Hyperparasitism of Scytalidium uredinicola on western gall rust, Endocronartium harknessii

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Abstract
Scytalidium uredinicola is a destructive hyperparasite of western gall rust, Endocronartium harknessii, that reduces the inoculum potential of the rust. It disintegrates spores and the basal cell region of the active rust sori and produces abundant arthroconidia among the rust spores to give the infected sori a yellowish-green to whitish-gray appearance, depending on the stage of infection. Hyphae of S. uredinicola are able to penetrate the wood tissue of the galls and destroy rust hyphae to a depth of 300 μm below the sori. When the parasite hyphae accumulate in the wood tissue, rust hyphae below the invaded area also appear to be degraded. On water agar, hyphae of S. uredinicola disintegrate rust spores within 48–72 h, without penetration. The use of S. uredinicola for biological control of pine stem rusts is considered promising.