Pythium arrhenomanes , the Causal Agent of Maize Feeder‐Root Rot and Seedling Blight in Argentina

Abstract

Zea mays L. is one of the most important cereal crops in Argentina. In this study, ten isolates were recovered from symptomatic maize plants and rhizosphere soil collected in Pergamino, Argentina and preliminarily identified as Pythium spp. based on cultural and morphological characteristics. Two isolates (Pym 25/123 and Pym 25/125) were selected for detailed morphological and molecular characterisation using the ITS region and COI gene, and for pathogenicity assays on maize and sorghum. Their morphology was consistent with Pythium arrhenomanes , and ITS and COI sequences showed 99% identity with reference strain BR606. Phylogenetic analysis of concatenated ITS and COI sequences further supported their identification as P. arrhenomanes . In vitro assays showed a mean Disease Index of 0.62 for both isolates. In vivo, neither seedling death nor severe damping‐off was observed; however, both isolates significantly reduced root development in maize and sorghum compared with non‐inoculated controls. Re‐isolation from symptomatic roots fulfilled Koch's postulates. These results confirm the pathogenicity of Pym 25/123 and Pym 25/125 and identify them as P. arrhenomanes Drechs. To our knowledge, this is the first report of P. arrhenomanes causing maize feeder‐root rot in Argentina.