The goal of this project is to determine the genetic structure of an important fungal pathogen in the genus Colletotrichum, which infects wild and cultivated cranberries and related plant species throughout North America. This fungus is comprised of two evolutionary clades; one group is widespread and has been recognized as a pathogen of cranberry for more than a century while the other is an emerging disease. This research will examine how features of the ecological landscape interact with gene flow among wild and cultivated cranberry bogs, to shape the evolution and mode of reproduction of this pathogen at multiple spatial scales. The fungus is capable of reproducing both sexually and clonally and known to employ different reproductive strategies in different populations. Clonal populations have the ability to spread rapidly under favorable conditions while sexual populations tend to be more genetically diverse, and thus have a greater adaptive potential in the face of environmental perturbations. Therefore, understanding the reproductive strategy of this pathogen and its dependence on landscape features provides general insight into how emergent diseases may spread.
This research has important implications for the development of effective management tools that will assist in mitigating significant economic losses caused by this pathogen on cranberry farms. A molecular marker system developed as part of this project will facilitate other research on the evolution, systematics and disease ecology of this fungus. This project will also support the training of high school students in molecular and fungal biology. The project strengthens a collaborative relationship between two research institutions, the P.E. Marucci Center for Blueberry and Cranberry Research and the New York Botanical Garden.
Understanding the factors that drive the evolution of pathogenic fungi is central to developing effective disease control measures. Prerequisite to these pursuits is the accurate recognition of species. Colletotrichum gloeosporioides s.l. is an aggregate of closely related plant pathogenic and non-pathogenic fungi that are difficult to identify. However, with the application of tools from molecular biology, reliable species recognition has become possible. Colletotrichum has long been known to be an important pathogen of cranberry fruit, but despite the long history of cranberry cultivation in North America and the economic impact of Colletotrichum on the cranberry industry, relatively little it is known about the biology of these species. We collected strains of Colletotrichum to characterize the diversity of the species group, isolating strains from different host species growing alongside cranberry, from different ecosystems, such as wild and agricultural, and from different plant organs, such as fruit and stems. We used recently developed molecular tools to understand how factors like these might impact species diversity. We also asked the question: Are multiple species of Colletotrichum important pathogens of cranberry? We found several species of the Colletotrichum gloeosporioides aggregate are present within native and agricultural cranberry bogs, and that a composite of several factors influences the species diversity of Colletotrichum within the cranberry ecosystem, including the plant organ, the type of ecosystem, and the host species. Furthermore, we discovered that two different species are important pathogens of cranberry and responsible for distinct diseases; one an emerging pathogen of stems and the other long known for its economic impact as a fruit pathogen. We developed DNA-based tools to characterize the distribution of genetic diversity of one pathogenic species within and across geographical regions to understand how agricultural management practices, landscape structure (i.e. watersheds), and other biological influences impact the ability of this species to adapt. We found that the separation among different growing regions limited the movement of pathogens from one region to the next. However, this limitation is overcome by management practices that move plant material within regions and from one region to the next to establish new farms. We also found that alternate host species are not an important reservoir for the subsequent infection of cranberry. Furthermore, we have learned that the ability to reproduce asexually allows this pathogen to increase the frequency of pathogenic genotypes, while occasional sexual reproduction allows it to increase genetic diversity providing the means for adaptation. This research, made possible by funds from a National Science Foundation Doctoral Dissertation Improvement Grant, has led to the development of a better understanding of a group of important pathogens on one of North America’s few native crop plants. It has provided training for graduate students and high school students in a broad range of scientific disciplines including evolution, molecular biology, plant pathology and mycology. Through this research we have developed new tools for continued research on this group of important pathogens, which will be particularly useful for plant pathologists working to ameliorate the impact of cranberry pathogens, plant breeders working to develop disease resistant cultivars, and mycologists working to better understand the factors that influence fungal species diversity.
