Genetic homogeneity in Juglans nigra (Juglandaceae) at nuclear microsatellites

Abstract

Broad‐scale studies of genetic structure and diversity are indicative of the recent evolutionary history of a species and are relevant to conservation efforts. We have estimated current levels of genetic diversity and population structure for black walnut (Juglans nigra L.), a highly valuable timber species, in the central hardwood region of the United States. Black walnut trees from 43 populations across this region were genotyped at 12 highly polymorphic microsatellite loci. Genetic diversity was high and populations only slightly deviated from Hardy‐Weinberg proportions (FIS = 0.017). Considering the scale of our sampling, the species was remarkably genetically homogenous: FST was quite low (0.017), and in a Bayesian analysis the optimal higher‐order partition was into a single group comprised of all 43 populations. Although black walnut is predominantly a bottomland species, very little genetic variance was partitioned among broad‐scale hydrologic regions (FPT = 0.002). However, a weak, but statistically significant pattern of isolation by distance was detected. The results are consistent with a scenario in which black walnut recolonized its current range from a single glacial refugium, and where subsequent genetic effects associated with deforestation and habitat fragmentation have been mitigated by high levels of pollen flow. Nuclear microsatellites alone may be insufficient to identify hotspots for black walnut conservation.

SSR and RAPD analysis of genetic diversity in walnut (Juglans regia L.) genotypes from Jammu and Kashmir, India

“…The genetic parameters estimated from the microsatellite data indicated that there are substantial levels of genetic diversity in all sampled populations. This result is in accordance with the common observation of high levels of variation detected in wind pollinated, long-lived tree species (Streiff et al 1998;Victory et al 2006;Karimi et al 2010). In the present study, SSR markers showed interspecific transferability and polymorphism but Gunn et al 2010 showed that SSR markers lack interspecific differentiation between J. regia and J. sigillata.…”

“…The high level of variability observed at 26 SSR loci we used is consistent with results from studies carried out on different species (Carriero et al 2002). For all loci, the observed number of alleles was lower than that reported in J. nigra (Victory et al 2006), the species from which the markers were originally developed . This may be because of the large number of samples and populations analyzed in previous J. nigra studies (Ana et al 2000).…”

“…Previously, in addition to morphological identification (Zenelli et al 2005), various biochemical and molecular markers have been used for genetic characterization of walnut genotypes. These included isozymes (Fornari et al 2001;Busov et al 2002;Ninot and Aleta 2003;Vyas et al 2003,), restriction fragment length polymorphisms (RFLPs) (Fjellstrom et al1995), randomly amplified polymorphic DNAs (RAPDs) (Nicese et al1998;Yan-Min et al 2000;Zhang Li et al 2007), intersimple sequence repeats (ISSRs) (Potter et al 2002), simple sequence repeats (SSRs) Dangl et al 2005;Foroni et al 2005;Victory et al 2006;Robichaud et al 2006;Karimi et al 2010), amplified fragment length polymorphisms (Kafkas et al 2005;Bayazit et al 2007) and SNPs (Ciarmiello et al 2011). In our study, the average number of alleles per locus was 2 which is higher than 1.3 detected in J. regia with RAPDs (Nicese et al 1998) but lesser than 3.9 and 5.5 using ISSR (Potter et al 2002) and SSR (Foroni et al 2007) markers respectively.…”

“…Microsatellite markers are useful for genetic diversity analysis studies at varietal, species and genus level due to their sequence conservation at flanking regions (Hamza et al 2004). Although a great number of population genetic studies have been conducted on Juglans species (Fornari et al 2001;Victory et al 2006), no genetic research based on the use of molecular markers has been published previously on J. regia populations in India. In our work, inter specific transferability of walnut microsatellites, originally selected to study the genetic diversity in J. nigra , has been tested on J. regia varieties.…”

Walnut: past and future of genetic improvement

“…The following sections depict an overview of these molecular studies and their application (Table 2). Woeste et al 2002;Dangl et al 2005;Hoban et al 2008;Zhang et al 2010;Qi et al 2011;Yi et al 2011;Wu et al 2012;Zhang et al 2013;Chen et al 2013;Najafi et al 2014;Topçu et al 2015;Ikhsan et al 2016;Dang et al 2015;Hu et al 2015;Dang et al 2016 Interspecific hybrids identification Pollegioni et al 2008Pollegioni et al , 2009 Genetic diversity/relationships determination Foroni et al 2005;Dangl et al 2005;Victory et al 2006;Robichaud et al 2006;Wang et al 2008;Aradhya et al 2009;Gunn et al 2010;Karimi et al 2010;Bai et al 2010;Mohsenipoor et al 2010;Ebrahimi et al 2011;Ruiz-Garcia et al 2011;Pollegioni et al 2011;Qi et al 2011;Grauke et al 2012;Mahmoodi et al 2013;Zhang et al 2013;Pop et al 2013;Najafi et al 2014;Dang et al 2015;Hu et al 2015;Han et al 2016;Noor Shah et al 2016;Ćelepirović et al 2016;Wang et al 2016;…”