rendering chemical control ineffective. Given the need for sustainable solutions, this study aimed to evaluate the fungal diversity of isolates as potential biocontrol agents for Amaranthus species. Amaranthus spp. plants exhibiting leaf and stem lesions were collected in the Brazilian states of Minas Gerais, São Paulo and Goiás, resulting in 192 fungal isolates. Pathogenicity tests conducted on six Amaranthus species and one hybrid ( A. deflexus , A. hybridus , A. lividus , A. retroflexus , A. spinosus , A. viridis and A. hybridus var. patulus ) identified 45 phytopathogenic isolates. Of these, 24 showed promising potential, inducing necrotic lesions and plant mortality 7 days after inoculation. Gene correlation analysis identified isolates belonging to nine genera: Alternaria , Fusarium and Epicoccum were the most frequent, with the most aggressive isolates and the highest number of Amaranthus seedling deaths. Spatial distribution analysis revealed three climatic clusters, highlighting the environmental adaptability of these taxa, which is crucial for field success in the development of a commercial bioherbicide. These results identify fungal isolates as viable candidates for managing herbicide‐resistant Amaranthus populations.