Widespread Occurrence of Pythium arrhenomanes Pathogenic to Rice Seedlings

Toda, T., Iwasa, A., Fuji, S., and Furuya, H. 2015. Widespread occurrence of Pythium arrhenomanes pathogenic to rice seedlings around japanese rice fields. Plant Dis. 99:1823-1831. In Japan, rice seedlings grown in nurseries and used for transplanting are subject to a damping-off disease caused by Pythium spp. In this study, 148isolatesofPythiumspp.wereobtainedfromriceseedlingsin39locationsofnorthernJapan.Amongtheisolates,137wereidentifiedasPythium arrhenomanes using polymerase chain reaction (PCR) with speciesspecific primers, DNA sequencing analyses of the internal transcribed regions of ribosomal DNA, and the morphologies of oogonia, antheridia, oospores,andzoosporangia.InoculationtestsshowedthattheisolatesidentifiedasP.arrhenomaneswerepathogenictoriceseedlingsandparasiticto southern crabgrass with only minor damage. P. arrhenomanes was reisolated from the roots of both rice seedlings and southern crabgrass. Poaceae weeds, hosts of Pythium spp., grow in and around nurseries and in ridges surrounding rice fields. To detect Pythium spp., 188 Poaceae weeds were collected from 37 locations in Akita Prefecture. P. arrhenomanes was frequently detected in 164 weed roots from all locations by PCR using species-specific primers.Thus,we determinedthatP. arrhenomanesexists in and around rice seedling nurseries and rice fields, and that it is much more widely distributed than previously recognized in northern Japan.