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Tim Rinehart and Sandy Reed

Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Most cultivars in production belong to the species Hydrangea macrophylla but H. paniculata, H. arborescens, H. serrata, H. aspera, H. heteromalla, H. integrifolia, H. anomala, H. seemanii, and H. quercifolia are also commercially available. In addition to species diversity there is high intra-species variation, particularly in H. macrophylla, which includes mopheads, lacecaps, French, Japanese, dwarf, and variegated varieties. Relatively little is known about the genetic background or combinability of these plants. DNA sequence data, genome size, RAPD, AFLP, and ISSR markers have been used for taxonomic identification and to estimate diversity within the genus. All of these methods have limited usefulness in a large scale breeding program. We recently established microsatellite markers for Hydrangea and evaluated their utility for estimating species diversity and identifying cultivars within H. macrophylla and H. paniculata. We also verified an inter-specific cross between H. macrophylla and H. paniculata using these markers. Future research includes marker assisted breeding, particularly with respect to remontant flowering traits.

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Hong Y. Yang, Schuyler S. Korban, Jutta Kruger, and Hanna Schmidt

Apple scab, caused by Venturia inaequalis (Cke.) Wint., is the most serious disease of apple trees. Resistance to V. inaequalis, derived from the small-fruited species Malus floribunda 821, is determined by a major dominant gene Vf. Our major objective is to identify RAPD markers linked to the Vf gene. The approach in this paper is based on the introgression of the Vf gene from M. floribunda into commercial cultivars. Almost 200 random sequence decamer-primers have been used to screen a pair of bulked samples and the donor parent M. floribunda clone 821 for markers linked to the Vf gene conferring resistance to apple scab. A single primer has been identified which generated a PCR fragment, OPK16/1300, from the donor parent M. floribunda clone 821 and the scab-resistant selections/cultivars bulk, but not from the scab-susceptible recurrent parent bulk. Co-segregation analysis using a segregating apple progeny and polymorphism analysis of individual scab-resistant Coop selections/cultivars have confirmed that this marker is linked to the scab-resistance gene Vf. OPK16/1300 has since been cloned and sequenced. Sequence-specific primers of 25 oligonucleotides based on the marker have been synthesized and used to screen further M. floribunda clone 821, scab-susceptible apple cultivars, scab-resistant apple cultivars, and scab-resistant Coop selections. The sequence-specific primers have identified polymorphisms of OPK16/1300 based on the presence or absence of a single band.

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Martha Dávila, Dermot Coyne, Shree Singh, and Guenhwa Jung

The genes involved in F1 seedling abnormal development and lethality in inter-gene pool crosses have been designated as Dl1 (MesoAmerican=MA) and Dl2 (Andean=A) (Shii et al., 1980, J. Hered. 71:218–222). The different degrees of leaf crippling (C) in segregating populations of crosses was due to the interaction between the Dl1 or Dl2 loci, growing environment, and the lcr allele (Singh and Molina, 1996, J. Hered., In press). The objective was to identify RAPD markers linked to the genes for crippling (lcr) and seedling lethality (Dl) using the bulked segregation analysis procedure for F2 of MA × A crosses. Crosses were made between C lines, FB 10413-24-2, WA 7807-305, and TY 5578-220 and normal (N) parents and tester stocks for Dl1 and Dl2 genes. The F2 FB 10413-24-2 × Carioca segregated 13 N:3C. F3 families segregated 3N:1C. RAPD marker OPB-10 was linked to Lcr at 31.2 cM. F3 families segregated 1N:3C. RAPD marker OPO16 was linked to Dl1 at 27 cM. The F2 WA-7807-305 × Rio Tibagi segregated 3N:1C. RAPD marker OPS-03 was linked to Lcr at 32.6 cM.

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Soon O. Park, Dermot P. Coyne, and James R. Steadman

Bean rust, caused by Uromyces appendiculatus, is an important disease of common bean (Phaseolus vulgaris L.). The objective was to identify RAPD markers linked to the gene (Ur-6) for specific resistance to rust race 51 using bulked segregant analysis in an F2 segregating population from the common bean cross pinto `Olathe' (resistant to rust) × great northern Nebraska #1 selection 27 (susceptible to rust). A single dominant gene controlling specific resistance to race 51 was hypothesized based on F2 segregation, and then was confirmed in the F3 generation. A good fit to a 3:1 ratio for band presence to band absence for each of three markers was observed in 100 F2 plants. Three RAPD markers were detected in a coupling phase linkage with the Ur-6 gene. Coupling-phase RAPD marker OAB14.600 was the most closely linked to the Ur-6 gene at a distance of 3.5 cM among these markers. No RAPD markers were identified in a repulsion phase linkage with the Ur-6 gene. The RAPD markers linked to the gene for specific rust resistance of Middle American origin detected here, along with other independent rust resistance genes from other germplasm, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.

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Yiqi Zhen, Zuozhou Li, Hongwen Huang, and Ying Wang

Forty-eight kiwifruit cultivars and selections, representing more than 90% of total world kiwifruit production, were investigated using nine SSR markers to establish genetic identities, and evaluate genetic diversity and relatedness. These nine SSRs were polymorphic and a total of 213 alleles were detected, resulting in a mean number of 23.7 alleles per locus, ranging from nine to 38 alleles. One hundred and thirty-three alleles were found to be common to both A. chinensis and A. deliciosa, while 33 and 36 were specific to A. chinensis and A. deliciosa, respectively. In addition, 34 alleles were specific to one single genotype and provided a set of valuable alleles for cultivar identification. A single SSR locus UDK 96-414 could differentiate all 48 genotypes except two presumable clones. Mean number of alleles per locus (A), percentage of polymorphic loci (P), and direct count heterozygosity (Ho) assessed for each genotype over all loci revealed considerable differences among these 48 genotypes. On average, A = 2.6, P = 89.4% and Ho = 0.546 were found in A. chinensis cultivars, while A = 3.5, P = 97.0% and Ho = 0.671 in A. deliciosa cultivars. Consensus fingerprint profiling using SSR markers is a useful and reliable method for establishing genetic identities of kiwifruit cultivars and selections. It also improves evaluation effectiveness of genetic diversity and relatedness compared to RAPD markers.

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M. Dolores Loureiro, M. Carmen Martínez, Jean-Michel Boursiquot, and Patrice This

`Albariño' (Vitis vinifera L.) is an important grape cultivar in Spain, morphologically diverse but subject to much misnaming. The objectives of the present work were to correct some of the more common misnamings concerning `Albariño' and to evaluate the genetic variability within this cultivar by analyzing DNA polymorphisms using randomly amplified polymorphic DNA (RAPD) markers and microsatellite techniques. Several accessions of `Albariño' (16 accessions from Misión Biológica de Galicia, one accession from El Encin, one accession from Rancho de la Merced), related cultivars (`Alvarinho', `Caíño blanco', `Cainho branco', `Loureiro'), and cultivars presumably identical to misnomers (`Savagnin blanc' and `Gewürztraminer') were analyzed using 20 RAPD markers and six microsatellite loci. Both techniques revealed polymorphism among `Albariño', `Caíño blanco', `Albariño' from Rancho de la Merced and `Loureiro'. No polymorphism was detected among the 16 `Albariño' accessions from Galicia, the `Albariño' accession from El Encin and `Alvarinho', nor among the `Albariño' accession from Rancho de la Merced, `Savagnin blanc' and `Gewürztraminer', nor between `Caíño blanco' and `Cainho branco'. These results enabled us to clarify the main misnomers concerning these cultivars. The absence of polymorphism among the true `Albariño' accessions did not allow the detection of any clonal variation. The suitability of both techniques for defining the cultivar level for grapevine is discussed.

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Robert R. Krueger and Mikeal L. Roose

New potential citrus germplasm accessions may be received as seed rather than budwood, thereby reducing phytosanitary risks. However, trueness-to-type may be an issue with seed materials because many varieties produce both apomictic (nucellar) and sexual (zygotic) embryos and most citrus is fairly heterozygous. To identify nucellar seedlings of polyembryonic types and to retain these as representing the type, we screened 1340 seedlings from 88 seed sources for markers amplified with two inter-simple sequence repeat (ISSR) primers. Sixteen seed sources produced no seedlings classified as being of nucellar origin. Among the remaining seed sources, seedlings classed as nucellar were identified for potential addition to the collection. In 37 accessions, both nucellar and zygotic seedlings were detected, and in some cases both types were retained. Inclusion of established accessions of the same cultivar group in the analysis allowed an initial assessment of similarity to existing accessions. This technique improved the efficiency of acquiring new germplasm of polyembryonic types by seed. The method identifies those seed sources that produce few or no nucellar seedlings, but it is not useful for determining which seedlings of monoembryonic types should be retained in collections.

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Kentaro Kitahara, Shogo Matsumoto, Toshiya Yamamoto, Junichi Soejima, Tetsuya Kimura, Hiromitsu Komatsu, and Kazuyuki Abe

We examined the genetic diversity and relatedness among apple (Malus ×domestica Borkh.) cultivars in Japan. The 42 apple cultivars, including major cultivars in Japan, were divided into five groups based on SSR genotypes. Most economically important cultivars belong in three groups: Fuji-Delicious, Golden Delicious, and Jonathan groups, and their genetic backgrounds seemed to be narrow. We also investigated the parent-offspring relationships of nine apple cultivars. `Jonathan', `Fuji', and `Rero 11' were identified as the respective paternal parents of three cultivars described as having unknown paternal parents (i.e., `Akagi', `Ambitious', and `Hokuto'). `Starking Delicious', `Senshu', and `Golden Delicious', rather than `Ralls Janet', `Hatsuaki', and `Indo', seemed to be the paternal parents of `Kinsei', `Kiou', and `Mellow', respectively. `Carolina Red June' was excluded as a paternal parent of `Ranzan'. Both attributed parents of `Scarlet' (`Akane' and `Starking Delicious') were excluded, and it was suggested that `Fuji' was used as either a maternal or a paternal parent of `Scarlet'. `Jonathan' rather than `McIntosh' seems to be a maternal parent of `Yukari'.

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Margaret R. Pooler, Louise G.H. Riedel, S.E. Bentz, and A.M. Townsend

Controlled pollinations were made between five hemlock (Tsuga) species from eastern North America and Asia, resulting in over 5700 germinating seedlings. A subset of putative hybrid seedlings from each cross was tested for authenticity by various DNA marker systems. The most reliable and useful system for verifying hybrids was amplified fragment-length polymorphism (AFLP) markers. Hybridizations between the eastern North American species, T. canadensis [L.] Carriere and T. caroliniana Engelm., and the Asian species, T. chinensis (Franch.) E. Pritz., were used as a model to test the inheritance, reliability, and ease of use of these markers. Using AFLP markers, we were able to verify 58 hybrids between T. caroliniana and T. chinensis, one hybrid between T. caroliniana and T. canadensis, but could find no definitive hybrids between T. canadensis and T. chinensis. Results using other marker systems, including RAPD, SCAR, ITS, and SSR, are also presented.

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Darlene M. Lawson, Minou Hemmat, and Norman F. Weeden

Five morphological and developmental traits (branching habit, vegetative budbreak, reproductive budbreak, bloom time, and root suckering) were analyzed in a family obtained from the apple (Malus domestica Borkh) cross `Rome Beauty' × `White Angel'. The phenotypic variation in these traits was compared with a selected set of marker loci covering the known genome of each of the parents to locate genes with major effects on the traits. The contrasting branching habits of the two parents appeared to be controlled by at least two loci. One of these, Tb, governed the presence or absence of lateral branches, particularly on the lower half of shoots. The locus was heterozygous in `White Angel' and was mapped to a 5 CM interval on linkage group 6. At least one other locus conditioning spur-type branching appeared to be segregating, but the locus or loci could not be linked to segregating markers. The timing of initial vegetative growth was tightly associated with the chromosomal region in which the Tb gene is located and maybe a pleiotropic effect of this gene. Time of reproductive budbreak correlated with segregation at the isozyme marker, Prx-c, on linkage group 5. Variation in time of bloom and later stages in flower development appeared to be controlled by different genes not linked to Prx-c. The tendency to produce root suckers cosegregated with a marker on `White Angel' linkage group 1, suggesting control by a single locus, Rs. Data from a `Rome Beauty' x `Robusta 5' family provided additional information on the inheritance of these traits.