Department of Plant Plathology and Microbiology @ UCR

Much of my research has focused on the population biology, genetics and ecology of pleomorphic (e.g., Tapesia, Hypomyces) and putative asexual fungi (e.g., arbuscular mycorrhizae, Cenococcum). These fungi represent a range of ecological life histories including plant and fungal parasites and mutualists. My studies include examining the population structure of fungal species over spatial scales ranging from centimeters to large landscapes using a number of molecular methodologies including multilocus genotyping and multi-gene genealogies. More recently, I have been moving towards broader studies of coevolution/cospeciation and host specificity, within a fungal-fungal system (boletes-Hypomyces). I'm also examining the potential role of recombination and cryptic speciation within the putative asexual ectomycorrhizal fungus Cenococcum geophilum from local to global scales.

My program is also focusing on developing rootstocks for avocado that are resistant to Phytophthora cinnamomi, the most destructive and important pathogen of avocado worldwide. One of the key features of this program is to consistently select the best varieties that show tolerance to root rot and continually plant them into breeding blocks. The objective is to then select and screen progeny from these blocks with the hope that a better rootstock will be found. Since some pollen donors in avocado are better than others, I also plan on studying the parentage of the varieties from the breeding blocks. This information would enable us to set up appropriate breeding blocks to maximize genetic exchange among all the best resistant rootstock varieties.

Additonal projects: Ecological speciation within Claviceps purpurea, Mating system of Morchella, Population genetics of the turfgrass pathogens Waitea circinata, Pyricularia grisea, and Labyrinthula terrestris, population genetics of Armillaria galica, oak mycorrhizae community structure dynamics, and endophyte and epiphyte fungi associated with California bay laurel (Umbellularia californica).

1. Dyer, P. S., Furneaux, P. A., Douhan, G. W., and Murray, T. D. 2001. A multiplex PCR test for determination of mating-type applied to the plant pathogens Tapesia yallundae and Tapesia acuformis. Fungal Genetics and Biology 33:173-180

2. Douhan, G.W. and Murray, T. D. 2001. Infection of winter wheat by a ß –Glucuronidase –transformed isolate of Cephalosporium gramineum. Phytopathology 91:232-239

3. Douhan, G. W., Peever, T. L., and Murray, T. D. 2002. Mulitlocus population structure of Tapesia yallundae in Washington State. Molecular Ecology 11: 2229-2239

4. Douhan, G. W., Murray, T. D., and Dyer, P. S. 2002. Species and mating-type distribution of Tapesia yallundae and Tapesia acuformis and occurrence of apothecia in the U.S. Pacific Northwest. Phytopathology 92:703-709

5. Douhan, G. W., Murray, T. D., and Dyer, P. S. 2003. Genetic structure of Tapesia acuformis in Washington, USA. Phytopathology 93:650-656

6. Douhan, G. W. and Rizzo, D. M. 2003. Amplified Fragment Length Microsatellites (AFLM): A method to develop microsatellite markers in organisms with limited amounts of DNA applied to Arbuscular Mycorrhizal (AM) fungi. Mycologia 95: 368-373 (Erratum 96:196)

7. Douhan, G. W. and Rizzo, D. M. 2003. Host-parasite relationships among bolete infecting Hypomyces species. Mycological Research 107: 1342-1349

8. Kerrigan, J. L., Smith, M. T., Rogers, J. D. Poot, G. A. and Douhan, G. W. 2003. Ascobotryozyma cognata, a new ascomycetous yeast species associated with nematodes from wood-boring beetle galleries. Mycological Research 107:1110-1120

9. Douhan, G. W. and Rizzo, D. M. 2005. Phylogenetic divergence in a local population of the ectomycorrhizal fungus Cenococcum geophilum. New Phytologist 166:263-271

10. Douhan, G. W., Peterson, C., Bledsoe, C., and Rizzo, D. M. 2005. Contrasting root associated fungi of three common oak-woodland plant species based on molecular identification: host specificity or non-specific amplification? Mycorrhiza 15:365-372

11. Caswell-Chen, E. P., Chen, J., Lewis, E. E., Douhan, G. W., and Carey, J. R. 2006. Revising the standard wisdom of C. elegans natural history: ecology of longevity. SAGE KE 40: 30-36

12. Bergemann, S. E., Douhan, G. W., Garbelotto, M., and Miller, S. L. 2006. No evidence of population structure across three sub-populations of Russula brevipes in an oak/pine woodland. New Phytologist 170: 177-184

13. Smith, M. E., Douhan, G. W., and Rizzo D. M. 2007. Ectomycorrhizal community structure in a xeric Quercus woodland as inferred from rDNA sequence analysis of pooled EM roots and sporocarps. New Phytologist 174: 847-863

14. de la Cerda, K. A., Douhan, G. W., and Wong, F. 2007. Discovery and Characterization of Waitea circinata var. circinata affecting Annual Bluegrass from the western United States. Plant Disease 91: 791-797

15. Smith, M. E., Douhan, G. W., and Rizzo, D. M. 2007. Intra-specific and intra-sporocarp ITS variation of ectomycorrhizal fungi as assessed by rDNA sequencing of sporocarps and pooled ectomycorrhizal roots from a Quercus woodland. Mycorrhiza 18: 15-22

16. Douhan, G. W., Martin, D. P., and Rizzo, D. M. 2007. Using the putative asexual fungus Cenococcum geophilum as a model to test how species concepts influence recombinatiion analyses using sequence data from multiple loci. Current Genetics 52: 191-201

17. Chen, C. M., Douhan, G. W., and Wong, F. P. 2007. First report of Waitea circinata var circinata causing Brown Ring Patch Poa trivialis in California. Plant Disease 91: 168.
18. Douhan, G. W., Huryn, K. L., and Douhan, L. I. 2007. Significant diversity and potential problems associated with inferring population structure within the Cenococcum geophilum species complex. Mycologia 99: 748-755
19. Douhan, G. W., Smith, M. E., Huryn, K. L., Westbrook, A., Fisher, A. J., and Beerli, P. 2008. Multigene analysis suggests ecological speciation in the fungal pathogen Claviceps purpurea. Molecular Ecology 17: 2276-2286
20. Urak, R. Z., Douhan, G. W. and Wong, F. 2008. Mating-type distribution of the rice blast fungus Pyriculuaria grisea in California. University of California, Riverside. Undergraduate Research Journal 2: 61-66

21. Chen, C., de la Cerda, K., Kaminski, J. E., DouhanG. W., and Wong, F. 2009. Geographic distribution and rDNA-ITS region sequence diversity of Waitea circinata var. circinata isolated from annual bluegrass in the U.S. Plant Disease 93: 906-911
22. Smith, M. E., Douhan, G. W., Fremier, A. K., and Rizzo, D. M. 2009. Are true multihost fungi the exception or the rule? Dominant ectomycorrhizal fungi on Pinus sabiniana differ from those on co-occurring Quercus species. New Phytologist 182: 295-299
23. Douhan, G. W., Olsen, M. W., Herrell, A., Winder, C., Wong, F., and Entwistle, K. 2009. Genetic diversity of Labyrinthula terrestris, a newly emrgent plant pathogen, and the discovery of new Labyrinthulid organisms. Mycological Research 113: 1192-1199

24. Uribe, G. and Douhan, G. W. Geographic structure of a bolete infecting cryptic species within the Hypomyces microspermus species complex in Western California (in review)

25. Douhan, G. W., de la Cerda, K. A., Huryn, K., Greer, C. A., and Wong, F. P. Contrasting genetic structure between Magnaporthe grisea populations associated with the golf course turfgrasses Lolium perenne (perennial ryegrass) and Pennisetum clandestinum (kikuyugrass): evidence for potential sexual reproduction and introductions into California? (in review)