Stem rot (Sclerotium oryzae) in rice crops on the southern region of Paraguay

The expansion of rice cultivation in Paraguay observed in the last five agricultural seasons, together with the new technologies applied, has been accompanied by an increase in the presence of diseases affecting rice leaf sheaths and stems. In view of the scarcity of information in the country on some of these diseases, this study was carried out to characterise rice stem rot. Samples of symptomatic plants were collected from commercial lots located in the southern region of the country, and routine techniques in plant pathology for the study of mycoses were applied, such as macro and microscopic observations, in vitro sowings, and the study of morphological and cultural characteristics of the fungus. The pathogenicity of the fungus was determined by inoculations on healthy 50-day-old rice plants. Associated with the symptoms observed on rice pods and stems, the fungus Sclerotium oryzae Catt was identified as causing irregular black lesions on the leaf sheaths at the water line. As the disease progressed, it caused lesions on the sheaths and leaf blades, and finally stem rot with the formation of sclerotia inside the affected stems. The symptomatology observed in the rice plants and the cultural and morphometric characteristics of the pathogen Sclerotium oryzae were consistent with those reported in the bibliographical references analysed.