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James J. Luby, David K. Wildung, and Gene J. Galletta

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James J. Luby, David K. Wildung, and Gene J. Galletta

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Shengrui Yao, James J. Luby, and David K. Wildung

As part of our hardy strawberry (Fragaria ×ananassa) breeding program, winter hardiness of 15 strawberry cultivars was evaluated in the field after Winter 2005–2006 and a test Winter 2006–2007 with no snow cover at Grand Rapids, MN. After the snow-covered Winter 2005–2006, plant stand (percent leaf coverage for the designated area for each plot) increased for all cultivars in the mulched treatment and some cultivars in the unmulched treatment with slight decreases only for several cultivars in the unmulched treatment. However, after Winter 2006–2007, the plant stands of all cultivars drastically decreased in both mulched and unmulched treatments. ‘Clancy’, ‘Evangeline’, and ‘L'Amour’ were the three most sensitive cultivars among the 15 cultivars tested. ‘Kent’, ‘Mesabi™’, ‘Cavendish’, and ‘Brunswick’ were the highest yielding cultivars for both 2006 and 2007 in the mulched treatment. In the unmulched treatment, ‘Brunswick’, ‘Mesabi™ ’, ‘Cavendish’, ‘Sable’, and ‘Kent’ were the top yielding cultivars after Winter 2006–2007. During Winter 2005–2006, with 20 to 30 cm snow cover throughout the season, the 5- and 10-cm soil temperatures remained constant at ≈30 to 31.5 °F in both mulched and unmulched treatments. In contrast, during Winter 2006–2007, there were 16 and 24 days (consecutive) in February below 18 °F at 5-cm soil depths for mulched and unmulched treatments, respectively, which probably led to the severe winter damage. Although straw mulch afforded the plants some protection, snow cover is critical to the survival of strawberries in northern Minnesota and other areas with similar weather conditions.

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Debbv M. Filler, James J. Luby, and Peter D. Ascher

Three classes of crosses using four genotypes of V. riparia (wild Riverbank grape) as maternal parents were evaluated for evidence of reproductive expression of genetic incongruity. The classes were: I V. riparia x V. vinifera cultivars (European domesticated grape); II V. riparia x French Hybrids (complex interspecific hybrids); III V. riparia x V. riparia. Percent fruit set and seeds per berry were recorded for two years. If incongruity is a factor in interspecific grape crosses, then the values for these traits would be expected to be lower in classes I and II than in class III. Analysis of variance indicated significant differences for some half-sib families. Fruit and seed set were lower in classes I and II than in class III, suggesting that incongruity is operative in wide grape crosses. In the process of creating French hybrids, genomes of several species came together over generations of hybridization. In concert with selection for fertility, repeated interspecific genomic exposure would be expected to have ameliorated the effects of initial incongruity between American species and V. vinifera, increasing their value as genetic bridges in breeding programs.

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Neil O. Anderson, Peter D. Ascher, and James J. Luby

The change from asexual to sexual propagation for annual and perennial bedding plants has been successfully accomplished for floral crops, e.g., Pelargonium. Seed-propagated cultivars do not necessarily possess the clonal uniformity of vegetatively propagated cultivars. In the development of F1 hybrid garden chrysanthemums, this lack of uniformity was assessed with the use of consumer sensory evaluations. Seedlings (n = 10–20 plants/cross) were transplanted for field trials in St. Paul and five Minnesota branch stations each year during 1988–94 to test for G × E. Early flowering F1 hybrids, developed from inbred parents with general combining ability, were evaluated for flowering earliness, plant uniformity, and a general rating. Consumer rankings of top performers were not significantly different (5% level) from mum breeders. The top performers for all three ratings were selected each year for repeat evaluation the next year. The two highest performing F1 hybrids were submitted for All American Selection Trials in 1995.

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Richard E. Harrison, James J. Luby, and Peter D. Ascher

Pollination of the half-high blueberry (Vaccinium corymbosum L./V. anugustifolium Ait.) cultivars St. Cloud, Northsky, Northcountry, and Northblue with self, outcross, and outcross/self pollen mixtures suggests that outcross fertilization maximizes percent fruit set, berry weight, seeds per berry, and seeds per pollination while minimizing days to harvest. Based on these results, mixed plantings of at least two blueberry cultivars are recommended for these cultivars. Fruit and seed set were negatively associated with increased percentages of self pollen in outcross/self pollen mixtures. These responses were linear for `Northblue' due to a tendency to parthenocarpy, and nonlinear for `St. Cloud', `Northsky', and `Northcountry', due to low fruit set following self-pollination. These data indicate that post-fertilization abortion affected seed formation, which was, in turn, correlated positively with fruit set.

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James Luby, Philip Forsline, Herb Aldwinckle, Vincent Bus, and Martin Geibel

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Richard E. Harrison, James J. Luby, and Glenn R. Furnier

Restriction fragment-length polymorphisms (RFLPs) of chloroplast DNA (cpDNA) were used to study phylogenetic relationships among twenty-six Fragaria taxa and two closely related species, Potentilla fruticosa L. and Duchesnea indica (Andrews) Focke. Sixteen restriction enzymes and probes of the entire Nicotiana tabacum L. chloroplast genome revealed a very low level of variation among the Fragaria taxa, limiting phylogenetic resolution. However, Fragaria appears to be more closely related to Potentilla than Duchesnea. The diploid taxa, F. iinumae Makino, F. nilgerrensis Schlect. and F. vesca L. were the most divergent Fragaria taxa and F. iinumae appears to be the most ancestral taxon. Little variation was revealed within the economically important octoploid group of taxa, which gave rise to the cultivated strawberry, and no progenitor taxa to the octoploid group could be identified. The lack of variation in the chloroplast genome suggests that these Fragaria species may be of relatively recent evolutionary origin.

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Cynthia Fellman, Emily Hoover, Peter D. Ascher, and James Luby

We evaluated the extent to which `Swenson Red' seeded grape (Vitis × spp.) responded to single and repeated GA3 applications to induce seedless fruit development. Field studies were conducted to test the time of pre-anthesis GA3 application (18, or 24 May or 3 June), the usefulness of postanthesis application, the optimum GA3 concentration (0, 0.075, 0.15, or 0.3 mm), and the method of application. The treatment dates that gave a high percentage of seedless berries with an acceptable berry count per cluster were 24 May with postanthesis application and 3 June pre-anthesis only. The optimum GA3 concentration was 0.15 mm applied both before and after anthesis. The most seedless berries developed when pre- and postanthesis applications were used, indicating many seedless fruit developed from flowers that would have abscised. There was no difference in percent heedlessness, number of berries per cluster, or number of seeds per berry between clusters dipped or sprayed with 0.3 mm GA3. Chemical uame used: gibberellic acid (GA3).

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Harpartap Mann, David Bedford, James Luby, Zata Vickers, and Cindy Tong

During storage, many apple (Malus ×domestica Borkh.) genotypes lose their desirable textural qualities, but some like `Honeycrisp', maintain their sensory Crispness and Firmness. To understand this differential response of genotypes to postharvest changes in texture, reliable and quantifiable methods of texture measurement are needed. This study integrated data from a snapping test, confocal laser scanning microscopy (CLSM), and sensory panels to study postharvest textural changes and to predict sensory textural attributes of Firmness, Crispness, Mealiness, and Juiciness. Three separate analyses on fresh, stored, and combined fresh and stored fruit data yielded different predictors for the same sensory attributes. Change in Crispness during storage was successfully predicted by change in Work during storage. Cell number and size were related to fresh fruit texture and its maintenance during storage. Unique textural properties of `Honeycrisp' were found to be inherited by its progeny.