|Grunwald, Niklaus - Nik|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2006
Publication Date: 4/3/2007
Citation: Malvarez, G., Carbone, I., Grunwald, N.J., Subbarao, K.V., Schafer, M., Kohn, L.M. 2007. New populations of Sclerotinia sclerotiorum from lettuce in California and peas and lentils in Washington. Phytopathology. 97(4): 470-483. Interpretive Summary: Sclerotinia sclerotiorum is an important plant pathogen with a wide host range affecting crops such as legumes, lettuce, potato and canola. The pathogen, until recently, was thought to reproduce mostly clonally. The present study characterized S. sclerotiorum populations in the Western United States using a range of molecular markers that can provide information on the relative degree of clonal versus sexual reproduction. Isolates of S. sclerotiorum were determined to represent three genetically differentiated populations: California (CA, lettuce), Washington (WA, pea/lentil), and Ontario (ON, lettuce). CA was the most diverse population yet sampled in North America. Clonality was detected in ON and WA. No DNA fingerprints were common among the populations.
Technical Abstract: Four populations of Sclerotinia sclerotiorum in North America were inferred previously, based on analyses of both rapidly evolving markers (DNA fingerprint and mycelial compatiblity), and multilocus DNA sequence spanning the range between fast and slow evolution. Each population was defined as an interbreeding unit of conspecific individuals sharing a common recent ancestor and arising in a unique evolutionary event. The present study applies this standard to extend characterization of S. sclerotiorum populations to the Western United States. Isolates of S. sclerotiorum (N = 294) were determined to represent three genetically differentiated populations: California (CA, lettuce), Washington (WA, pea/lentil), and Ontario (ON, lettuce). CA was the most diverse population yet sampled in North America. Clonality was detected in ON and WA. No DNA fingerprints were common among the populations. The index of association (IA), based on fingerprint, was closer to zero (0) for CA than it was for the other populations. High diversity and lack of association of markers in California are consistent either with genetic exchange and recombination, or with large population size and high standing genetic variation. Intra- and interlocus conflict among three DNA sequence loci was consistent with recombination. The coalescent IGS genealogy confirmed subdivision and showed CA to be older than WA or ON. The Nearest Neighbor statistic on combined data confirmed subdivision among all present and previously defined populations. All isolates had both MAT1-1 and MAT1-2, consistent with uniform homothallism.