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Title: Tumbleweed (Salsola, secion Kali) species and speciation in California

Author
item AYRES, DEBRA - UNIV OF CALIFORNIA-DAVIS
item Ryan, Frederick
item GROTKOPP, EVA - UNIV OF CALIFORNIA-DAVIS
item BAILEY, JOHN - UNIV OF LEICESTER
item Gaskin, John

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2007
Publication Date: 10/28/2008
Citation: Ayres, D., Ryan, F.J., Grotkopp, E., Bailey, J., Gaskin, J.F. 2008. Tumbleweed (Salsola, secion Kali) Species and Speciation in California. Biological Invasions. 11(5):1175-1187.

Interpretive Summary: Tumbleweeds are road side and rangeland pest plants throughout the 48 contiguous states in the US. Three described tumbleweed species and two undescribed species occur in California. The known species are Russian thistle, Salsola tragus, introduced from Eurasia in the 1800s, Russian barbwire thistle, S. paulsenii, which grows in the desert regions of California, and is also native to Eurasia, and the recently identified S. kali subspecies austroafricana, possibly native to South Africa. Our goals were to use DNA analysis and comparison of chromosome number to further identify the unknown species. These analyses indicated that one undescribed species is a new hybrid between S. tragus and S.kali subspecies austroafricana, and the other undescribed species appears to be a complex hybrid involving all three described species. The invasion potentials for the hybrid taxa are unknown. Tumbleweeds are the focus of biological controls efforts but the identification of suitable agents for the hybrid taxa may be problematic because of the large amount of genetic variability encompassed within this evolving Salsola complex.

Technical Abstract: Tumbleweeds (Salsola species, section Kali) are road side and rangeland pest plants throughout the 48 contiguous states in the US. Three described tumbleweed species and two undescribed Salsola taxa occur in California. The known species are Russian thistle, Salsola tragus, introduced from Eurasia in the 1800s, Russian barbwire thistle, S. paulsenii, which grows in the desert regions of California, and is also native to Eurasia, and the recently identified S. kali subspecies austroafricana, possibly native to South Africa. Our goals were to investigate karyology, genome size, and molecular genetic affinities of the described species and the other taxa within their ranges in California using recently developed microsatellite loci, dominant nuclear DNA markers (RAPD and ISSR), and DNA sequence data. Chromosome counts and genome size assessments made with flow cytometry were compared. These analyses indicated that one undescribed taxon is a new allopolyploid hybrid between S. tragus and S.kali subspecies austroafricana, and the other undescribed taxon appears to be a complex hybrid involving all three described species. The invasion potentials for the hybrid taxa are unknown. Tumbleweeds are the focus of biological controls efforts but the identification of suitable agents for the hybrid taxa may be problematic because of the large amount of genetic variability encompassed within this evolving Salsola complex.