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Sedat Serçe and James F. Hancock

The inheritance of day-neutrality in octoploid Fragaria L. was investigated in crosses between day-neutral (DN) × short day (SD) and DN × DN types using F. ×ananassa Duchesne in Lamarck cultivars and elite selections of F. virginiana Miller and F. chiloensis (L.) Miller. Genotypes were considered as DN if they flowered under both the SDs of spring before 30 May (<14 hours) and the long days of summer after 24 July (>15 hours). Wide ranges in the percentage of DN progeny were found among the families regardless of species background (30% to 87% in DN × SD and 22% to 93% in DN × DN crosses). None of the families fit the segregation ratios expected if DN was regulated by recessive alleles at one locus, and only about half of the families fit the segregation ratios expected if a single dominant allele regulated DN. Several two-gene models fit the segregation data better than the single locus ones, but none of the genetic models tested fit the DN segregation ratios at the ends of the distribution range. The wide range observed in the percentage of DN progeny across all the families is most consistent with a polygenic model. Several other kinds of observations supported the multigenic regulation of DN: 1) Different DN parents crossed to the same SD genotype often produced different percentages of DN progeny, 2) Some of the day-neutrality sources were more powerful than others in producing of DNs, and 3) None of the DN parents produced 100% DN progeny, which would be expected if there were homozygous dominant DN individuals. Specific combining abilities for DN and flowering strength were significant, while general combining abilities for these traits were not. Our results suggest that parental combinations can be selected that will generate very high proportions of DN progeny that bloom for long periods of time.

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Jim Hancock, Pete Callow, Sedat Serçe, Eric Hanson and Randy Beaudry

Controlled-atmosphere storage had little effect on the quality of fruit of eight cultivars held under 2 kPa oxygen (O2) and 8 kPa carbon dioxide (CO2) versus ambient air. ‘Elliott’ fruit harvested from bushes with only 30% ripe fruit had significantly better storage quality than fruit picked later; however, there was no significant difference in the storage life of fruit that was stored fully blue versus partially green. Fruit from the first harvest of four cultivars had superior storage quality to that of the second. In one comparison of the long-term storability of nine cultivars, ‘Bluegold’, ‘Brigitta’, and ‘Legacy’ performed the best, storing for 4 to 7 weeks. In another postharvest trial of 17 cultivars, ‘Brigitta’ stored the longest (8 weeks) followed by ‘Aurora’ and ‘Draper’ (7 weeks). The most resistant genotypes to Alternaria spp. were ‘Brigitta’, ‘Aurora’, ‘Elliott’, and ‘Draper’, whereas the most resistant genotypes to Colletotrichum spp. were ‘Elliott’, ‘Brigitta’, ‘Toro’, ‘Draper’, and ‘Bluejay’.

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Sedat Serce, John P. Navazio, Ali F. Gokce and Jack E. Staub

Four nearly isogenic cucumber lines (Cucumis sativus L.) differing in leaf size [standard leaf (LL) vs. little leaf (ll)] and plant habit [indeterminate (DeDe) vs. determinate (dede)] were compared for their response to high soil moisture tensions in 1990 and 1996. Comparisons were made between lines for aboveground vegetative and fruit response, between two irrigation regimes, and among three postharvest treatments. Differences in vegetative plant response between lines were documented by wilting ratings, plant dry weight, fruit number and fresh weight, and fruit quality [i.e., fruit shape, seed size, seed cavity size, and pillowy fruit disorder (PFD)] ratings depending upon the stress environment. Postharvest treatment affected the quality of fruit recovered from plants subjected to water stress. Exposure of fruit at 15 °C and 85% relative humidity (RH) for 4 days after hydrocooling, resulted in lower PFD than storage of fruit at 26 °C and 60% RH for 2 days without hydrocooling. Cucumber genotypes showed differential response to water stress indicating that plant habit and leaf size can be important genetic determinants of plant response to water stress. Although plant productivity was not affected by water stress, PFD, shape, seed size, and seed cavity size of fruit from lldede plants were more severely affected by water stress than its llDeDe counterpart. Plants homozygous ll, in either a determinate or indeterminate background, were less susceptible to wilting under water stress conditions than their normal leaf (LL) counterparts. However, plant dry weight and fruit number and weight were higher in LLDeDe plants when compared to their llDeDe counterparts. Fruit recovered from LLDeDe plants were of higher quality than those recovered from llDeDe plants. Thus, wilting response to water stress is not necessarily indicative of a cucumber plant's tolerance to water stress in the reproductive stage.

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Salih Kafkas, Mustafa Özgen, Yıldız Doğan, Burcu Özcan, Sezai Ercişli and Sedat Serçe

Mulberries (Morus L.) show a great deal of genetic variability and adaptability to various environments. There are more than 24 species of mulberries in cultivated and wild forms. In Turkey, three Morus species, M. alba L., M. nigra L., and M. rubra L., are grown. In this study, we attempted to characterize 43 Morus accessions originating from distinct regions of Turkey using fluorescent dye amplified fragment length polymorphism (AFLP) markers and capillary electrophoresis. The accessions belonged to M. alba, M. nigra, and M. rubra; M. alba consisted of white- and purple-fruited samples. Eight primer combinations generated a total of 416 bands, 337 of which were polymorphic (80.5%). Resolving powers of the AFLP primers ranged from 0.410 to 0.942 making a total of 5.015, whereas the polymorphic information content ranged from 0.662 to 0.898 with an average of 0.812. Unweighted pair-group method of arithmetic mean (UPGMA) clustering of the accessions showed three major groups representing M. nigra, M. rubra, and M. alba accessions. The M. alba group had two subgroups that were not correlated with fruit color. The UPGMA dendrogram of average taxonomic differences confirmed these results. The principle coordinate analysis demonstrated that M. nigra accessions had limited genetic variation. In conclusion, our study indicated that M. nigra and M. rubra are molecularly distinct from M. alba. Our results also suggest that M. nigra accessions having a low level of morphological variation are molecularly similar.

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Chad E. Finn, Andrew L. Thomas, Patrick L. Byers and Sedat Serçe

American (Sambucus canadensis L.) elderberry genotypes were evaluated at multiple locations, whereas European (S. nigra L.) elderberry genotypes were evaluated at a single location to assess genotypic differences and, for genotypes evaluated at multiple locations, to determine genotype × environment interactions (G × E). Seventeen S. canadensis genotypes were planted in replicated trials at Missouri State University (Mountain Grove, MO) and at the University of Missouri (Mt. Vernon, MO) or at the U.S. Department of Agriculture–Agricultural Research Service in Oregon (Corvallis). ‘Johns’, ‘Netzer’, ‘Adams II’, and ‘Gordon B’ were in common at all locations. In addition, three genotypes of S. nigra, which are not winter-hardy in Missouri, were planted in Oregon. All plants were established in 2003 and evaluated in 2004, 2005, and, for some traits, in 2006. Plants were evaluated for phenology (e.g., dates of budbreak, first flowering, full flowering, and first ripening), vegetative growth (e.g., number of shoots and plant height), yield components (e.g., total yield, number of cymes, cyme weight, and berry weight), and for pest incidence (e.g., eriophyid mites). For the genotypes in common to all locations, there were significant differences resulting from genotype, location, year, and the interactions for various traits. Although the trend was for Corvallis to have the highest and Mt. Vernon the lowest yield, there was no significant location effect. The significant genotype × environment interaction appeared to be primarily the result of the differential performance of ‘Johns’, which was generally high-yielding in Corvallis and low-yielding at both Missouri locations. The significant G × E suggests that as the Missouri institutions develop new cultivars, it will be important to test them individually at other locations and not rely on their relative performance compared with standards in Missouri. For the genotypes in common to the two Missouri sites, there was significant variation for many traits. Although there were no differences among genotypes for yield across the locations, there was a significant G × E. Although there were some small changes in performance among the sites for yield, the most dramatic changes were for ‘Wyldewood 1’ that was the second highest yielding genotype at Mountain Grove and the second worst at Mt. Vernon. Plant growth in Oregon was 40% and 60% greater than at Mountain Grove and Mt. Vernon, respectively, when the plants were first measured. In Oregon, the two Sambucus species behaved differently. Phenologically, although the S. nigra genotypes flowered ≈3 weeks earlier than the S. canadensis genotypes, they ripened at the same time, thereby shortening their exposure to potential biotic and abiotic stress. ‘Johns’, ‘York’, ‘Golden’, and ‘Gordon B’ were the highest yielding S. canadensis genotypes and ‘Korsør’ the highest of the S. nigra genotypes. Although ‘Korsør’ is considered high-yielding in Denmark, it did not yield as well as the highest yielding S. canadensis cultivars.

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James F. Hancock, Chad E. Finn, James J. Luby, Adam Dale, Pete W. Callow and Sedat Serçe

The germplasm base of strawberries is restricted. The major cultivated strawberry species, Fragaria ×ananassa, originated ≈250 years ago when South American F. chiloensis subsp. chiloensis forma chiloensis and North American F. virginiana subsp. virginiana accidentally hybridized in European gardens. Since that time, only a handful of native clones have been used by breeders. As a novel way to expand the germplasm base of the strawberry, we preselected native clones of F. virginiana and F. chiloensis for a wide range of horticulturally important characteristics and then reconstructed F. ×ananassa by crossing superior clones of each. Before crossing between species, we undertook one round of selection within species to maximize diversity. Reconstruction appeared to be an effective method of strawberry improvement, because superior families and individuals were identified that had outstanding vigor, high productivity, seed set, fruit color, and firmness. None of the fruit were of commercial size, but one reconstruction family, FVC 11 [(F. virginiana Frederick 9 × LH 50-4) × (F. chiloensis Scotts Creek × 2 MAR 1A)], had individuals with fruit weights of almost 20 g.

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James F. Hancock, Peter W. Callow, Sedat Serçe and Annemiek C. Schilder

The performance of four California and 11 eastern cultivars of Fragaria×ananassa Duchesne in Lamarck, and 12 elite F1 hybrids of Fragaria×ananassa with F. virginiana Miller in their immediate background was evaluated in a producer's field with and without methyl bromide-chloropicrin fumigation. Averaged across all genotypes, plants in nonfumigated soils had 43% fewer runners, 18% smaller fruit, and 46% lower yields than did plants on fumigated soil. They also had an average of 27% fewer crowns, 49% more root discoloration, significantly fewer fine roots, and showed symptoms of the black root rot syndrome. The most commonly isolated pathogens from discolored roots were Pythium sp., Rhizoctonia sp., Idriella lunata P.E. Nelson & K. Wilh., and the root-knot nematode (Meloidogyne hapla Chitwood). The performance of all genotypes was enhanced by fumigation, although the F. virginiana hybrids performed comparatively better than the other cultivars on nonfumigated soils.

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Sedat Serçe, Kazim Gündüz, Sevgi Paydas, Nurettin Kaska, Emine Özdemir and Jim Hancock

Fragaria species are in different plodiy levels (from 2n = 2x = 14 to 2n = 8x = 56) and distributed in almost all parts of the arable areas of the world. The flora of Turkey has wild strawberries, some of which are harvested for their small, but very aromatic berries. There are also old cultivars found in Turkey that are known for their aromatic fruits. We made collection trips to the Marmara and Black Sea areas to collect both wild strawberries and old cultivars in Summer 2004. During these trips, we sampled 50 populations from the altitudes of 6 to 2007 m, lat. 35°91'N to 41°76'N latitudes, and long. 26°81'E to 42°65'E. The samples were propagated in a greenhouse and evaluated in a replicated trail for both taxonomic and horticultural traits in an unheated greenhouse. The chromosome numbers of the genotypes were also determined. The results indicate that Turkish strawberry germplasm consists of both diploid and octoploid species. The principal components and cluster analysis separated the genotypes into three groups: octoploid cultivars and/or derivatives (e.g., `Madame Moutot'), and two diploid Fragaria species, vesca and viridis. Further relationships of the genotypes will be discussed.

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Eric J. Hanson, Philip A. Throop, Sedat Serce, John Ravenscroft and Eldor A. Paul

Highbush blueberries (Vaccinium corymbosum L.) are long lived perennial plants that are grown on acidic soils. The goal of this study was to determine how blueberry cultivation might influence the nitrification capacity of acidic soils by comparing the nitrification potential of blueberry soils to adjacent noncultivated forest soils. The net nitrification potential of blueberry and forest soils was compared by treating soils with 15N enriched (NH4)2SO4, and monitoring nitrate (NO3 --N) production during a 34-day incubation period in plastic bags at 18 °C. Net nitrification was also compared by an aerobic slurry method. Autotrophic nitrifiers were quantified by the most probable number method. Nitrate production from labeled ammonium (15NH4 +) indicated that nitrification was more rapid in blueberry soils than in forest soils from six of the seven study sites. Slurry nitrification assays provided similar results. Blueberry soils also contained higher numbers of nitrifying bacteria compared to forest soils. Nitrification in forest soils did not appear to be limited by availability of NH4 + substrate. Results suggest that blueberry production practices lead to greater numbers of autotrophic nitrifying bacteria and increased nitrification capacity, possibly resulting from annual application of ammonium containing fertilizers.