Life-history studies of the species of phomopsis occurring on conifers. Part 1

Abstract

An investigation of the present known Phomopsis species on conifers has been undertaken for the purpose of differentiating P. Pseudotsugae the cause of the Phomopsis disease of Douglas fir, from closely allied forms occurring on Douglas fir and other conifer hosts. The present status of the genus Phomopsis , now generally regarded as the imperfect stage of Diaporthe , is discussed. Upon the basis of a broad conception of the genus certain atypical forms whose perfect stages are still unknown are included in the Phomopsis group. These forms approach the form genus Fusicoccum although they appear to have a greater affiliation with Phomopsis . Until the perfect stages have been discovered these species on the border-line of the genus have been placed provisionally in Phomopsis . Eight species are differentiated— Phomopsis occulta Trav. [ Diaporthe conorum (Desm.) Niessl], P. juniperovora Hahn, P. conorum (Sacc.) Died., P. montanensis n. sp., P. Strobi Syd., P. Pseudotsugae Wilson, P. abietina (Hart.) Wilson & Hahn and P. Boycei n. sp. A dichotomous key is given. Phomopsis occulta which has been culturally proven the imperfect stage of Diaporthe conorum is the only species of the conifer group whose complete life-history has been discovered. P. conorum , which inhabits cones and other plant parts as well, does not belong to the life-history of D. conorum . The conifer Phomopsis spp. exhibited great constancy with regard to culture growth characteristics. The characters on a single medium are described for the group. Variability amongst the morphological characters was observed. The characters of the pycnidial stromata were by no means constant. Spore shape and size on the other hand were fairly constant and could be relied upon as specific characters, providing the same type of spore was considered. Variation in size occurred, but within a specific range, which could be determined by a measurement study of forms throughout the host range of the species. Spores produced in culture on artificial and natural media showed satisfactory agreement with spores produced in nature. There were indications of physiological strains within the groups of forms studied. The conifer Phomopsis spp. showed both wide and extremely limited host relationships. Certain of the species are now known to be widely distributed geographically, occurring on a comparatively large number of hosts, e.g. P. occulta occurred on fourteen host genera and its habitat included both North America and Europe, whereas P. abietina appeared to be limited to the smaller branches of a single host, and to occur only on the Continent in Germany and France.