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. 2022 Jun 22;11(13):1652.
doi: 10.3390/plants11131652.

Genetic Diversity and Structure of Persian Walnut (Juglans regia L.) in Pakistan: Implications for Conservation

Ephie A Magige  1   2   3 , Peng-Zhen Fan  2   3 , Moses C Wambulwa  1   2   4 , Richard Milne  5 , Zeng-Yuan Wu  1   2   3 , Ya-Huang Luo  1   2 , Raees Khan  6 , Hong-Yu Wu  1   3 , Hai-Ling Qi  7 , Guang-Fu Zhu  2   3 , Debabrata Maity  8 , Ikramullah Khan  9 , Lian-Ming Gao  1   2   10 , Jie Liu  1   2
Affiliations

Genetic Diversity and Structure of Persian Walnut (Juglans regia L.) in Pakistan: Implications for Conservation

Ephie A Magige et al. Plants (Basel). .

Abstract

Persian (Common) walnut (Juglans regia L.) is a famous fruit tree species valued for its nutritious nuts and high-quality wood. Although walnut is widely distributed and plays an important role in the economy and culture of Pakistan, the genetic diversity and structure of its populations in the country remains poorly understood. Therefore, using 31 nuclear microsatellites, we assessed the genetic diversity and population structure of 12 walnut populations sampled across Pakistan. We also implemented the geostatistical IDW technique in ArcGIS to reveal "hotspots" of genetic diversity. Generally, the studied populations registered relatively low indices of genetic diversity (NA = 3.839, HO = 0.558, UHE = 0.580), and eight populations had positive inbreeding coefficient (FIS) values. Low among-population differentiation was indicated by AMOVA, pairwise FST and DC. STRUCTURE, PCoA and neighbor joining (NJ) analysis revealed a general lack of clear clustering in the populations except that one population in Upper Dir was clearly genetically distinct from the rest. Furthermore, the Mantel test showed no correlation between the geographic and genetic distance (r = 0.14, p = 0.22), while barrier analysis suggested three statistically significant genetic barriers. Finally, the spatial interpolation results indicated that populations in Ziarat, Kashmir, Dir, Swat, Chitral, and upper Dir had high intrapopulation genetic diversity, suggesting the need to conserve populations in those areas. The results from this study will be important for future breeding improvement and conservation of walnuts in Pakistan.

Keywords: Juglans regia; Pakistan; conservation; genetic diversity; genetic structure; microsatellite.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Sampling map of the 12 populations of walnut in this study. Sampling locations are indicated by black dots.
Figure 2
Figure 2
Genetic differentiation, distance and phylogenetic relationship among the studied populations. (a) Heat map for the pairwise genetic distance among populations. The upper part represents FST while the lower part denotes the Dc (Cavalli-Sforza). The values were computed based on 1000 permutations. (b) Neighbor-joining tree showing genetic relationships among 12 populations of walnut produced from 31 SSR markers.
Figure 3
Figure 3
Genetic clustering of 12 populations of J. regia based on 31 SSR loci. (a) Bayesian inference of population structure at K = 2 and K = 3 using STRUCTURE. (b) Inference of the optimal K value using the Delta K. (c) Relationship among the walnut populations represented by the first two coordinates of the PCoA.
Figure 4
Figure 4
Spatial genetic structure of walnut in Pakistan. Pie color and proportion is in accordance to with genetic structure analysis results (Figure 3a). The three main detected barriers (B1, B2 and B3) are shown in red line, with the thin black lines indicating the administrative boundaries.
See this image and copyright information in PMC

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