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Title: Life history studies of the species of Phomopsis occurring on conifers
Author: Hahn, Glen Gardner
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1928
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An investigation of the present known phomopsis species on conifers has been undertaken. Eight species are differentiated and their synonomy is given; two species are described provisionally as new, - Phomopsis L.ontanensis n. sp. and P. Boycei n. sp. The cultural life-history of Diaporthe conorum, (Desm.) Miessl (syn.:D. occulta, (Fuck.) Mke., D. pitya, Sacc.) ls given. Monoascospore cultures of D. conorum produced both the perfect and the imperfect stage, Phomopsis occulta, Trav. Monopycnidiospores obtained from a culture derived from a monoascospore isolation, reproduced the ascomycetous stage, D. conorum. Diaporthe conorum produced the perfect stage as readily from monoascospore cultures, as from cultures derived from monoascus isolations, or the mixture of two monoascospore strains. The addition of Taka-diastase to cultures of D. conorum did not appreciably stimulate perithecial production. Phomopsis conorum, (Sacc.) a species distinct morphologically and physiologically from Phomopsis occulta (D. conorum). The perfect stage of P. conorum, which inhabits not only cones but other plant parts as well, is not known. Limited tests in which strains of Phomopsis Pseudotsugae, Wilson from Great Britain and the continent, were mixed in culture, gave negative results so far as ascogenous stage formation was concerned. The perfect stage of this fungus as yet has not been proven definitely. Phomopsis species isolated from conifers showed a general agreement amongst their forms with regard to the constancy and persistency of the culture growth characteristics. This uniformity applied equally to forms collected from hosts widely separated both geographically and phylogenetically. Spore shape proved to be a valuable morphological character for the differentiation of species. The shape of culturally-produced spores both A and B showed generally excellent agreement with that of spores produced in nature. Variation in spore size occurred both for the ascospores of Diaporthe conorum and the pycnidiospores of the various Phomopsis species investigated. This variation took place within a given specific range which appeared to be fairly constant. It was found that the specific range of the fungus species could be determined by a study of forms of the particular organism throughout its host range. Neither the shape nor the size of ascospores' was influenced by artificial growth of D. conorum on broad- leaved host substrata. The relationship between this conifer Diaporthe,and forms on broad - leaved hosts is indicated. The conifer Phomopses 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 14 host genera and its habitat included both North America and Europe. Species such as P. ahietina appeared to be limited to a single host, and to the smaller branches of that host. This fungus is known only to occur on the continent in Germany and France. In artificial inoculation experiments, negative results were obtained in attempting to infect Abies pectinata with Phomopsis abietina, (Hart.) Wilson et Hahn. Negative results are also reported for Phomopsis conorum upon Pseudotsuga Douglasii, and for P. occulta from the same host. A discussion upon the formation and germination of the B or filamentous spore is given, together with a brief consideration of sex in the genus Diaporthe. There were evidences of sex isolation in the group Diaporthe; for strains of this ascomycete were fully capable of reproducing the perfect stage from monoascospore isolation cultures. Strains of Phomopsis occulta isolated from nature rarely produced the perfect stage. Only two cases were ob- served. Eighty-one forms of Phomopsis occulta continued to reproduce the imperfect stage generation after generation on both hard agars and natural media In all 177 forms of conifer Phomopses (8 species) were observed in culture and the perfect stage was found only in two instances.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available