PM 7/93 (2) Melampsora medusae

Abstract

Melampsora medusae is a heteroecious rust fungus with Populus spp. as telial hosts (primary hosts on which uredinia and telia are produced) and various conifers as aecial hosts (on which spermagonia and aecia are pro duced). As is the case for other Melampsora species in fecting poplars, M. medusae causes abundant uredinia production on leaves, which can lead to premature de foliation and growth reduction. After several years of severe infection leading to repeated defoliation, the dis ease may predispose the trees to dieback or, for younger trees, even lead to death. Shain (1988) showed evidence of the existence of two formae speciales within M. medusae and named them M. medusae f. sp. deltoidae (syn deltoidis) and M. medusae f. sp. tremuloidae (syn 'tremuloidis'). Unlike M. medusae f. sp. deltoidae which is pathogenic on the poplars of the sections Aigeiros and Tacamahaca, i.e. Populus nigra, P. deltoides, P. trichocarpa, P. balsamifera, P. maximowiczii and their interspecific hybrids (P. × canadensis, P. × generosa and P. × jackii) (Frey et al., 2005; Vialle et al., 2011), the only telial host of M. medusae f. sp. tremuloidae with reported infections in nature in North America is P. tremuloides, belonging to the section Populus (EPPO, 2023a; Vialle et al., 2011).Melampsora medusae originates from North America. Since M. medusae was only reported in Europe on pop lars from the sections Aigeiros and Tacamahaca, and in respect with the host specialization, it can be concluded that only M. medusae f. sp. deltoidae has been reported in Europe so far (EPPO, 2023a; Pinon, 1991; Pinon & Frey, 2005).In addition to M. medusae f. sp. deltoidae, eight Melampsora species have been reported on poplars in Europe to date (Cellerino, 1999; Pinon, 1973; Vialle et al., 2011 Vialle et al., , 2013. Two of them, namely M. laricis-populina and M. allii-populina are pathogenic on the poplars of the sections Aigeiros and Tacamahaca. The six other species, namely M. aecidioides, M. laricis-tremulae, M. magnusiana, M. pinitorqua, M. pulcherrima and M. rostrupii, are only pathogenic on species of the sec tion Populus, i.e. P. alba, P. tremula and their interspe cific hybrids (Frey et al., 2005; Vialle et al., 2011). The eight other Melampsora species have been described on poplar in Europe are also present in other parts of the world (Vialle et al., 2011).For more information on the biology of the pest see the EPPO Datasheet (EPPO, 2023b) and in the Scientific Opinion on the pest categorization of Melampsora medusae (EFSA, 2018).A Flow diagram describing the diagnostic procedure for Melampsora medusae (including the specific diagnostic of M. medusae f. sp. tremuloidae) is presented in Figure 1. | I DEN T I T YName: Melampsora medusae Thümen. Other Scientific Names: Melampsora albertensis J.C. Ar thur, Uredo medusae Thümen (uredinial stage). Caeoma faulliana Hunter (aecial stage) is considered as a syn onym in Global Database. Taxonomic position: Fungi: Basidiomycota: Uredinales. Notes on taxonomy and nomenclature: Note on the name ...