title: Genetic variation in walnuts (Juglans regia and J. sigillata; Juglandaceae): Species distinctions, human impacts, and the conservation of agrobiodiversity in Yunnan, China.
abstract: Walnuts are a major crop of many countries and mostly cultivated in large-scale plantations with few cultivars. Landraces provide important genetic reservoirs; thus, understanding factors influencing the geographic distribution of genetic variation in crop resources is a fundamental goal of agrobiodiversity conservation. Here, we investigated the role of human settlements and kinship on genetic variation and population structure of two walnut species: Juglans regia, an introduced species widely cultivated for its nuts, and J. sigillata, a native species cultivated locally in Yunnan. The objectives of this study were to characterize sympatric populations of J. regia and J. sigillata using 14 molecular markers and evaluate the role of Tibetan villages and kin groups (related households) on genotypic variation and population structure of J. regia and J. sigillata. Our results based on 220 walnut trees from six Tibetan villages show that although J. regia and J. sigillata are morphologically distinct, the two species are indistinguishable based on microsatellite data. Despite the lack of interspecific differences, AMOVAs partitioned among villages (5.41%, P = 0.0068) and kin groups within villages (3.34%, P = 0.0068) showed significant genetic variation. These findings suggest that village environments and familial relationships are factors contributing to the geographic structure of genetic variation in Tibetan walnuts.
authors.affiliation: Missouri Botanical Garden, St. Louis, Missouri 63166 USA; and Research School of Biology, Division of Evolution, Ecology and Genetics, The Australian National University, Bldg. 116 Daley Road, Canberra, ACT, 0200, Australia.
authors.forename: Bee F
authors.initials: BF
authors.lastname: Gunn
authors.forename: Mallikarjuna
authors.initials: M
authors.lastname: Aradhya
authors.forename: Jan M
authors.initials: JM
authors.lastname: Salick
authors.forename: Allison J
authors.initials: AJ
authors.lastname: Miller
authors.forename: Yang
authors.initials: Y
authors.lastname: Yongping
authors.forename: Liu
authors.initials: L
authors.lastname: Lin
authors.forename: Hai
authors.initials: H
authors.lastname: Xian