Heterobasidion irregulare in Minnesota: New studies on detection, composition of different fungi in pines, and antagonism assays with native fungi
2022-09
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Heterobasidion irregulare in Minnesota: New studies on detection, composition of different fungi in pines, and antagonism assays with native fungi
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2022-09
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The species complex, Heterobasidion annosum sensu lato, contains some of the most devasting forest pathogens of the northern hemisphere. Over the years this species complex also has generated a vast amount of research on the diseases it causes known collectively as Heterobasidion root disease or Heterobasidion root rot. Within this species complex, is the species H. irregulare, which is a threat to conifers in the Midwest including Minnesota. The discovery of H. irregulare in Minnesota was the impetus for this research project. The project’s overall goals were to determine the locations of H. irregulare throughout Minnesota, identify native fungi that inhabit forests where H. irregulare could be present, and test these native fungi against H. irregulare to examine their interactions and determine their potential as biological control agents. Phlebiopsis gigantea was a fungus of great interest in these studies as it has previously been established as a biological control agent against H. irregulare. Determining how abundant it was in Minnesota was a top priority.
After H. irregulare was discovered in Minnesota, substantial field surveys were conducted throughout the state as part of this research. Areas of highest concern were red pine stands that were thinned and located near the initial discovery in southeast Minnesota. A combination of traditional culturing and molecular methods were used in diagnosis and also to identify native fungi of interest. Heterobasidion irregulare was not detected using these methods, but multiple fungi of interest were obtained that were used in subsequent studies. Spore surveys were also utilized as an additional method to locate areas of concern. The spore surveys were used in combination with qPCR, which allowed for the calculation of the number of spores landing at each research site. A low to moderate number of spores were detected in Minnesota indicating that areas with higher numbers of spores are of concern for the potential establishment of H. irregulare.
Fungi associated with red pine forests and specifically stumps is a topic that has had minimal research over the years. Understanding the composition of fungi in woody substrates, and most importantly in stumps, is of great importance to help determine if these fungi are naturally preventing H. irregulare from colonizing. A specific study examined the diversity of fungi in red pine sumps in the native and non-native range of red pine and additionally these locations were harvested at different times. This allowed for the examination of how fungi differ in the native and non-native range of red pine and also how they change as decay in the stumps progress. Traditional culturing as well as metabarcoding was used to decipher the fungi in these stumps. A main result of these studies was the abundance of P. gigantea on recently harvested stumps, particularly in the native range of red pine or in north central Minnesota compared to the southeastern sites. This could provide evidence that sites with red pine in the non-native range might be more susceptible to H. irregulare while northern sites with an abundance of P. gigantea are more resistant.
Finally, having a grasp on the fungi that inhabit forests where H. irregulare could occur in Minnesota they were then tested against H. irregulare to determine any antagonism present. Multiple antagonism assays were conducted in vitro and ex vitro to help elucidate antagonism present in these fungi against H. irregulare. Overall, P. gigantea proved to be the most effective competitor against H. irregulare, but the fungi Sistotrema brinkmannii, Phanerochaete livescens, and others also showed promise as future biological control agents.
This research provided new insights on multiple topics relating to H. irregulare. Locations and the overall threat that H. irregulare poses to Minnesota were clarified with the use of field surveys and spore surveys. A better understanding of fungi in pine forests where H. irregulare could occur in Minnesota was revealed. Finally, an examination of antagonism assays of native fungi against H. irregulare provided information on the role of different fungi in possibly preventing the establishment of H. irregulare in Minnesota and also their potential future use as biological control agents.
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University of Minnesota Ph.D. dissertation.September 2022. Major: Plant Pathology. Advisor: Robert Blanchette. 1 computer file (PDF); xii, 130 pages.
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Otto, Eric. (2022). Heterobasidion irregulare in Minnesota: New studies on detection, composition of different fungi in pines, and antagonism assays with native fungi. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/250036.
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