Investigations of the plant genus Chenopodium using both plastid and single-copy nuclear markers.

摘要

The plant genus Chenopodium is poorly understood despite being domesticated as many as five times, and being one of the most noxious weeds known in agricultural and urban settings. Taxonomic problems at both the genus and species level have persisted for over 250 years. Due to the large number of species, nomenclatural inconsistencies, high degree of morphological trait plasticity, and trait similarities among relatively distantly related species, researchers have progressed very slowly in understanding Chenopodium. This dissertation addresses some of the most challenging questions concerning Chenopodium. In Chapter 1 the non-coding plastid marker trnQ-rsp16 is used to construct a phylogeny to infer the monophyly of the genus as well as test recent nomenclatural changes. Our results were consistent with most recently proposed nomenclatural changes. The inclusion of species never before included in phylogenetic analyses, C. bryonifolium from China, and C. mucronatum from South Africa, supports an Old World origin from American Chenopodium. Chapter 2 investigates the allopolyploid species of Chenopodium using a phylogeny constructed from the single-copy nuclear locus, Salt Overly Sensitive 1 (SOS1). Two distinct polyploidy lineages were identified, one American tertaploids, and the other Eurasian hexaploids. These lineages possess different combinations of homeologs indicating separate polyploidy origins. Chapter 3 tests hypotheses of whether two domesticated Chenopodium cultigens were independently domesticated or share the same domestication event. The Mesoamerican cultigen, C. berlandieri subsp. nuttalliae, is endemic to the Trans-Mexican Volcanic belt, and is still cultivated. The cultigen, C. berlandieri subsp. jonesianum, is known from its presence at many archaeological sites within Eastern North America. This cultigens is extinct, but was a major element of subsistence agriculture roughly 2500-1000 years ago in Eastern North America. Sequences data obtained from archaeological C. berlandieri subsp. jonesianum seeds were compared to modern accessions of C. berlandieri subsp. nuttalliae. Shared genetic markers support a single domestication giving rise to both crops. In light of a well documented 4000 year archaeological history of domesticated Chenopodium in Eastern North America, compared to the 500 year history reported in Mexico, domesticated Chenopodium was likely introduced to Mexico from Eastern North America.