Simple Sequence Repeat Analysis of Genetic Diversity in Primary Core Collection of Peach （Prunus persica）

In this study, the genetic diversity of 51 cultivars in the primary core collection of peach （Prunus persica （L.） Batsch） was evaluated by using simple sequence repeats （SSRs）. The phylogenetic relationships and the evolutionary history among different cultivars were determined on the basis of SSR data. Twenty-two polymorphic SSR primer pairs were selected, and a total of 111 alleles were identified in the 51 cultivars, with an average of 5 alleles per locus. According to traditional Chinese classification of peach cultivars, the 51 cultivars in the peach primary core collection belong to six variety groups. The SSR analysis revealed that the levels of the genetic diversity within each variety group were ranked as Sweet peach 〉 Crisp peach 〉 Flat peach 〉 Nectarine 〉 Honey Peach 〉 Yellow fleshed peach. The genetic diversity among the Chinese cultivars was higher than that among the introduced cultivars. Cluster analysis by the unweighted pair group method with arithmetic averaging （UPGMA） placed the 51 cultivars into five linkage clusters. Cultivar members from the same variety group were distributed in different UPGMA clusters and some members from different variety groups were placed under the same cluster. Different variety groups could not be differentiated in accordance with SSR markers. The SSR analysis revealed rich genetic diversity in the peach primary core collection, representative of genetic resources of peach.     

基于引物“随机组合”构建观赏桃SSR指纹图谱

近年来,我国观赏桃新品种日渐繁多、名称混乱、市场难以监管,同时用以区分品种的SSR指纹图谱的构建方法在研究界无统一的科学标准,尤其是构成最终引物组合的核心引物的确定,具体操作流程层出不穷、五花八门。为探索筛选SSR指纹图谱核心引物的科学方法,同时构建观赏桃SSR指纹图谱,该研究选用35对已报道的SSR引物对22份观赏桃种质进行试验。结果表明:通过PCR扩增与分析,多态性较高的8对引物——候选引物总共扩增出31个多态性条带,变幅为3~5个,PIC值变幅为0.458~0.668,MI值变幅为1.374~3.340。采用"随机组合"法对8对引物进行C_8~1、C_8~2、C_8~3…依次分析,得到区分能力最强的3种不同的最少引物组合方式——候选组合,并能区分出18份种质,从中发现区分能力最强的3种引物组合方式并不都是由引物PIC值、alleles数量或MI值等多态性指标最高的引物组成,而是由互补性最强的引物组成。选用组合内各引物多态性条带总数最多的组合方式"4-3"(BPPCT001+BPPCT015a+BPPCT017+BPPCT025)为22份观赏桃种质构建了指纹图谱。基于此,通过常规多态性指标筛选候选引物可以确定出单对引物鉴别能力最强的少量引物;通过"随机组合"筛选候选组合可以进一步确定出引物之间互补性最强的几种组合方式;根据组合内各引物的多态性条带总数确定最终核心引物可以确定出可扩容性最大的引物组合。该研究最终建立了候选引物——候选组合——核心引物组合"三步法"确定SSR指纹图谱核心引物组合的科学方法,不仅为22份供试观赏桃种质构建了SSR指纹图谱,也为其它作物SSR指纹图谱的构建提供了新的思路。     

Population structure and marker–trait associations for pomological traits in peach and nectarine cultivars

Marker–trait associations based on populations from controlled crosses have been established in peach using markers mapped on the peach consensus map. In this study, we explored the utility of unstructured populations for association mapping to determine useful marker–trait associations in peach/nectarine cultivars. We used 94 peach cultivars representing local Spanish and modern cultivars from international breeding programs that are maintained at the Experimental Station of Aula Dei, Spain. This collection was characterized for pomological traits and was screened with 40 SSR markers that span the peach genome. Population structure analysis using STRUCTURE software identified two subpopulations, the local and modern cultivars, with admixture within both groups. The local Spanish cultivars were somewhat less diverse than modern cultivars. Marker–trait associations were determined in TASSEL with and without modelling coefficient of membership (Q) values as covariates. The results showed significant associations with pomological traits. We chose three markers on LG4 because of their proximity to the endoPG locus (freestone–melting flesh) that strongly affects pomological traits. Two genotypes of BPPCT015 marker showed significant associations with harvest date, flavonoids and sorbitol. Also, two genotypes of CPPCT028 showed associations with harvest date, total phenolics, RAC, and total sugars. Finally, two genotypes of endoPG1 showed associations with flesh firmness and total sugars. The analysis of linkage disequilibrium (LD) revealed a high level of LD up to 20 cM, and decay at farther distances. Therefore, association mapping could be a powerful tool for identifying marker–trait associations and would be useful for marker-assisted selection in peach breeding.     

Leucoanthocyanidin dioxygenase gene (PpLDOX): a potential functional marker for cold storage browning in peach

Enzymatic browning of the peach fruit mesocarp is a major component of the postharvest physiological disorder commonly called chilling injury or internal breakdown (IB). Previously, we detected a major quantitative trait locus (QTL; qP-Brn5.1^m) affecting browning in peach using two related progeny populations (Pop-DG and Pop-G). In this report, a gene encoding the leucoanthocanidin dioxygenase (PpLDOX) enzyme was identified as the gene potentially responsible for this QTL. PpLDOX has a high similarity with the LDOX gene of the anthocyanin biosynthesis pathway of Arabidopsis thaliana. It was co-located with qP-Brn5.1^m via the bin mapping technique with the Prunus reference T×E map. A silent SNP within the PpLDOX coding sequence was used to locate the gene more precisely on the Pop-DG map and confirm its bin assignment. These results demonstrate both the utility of comparative mapping within Prunus using the T×E reference map and the power of the bin mapping approach for easily mapping genes in the Prunus genome. An SSR polymorphism was observed in the intron of PpLDOX gene sequence. The SSR co-segregated with the SNP and was used to assess association of PpLDOX with browning in 27 peach and nectarine cultivars. Cumulative evidence obtained indicates that PpLDOX partially explains genetic variation for cold storage browning susceptibility in peach and nectarine. This functional gene has potential use in marker-assisted breeding of new cultivars with lower IB susceptibility and for genotyping current cultivars for possible differential handling during storage to reduce symptom incidence.     

Comparative Analysis of SSR Markers Developed in Exon,Intron, and Intergenic Regions and Distributed in Regions Controlling Fruit Quality Traits in <Emphasis Type="Italic">Prunus</Emphasis> Species: Genetic Diversity and Association Studies

Simple sequence repeats (SSRs) are genome domains located in both coding and non-coding regions in eukaryotic genomes. Although SSRs are often characterized by low polymorphism, their DNA-flanking sequences could be a useful source of DNA markers, which could help in genetic studies and breeding because they are associated with genes that control traits of interest. In this study, 56 genotypes from different Prunus species were used, including peach, apricot, plum, and almond (already phenotyped for several agronomical traits, including self-compatibility, flowering and ripening time, fruit type, skin and flesh color, and shell hardness). These Prunus genotypes were molecularly characterized using 28 SSR markers developed in exons, introns, and intergenic regions. All these genes were located in specific regions where quantitative trait loci (QTLs) for certain fruit quality traits were also located, including flowering and ripening times and fruit flesh and skin color. A sum of 309 SSR alleles were identified in the whole panel of analyzed cultivars, with expected heterozygosity values of 0.61 (upstream SSRs), 0.17 (exonic SSRs), 0.65 (intronic SSRs), and 0.58 (downstream SSRs). These values prove the low level of polymorphism of the exonic (gene-coding regions) markers. Cluster and structural analysis based on SSR data clearly differentiated the genotypes according to either specie (for the four species) and pedigree (apricot) or geographic origin (Japanese plum). In addition, some SSR markers mainly developed in intergenic regions could be associated with genes that control traits of interest in breeding and could therefore help in marker-assisted breeding. These findings highlight the importance of using molecular markers able to discriminate between the functional roles of the gene allelic variants.     

Genetic diversity among alfalfa (Medicago sativa) cultivars coming from a breeding program, using SSR markers

Alfalfa (Medicago sativa) is an autotetraploid, allogamous and heterozygous species whose cultivars are synthetic populations. The breeders apply selection pressure for some agronomic traits within a breeding pool to increase the frequency of favorable individuals. The objective of this study was to investigate the differentiation level among seven cultivars originating from one breeding program, and between these cultivars and the breeding pool, with eight SSR markers. These highly polymorphic and codominant markers, together with recent population genetic statistics extended to autotetraploids, offer tools to analyse genetic diversity in alfalfa. The number of alleles per locus varied between 3 and 24. All loci were at a panmictic equilibrium in the cultivars, except one, probably because of null alleles. With seven SSR loci, each cultivar was at panmictic equilibrium. The mean gene diversity was high, ranging from 0.665 to 0.717 in the cultivars. The parameter F _ST indicated a low but significant diversity among cultivars. Among 21 pairs of cultivars, 15 were significantly different. The breeding pool also had a high diversity, and was significantly different from each cultivar except the most recent one. Considering the characteristics of the breeding program and the mode of cultivar elaboration, we found that they were unable to generate a large variety differentiation. Estimation of population genetics parameters at SSR loci can be applied for assessing the differences between cultivars or populations, either for variety distinction or the management of genetic resources.     

我国茶树主要骨干亲本及其衍生品种(系)的SSR分析

铁观音、黄棪和福鼎大白茶分别是我国乌龙茶和红绿茶育种中的骨干亲本,由他们衍生出了一系列的优良品种,研究他们的遗传多样性及构建指纹图谱将有助于今后茶树育种工作中骨干亲本的合理利用和品种权的保护。本研究利用40对SSR引物对我国乌龙茶骨干亲本铁观音、黄棪及其衍生品种(系)和红绿茶骨干亲本福鼎大白茶及衍生品种进行了研究。结果表明,34份供试品种(系)的基因多样性指数（H）为0.54,平均遗传距离0.58,表明我国茶树主要骨干亲本及其衍生品种(系)具有较高的遗传多样性水平和较大的遗传变异,且90%的遗传多样性来自品种之间的遗传差异。聚类结果表明两套品种(系)各自聚为一类,遗传结构分析也显示两套品种(系)之间存在明显的差异。利用其中5对引物组合构建了供试材料的数码指纹图谱。     

Genetic variability of introduced and local Spanish peach cultivars determined by SSR markers

A set of 94 peach cultivars including Spanish native peach and foreign commercial cultivars were analyzed using 15 SSR markers, selected for their high level of polymorphism. The number of alleles obtained varied from two to 11 with an average of 6.73 giving 185 different genotypes. All the cultivars showed a unique genetic profile, each one using different genotypic combination of all loci. BPPCT001 was the most informative locus showing also the highest discrimination power. Only six loci allowed the unambiguous separation of all the Spanish native cultivars studied, and the genotypic combination of only eight loci permitted the total differentiation of the 94 peach cultivars analyzed. The six selected loci (BPPCT001, BPPCT006, BPPCT008, PS9f8, UDP98-022, and UDP98-412) seem to be very useful for future Spanish peach identification works, and they will help to establish a molecular data base for native peach cultivars. UPGMA analysis was performed from the genetic distance matrix, and allowed the arrangement of all genotypes according to their genetic diversity. The genetic diversity among cultivars, observed in this work, led to their separation according to their regional origin, their morphological characteristics, and especially according to their fruit traits. Analysis of molecular variance was performed for seven populations from different regions of Spain and USA to examine the distribution of genetic variation of the studied accessions, showing that the major variation occurred within populations in each geographic site. The results reveal the existence of two diversity regions in Spain for peach germplasm.     

Genetic identification of 91 poplar cultivars based on SSR markers

Accurate genetic identification and relationship analysis of poplar cultivars is necessary to establish commercial poplar plantations and select suitable breeding strategies. In this study, 91 poplar cultivars belonging to four sections (Aigeiros, Tacamahaca, Populus and Turanga) and inter/intra-sectional hybrids were genotyped using 18 polymorphic simple sequence repeat (SSR) markers. In total, 222 alleles were amplified with an average of 12.3 alleles per marker. The mean polymorphic information content and power of discrimination were 0.706 and 0.813, respectively. Five SSR markers (ORPM_103, ORPM_247, GCPM_1048, GCPM_1255 and LG_X_19) constituted a core fingerprint and were sufficient to identify all the tested cultivars. With some notable exceptions, cultivars of the same species generally clustered together in cluster (UPGMA) and ordination (PCO) analyses. Flow cytometry indicated that 11 poplar cultivars were triploid. Among these, seven had three alleles at some loci, suggesting that SSR markers could indicate the ploidy level to some extent. This study provides useful genetic information for the identification and protection of poplar cultivars in China and offers a guideline for the selection of poplar crossing parents based on ploidy level and genetic relationships.     

Microsatellite DNA and RAPD fingerprinting,identification and genetic relationships of hybrid poplar (<Emphasis Type="Italic">Populus x canadensis</Emphasis>) cultivars

Microsatellite DNA markers of ten SSR loci and 248 RAPD loci (resolved by 26 RAPD primers) were used for DNA fingerprinting and differentiation of 17 widely grown Populus x canadensis syn. Populus x euramericana (interspecific Populus deltoides x Populus nigra hybrids) cultivars ("Baden 431", "Blanc du Poitou", "Canada Blanc", "Dorskamp 925", "Eugenei", "Gelrica", "Grandis", "Heidemij", "I-55/56", "I-132/56", "I-214", "Jacometti", "Ostia", "Regenerata", "Robusta", "Steckby" and "Zurich 03/3"), and determination of their genetic interrelationships. Informativeness of microsatellite and RAPD markers was also evaluated in comparison with allozyme markers for clone/cultivar identification in P. x canadensis. High microsatellite DNA and RAPD genetic diversity was observed in the sampled cultivars. All of the 17 P. x canadensis cultivars could be differentiated by their multilocus genotypes at four SSR loci, and were heterozygous for their parental species-specific alleles at the PTR6 SSR locus. Except for "Canada Blanc" and "Ostia", which had identical RAPD patterns, all cultivars could also be differentiated by RAPD fingerprints produced by each of the two RAPD primers, OPA07 and OPB15. For microsatellites, the mean number of alleles, polymorphic information content, observed heterozygosity, observed number of genotypes and the number of cultivars with unique genotypes per locus was 5.2, 0.64, 0.67, 5.7 and 2.2, respectively. For RAPD markers, the number of haplotypes per locus, and the number of cultivars with unique RAPD profiles per locus were 1.06 and 0.72, respectively. Overall, microsatellite DNA markers were the most informative for DNA fingerprinting of P. x canadensis cultivars. On the per locus basis, microsatellites were about six-times more informative than RAPD markers and about nine-times more informative than allozyme markers. However, on the per primer basis, RAPD markers were more informative. The UPGMA cluster plots separated the 17 cultivars into two major groups based on their microsatellite genotypic similarities, and into three major groups based on their RAPD fragment similarities. Both the microsatellite and RAPD data suggest that the cultivars "Baden 431", "Heidemij", "Robusta" and "Steckby" are genetically closely related. The inter-cultivar genetic relationships from microsatellite DNA and RAPD markers were consistent with those observed from allozyme markers, and were in general agreement with their speculated origin. Microsatellite DNA and RAPD markers could be used for clone and cultivar identification, varietal control and registration, and stock handling in P. x canadensis.     

Selection of high heterozygosity popcorn varieties in Brazil based on SSR markers

We analyzed genetic structure and diversity among eight populations of popcorn, using SSR loci as genetic markers. Our objectives were to select SSR loci that could be used to estimate genetic diversity within popcorn populations, and to analyze the genetic structure of promising populations with high levels of heterozygosity that could be used in breeding programs. Fifty-seven alleles (3.7 alleles per locus) were detected; the highest effective number of alleles (4.21) and the highest gene diversity (0.763) were found for the Umc2226 locus. A very high level of population differentiation was found (F(ST) = 0.3664), with F(ST) for each locus ranging from 0.1029 (Umc1664) to 0.6010 (Umc2350). This analysis allowed us to identify SSR loci with high levels of heterozygosity and heterozygous varieties, which could be selected for production of inbred lines and for developing new cultivars.     

Genetic variation and comparison of orchardgrass (Dactylis glomerata L.) cultivars and wild accessions as revealed by SSR markers

Orchardgrass is a highly variable, perennial forage grass that is cultivated throughout temperate and subtropical regions of the world. Despite its economic importance, the genetic relationship and distance among and within cultivars are largely unknown but would be of great interest for breeding programs. We investigated the molecular variation and structure of cultivar populations, compared the level of genetic diversity among cultivars (Baoxing, Anba, Bote, and Kaimo), subspecies (Dactylis glomerata ssp Woronowii) and advanced breeding line (YA02-116) to determine whether there is still sufficient genetic diversity within presently used cultivars for future breeding progress in China. Twenty individuals were analyzed from each of six accessions using SSR markers; 114 easily scored bands were generated from 15 SSR primer pairs, with an average of 7.6 alleles per locus. The polymorphic rate was 100% among the 120 individuals, reflecting a high degree of genetic diversity. Among the six accessions, the highest genetic diversity was observed in Kaimo (H = 0.2518; I = 0.3916; P = 87.3%) and 02-116 had a lower level of genetic diversity (H = 0.1806; I = 0.2788; P = 58.73%) compared with other cultivars tested. An of molecular variance revealed a much larger genetic variation within accessions (65%) than between them (35%). This observation suggests that these cultivars have potential for providing rich genetic resource for further breeding program. Furthermore, the study also indicated that Chinese orchardgrass breeding has involved strong selection for adaptation to forage production, which may result in restricted genetic base of orchardgrass cultivar.     

Microsatellite marker-based identification and genetic relationships of olive cultivars from the Extremadura region of Spain

Seventy-seven olive accessions corresponding to 25 cultivars from the Extremadura region of Spain were studied using four microsatellite or SSR markers in order to fingerprint them, and evaluate genetic similarity and relationships between local and introduced olive cultivars. The number of alleles per locus ranged from 4 to 8, with a mean of 6.25 alleles per primer pair (a total of 25 alleles). The observed heterozygosity ranged from 0.58 to 0.95, while the expected heterozygosity varied between 0.68 and 0.83. The polymorphism information content values ranged from 0.63 to 0.79. The mean polymorphism information content value of 0.70 for the SSR loci provided sufficient discriminating ability to evaluate the genetic diversity among the cultivars. The SSR data allowed unequivocal identification of all the cultivars; a combination of three SSR markers was sufficient to discriminate all 25 olive cultivars. A dendrogram was prepared, using the unweighted pair-group method with arithmetic mean clustering algorithm; it depicted the pattern of relationships between the cultivars. Most of the local cultivars grouped according to their geographic origin. No clear clustering trends were observed when the morphological traits of fruit endocarps or fruit use of cultivars were employed as analysis criteria. We conclude that there is a high level of variability among local olive cultivars from the Extremadura region at both the morphological and molecular levels; these data should be useful for identifying and distinguishing local germplasm.     

葡萄品种DNA指纹数据库的构建及遗传多样性分析

利用SSR分子标记技术对314份葡萄品种进行了DNA指纹数据库构建和遗传多样性分析,为葡萄品种鉴定、亲缘关系分析和植物品种权保护提供科学依据。结果表明:9对引物共扩增出199个等位基因,多态性位点为199个,多态性比率达100%,每个标记检测到的位点数在17~31之间,平均为22.1个;多态性信息含量(PIC)值变幅在0.793~0.886之间,平均值为0.839。本研究发现3组同名异物品种和9组疑似同物异名品种,除此之外的290份品种中,70份品种仅需1对引物即可区分开,其余品种需要引物组合来实现品种之间的区分。最少选用8对引物即可完全区分开290份葡萄品种。最终利用8对多态性SSR引物构建了314份供试材料的DNA指纹数据库,聚类分析结果表明:263份二倍体供试材料可被分为真葡萄亚属和圆叶葡萄亚属两大类,而真葡萄亚属又被分为15个亚类。51份多倍体供试材料被分为3组,聚类结果与供试材料已知的系谱来源基本吻合。     

Development of SSR markers for typing cultivars in the mushroom Auricularia auricula-judae

Auricularia auricula-judae, also known as black wood ear, is one of the most popular edible mushrooms in China. But the confusion about cultivars has limited the development of A. auricula-judae production. In this article, 17 polymorphic SSR markers were cloned and used to differentiate the cultivars of A. auricula-judae. The polymorphism information content (PIC) of these SSR ranged from 0.10 to 0.84, while the average was 0.47. The number of alleles detected for each locus was 2–11, with an average of 4.7 alleles per locus. The dendrogram, based on 17 SSR markers by UPGMA clustering, could differentiate the 16 A. auricula-judae cultivars in this study. In fact, the 16 cultivars analyzed in this study could be efficiently differentiated using a combination of three polymorphic SSR loci with high PIC. The total of 17 polymorphic SSR loci could also be amplified correctly in the A. polytricha strains surveyed. This is the first report on the development of SSR markers in the genus Auricularia.     

SSR allelic variation in almond (Prunus dulcis Mill.)

Sixteen SSR markers including eight EST-SSR and eight genomic SSRs were used for genetic diversity analysis of 23 Chinese and 15 international almond cultivars. EST- and genomic SSR markers previously reported in species of Prunus, mainly peach, proved to be useful for almond genetic analysis. DNA sequences of 117 alleles of six of the 16 SSR loci were analysed to reveal sequence variation among the 38 almond accessions. For the four SSR loci with AG/CT repeats, no insertions or deletions were observed in the flanking regions of the 98 alleles sequenced. Allelic size variation of these loci resulted exclusively from differences in the structures of repeat motifs, which involved interruptions or occurrences of new motif repeats in addition to varying number of AG/CT repeats. Some alleles had a high number of uninterrupted repeat motifs, indicating that SSR mutational patterns differ among alleles at a given SSR locus within the almond species. Allelic homoplasy was observed in the SSR loci because of base substitutions, interruptions or compound repeat motifs. Substitutions in the repeat regions were found at two SSR loci, suggesting that point mutations operate on SSRs and hinder the further SSR expansion by introducing repeat interruptions to stabilize SSR loci. Furthermore, it was shown that some potential point mutations in the flanking regions are linked with new SSR repeat motif variation in almond and peach. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Isolation and characterization of new polymorphic simple sequence repeat loci in grape (Vitis vinifera L.).

Four new simple sequence repeat (SSR) loci (designated VVMD5, VVMD6, VVMD7, and VVMD8) were characterized in grape and analyzed by silver staining in 77 cultivars of Vitis vinifera. Amplification products ranged in size from 141 to 263 base pairs (bp). The number of alleles observed per locus ranged from 5 to 11 and the number of diploid genotypes per locus ranged from 13 to 27. At each locus at least 75% of the cultivars were heterozygous. Alleles differing in length by only 1 bp could be distinguished by silver staining, and size estimates were within 1 or 2 bp, depending on the locus, of those obtained by fluorescence detection at previously reported loci. Allele frequencies were generally similar in wine grapes and table grapes, with some exceptions. Some alleles were found only in one of the two groups of cultivars. All 77 cultivars were distinguished by the four loci with the exception of four wine grapes considered to be somatic variants of the same cultivar, 'Pinot noir', 'Pinot gris', 'Pinot blanc', and 'Meunier'; two table grapes that are known to be synonymous, 'Keshmesh' and 'Thompson Seedless'; and three table grapes, 'Dattier', 'Rhazaki Arhanon', and 'Markandi', the first two of which have been suggested to be synonymous. Although the high polymorphism at grape SSR loci suggests that very few loci would theoretically be needed to separate all cultivars, the economic and legal significance of grape variety identification requires the increased resolution that can be provided by a larger number of loci. The ease with which SSR markers and data can be shared internationally should encourage their broad use, which will in turn increase the power of these markers for both identification and genetic analysis of grape. Key words : grape, Vitis, microsatellite, simple sequence repeat, DNA typing, identification.     

Genome-Wide Computational Analysis of Musa Microsatellites: Classification,Cross-Taxon Transferability,Functional Annotation,Association with Transposons & miRNAs,and Genetic Marker Potential

The development of organized, informative, robust, user-friendly, and freely accessible molecular markers is imperative to the Musa marker assisted breeding program. Although several hundred SSR markers have already been developed, the number of informative, robust, and freely accessible Musa markers remains inadequate for some breeding applications. In view of this issue, we surveyed SSRs in four different data sets, developed large-scale non-redundant highly informative therapeutic SSR markers, and classified them according to their attributes, as well as analyzed their cross-taxon transferability and utility for the genetic study of Musa and its relatives. A high SSR frequency (177 per Mbp) was found in the Musa genome. AT-rich dinucleotide repeats are predominant, and trinucleotide repeats are the most abundant in transcribed regions. A significant number of Musa SSRs are associated with pre-miRNAs, and 83% of these SSRs are promising candidates for the development of therapeutic SSR markers. Overall, 74% of the SSR markers were polymorphic, and 94% were transferable to at least one Musa spp. Two hundred forty-three markers generated a total of 1047 alleles, with 2-8 alleles each and an average of 4.38 alleles per locus. The PIC values ranged from 0.31 to 0.89 and averaged 0.71. We report the largest set of non-redundant, polymorphic, new SSR markers to be developed in Musa. These additional markers could be a valuable resource for marker-assisted breeding, genetic diversity and genomic studies of Musa and related species.     

Genetic diversity of different apricot geographical groups determined by SSR markers.

Forty apricot cultivars with different geographic origins belonging to the germplasm collections of St. Istvan University (Budapest, Hungary) and the Instituto Valenciano de Investigaciones Agrarias (IVIA) (Valencia, Spain) were studied by means of SSR markers. The aim of the study was to determine the genetic relationships among genotypes from different eco-geographical groups. Sixteen primer pairs flanking microsatellite sequences in the peach genome were assayed. Eleven of them were polymorphic in the set of cultivars studied and allowed every genotype to be unambiguously distinguished. Genetic diversity in the population studied was analyzed using several variability parameters. A total of 34 alleles were detected with a mean value of 3.1 alleles/locus. The expected heterozygosity mean was 0.46 and the observed heterozygosity was 32% on an average leading to a high value of the Wright's fixation index (0.32). Additionally, UPGMA cluster analysis based on Nei's genetic distance grouped genotypes according to their geographic origins and pedigrees. SSR markers have proved to be an efficient tool for fingerprinting cultivars and conducting genetic-diversity studies in apricot.     

Mapping Rm2 gene conferring resistance to the green peach aphid (Myzus persicae Sulzer) in the peach cultivar ��Rubira?��

The green peach aphid (GPA), Myzus persicae (Sulzer), is a widespread pest insect that significantly reduces yield in peach orchards [Prunus persica (L.) Batsch]. Chemical control of the GPA population in the orchards showed little efficiency because of the development of resistance to most classes of insecticides. Biological control partially gave convincing results. Breeding for resistant peach cultivars is therefore a serious option to take into account for the development of sustainable pest management. Among the few available resistance cultivars, the rootstock peach “Rubira?” shows a strong induced antixenosis-type GPA resistance. This was demonstrated segregating as a single dominant gene. In order to investigate the genetic basis of resistance and develop molecular tools useful in breeding programs, a F₂ population derived from “Rubira?” also segregating for leaf color was grown and scored for GPA resistance under contrasted environmental conditions. An SSR-based genetic linkage map composed of 120 SSR loci spanned over a distance of 497.8 cM was then established. The GPA resistance mapped to a single locus at the bottom end of linkage group 1. We propose to name Rm2 the dominant allele of the underlying gene. Additionally, a reciprocal translocation was identified near the Gr gene controlling leaf color. The red-leaf parent “Rubira?” was demonstrated responsible for the translocation. This study provides the basis for future molecular analysis for the use of Rm2 in peach breeding programs against GPA in peach orchards.