Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1986 Epidemiology of Mycosphaerella populorum Thompson on the foliage and stems of Populus species Christopher John Luley Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agriculture Commons, and the Plant Pathology Commons Recommended Citation Luley, Christopher John, "Epidemiology of Mycosphaerella populorum Thompson on the foliage and stems of Populus species " (1986). Retrospective Theses and Dissertations. 8096. https://lib.dr.iastate.edu/rtd/8096 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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Other University Microfilms International Epidemiology of Mycosphaerella populorum Thompson on the foliage and stems of Populus species by Christopher John Luley A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Plant Pathology, Seed and Weed Sciences Major; Plant Pathology Approved: Signature was redacted for privacy. xri èharge of Signature was redacted for privacy. For the Majgp/Department Signature was redacted for privacy. Iowa State University Ames, Iowa 1986 ii TABLE OF CONTENTS Page GENERAL INTRODUCTION 1 SECTION I. ASCOSPORE PRODUCTION, RELEASE AND INFECTION 5 OF POPULUS BY MYCOSPHAERELLA POPULORUM INTRODUCTION 6 LITERATURE REVIEW 8 MATERIALS AND METHODS 20 RESULTS 29 DISCUSSION 57 LITERATURE CITED 65 SECTION II. CONIDIAL RELEASE, GERMINATION AND INFECTION 71 OF POPULUS BY SEPTORIA MUSIVA INTRODUCTION 72 LITERATURE REVIEW 74 MATERIALS AND METHODS 84 RESULTS 87 DISCUSSION 111 LITERATURE CITED 117 SECTION III. IN VITRO ASCOCARP PRODUCTION 121 OF MYCOSPHAERELLA POPULORUM INTRODUCTION 122 LITERATURE REVIEW 123 MATERIALS AND METHODS 129 RESULTS 131 DISCUSSION 134 iii Page LITERATURE CITED 135 SUMMARY AND CONCLUSIONS 138 LITERATURE CITED 143 APPENDIX: FIGURES AND TABLES 145 ACKNOWLEDGMENTS 157 1 GENERAL INTRODUCTION Septoria leaf spot and canker are serious foliar and stem diseases of certain Populus species and hybrids in North America (Waterman, 1954). Introduced poplars or hybrids with P. trichocarpa Torr. and Gray, 2i, balsamifera L., or deltoides Bartr. parentage were reported as being particularly susceptible (Waterman, 1954). Resistance to both the leaf spot and canker can vary greatly among locations and hybrids of common parentage (Ostry and McNabb, 1985; Cooper and Filer, 1976). Most literature attributes foliar and stem infection to the anamorph, Septoria musiva Peck, which is commonly isolated from stems and leaves during the growing season (Bier, 1939). Thompson's (1941) description of the loculoascomycete Mycosphaerella populorum Thompson identified the perfect state of the fungus and established overwintered leaves as the source of primary inoculum in the spring. Additional research is still needed to determine the relative contribution of each spore state to intensification of the leaf and stem diseases in the field. The impact of Septoria leaf spot and canker in natural forest ecosystems is minimal although all indigenous Populus species tested were found susceptible to foliar infection (Waterman, 1954). Balances inherent in forest communities (Dinus, 1974) apparently limit M. populorum to an endemic leaf spot pathogen. Selection of Populus and Populus hybrids for utilization in intensive culture systems has dramatically increased the importance of both the foliar and stem disease. 2 Selection for resistance to diseases has been a priority since the initiation of Populus breeding programs for "mini-rotation" or short rotation forestry (Schreiner, 1970; Stout and Schreiner, 1933). Despite this, damage caused by infection of foliage and stems by ^ populorum has limited use of many fast growing Populus hybrids in short rotation, intensive culture (Waterman, 1954; Ostry and McNabb, 1985). Disease losses have continued to occur in nurseries and stool beds (Zalasky, 1978; Filer et al., 1971), shelterbelts and plantations (Bier, 1939; Waterman, 1954; Weiss et al., 1976) and stands coppiced for regeneration (Moore et al., 1982; McNabb et al., 1982). In experimental plantations in Iowa, populorum reduced biomass production of a susceptible clone to 632 of a resistant clone after three years growth (McNabb et al., 1932). Stand reduction from stem infection and girdling was 30Ï one year after coppicing on the same clone. Similar, although unquantified, reports of losses have been made from Canada (Bier, 1939; Zalasky et al., 1968) and northeastern (Waterman, 1954) and southern (Weiss et al., 1976) United States. Despite the apparent omnipresence and importance of populorum to intensive Populus production, the epidemiology of populorum has been virtually unstudied. Quantitative analysis of epidemics in other forest and agricultural pathosystems has facilitated an understanding of the factors that contribute to disease outbreaks and has set the strategy for the development of management practices (Van Der Plank, 1963). Most quantitative epidemiological research on 2^ populorum has focused on either studying the effect of silvicultural practices on disease losses 3 (Bowersox and Merrill, 1976; Moore et al., 1982; McNabb et al., 1982) or on identifying resistance present in fast growing Populus selections (Ostry and McNabb, 1985; Cooper and Filer, 1976). These studies have contributed important observations on the various host, pathogen and environmental factors that appeared to affect disease development. Factors that have been observed to affect disease buildup include microclimatic conditions associated with stand density (Waterman, 1954; McNabb et al., 1932), inoculum density and source (Waterman, 1954; Waterman and Aldrich, 1952; McNabb et al., 1982), availability of infection courts (Bowersox and Merrill, 1976) and host resistance (Ostry and McNabb,1985; Waterman, 1954; Bier 1939). Gerstenberger (1983) formalized these observations with a conceptual model of the Mycosphaerella-Populus system. In most cases, the host, pathogen and environmental factors were not quantified or studied further to determine how they affected the epidemiology of 2^ populorum. Mathematical modeling and simulation of epidemics can help to reveal underlying relationships and are prerequisites to developing disease forecasting systems (Kranz, 1974). Quantification and mathematical modeling