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Structure analysis of 1082 individuals from 46 Juglans regia populations by Bayesian inference clustering. (a) The optimal K value using the delta K (ΔK) method, the maximum population number (K) was estimated at K = 3. (b) Average log-likelihood of the data (Ln(K) ± SD) against K number. (c) Bayesian clustering of 1082 J. regia individuals from K = 2 to K = 4. Different colors indicate different genetic groups: blue for group 1 (G1), light blue for group 2 (G2), and yellow for group 3 (G3). Courtesy of Jie Liu et al.
Understanding the factors influencing species distribution, differentiation and genetic diversity is important for sustainable conservation and effective management, as well as for the rational utilization of species genetic resources.
Genetic diversity, an important component of biodiversity, provides important information about the adaptation and evolutionary potential of plant species. In particular, the genetic diversity of forest trees has been severely affected by increased harvesting (for nuts, bark, wood, etc.) and human intervention (excessive logging, overgrazing, etc.), causing habitat fragmentation and a significant reduction in forest area.
Juglans regia L. (Juglandaceae), commonly known as walnut, is a deciduous tree species native to and cultivated in mountainous regions of subtropical and temperate regions of Asia, from the Balkans eastward to China, Iran, Kazakhstan, Afghanistan and Pakistan. Currently, J. regia is cultivated in over 60 countries, with China being the largest producer (31% of the total harvest). Walnuts are also among the top three most consumed nuts in the world.
Despite walnuts being among the top three most consumed nuts in the world, there has been no comprehensive assessment of the population genetics of walnut trees, and this is especially true for walnuts in Afghanistan and China's Xinjiang Autonomous Region.
In a study published in the journal Plant Diversity, an international team of researchers investigated the genetic diversity and population structure of 1,082 individuals from 46 populations across Central Asia through the Walnut Research Network.
Geographic distribution of walnut genetic structure in Central Asia. The colors and percentages in the pie chart correspond to the results of genetic structure analysis at K = 3. The solid and bold lines represent the locations of the two most likely barriers (B1 and B2) detected by the barrier analysis. Credit: Jie Liu et al.
“We found moderate genetic diversity of J. regia across Central Asia, with 46 populations clustered into three groups, and there is a weak relationship between genetic and geographic distance,” says Jie Liu, the study's first and corresponding author. “Our results suggest that the western Himalayas may be the core region for common walnut genetic diversity in Central Asia, and that, except for the two populations in Gongliu Wild Walnut Valley, humans may have introduced walnut populations into Xinjiang, China.”
The observed distribution of genetic landscapes is likely influenced by historical climatic changes, breeding systems and long-term anthropogenic activities.
“We propose to conserve the core genetic diversity resources in the western Himalayas, with special attention to the open-stream populations in Xinjiang,” Liu added. “Our findings will improve our understanding of the genetic variation of J. regia across its distribution range in Central Asia, which is an important prerequisite for evidence-based conservation and management.”
Further information: Linjiang Ye et al., “Population genetic insights into walnut (Juglans regia) conservation in Central Asia,” Plant Diversity (2024). DOI: 10.1016/j.pld.2024.06.001
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Source: Population genetic insights for walnut (Juglans regia) conservation in Central Asia (August 27, 2024) Retrieved August 27, 2024 from https://phys.org/news/2024-08-population-genetic-insights-common-walnut.html
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