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Evaluation of genetic differentiation among healthy and infected Buxus hyrcana with boxwood blight using RAPD and ISSR markers

Evaluation of genetic differentiation among healthy and infected Buxus hyrcana with boxwood... Background: Buxus hyrcana (boxwood) is an endangered species in the Hyrcanian forests in the north of Iran. This tree is threatened by habitat loss but faces additional threats from the introduced disease the boxwood blight (caused by the fungus Calonectria pseudonaviculata syn. Cylindrocladium pseudonaviculatum, Cy. buxicola) and the potential effects of climate change. As wide range of genetic polymorphism is necessary to ensure successful adaptation to rapid climatic changes. Methods: Genetic diversity and differentiation between 15 healthy and 15 infected trees of each of two populations were studied using RAPD and ISSR molecular markers. Results: High-band polymorphism was found in pooled samples of B. hyrcana using both ISSR (58%) and RAPD (73%) markers. The ISSR data and the combined data set classified the trees into two groups. However, data from RAPD clustered the trees into three groups. These results indicate different degrees of genetic variation in the sequences of the tested B. hyrcana genomes targeted by the two marker types used. Genetic variation was found to be relatively high, with most of the diversity occurring within populations. Analyses of healthy versus infected pooled samples based on both marker types indicated that genetic diversity parameters were mostly higher in healthy trees. Conclusions: Boxwood blight has had a major effect on B. hyrcana, killing individual stems quickly especially in dense populations and reducing population size (as observed in all populations). Considerable within-population diversity, and higher genetic variability in healthy trees than infected ones, suggested conservation efforts should focus on survivor trees in each population and consider the establishment of tree reservations. Propagation of plants from seeds is preferred, since it would include the widest range of genetic variation. Keywords: Blight, Buxus hyrcana, Genetic variation, ISSR, RAPD Background was reported in England in the mid-1990s and then in Buxus hyrcana is an evergreen shrub or small tree New Zealand in 2002. Since the first reports, this disease growing up to 1 to 12 m tall. It usually occurs as part of has spread into European countries such as Austria, the understorey in the Hyrcanian forests of northern Belgium, Croatia, Czech Republic, Denmark, France, Iran. In the summer 2012, a boxwood blight disease was Georgia, Germany, Ireland, Italy, the Netherlands, reported in the forests there (Mirabolfathy et al. 2013). Norway, Slovenia, Spain, Sweden, Switzerland and Turkey To date, more than 70% of B. hyrcana trees in Hyrcanian (Henricot et al. 2000;Brand 2005;Crepeland forests have been infected by boxwood blight (Fig. 1). Inghelbrecht 2003;Saracchi et al. 2008; Pintos Varela et al. Boxwood blight, caused by Calonectria pseudonaviculata, 2009; Cech et al. 2010; Gorgiladze et al. 2011;Akilliet al. 2012). Iran is the only Asian country that has reported this disease. * Correspondence: psalehi1@gmail.com; psalehi@rifr-ac.ir Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization, P.O. Box 13185-116, Tehran, Iran © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 2 of 10 Fig. 1 General view of B. hyrcana in Hyrcanian forests that have been infected by boxwood blight (caused by Calonectria pseudonaviculata, syn. Cylindrocladium pseudonaviculatum, Cy. Buxicola); Tuscatoc (right) and Escolac (left) Devastating pest and disease epidemics have been created new opportunities for Buxus research. Gande- reported in many parts of the world over the last 120 hari et al. (2013a, b) detected desirable genetic variation years, affecting trees of great economic and/or ecological using random amplified polymorphic DNA (RAPD) and importance (Boyd et al. 2013). American chestnut inter-simple sequence repeat (ISSR) markers in B. hyrcana (Castanea dentata (Marshall) Borkh.) was decimated by a populations. An amplified fragment length polymorphism blight disease, caused by Cryphonectria parasitica Murr. (AFLP) marker was used to specify and distinguish the Barr., and the species became effectively extinct from its European and Asian Buxus taxa (Van Laere et al. 2011). native range in a period of 40 years (Choi and Nuss 1992). Also, internal transcribed spacer regions and plastid ndhF Dutch elm disease, caused by the fungus Ophiostoma sequences were used to describe the phylogenetic relation- ulmi, Buisman Nannt., and later by Ophiostoma ships (Von Balthazar et al. 2000). Thammina et al. (2014, novo-ulmi Brasier spread through native populations of 2016) studied the advantages of genic SSR markers and elm (Ulmus spp.) trees in countries such as America, New ploidy analysis for specifying the diversity (and, in some Zealand and Europe causing widespread tree death cases, for identifying accessions) of Buxus in the National (Comeau et al. 2015). Black sigatoka is a fungal Buxus Collection at the United State Department of (Mycosphaerella fijiensis) disease that affects the produc- Agriculture (USDA). tion and export of banana and plantain in various coun- It is clear that species with limited genetic variation tries, with Grenada suffering complete loss of its often cannot cope with the changing environments plantations (Marin et al. 2003). Anthracnose fungi (usually (Schaal et al. 1991) and that adaptive responses to stresses Colletotrichum or Gloeosporium species) are a threat for also depend on the level of remaining of genetic variation many hardwood tree species (Berry 1985). Fusiform rust is as well (Ayala and Kiger 1984). Therefore, knowledge of afungal (Cronartium quercuum f. sp. fusiforme) disease the distribution of genetic variation among and within that affects the southern pines (Pinus spp.), leading to an- host species populations is necessary for better under- nual losses of millions of dollars for timber growers. Huge standing of ecosystem functioning. Such knowledge will losses have occurred across Europe following ash (Fraxi- also provide valuable insights into the direct and indirect nus spp.) dieback caused by Hymenoscyphus fraxineus effects of the pathogens introduced on native indigenous (Harper et al. 2016). These and many other fungal patho- hosts, as well as into potential host maladaptation to gens have serious effects on the future of tree species eco- climate change amplified epidemics of indigenous patho- nomically and ecologically. gens (Burdon & Thompson 1995). This knowledge is also Buxus hyrcana has been examined in a few biochemical of practical use for monitoring the diseases in tree hosts (Ata et al. 2010) and ecological studies (Asadi et al. 2011; planted beyond their natural range. Asadi et al. 2012; Soleymanipoor and Esmailzadeh 2015; This study aims to investigate the variation in Kaviani and Negahdar 2016; Hosseinzadeh and Esmailza- genetic markers in relation to the disease status in B. deh 2017). Reports indicated an ecological range of box hyrcana and compares the merits of two methods trees from sea level up to 1700-m elevation in mountain (RAPD and ISSR markers) for evaluating the genetic forests of north Iran (Soleymanipoor and Esmailzadeh variation of the healthy and infected groups of B. 2015; Hosseinzadeh and Esmailzadeh 2017). However, hyrcana. The markers are two widely applicable until recently, the genetics of B. hyrcana had been lit- techniques to identify relationships at the species and tle studied. Development of molecular methods has populations levels (Wali et al. 2007; Mehes-Smith et Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 3 of 10 al. 2010;Phong et al. 2011;Zhiqiangetal. 2015;Elm- Table 1 List of primers and their nucleotide sequences, annealing temperature, number of observed bands and the eer et al. 2017), because they are rapid, simple to per- percentage of polymorphism produced by different ISSR and form and inexpensive; they do not require prior RAPD markers knowledge of DNA sequences; and only a small Molecular Primer Sequence 5′-3′ Annealing No. Polymor amount of DNA is needed (Esselman et al. 1999). type code Temperature observed phism Selection of collection sites was difficult due to the (°C) bands % limited numbers of healthy trees. Healthy and infected ISSR ISSR 7 CACACACAC 53 9 78 ± 5 B. hyrcana trees belonging to two different local popu- ACAGT lations were evaluated for genetic variation using two ISSR 3 CTCTCTCTC 53 14 61 ± 12 types of marker based on DNA amplification (RAPD TCTCTCTTG and ISSR). Furthermore, we investigated whether or ISSR 19 AGAGAGAGA 52 9 46 ± 27 not the methods are beneficial for exhibiting a link GAGAGGT between the geographical origin of a given population P 26 CCACTCTCT 51 9 42 ± 24 CTCTCTCTCT and the evaluated genetic variation. P 12 GAGAGAGAG 52 8 4 AGAGAGAT Materials and methods Genomic DNA extraction from plant material P 5 ACACACACA 52 8 2 CACACACG In total, 60 healthy (30 apparently free of boxwood RAPD OPJ 13 CCACACTACC 40 8 81 ± 4 blight) and infected (i.e. 30 with major branches dead) B. hyrcana were collected from Hyrcanian forests at two OPO 10 TCAGAGCGCC 40 10 78 ± 9 different localities (Escolac, 37° 01′ N and 49° 33′ E, and OPJ 19 GGACACCACT 40 9 75 ± 7 Toscatoc 36° 34′ N and 51° 44′ E). Choice of site was OPA 04 AATCGGGCTG 40 10 70 ± 8 subject to finding at least 15 healthy trees per collection OPJ 04 CCGAACACGG 40 12 65 ± 7 area. The sampling area in each site was approximately OPA 06 GGTCCCTGAC 40 8 2 10 km and distance between sampling trees was at least OPA 07 GAAACGGGTG 40 7 2 20 m. The voucher numbers of deposited samples in TARI Herbarium are Iran36913 and Iran36914. Nuclear OPJ 14 CACCCGGATG 40 8 2 DNA was extracted from bud tissues of each individual OPJ 18 TGGTCGCAGA 40 8 2 and used for marker analysis (Dellaporta et al. 1983). OPO 11 GACAGGAGGT 40 8 2 OPO 09 TCCCACGCAA 40 7 1 ISSR analysis OPA 03 AGTCAGCCAC 40 7 1 Polymerase chain reaction (PCR) was conducted OPA 05 AGGGGTCTTG 40 8 1 according to Zietkiewicz et al. (1994). Six ISSR primers were initially screened but only four primers were used in the analysis (Table 1). The clear and reproducible banding patterns were used to evaluate genetic variation. banding patterns generated were used to evaluate The reaction conditions were optimised, and mixtures genetic variation. The reaction conditions were were composed of 40 ng of DNA, 10× PCR reaction optimised and mixtures were composed of 20 ng of buffer (10 mM Tris-HCl, pH 9.0; 50 mM KCl; 1.5 mM DNA, 10× buffer (20 mM Tris-HCl pH 8.4; 50 mM MgCl ), 1 U TaqDNA polymerase, 0.1 mM dNTP, KCl), 1 U TaqDNA polymerase, 2 mM MgCl ,0.2mM 0.4 μM primer and 1.2 mM MgCl . The amplifications 2 2 dNTP, and 0.8 μM primer. The PCR amplification included 1 cycle of 5 min at 94 °C and following 45 cycles protocol includes one cycle for 5 min at 94 °C and of 1 min at 94 °C, 2 min at 40 °C, 2 min at 72 °C and then is followed by 42 cycles for 30 s at 94 °C, 1 min finally was extended for 7 min at 72 °C. Amplification at 51–53 °C (Table 1), 1 min at 72 °C and 5 min for products (10 mL) were mixed with 5 mL bromophenol final extension at 72 °C. Amplification productions blue separated on 1.5% agarose gel and were marked (10 mL) are mixed with 5 mL bromophenol blue with 5 mL of SYBR Green and then photographed. separated on 1.5% agarose gel and marked with 5 mL of SYBR Green and then photographed. Data analysis Amplification reactions from all individuals were scored; RAPD analysis then, genetic variation statistics were computed using the Polymerase chain reaction (PCR) was conducted accord- GENAlEX 6.5 software for binary data (Peakall and ing to Williams et al. (1990). Thirteen RAPD primers Smouse 2012). The number of observed and private bands were initially screened, but only five primers were used (number of bands unique to a single population), mean in the analysis (Table 2). Only the clear and reproducible number of alleles (Na), effective number of alleles (Ne), Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 4 of 10 Table 2 Genetic variation statistics revealed through RAPD and Table 3 Genetic variation statistics revealed through RAPD and ISSR markers among the B. hyrcana genotypes ISSR markers among the B. hyrcana populations Molecular Na (SD) Ne (SD) I (SD) He (SD) %P (SD) Molecular Pop. No. No. Na Ne I He %P type type bands private bands ISSR 1.171 1.213 0.222 0.138 57.890 (0.080) (0.024) (0.019) (0.013) (8.790) ISSR Tuscatoc 32 16 1.684 1.315 0.318 0.199 84.21 RAPD 1.500 1.314 0.308 0.196 72.95 Escolac 22 6 1.158 1.140 0.166 0.097 57.89 (0.060) (0.023) (0.018) (0.013) (4.19) RAPD Tuscatoc 46 7 1.878 1.361 0.361 0.227 93.88 Na mean number of alleles, Ne effective number of alleles, I Shannon’s Escolac 42 3 1.714 1.347 0.345 0.218 85.71 information index, He expected heterozygosity, %P percentage of polymorphic loci Na mean number of alleles, Ne effective number of alleles, I Shannon’s information index, He expected heterozygosity, %P percentage of polymorphic loci Shannon’s information index (I), expected heterozygosity (He) and percentage of polymorphic loci (%P) were evaluated according to Nei (1978). According to Nei’s mostly higher in healthy trees using both marker types method (1978), the genetic distances were calculated and (Table 4). the similarity matrix was subjected to principal coordinate UPGMA dendrograms were generated using ISSR and analysis (PCoA). Mantel (1967) was used for evaluating RAPD datasets to elucidate genetic diversity and population the relationship between the calculated distance matrices structure among genotypes (Additional files 1 and 2). In and the statistic tested for significance against 999 random order to examine the relationships among the B. hyrcana permutations. The SIMJACARD code of the software genotypes, a combined UPGMA clustering was estimated package NTSYS-pc: 2.11 was used to estimate pairwise based on the genetic similarity matrix by combining 87 genetic similarity (Rohlf 2004). A similarity matrix based polymorphic bands obtained from ISSR as well as RAPD on the unweighted pair group method and arithmetic data. The dendrogram delineated based on the combined means (UPGMA) was generated using Jacard’s similarities data set (ISSR and RAPD) is shown in Fig. 2.Clustersof and SHAN of NTSYS-pc to construct the dendrogram of two groups of data points displaying a similar coefficient all the 60 genotypes. Cophenetic matrices were calculated value (0.67) are apparent in this diagram. Thus, the for characterising the correlations between the dendro- combined data indicated similar results to the ISSR except grams and similarity matrices. for some minor changes in branch positions. The cophe- netic correlation was r=0.99, andthisimpliesavery good Results fit. Group I included healthy and infected genotypes of the Of the six ISSR primers used in this study, four showed Toscatoc population with slight differences in branch posi- polymorphism. The number of polymorphic fragments tions as compared with the ISSR dendrogram (Fig. 2). ranged from 9 to 14, with an average of 9.5 per primer Group II included genotypes similar to the ISSR clustering. (Table 1). Thirteen RAPD primers were studied, and five Healthy and infected genotypes could not be differentiated of these showed worthwhile polymorphism. The number from each other using either ISSR or RAPD dendrograms. of polymorphic fragments ranged from 8 to 12, with a Results of principal component analyses (PCoA) using per-primer average of 9.8 (Table 1). both the ISSR and RAPD data, in order to study further From across all analysed B. hyrcana trees (healthy the genetic diversity among the B. hyrcana genotypes andinfectedgroupsoftwo populations),genetic vari- are shown in Fig. 3. A total of 72% variation was ationstatisticsare showninTable 2. High band poly- assigned to the first three components of PCoA using morphism was found in the pooled population samples of B. hyrcana using both ISSR (58%) and RAPD (73%) Table 4 Genetic variation statistics revealed through RAPD and markers. Comparing the two marker systems, RAPDs ISSR markers comparing the healthy and infected B. hyrcana (19.6%) showed higher genetic diversity statistics (He) genotypes than ISSRs (13.8%) (Table 2). Also, He was higher in Molecular Pop. No. No. Na Ne I He %P the Toscatoc population than in the Escolac population type bands private bands using both ISSR and RAPD markers (Table 3). In contrast to ISSRs, the RAPD assays generated similar values of the ISSR Healthy 30 3 1.579 1.247 0.275 0.166 79.95 genetic variation parameters for the studied populations. Infected 35 8 1.842 1.224 0.272 0.158 92.11 This indicated the suitability of ISSRs in population RAPD Healthy 49 7 2.000 1.398 0.404 0.254 100.00 genetics research. Results of analyses of healthy versus Infected 42 0 1.714 1.299 0.318 0.196 85.71 infected trees in pooled across-populations samples are Na mean number of alleles, Ne effective number of alleles, I Shannon’s summarised in Table 4. Effective number of alleles, Shan- information index, He expected heterozygosity, %P percentage of non’s information index and expected heterozygosity were polymorphic loci Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 5 of 10 Fig. 2 UPGMA dendrogram (based on combined ISSR and RAPD data) of the 60 healthy (h) and infected (i) B. hyrcana genotypes originating from two populations Tuscatoc (T) and Escolac (E) in the Hyrcanian forests ISSRs, and 70% of the total variation was thus assigned using RAPDs. The first principal coordinate accounted for 42% of the total variation using ISSR data, and the Tuscatoc population was clearly sepa- rated from the Escolac population (Fig. 3a). The in- fected trees of Tuscatoc were partially separated from the healthy trees across the second principal coordin- ate, which explained 17% of the total variation. Re- sults of the AMOVA using ISSR data implied that 34% of the genetic variation occurred between popu- lations, 3% between healthy and infected trees, and most of the variation occurred within populations (Table 5). According to the RAPD data only, the first principal coordinate (which explained 32% of the total variation) separated infected and healthy trees of the Tuscatoc population (Fig. 3b). The studied populations were partially separated, based on the second principal coord- inate (which explained 24% of the total variation). Results of the AMOVA using RAPD data showed that 16% of the genetic variation exists between populations, 5% among healthy and infected trees and most of the marker variation occurred within populations (Table 5). A combined PCoA using both the ISSR and RAPD datasets (Fig. 3c) was similar to the PCoA using only ISSRs data (Fig. 3a), i.e. genotypes were separated into two populations. The combined UPGMA clustering patterns and combined PCoA of genotypes were com- parable (Figs. 2 and 3c respectively), and both partially separated the two populations, but the healthy and infected genotypes were not distinguished from each other. Mantel’s test showed no real correlation between two marker systems (r = 0.06). This result suggests that the two marker systems give somewhat different estimates of genetic relations among genotypes. Discussion This study aimed to compare the genetic variation of healthy and infected Buxus hyrcana trees originating from two populations in Hyrcanian forests using ISSR and RAPD markers. Both RAPD and ISSR markers have been widely applied in population genetic re- search of various species in not only wild (Dikshit et al. 2007; Yao et al. 2008;Chenetal. 2013)butalso cul- tivated plants (Nagaoka and Ogihara 1997;Sikdaret al. 2010). Generally, all these studies have revealed the informativeness and efficiency of ISSR primers com- pared with RAPD primers. Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 6 of 10 Fig. 3 Scatter diagram of the 60 healthy and infected B. hyrcana genotypes originating from two populations Tuscatoc and Escolac in Hyrcanian forests on the basis of data from ISSR (a), RAPD (b) and combined ISSR and RAPD (c). Healthy trees from Tuscatoc, black diamond; infected trees from Tuscatoc, white diamond; healthy trees from Escolac, black circle; infected trees from Escolac, white circle Considerable genetic marker variation for B. hyrcana (2013a, b) in populations not infected by boxwood was observed based on the mean values of the He for blight in Hyrcanian forests using ISSR (0.34) and each marker type (ISSR: 0.138 and RAPD: 0.196). The RAPD (0.25). A possibility is that the differences were reason for the variation detected within populations may due to genetic drift caused by the high degree of tree be related to genetic structure, which is probably due to mortality and corresponding reduction in population heterozygosity resulting from cross-pollination of B. hyr- size. The loss of genetic variation within natural pop- cana (Lazaro and Traveset 2006). However, average ulations may occur through bottlenecks, namely levels of genetic variation within either healthy or severe reductions of population size over a relatively infected B. hyrcana populations included in this study short period. Bottlenecks may determine reductions of are lower than those reported by Ghandehari et al. within-population genetic diversity owing to the loss Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 7 of 10 Table 5 Results of analysis of molecular variance (AMOVA) on Ginkgo biloba L. (Mei et al. 2014), Tectona grandis L.f. the basis of ISSR and RAPD markers for the healthy and infected (Narayanan et al. 2015), Salix spp. (Trybush et al. 2008; B. hyrcana trees originating from two populations in the Zhai et al. 2016; Sulima et al. 2018), and Morus alba L. Hyrcanian forests (Saha et al. 2016) have consistently indicated that geno- Molecular Source Df. MS Est. Variation types with different geographic origins are quite differ- type Var. % ent genetically as well. The geographical separation of ISSR Among Populations 1 60.300 1.888 34% the two boxwood populations through ISSRs can be Within Populations 58 3.675 3.675 66% explained by mesoclimatic differences, restricted pollin- Among healthy and 1 9.433 0.163 3% ation and seed dispersal (by gravity) in an understorey infected tree groups species or small tree species (Shah et al. 2008; Jenkins Within groups 58 4.552 4.552 97% et al. 2010;Zengetal. 2012). More importantly, the current study aimed to find whether or not different RAPD Among Populations 1 41.100 1.162 16% marker systems reflect different aspects of genetic rela- Within Populations 58 6.230 6.230 84% tionships. Due to higher number of alleles per locus Among healthy and 1 19.733 0.416 5% and a moderate value of He, a higher level of poly- infected tree groups morphism (ISSR 58% and RAPD 73%) was observed Within groups 58 7.262 7.262 95% using RAPDs. Differences in genetic relationships Df degrees of freedom, MS mean squares, Est. Var estimate of variance (based on the two marker systems studied) may simply of alleles through genetic drift or random fluctuations reflect differences in the levels of polymorphism in allele frequencies (Spielman et al. 2004). McDonald detected by each marker system. Discordance between et al. (1998) studied the impact of an oak wilt epidemic on different marker systems may or may not be very the genetic structure of a live oak (Quercus fusiformis informative for understanding genetic relationships Small) population in Texas, USA, by allozyme comparison within a study group. of pre-epidemic and post-epidemic (survivors of a wilt The mean values of genetic diversity parameters epidemic) trees. They demonstrated that disease affects (Neand He) of healthy trees (pooled from the two the genetic structure of a natural host population. populations) were higher than in the trees infected by Results from the current study revealed that more genetic boxwood blight based on both ISSR and RAPD data variation occurred within populations of B. hyrcana than even though AMOVA showed a low degree of genetic between populations using both ISSR (66% and 34%, differentiation between healthy and infected B. respectively) and RAPD markers (84% and 16%, respect- hyrcana groups (ISSR: 5%, RAPD: 13%). Houston and ively). These observations are consistent with earlier studies Houston (2000) indicated that genetic parameters of on B. hyrcana in Hyrcanian forests (Ghandehari et al. resistant and susceptible trees to beech bark disease 2013a, b) and on other tree and shrub species that are using isozyme data were similar, while the heterozygosity characterised by high genetic variation within populations observed was actually higher in the susceptible population. (Hamrick et al. 1992). As quoted by Hamrick and Godt They postulated that the larger within-stand heterozygote (1996), reproductive biology is one of the most important deficits in these resistant groups of trees led to underlying factors for specifying the genetic structure of plant popula- genetic differences between resistant and susceptible tions. They showed that 10–20% of the genetic variation populations which are related to adaptation, tree vigour occurring among populations is typical of outcrossing plant and stand history. Studies have also shown that infection species, while 50% of the variation occurring among popu- by fungal pathogens may change significantly the fre- lations is typical of self-pollinating species. Therefore, quencies at which particular resistance genes occur partial inbreeding can explain the observed genetic (e.g. Burdon and Thompson 1995; Webster et al. variation among studied populations. Buxus hyrcana is an 1986). According to the study by Burdon and Thomp- ambophilous (i.e. pollinated by wind and insects) species son (1995), arustepidemic(caused by Melampsora and is an outcrosser that shows partial self-compatibility lini Ehrenb. Lev.) changed significantly the profile of based on studies of flowering and pollination biology (Von resistant genes in a natural population of wild flax Balthazar and Endress 2002). Lazaro Traveset 2006). (Linum marginale A. Cum. ex Planch.). Although the The genetic correlation among the genotypes, speci- resistance structure of the flax population changed, fied by ISSR and RAPD markers, is partially related to its resistance to the predominant pathogen genotypes the geographical origin of B. hyrcana genotypes, espe- did not improve. These results indicated that the cially with ISSR data. Previous results for various Picea effects of selection may be unforeseeable. Also, the ef- species (Nkongolo et al. 2005; Tayefeh Aliakbarkhani et fects of fungal disease including chestnut blight, al. 2015), Angelica sinensis (Oliv.) Diels (Mei et al. Dutch elm disease and Gilbertson root rot (caused by 2007), Dalbergia oliveri Prain (Phong et al. 2011), Phellinus weirii, Murrill) on the composition of plant Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 8 of 10 communities have been reported in the western Additional File 2: UPGMA dendrogram of the 60 healthy (h) and mountain forests of North America (Harper 1990; infected (i) B. hyrcana genotypes originating from two populations Tuscatoc (T) and Escolac (E) in Hyrcanian forests based on RAPD marker. Holah et al. 1997). In addition, a study of isozyme vari- (JPG 1184 kb) ation among nine populations of Ozark chinkapin (Casta- nea pumila (L.) Mill.) threatened by their susceptibility to Abbreviations chestnut blight (Cryphonectria parasitica) revealed higher %P: Percentage of polymorphic bands; He: Expected heterozygosity; genetic variation (He = 0.227) compared to other Casta- I: Shannon’s information Index; Na: Average number of observed bands; Nb: Number of bands; Ne: Effective number of bands; Nf: Number of frequent nea species (He = 0.115) on the North American contin- bands freq. ≥ 5%; Np: Number of private bands ent that were not susceptible to infection by this disease (Dane and Hawkins 1999; Huang et al. 1994a, 1994b; Acknowledgements This work was supported by the Agricultural Research, Education and Huang et al. 1998). According to these studies, popula- Extension Organization, and Research Institute of Forests and Rangelands tions with high levels of genetic variation and unusual al- (RIFR), Iran; Project no. 14-09-09-9354-93007. leles should be subject to further study by conservation Funding biologists in order to capture as much of the genetic vari- None. ation of the species as possible. Availability of data and materials Please contact author for data requests. Conclusion Authors’ contributions Boxwood blight has had a major effect on B. hyrcana, kill- PSS planned and directed the study, analysed the data and interpretation of ing individual stems quickly especially in dense populations results and drafted the manuscript. HJ was responsible for the correction of manuscript. LR was responsible for the production of data. MA was and reducing population size in all populations. Consider- responsible for the collection of field specimens. All authors read and able within-population genetic diversity, and generally approved the final manuscript. higher genetic diversity in healthy genotypes compared with Ethics approval and consent to participate infected ones, suggested conservation efforts should focus Not applicable. on survivor trees in every population and consider the establishment of tree reserves. Propagation of plants from Consent for publication Not applicable. seeds is preferred, since it would include the widest range of genetic variation. Competing interests The present study compares the markers analysis among The authors declare that they have no competing interests. the B. hyrcana genotypes. Low correlation between the marker types cautions against reliance on a single marker Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in technique in B. hyrcana. 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Evaluation of genetic differentiation among healthy and infected Buxus hyrcana with boxwood blight using RAPD and ISSR markers

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Copyright © 2018 by The Author(s).
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Life Sciences; Forestry
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Abstract

Background: Buxus hyrcana (boxwood) is an endangered species in the Hyrcanian forests in the north of Iran. This tree is threatened by habitat loss but faces additional threats from the introduced disease the boxwood blight (caused by the fungus Calonectria pseudonaviculata syn. Cylindrocladium pseudonaviculatum, Cy. buxicola) and the potential effects of climate change. As wide range of genetic polymorphism is necessary to ensure successful adaptation to rapid climatic changes. Methods: Genetic diversity and differentiation between 15 healthy and 15 infected trees of each of two populations were studied using RAPD and ISSR molecular markers. Results: High-band polymorphism was found in pooled samples of B. hyrcana using both ISSR (58%) and RAPD (73%) markers. The ISSR data and the combined data set classified the trees into two groups. However, data from RAPD clustered the trees into three groups. These results indicate different degrees of genetic variation in the sequences of the tested B. hyrcana genomes targeted by the two marker types used. Genetic variation was found to be relatively high, with most of the diversity occurring within populations. Analyses of healthy versus infected pooled samples based on both marker types indicated that genetic diversity parameters were mostly higher in healthy trees. Conclusions: Boxwood blight has had a major effect on B. hyrcana, killing individual stems quickly especially in dense populations and reducing population size (as observed in all populations). Considerable within-population diversity, and higher genetic variability in healthy trees than infected ones, suggested conservation efforts should focus on survivor trees in each population and consider the establishment of tree reservations. Propagation of plants from seeds is preferred, since it would include the widest range of genetic variation. Keywords: Blight, Buxus hyrcana, Genetic variation, ISSR, RAPD Background was reported in England in the mid-1990s and then in Buxus hyrcana is an evergreen shrub or small tree New Zealand in 2002. Since the first reports, this disease growing up to 1 to 12 m tall. It usually occurs as part of has spread into European countries such as Austria, the understorey in the Hyrcanian forests of northern Belgium, Croatia, Czech Republic, Denmark, France, Iran. In the summer 2012, a boxwood blight disease was Georgia, Germany, Ireland, Italy, the Netherlands, reported in the forests there (Mirabolfathy et al. 2013). Norway, Slovenia, Spain, Sweden, Switzerland and Turkey To date, more than 70% of B. hyrcana trees in Hyrcanian (Henricot et al. 2000;Brand 2005;Crepeland forests have been infected by boxwood blight (Fig. 1). Inghelbrecht 2003;Saracchi et al. 2008; Pintos Varela et al. Boxwood blight, caused by Calonectria pseudonaviculata, 2009; Cech et al. 2010; Gorgiladze et al. 2011;Akilliet al. 2012). Iran is the only Asian country that has reported this disease. * Correspondence: psalehi1@gmail.com; psalehi@rifr-ac.ir Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization, P.O. Box 13185-116, Tehran, Iran © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 2 of 10 Fig. 1 General view of B. hyrcana in Hyrcanian forests that have been infected by boxwood blight (caused by Calonectria pseudonaviculata, syn. Cylindrocladium pseudonaviculatum, Cy. Buxicola); Tuscatoc (right) and Escolac (left) Devastating pest and disease epidemics have been created new opportunities for Buxus research. Gande- reported in many parts of the world over the last 120 hari et al. (2013a, b) detected desirable genetic variation years, affecting trees of great economic and/or ecological using random amplified polymorphic DNA (RAPD) and importance (Boyd et al. 2013). American chestnut inter-simple sequence repeat (ISSR) markers in B. hyrcana (Castanea dentata (Marshall) Borkh.) was decimated by a populations. An amplified fragment length polymorphism blight disease, caused by Cryphonectria parasitica Murr. (AFLP) marker was used to specify and distinguish the Barr., and the species became effectively extinct from its European and Asian Buxus taxa (Van Laere et al. 2011). native range in a period of 40 years (Choi and Nuss 1992). Also, internal transcribed spacer regions and plastid ndhF Dutch elm disease, caused by the fungus Ophiostoma sequences were used to describe the phylogenetic relation- ulmi, Buisman Nannt., and later by Ophiostoma ships (Von Balthazar et al. 2000). Thammina et al. (2014, novo-ulmi Brasier spread through native populations of 2016) studied the advantages of genic SSR markers and elm (Ulmus spp.) trees in countries such as America, New ploidy analysis for specifying the diversity (and, in some Zealand and Europe causing widespread tree death cases, for identifying accessions) of Buxus in the National (Comeau et al. 2015). Black sigatoka is a fungal Buxus Collection at the United State Department of (Mycosphaerella fijiensis) disease that affects the produc- Agriculture (USDA). tion and export of banana and plantain in various coun- It is clear that species with limited genetic variation tries, with Grenada suffering complete loss of its often cannot cope with the changing environments plantations (Marin et al. 2003). Anthracnose fungi (usually (Schaal et al. 1991) and that adaptive responses to stresses Colletotrichum or Gloeosporium species) are a threat for also depend on the level of remaining of genetic variation many hardwood tree species (Berry 1985). Fusiform rust is as well (Ayala and Kiger 1984). Therefore, knowledge of afungal (Cronartium quercuum f. sp. fusiforme) disease the distribution of genetic variation among and within that affects the southern pines (Pinus spp.), leading to an- host species populations is necessary for better under- nual losses of millions of dollars for timber growers. Huge standing of ecosystem functioning. Such knowledge will losses have occurred across Europe following ash (Fraxi- also provide valuable insights into the direct and indirect nus spp.) dieback caused by Hymenoscyphus fraxineus effects of the pathogens introduced on native indigenous (Harper et al. 2016). These and many other fungal patho- hosts, as well as into potential host maladaptation to gens have serious effects on the future of tree species eco- climate change amplified epidemics of indigenous patho- nomically and ecologically. gens (Burdon & Thompson 1995). This knowledge is also Buxus hyrcana has been examined in a few biochemical of practical use for monitoring the diseases in tree hosts (Ata et al. 2010) and ecological studies (Asadi et al. 2011; planted beyond their natural range. Asadi et al. 2012; Soleymanipoor and Esmailzadeh 2015; This study aims to investigate the variation in Kaviani and Negahdar 2016; Hosseinzadeh and Esmailza- genetic markers in relation to the disease status in B. deh 2017). Reports indicated an ecological range of box hyrcana and compares the merits of two methods trees from sea level up to 1700-m elevation in mountain (RAPD and ISSR markers) for evaluating the genetic forests of north Iran (Soleymanipoor and Esmailzadeh variation of the healthy and infected groups of B. 2015; Hosseinzadeh and Esmailzadeh 2017). However, hyrcana. The markers are two widely applicable until recently, the genetics of B. hyrcana had been lit- techniques to identify relationships at the species and tle studied. Development of molecular methods has populations levels (Wali et al. 2007; Mehes-Smith et Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 3 of 10 al. 2010;Phong et al. 2011;Zhiqiangetal. 2015;Elm- Table 1 List of primers and their nucleotide sequences, annealing temperature, number of observed bands and the eer et al. 2017), because they are rapid, simple to per- percentage of polymorphism produced by different ISSR and form and inexpensive; they do not require prior RAPD markers knowledge of DNA sequences; and only a small Molecular Primer Sequence 5′-3′ Annealing No. Polymor amount of DNA is needed (Esselman et al. 1999). type code Temperature observed phism Selection of collection sites was difficult due to the (°C) bands % limited numbers of healthy trees. Healthy and infected ISSR ISSR 7 CACACACAC 53 9 78 ± 5 B. hyrcana trees belonging to two different local popu- ACAGT lations were evaluated for genetic variation using two ISSR 3 CTCTCTCTC 53 14 61 ± 12 types of marker based on DNA amplification (RAPD TCTCTCTTG and ISSR). Furthermore, we investigated whether or ISSR 19 AGAGAGAGA 52 9 46 ± 27 not the methods are beneficial for exhibiting a link GAGAGGT between the geographical origin of a given population P 26 CCACTCTCT 51 9 42 ± 24 CTCTCTCTCT and the evaluated genetic variation. P 12 GAGAGAGAG 52 8 4 AGAGAGAT Materials and methods Genomic DNA extraction from plant material P 5 ACACACACA 52 8 2 CACACACG In total, 60 healthy (30 apparently free of boxwood RAPD OPJ 13 CCACACTACC 40 8 81 ± 4 blight) and infected (i.e. 30 with major branches dead) B. hyrcana were collected from Hyrcanian forests at two OPO 10 TCAGAGCGCC 40 10 78 ± 9 different localities (Escolac, 37° 01′ N and 49° 33′ E, and OPJ 19 GGACACCACT 40 9 75 ± 7 Toscatoc 36° 34′ N and 51° 44′ E). Choice of site was OPA 04 AATCGGGCTG 40 10 70 ± 8 subject to finding at least 15 healthy trees per collection OPJ 04 CCGAACACGG 40 12 65 ± 7 area. The sampling area in each site was approximately OPA 06 GGTCCCTGAC 40 8 2 10 km and distance between sampling trees was at least OPA 07 GAAACGGGTG 40 7 2 20 m. The voucher numbers of deposited samples in TARI Herbarium are Iran36913 and Iran36914. Nuclear OPJ 14 CACCCGGATG 40 8 2 DNA was extracted from bud tissues of each individual OPJ 18 TGGTCGCAGA 40 8 2 and used for marker analysis (Dellaporta et al. 1983). OPO 11 GACAGGAGGT 40 8 2 OPO 09 TCCCACGCAA 40 7 1 ISSR analysis OPA 03 AGTCAGCCAC 40 7 1 Polymerase chain reaction (PCR) was conducted OPA 05 AGGGGTCTTG 40 8 1 according to Zietkiewicz et al. (1994). Six ISSR primers were initially screened but only four primers were used in the analysis (Table 1). The clear and reproducible banding patterns were used to evaluate genetic variation. banding patterns generated were used to evaluate The reaction conditions were optimised, and mixtures genetic variation. The reaction conditions were were composed of 40 ng of DNA, 10× PCR reaction optimised and mixtures were composed of 20 ng of buffer (10 mM Tris-HCl, pH 9.0; 50 mM KCl; 1.5 mM DNA, 10× buffer (20 mM Tris-HCl pH 8.4; 50 mM MgCl ), 1 U TaqDNA polymerase, 0.1 mM dNTP, KCl), 1 U TaqDNA polymerase, 2 mM MgCl ,0.2mM 0.4 μM primer and 1.2 mM MgCl . The amplifications 2 2 dNTP, and 0.8 μM primer. The PCR amplification included 1 cycle of 5 min at 94 °C and following 45 cycles protocol includes one cycle for 5 min at 94 °C and of 1 min at 94 °C, 2 min at 40 °C, 2 min at 72 °C and then is followed by 42 cycles for 30 s at 94 °C, 1 min finally was extended for 7 min at 72 °C. Amplification at 51–53 °C (Table 1), 1 min at 72 °C and 5 min for products (10 mL) were mixed with 5 mL bromophenol final extension at 72 °C. Amplification productions blue separated on 1.5% agarose gel and were marked (10 mL) are mixed with 5 mL bromophenol blue with 5 mL of SYBR Green and then photographed. separated on 1.5% agarose gel and marked with 5 mL of SYBR Green and then photographed. Data analysis Amplification reactions from all individuals were scored; RAPD analysis then, genetic variation statistics were computed using the Polymerase chain reaction (PCR) was conducted accord- GENAlEX 6.5 software for binary data (Peakall and ing to Williams et al. (1990). Thirteen RAPD primers Smouse 2012). The number of observed and private bands were initially screened, but only five primers were used (number of bands unique to a single population), mean in the analysis (Table 2). Only the clear and reproducible number of alleles (Na), effective number of alleles (Ne), Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 4 of 10 Table 2 Genetic variation statistics revealed through RAPD and Table 3 Genetic variation statistics revealed through RAPD and ISSR markers among the B. hyrcana genotypes ISSR markers among the B. hyrcana populations Molecular Na (SD) Ne (SD) I (SD) He (SD) %P (SD) Molecular Pop. No. No. Na Ne I He %P type type bands private bands ISSR 1.171 1.213 0.222 0.138 57.890 (0.080) (0.024) (0.019) (0.013) (8.790) ISSR Tuscatoc 32 16 1.684 1.315 0.318 0.199 84.21 RAPD 1.500 1.314 0.308 0.196 72.95 Escolac 22 6 1.158 1.140 0.166 0.097 57.89 (0.060) (0.023) (0.018) (0.013) (4.19) RAPD Tuscatoc 46 7 1.878 1.361 0.361 0.227 93.88 Na mean number of alleles, Ne effective number of alleles, I Shannon’s Escolac 42 3 1.714 1.347 0.345 0.218 85.71 information index, He expected heterozygosity, %P percentage of polymorphic loci Na mean number of alleles, Ne effective number of alleles, I Shannon’s information index, He expected heterozygosity, %P percentage of polymorphic loci Shannon’s information index (I), expected heterozygosity (He) and percentage of polymorphic loci (%P) were evaluated according to Nei (1978). According to Nei’s mostly higher in healthy trees using both marker types method (1978), the genetic distances were calculated and (Table 4). the similarity matrix was subjected to principal coordinate UPGMA dendrograms were generated using ISSR and analysis (PCoA). Mantel (1967) was used for evaluating RAPD datasets to elucidate genetic diversity and population the relationship between the calculated distance matrices structure among genotypes (Additional files 1 and 2). In and the statistic tested for significance against 999 random order to examine the relationships among the B. hyrcana permutations. The SIMJACARD code of the software genotypes, a combined UPGMA clustering was estimated package NTSYS-pc: 2.11 was used to estimate pairwise based on the genetic similarity matrix by combining 87 genetic similarity (Rohlf 2004). A similarity matrix based polymorphic bands obtained from ISSR as well as RAPD on the unweighted pair group method and arithmetic data. The dendrogram delineated based on the combined means (UPGMA) was generated using Jacard’s similarities data set (ISSR and RAPD) is shown in Fig. 2.Clustersof and SHAN of NTSYS-pc to construct the dendrogram of two groups of data points displaying a similar coefficient all the 60 genotypes. Cophenetic matrices were calculated value (0.67) are apparent in this diagram. Thus, the for characterising the correlations between the dendro- combined data indicated similar results to the ISSR except grams and similarity matrices. for some minor changes in branch positions. The cophe- netic correlation was r=0.99, andthisimpliesavery good Results fit. Group I included healthy and infected genotypes of the Of the six ISSR primers used in this study, four showed Toscatoc population with slight differences in branch posi- polymorphism. The number of polymorphic fragments tions as compared with the ISSR dendrogram (Fig. 2). ranged from 9 to 14, with an average of 9.5 per primer Group II included genotypes similar to the ISSR clustering. (Table 1). Thirteen RAPD primers were studied, and five Healthy and infected genotypes could not be differentiated of these showed worthwhile polymorphism. The number from each other using either ISSR or RAPD dendrograms. of polymorphic fragments ranged from 8 to 12, with a Results of principal component analyses (PCoA) using per-primer average of 9.8 (Table 1). both the ISSR and RAPD data, in order to study further From across all analysed B. hyrcana trees (healthy the genetic diversity among the B. hyrcana genotypes andinfectedgroupsoftwo populations),genetic vari- are shown in Fig. 3. A total of 72% variation was ationstatisticsare showninTable 2. High band poly- assigned to the first three components of PCoA using morphism was found in the pooled population samples of B. hyrcana using both ISSR (58%) and RAPD (73%) Table 4 Genetic variation statistics revealed through RAPD and markers. Comparing the two marker systems, RAPDs ISSR markers comparing the healthy and infected B. hyrcana (19.6%) showed higher genetic diversity statistics (He) genotypes than ISSRs (13.8%) (Table 2). Also, He was higher in Molecular Pop. No. No. Na Ne I He %P the Toscatoc population than in the Escolac population type bands private bands using both ISSR and RAPD markers (Table 3). In contrast to ISSRs, the RAPD assays generated similar values of the ISSR Healthy 30 3 1.579 1.247 0.275 0.166 79.95 genetic variation parameters for the studied populations. Infected 35 8 1.842 1.224 0.272 0.158 92.11 This indicated the suitability of ISSRs in population RAPD Healthy 49 7 2.000 1.398 0.404 0.254 100.00 genetics research. Results of analyses of healthy versus Infected 42 0 1.714 1.299 0.318 0.196 85.71 infected trees in pooled across-populations samples are Na mean number of alleles, Ne effective number of alleles, I Shannon’s summarised in Table 4. Effective number of alleles, Shan- information index, He expected heterozygosity, %P percentage of non’s information index and expected heterozygosity were polymorphic loci Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 5 of 10 Fig. 2 UPGMA dendrogram (based on combined ISSR and RAPD data) of the 60 healthy (h) and infected (i) B. hyrcana genotypes originating from two populations Tuscatoc (T) and Escolac (E) in the Hyrcanian forests ISSRs, and 70% of the total variation was thus assigned using RAPDs. The first principal coordinate accounted for 42% of the total variation using ISSR data, and the Tuscatoc population was clearly sepa- rated from the Escolac population (Fig. 3a). The in- fected trees of Tuscatoc were partially separated from the healthy trees across the second principal coordin- ate, which explained 17% of the total variation. Re- sults of the AMOVA using ISSR data implied that 34% of the genetic variation occurred between popu- lations, 3% between healthy and infected trees, and most of the variation occurred within populations (Table 5). According to the RAPD data only, the first principal coordinate (which explained 32% of the total variation) separated infected and healthy trees of the Tuscatoc population (Fig. 3b). The studied populations were partially separated, based on the second principal coord- inate (which explained 24% of the total variation). Results of the AMOVA using RAPD data showed that 16% of the genetic variation exists between populations, 5% among healthy and infected trees and most of the marker variation occurred within populations (Table 5). A combined PCoA using both the ISSR and RAPD datasets (Fig. 3c) was similar to the PCoA using only ISSRs data (Fig. 3a), i.e. genotypes were separated into two populations. The combined UPGMA clustering patterns and combined PCoA of genotypes were com- parable (Figs. 2 and 3c respectively), and both partially separated the two populations, but the healthy and infected genotypes were not distinguished from each other. Mantel’s test showed no real correlation between two marker systems (r = 0.06). This result suggests that the two marker systems give somewhat different estimates of genetic relations among genotypes. Discussion This study aimed to compare the genetic variation of healthy and infected Buxus hyrcana trees originating from two populations in Hyrcanian forests using ISSR and RAPD markers. Both RAPD and ISSR markers have been widely applied in population genetic re- search of various species in not only wild (Dikshit et al. 2007; Yao et al. 2008;Chenetal. 2013)butalso cul- tivated plants (Nagaoka and Ogihara 1997;Sikdaret al. 2010). Generally, all these studies have revealed the informativeness and efficiency of ISSR primers com- pared with RAPD primers. Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 6 of 10 Fig. 3 Scatter diagram of the 60 healthy and infected B. hyrcana genotypes originating from two populations Tuscatoc and Escolac in Hyrcanian forests on the basis of data from ISSR (a), RAPD (b) and combined ISSR and RAPD (c). Healthy trees from Tuscatoc, black diamond; infected trees from Tuscatoc, white diamond; healthy trees from Escolac, black circle; infected trees from Escolac, white circle Considerable genetic marker variation for B. hyrcana (2013a, b) in populations not infected by boxwood was observed based on the mean values of the He for blight in Hyrcanian forests using ISSR (0.34) and each marker type (ISSR: 0.138 and RAPD: 0.196). The RAPD (0.25). A possibility is that the differences were reason for the variation detected within populations may due to genetic drift caused by the high degree of tree be related to genetic structure, which is probably due to mortality and corresponding reduction in population heterozygosity resulting from cross-pollination of B. hyr- size. The loss of genetic variation within natural pop- cana (Lazaro and Traveset 2006). However, average ulations may occur through bottlenecks, namely levels of genetic variation within either healthy or severe reductions of population size over a relatively infected B. hyrcana populations included in this study short period. Bottlenecks may determine reductions of are lower than those reported by Ghandehari et al. within-population genetic diversity owing to the loss Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 7 of 10 Table 5 Results of analysis of molecular variance (AMOVA) on Ginkgo biloba L. (Mei et al. 2014), Tectona grandis L.f. the basis of ISSR and RAPD markers for the healthy and infected (Narayanan et al. 2015), Salix spp. (Trybush et al. 2008; B. hyrcana trees originating from two populations in the Zhai et al. 2016; Sulima et al. 2018), and Morus alba L. Hyrcanian forests (Saha et al. 2016) have consistently indicated that geno- Molecular Source Df. MS Est. Variation types with different geographic origins are quite differ- type Var. % ent genetically as well. The geographical separation of ISSR Among Populations 1 60.300 1.888 34% the two boxwood populations through ISSRs can be Within Populations 58 3.675 3.675 66% explained by mesoclimatic differences, restricted pollin- Among healthy and 1 9.433 0.163 3% ation and seed dispersal (by gravity) in an understorey infected tree groups species or small tree species (Shah et al. 2008; Jenkins Within groups 58 4.552 4.552 97% et al. 2010;Zengetal. 2012). More importantly, the current study aimed to find whether or not different RAPD Among Populations 1 41.100 1.162 16% marker systems reflect different aspects of genetic rela- Within Populations 58 6.230 6.230 84% tionships. Due to higher number of alleles per locus Among healthy and 1 19.733 0.416 5% and a moderate value of He, a higher level of poly- infected tree groups morphism (ISSR 58% and RAPD 73%) was observed Within groups 58 7.262 7.262 95% using RAPDs. Differences in genetic relationships Df degrees of freedom, MS mean squares, Est. Var estimate of variance (based on the two marker systems studied) may simply of alleles through genetic drift or random fluctuations reflect differences in the levels of polymorphism in allele frequencies (Spielman et al. 2004). McDonald detected by each marker system. Discordance between et al. (1998) studied the impact of an oak wilt epidemic on different marker systems may or may not be very the genetic structure of a live oak (Quercus fusiformis informative for understanding genetic relationships Small) population in Texas, USA, by allozyme comparison within a study group. of pre-epidemic and post-epidemic (survivors of a wilt The mean values of genetic diversity parameters epidemic) trees. They demonstrated that disease affects (Neand He) of healthy trees (pooled from the two the genetic structure of a natural host population. populations) were higher than in the trees infected by Results from the current study revealed that more genetic boxwood blight based on both ISSR and RAPD data variation occurred within populations of B. hyrcana than even though AMOVA showed a low degree of genetic between populations using both ISSR (66% and 34%, differentiation between healthy and infected B. respectively) and RAPD markers (84% and 16%, respect- hyrcana groups (ISSR: 5%, RAPD: 13%). Houston and ively). These observations are consistent with earlier studies Houston (2000) indicated that genetic parameters of on B. hyrcana in Hyrcanian forests (Ghandehari et al. resistant and susceptible trees to beech bark disease 2013a, b) and on other tree and shrub species that are using isozyme data were similar, while the heterozygosity characterised by high genetic variation within populations observed was actually higher in the susceptible population. (Hamrick et al. 1992). As quoted by Hamrick and Godt They postulated that the larger within-stand heterozygote (1996), reproductive biology is one of the most important deficits in these resistant groups of trees led to underlying factors for specifying the genetic structure of plant popula- genetic differences between resistant and susceptible tions. They showed that 10–20% of the genetic variation populations which are related to adaptation, tree vigour occurring among populations is typical of outcrossing plant and stand history. Studies have also shown that infection species, while 50% of the variation occurring among popu- by fungal pathogens may change significantly the fre- lations is typical of self-pollinating species. Therefore, quencies at which particular resistance genes occur partial inbreeding can explain the observed genetic (e.g. Burdon and Thompson 1995; Webster et al. variation among studied populations. Buxus hyrcana is an 1986). According to the study by Burdon and Thomp- ambophilous (i.e. pollinated by wind and insects) species son (1995), arustepidemic(caused by Melampsora and is an outcrosser that shows partial self-compatibility lini Ehrenb. Lev.) changed significantly the profile of based on studies of flowering and pollination biology (Von resistant genes in a natural population of wild flax Balthazar and Endress 2002). Lazaro Traveset 2006). (Linum marginale A. Cum. ex Planch.). Although the The genetic correlation among the genotypes, speci- resistance structure of the flax population changed, fied by ISSR and RAPD markers, is partially related to its resistance to the predominant pathogen genotypes the geographical origin of B. hyrcana genotypes, espe- did not improve. These results indicated that the cially with ISSR data. Previous results for various Picea effects of selection may be unforeseeable. Also, the ef- species (Nkongolo et al. 2005; Tayefeh Aliakbarkhani et fects of fungal disease including chestnut blight, al. 2015), Angelica sinensis (Oliv.) Diels (Mei et al. Dutch elm disease and Gilbertson root rot (caused by 2007), Dalbergia oliveri Prain (Phong et al. 2011), Phellinus weirii, Murrill) on the composition of plant Salehi Shanjani et al. New Zealand Journal of Forestry Science (2018) 48:15 Page 8 of 10 communities have been reported in the western Additional File 2: UPGMA dendrogram of the 60 healthy (h) and mountain forests of North America (Harper 1990; infected (i) B. hyrcana genotypes originating from two populations Tuscatoc (T) and Escolac (E) in Hyrcanian forests based on RAPD marker. Holah et al. 1997). In addition, a study of isozyme vari- (JPG 1184 kb) ation among nine populations of Ozark chinkapin (Casta- nea pumila (L.) Mill.) threatened by their susceptibility to Abbreviations chestnut blight (Cryphonectria parasitica) revealed higher %P: Percentage of polymorphic bands; He: Expected heterozygosity; genetic variation (He = 0.227) compared to other Casta- I: Shannon’s information Index; Na: Average number of observed bands; Nb: Number of bands; Ne: Effective number of bands; Nf: Number of frequent nea species (He = 0.115) on the North American contin- bands freq. ≥ 5%; Np: Number of private bands ent that were not susceptible to infection by this disease (Dane and Hawkins 1999; Huang et al. 1994a, 1994b; Acknowledgements This work was supported by the Agricultural Research, Education and Huang et al. 1998). According to these studies, popula- Extension Organization, and Research Institute of Forests and Rangelands tions with high levels of genetic variation and unusual al- (RIFR), Iran; Project no. 14-09-09-9354-93007. leles should be subject to further study by conservation Funding biologists in order to capture as much of the genetic vari- None. ation of the species as possible. Availability of data and materials Please contact author for data requests. Conclusion Authors’ contributions Boxwood blight has had a major effect on B. hyrcana, kill- PSS planned and directed the study, analysed the data and interpretation of ing individual stems quickly especially in dense populations results and drafted the manuscript. HJ was responsible for the correction of manuscript. LR was responsible for the production of data. MA was and reducing population size in all populations. Consider- responsible for the collection of field specimens. All authors read and able within-population genetic diversity, and generally approved the final manuscript. higher genetic diversity in healthy genotypes compared with Ethics approval and consent to participate infected ones, suggested conservation efforts should focus Not applicable. on survivor trees in every population and consider the establishment of tree reserves. Propagation of plants from Consent for publication Not applicable. seeds is preferred, since it would include the widest range of genetic variation. Competing interests The present study compares the markers analysis among The authors declare that they have no competing interests. the B. hyrcana genotypes. Low correlation between the marker types cautions against reliance on a single marker Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in technique in B. hyrcana. 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Published: Dec 28, 2018

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