Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2005
Publication Date: December 6, 2005
Citation: Lee, B.S., Kim, M.Y., Wang, R., Waldron, B.L. 2005. Relationships among three kochia species based on pcr-generated molecular markers. Genome 48:1104-1115 Interpretive Summary: Forage kochia, sometimes called prostrate kochia, prostrate summer cypress, is a long-lived, perennial, semi-evergreen half-shrub native to the heavily grazed arid and semiarid rangeland regions of Central Eurasia. It was first introduced into the U.S. in 1966 and became well adapted to semiarid rangelands in western states. Annual kochia, while sometimes used as forage, is considered as an agricultural weed throughout the western and midwestern U.S. Greenmolly or perennial summer cypress is probably the U.S. native equivalent of forage kochia. 'Immigrant', released in 1984, is currently the only cultivar of forage kochia in North America. The USDA has initiated a breeding program to develop types of forage kochia with increased stature and forage production using ecotypes from Kazakhstan and Uzbekistan. Genomic relationships among the three species have not been studied previously. To assess whether the annual kochia may contaminate forage kochia and if the perennial native greenmolly can serve as a gene pool for breeding forage kochia, species relationships among these three kochia species are assessed using the random amplified polymorphic DNA (RAPD) technique as well as sequence divergence analysis of the ndhF gene in their chloroplast genomes. Determining these relationships will also clarify the potential for introgression of the non-native forage kochia into native greenmolly. It was concluded that the three kochia species are so distinctly different that there is no gene flow between any two of them.
Technical Abstract: Forage kochia (Kochia prostrata ssp. virescens cv. 'Immigrant') is native to the arid and semiarid regions of Central Eurasia. It was introduced into U.S. in 1966 as PI 314929 and released as a perennial forage shrub in 1984. Kochia americana is a perennial native to U.S., whereas K. scorparia is an introduced annual species that became a weed. To assess both the breeding potential and the possibility of genetic contamination, relationships among the three Kochia species were analyzed using random amplified polymorphic DNA (RAPD) markers, as well as STS marker sequences of the chloroplast NADH dehyrogenase (ndhF) gene. Seventy decamer random primers yielded 458 polymorphic bands from nine accessions of K. americana, 20 accessions of K. prostrata, and seven accessions of K. scoparia. Fifty four and 55 species-specific RAPD markers were identifed for K. americana and K. prostrata, whereas 80 RAPD markers were specific to K. scoparia. Based on the presence or absence of informative RAPD markers in any subsets of the complete RAPD database, the three species always grouped into three distinct clusters in a NTSYSpc2.01b generated dendrogram. Both K. americana and K. prostrata produced one fragment of ca. 950 bp, whereas K. scoparia produced two fragments, with an additional fragment of >1500 bp, from amplification of the ndhF gene. The same relationships were found among the three Kochia species based on ndhF DNA sequence divergence. Using a set of seven STS markers that can identify each Kochia species we did not find a single interspecific hybrid from artificial hybridizations among the three Kochia species. It is concluded that these three Kochia species are so distantly related that gene introgression among them would be extremely rare.