The eastern Asian and eastern North American disjunction in Juglans offers an opportunity to estimate the time since divergence of the Eurasian and American lineages and to compare it with paleobotanical evidence. Five chloroplast DNA noncoding spacer (NCS) sequences: trnT−trnF, psbA−trnH, atpB−rbcL, trnV-16S rRNA, and trnS-trnfM and data from earlier studies (matK, ITS, and nuclear RFLP) were used to reconstruct phylogeny and to estimate the divergence time of major lineages. Seventeen taxa from four sections of Juglans and two outgroup taxa, Pterocarya stenoptera and Carya illinoiensis were included. NCS data was congruent only with matK data. Both maximum parsimony (MP) and maximum likelihood (ML) cladograms were concordant at the sectional level and revealed three well-supported monophyletic clades corresponding to sections Juglans, Cardiocaryon, and Rhysocaryon in both NCS and combined analyses. The single extant American butternut, Juglans cinerea was placed within the poorly resolved, but well-supported Rhysocaryon. Placement of taxa within Rhysocaryon and Cardiocaryon were inconsistent between NCS and combined analyses. Overall, the results suggest that: (1) the NCS sequence divergence observed within and between sections of Juglans is low and the addition of matK data only marginally improved resolution within Rhysocaryon;(2) the early divergence of section Juglans in both MP and ML analyses of NCS and combined data implies its ancient origin in contrast to fossil evidence, which suggests the earliest divergence of sections Rhysocaryon and Cardiocaryon; and (3) the extant taxa may not hold the footprints to unravel the evolutionary history of the genus.

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A genetic linkage map of grape was constructed, utilizing 116 progeny derived from a cross of two Vitis rupestris x V. arizonica interspecific hybrids, using the pseudo-testcross strategy. A total of 475 DNA markers-410 amplified fragment length polymorphism, 24 inter-simple sequence repeat, 32 random amplified polymorphic DNA, and nine simple sequence repeat markers-were used to construct the parental maps. Markers segregating 1:1 were used to construct parental framework maps with confidence levels >90% with the Plant Genome Research Initiative mapping program. In the maternal (D8909-15) map, 105 framework markers and 55 accessory markers were ordered in 17 linkage groups (756 cM). The paternal (F8909-17) map had 111 framework markers and 33 accessory markers ordered in 19 linkage groups (1,082 cM). One hundred eighty-one markers segregating 3:1 were used to connect the two parental maps' parents. This moderately dense map will be useful for the initial mapping of genes and/or QTL for resistance to the dagger nematode, Xiphinema index, and Xylella fastidiosa, the bacterial causal agent of Pierce's disease.

The utility of intersimple sequence repeat (ISSR) markers for identification of English or Persian walnut (Juglans regia L.) cultivars was explored. Four cultivars were screened with 47 ISSR primers; eight of these primers, which generated reproducible and informative data, were selected for further study. Two individuals from each of 48 cultivars, including many currently important in the California walnut industry as well as accessions from Europe and Asia, were then examined with the eight ISSR primers. Polymerase chain reaction (PCR) products were separated on agarose gels and stained with ethidium bromide. Fifty-four bands were scored as present or absent in each cultivar; of these, 31 (57%) were polymorphic among the 48 cultivars. Combined data from the eight ISSR primers provided a unique fingerprint for each of the cultivars tested. Fifteen of the cultivars could be distinguished from all others with just one primer, 31 with a minimum of two primers, and two required three primers. Pairwise genetic distances between the cultivars were calculated and a dendrogram was generated using the neighbor-joining algorithm. Some of the groupings in the dendrogram corresponded to groups which, based on known pedigrees, are genealogically closely related. Others included accessions from diverse genetic and/or geographic origins. These results can be attributed to a combination of the limitations of the ISSR method for inferring genetic relationships, on the one hand, and the complex history of walnut cultivar development involving extensive exchange and breeding of germplasm from different geographic regions, on the other.

Sequences from s6pdh, a gene that encodes sorbitol-6-phosphate dehydrogenase in the Rosaceae, are used to reconstruct the phylogeny of 22 species of Prunus. The s6pdh sequences alone and in combination with previously published sequences of the internal transcribed spacer (ITS) and the cpDNA trnL-trnF spacer are analyzed using parsimony and maximum likelihood methods. Both methods reconstructed the same phylogeny when s6pdh sequences are used alone and in combination with ITS and trnL-trnF, and the topology is in agreement with previous studies that used a larger sample size. The s6pdh sequences have about twice as many informative sites as ITS. A molecular clock is rejected for s6pdh, most likely due to greater rates of evolution in subgenera Padus and Laurocerasus than in the rest of the genus. Phylogenetic reconstruction of Prunus as determined by analysis of the combined data set suggests an early split into two clades. One is composed of subgenera Cerasus, Laurocerasus, and Padus. The second includes subgenera Amygdalus, Emplectocladus, and Prunus. Species of section Microcerasus (formerly in subgenus Cerasus) are nested within subgenus Prunus. The order of branching and relationships among early diverging lineages is weakly supported, as a result of very short branches that may indicate rapid radiation.

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A pseudo-testcross mapping strategy was used in combination with the random amplified polymorphism DNA (RAPD) and amplified fragment length polymorphism (AFLP) genotyping methods to develop two moderately dense genetic linkage maps for Betula platyphylla Suk. (Asian white birch) and B. pendula Roth (European white birch). Eighty F 1 progenies were screened with 291 RAPD markers and 451 AFLP markers. We selected 230 RAPD and 362 AFLP markers with 1:1 segregation and used them for constructing the parent-specific linkage maps. The resultant map for B. platyphylla was composed of 226 markers in 24 linkage groups (LGs), and spanned 2864.5 cM with an average of 14.3 cM between adjacent markers. The linkage map for B. pendula was composed of 226 markers in 23 LGs, covering 2489.7 cM. The average map distance between adjacent markers was 13.1 cM. Clustering of AFLP markers was observed on several LGs. The availability of these white birch linkage maps will contribute to the molecular genetics and the implementation of marker-assisted selection in these important forest species.

Based on the genetic inheritance and segregation of random amplified polymorphism DNA (RAPDs) markers, the first mid-density linkage map for silver birch was constructed by using a pseudo-testcross mapping strategy. A segregating population including 80 progenies from the cross between Betula pendula Roth and B. platyphylla Suk was obtained. A set of 1,200 random oligonucleotide primers were screened, and 208 primers were selected to generate RAPD markers within a sample of 80 F1 progenies. A total of 364 segregating sites were identified. Among them, 307 belonged to 1 : 1 segregating site, and 36 belonged to 3 : 1 segregating site, others were found distorted from the normal 1 : 1 ratio. Altogether 307 sites segregating 1 : 1 (testcross configuration) were used to construct parent-specific linkage maps, 145 for B. pendula and 162 for B. platyphylla. The resulting linkage maps consisted of 145 marker sites in 14 groups (four or more sites per group), 6 triples and 6 pairs for B. pendula, which covered the map distance about 955.6 cM (Kosambi units). The average map distance between adjacent markers was 14.9 cM, and 162 linked marker site for B. platyphylla were mapped onto 15 groups (four or more sites per group), 4 triples and 6 pairs, which covered the map distance about 1,545.8 cM, and the average map distance between adjacent markers was 15.2 cM. Further study is warranted to integrate the two maps to one density map and to locate important genes on the maps.