Microsatellites uncover extraordinary diversity in native American land races and wild populations of cultivated sunflower

Abstract

The contemporary oilseed sunflower (Helianthus annuus L.) gene pool is a product of multiple breeding and domestication bottlenecks. Despite substantial phenotypic diversity, modest differences in molecular genetic diversity have been uncovered in anciently and recently domesticated sunflowers. The paucity of molecular marker polymorphisms in early analyses led to the hypothesis of a single domestication origin. Phylogenetic analyses were performed on 47 domesticated and wild germplasm accessions using 122 microsatellite loci distributed throughout the sunflower genome. Extraordinary allelic diversity was found in the Native American land races and wild populations, and progressively less allelic diversity was found in germplasm produced by successive cycles of domestication and breeding. Of 1,341 microsatellite alleles, 489 were unique to land races, exotic domesticates and wild populations, whereas only 15 were unique to elite inbred lines. The number of taxon-specific alleles was 35-fold greater among wild populations (26.27) than elite inbred lines (0.75). Microsatellite genotyping uncovered the possibility of multiple domestication origins. Land races domesticated by Native Americans of the southwestern US (Hopi and Havasupai) formed a clade independent of land races domesticated by Native Americans of the Great Plains and eastern US (Arikara and Seneca). Predictably, domestication and breeding have ratcheted genetic diversity down in sunflower. The contemporary oilseed sunflower gene pool, while not imperiled, could profit from an infusion of novel alleles from the reservoir of latent genetic diversity present in wild populations and Native American land races.

Comparative analyses of genetic/epigenetic diversities and structures in a wild barley species (Hordeum brevisubulatum) using MSAP, SSAP and AFLP

“…This point has been proven in many species (Papa and Gepts, 2003;Tang and Knapp, 2003;Wright et al, 2005). Our result is coincident with it.…”

Contributions of Flowering Time Genes to Sunflower Domestication and Improvement

“…Sunflower was initially domesticated .4000 years ago from wild H. annuus populations in eastern North America (Heiser 1951;Rieseberg and Seiler 1990;Harter et al 2004;Smith 2006). Over its history as a crop, sunflower experienced several periods of intense selection and population bottlenecks (Putt 1997;Tang and Knapp 2003), including its transformation in the mid-20th century by breeders into a globally important oilseed crop. While wild H. annuus populations range from early to late flowering (Heiser 1954), native American landraces are primarily late or very late flowering (Heiser 1951).…”

Patterns of Nucleotide Diversity in Wild and Cultivated Sunflower

“…Moreover, wild sunflower is an obligate outcrosser, whereas cultivated sunflower has lost the sporophytic self-incompatibility that is typical of the genus. Despite this potentially major shift in breeding system, however, the extent to which cultivated sunflower actually self-pollinates in the field remains unknown.Although cultivated sunflower was long thought to be the product of a single origin of domestication .4000 years ago (Heiser 1954(Heiser , 1955Rieseberg and Seiler 1990; Crites 1993), this premise was subsequently called into question on the basis of both archaeological and genetic evidence (e.g., Heiser 1985; Lentz et al 2001;Tang and Knapp 2003). In the most comprehensive molecular analysis to date, however, Harter et al (2004) argued convincingly that the eight extant Native American landraces, from which the modern cultivars are presumably derived, can all be reliably assigned to a single population genetic cluster.…”

“…The 16 cultivated lines were composed of 8 Native American landraces, which represent the most primitive sunflower domesticates available, and 8 improved lines that were selected such that, when combined with the landraces, our collection of cultivars contained at least one representative from 9 of the 10 subsets that make up the NCRPIS H. annuus core collection. With the exception of cmsHA89, which is an elite inbred oilseed line that has been used in a variety of other studies (e.g., Burke et al 2002Burke et al , 2004Tang and Knapp 2003), the improved lines included here represent open-pollinated cultivars. Thus, the 16 cultivars included in this study are largely comparable to the ''exotic'' lines employed by Burke et al (2005).…”

“…Rather, analyses of genetic diversity in sunflower have thus far relied primarily on techniques such as allozyme (Rieseberg and Seiler 1990;Cronn et al 1997) and SSR (Tang and Knapp 2003;Harter et al 2004;Burke et al 2005) genotyping. Here we seek to rectify this situation by reporting on patterns of nucleotide polymorphism in a widespread sample of wild sunflower individuals, as well as a diverse collection of cultivars.…”