Blast disease associated with grass weeds in rice production systems of Paraguay

Karina Morinigo-Gimenez, Alfredo Urashima, Alice Chavez, Marta Alicia Fernández-Gamarra, Liliana Talavera-Stefani, Rocio Duarte, Cinthia Carolina Cazal-Martínez, Lidia Quintana

Abstract


Background: Several fungal species within the genus Pyricularia are associated with blast diseases affecting Poaceae crops, including wheat, rice, oat, barley, triticale, and various grass weeds. Among these, Pyricularia oryzae is recognized as a major pathogen due to its significant impact on cereal production worldwide. The fungus can survive on weed hosts, potentially serving as inoculum reservoirs. Objective: To characterize grass weed species acting as alternative hosts for Pyricularia spp. in rice agroecosystems in Paraguay. Methodology: During the 2020/2021 rice season, symptomatic weed samples exhibiting elongated or elliptical lesions with reddish-brown margins and lighter centers were collected across major rice-producing regions. Samples were processed at the Microbiology and Biotechnology laboratories of the Facultad de Ciencias y Tecnología, Universidad Nacional de Itapúa, and the Instituto Paraguayo de Tecnología Agraria (IPTA). Results: Morphological characterization of isolates cultured on oat agar revealed grayish to dark-gray colonies, with conidia hyaline, pyriform to obclavate, and containing two transverse septa. Molecular identification based on ITS region sequencing confirmed isolates from Cynodon dactylon as Pyricularia grisea (99.8% similarity) and from Echinochloa sp. as Pyricularia oryzae (100% similarity). Pathogenicity assays in rice seedlings (cv. IRGA 424) reproduced typical blast symptoms for the rice-derived isolate, whereas the Cynodon dactylon- and Echinochloa-derived isolates elicited differential reactions, including hypersensitive, incompatible, and mild blast-like symptoms. Implications: These findings underscore the epidemiological role of grass weeds as alternative hosts and potential inoculum reservoirs of Pyricularia spp., emphasizing the need to integrate weed monitoring and management into comprehensive blast disease control strategies in rice cultivation systems. Conclusion: Grass weed species present in rice agroecosystems of Paraguay were identified as reservoirs for Pyricularia spp., highlighting their potential role in pathogen survival and dissemination within rice fields.

Keywords


Alternative hosts; Inoculum reservoirs; blast rice disease

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References


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URN: http://www.revista.ccba.uady.mx/urn:ISSN:1870-0462-tsaes.v28i3.65859

DOI: http://dx.doi.org/10.56369/tsaes.6585

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Copyright (c) 2025 Alfredo Urashima, Beatriz Karina Morinigo Giménez, Cintia Cazal Martínez, Alicia Chávez, Liliana Talavera, Rocío Duarte, Marta Fernández Gamarra, Lidia Quintana

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