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  • Author or Editor: J.J. Luby x
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Introgression of Fragaria vesca, the diploid wild strawberry, and F. × ananassa, the octoploid cultivated strawberry, into octoploid F. virginiana collected from Minnesota and Wisconsin was suggested by gynodioecy and cluster analysis. Nine morphological traits separated collections into two main clusters, one associated with the northern hardwoods, and the other in the prairie-forest floristic province. Under field conditions, wild female clones were rated similarly to check cultivars for fruit set and plant productivity but always significantly higher than wild hermaphrodites, Increases in yield might be gained by selecting female clones for incorporation into a breeding program. Breeders anticipating rapid transfer of traits from the wild might concentrate on collections from the prairie-forest floristic province, since these materials contain F. × ananassa traits. Maximum genetic diversity would be gained using collection from both floristic provinces.

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Introgression of Fragaria vesca, the diploid wild strawberry, and F. × ananassa, the octoploid cultivated strawberry, into octoploid F. virginiana collected from Minnesota and Wisconsin was suggested by gynodioecy and cluster analysis. Nine morphological traits separated collections into two main clusters, one associated with the northern hardwoods, and the other in the prairie-forest floristic province. Under field conditions, wild female clones were rated similarly to check cultivars for fruit set and plant productivity but always significantly higher than wild hermaphrodites, Increases in yield might be gained by selecting female clones for incorporation into a breeding program. Breeders anticipating rapid transfer of traits from the wild might concentrate on collections from the prairie-forest floristic province, since these materials contain F. × ananassa traits. Maximum genetic diversity would be gained using collection from both floristic provinces.

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The effects of pH and N form on growth and nutrition of blueberry (Vaccinium corymbosum L. × V. angustifolium Ait. cv. Northblue) and cranberry (V. macrocarpon Ait. cv. Searles) were tested in separate greenhouse hydroponic experiments. A factorial treatment arrangement of two pH levels (4.5 and 6.5) and three N forms (NO3-N, NH4-N, and NH4-N/NO3-N) was used for each clone. Blueberry shoot growth and final dry weight were greatest at pH 4.5, regardless of N form. In contrast, cranberry fresh weight accumulation and final dry weight were higher with NH4-N/NO3-N or NH4-N than with NO3-N alone. Cranberry plants receiving NO3-N alone accumulated low levels of tissue N and grew relatively poorly at both pH levels. Differences in N response by these two species may be due partially to the environments in which they were selected. Soil from the site where `Northblue' blueberry was selected contained relatively high NO3-N and low NH4-N levels; soil from commercial `Searles' cranberry bogs had relatively low NO3-N and high NH4-N levels. Both species accumulated relatively high levels of root Fe, regardless of pH or N form. Levels of Fe in the root were as much as 100 times higher than in the shoot. Based on X-ray microanalysis of cranberry roots, most of the Fe appeared to be precipitated on the root surface as iron phosphate. Concentrations of Mn in shoots and roots depended on N form and pH. In general, root Mn was highest at pH 6.5 and apparently was precipitated with Fe.

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The commercially successful apple (Malus pumila Mill.) cultivar Honeycrisp is known for its high degrees of crispness and juiciness. This cultivar has been incorporated into numerous breeding programs in an effort to duplicate its desirable texture traits in conjunction with such other traits as reduced postharvest disorders, disease resistance, and improved tree vigor. This study characterizes variability and estimates heritability for several apple fruit texture traits within a large breeding population over several years. Five full-sib families, all sharing ‘Honeycrisp’ as a common parent, were assayed with respect to crispness, firmness, and juiciness using sensory evaluation panels and total work required to fracture tissue using instrumental methods. The incomplete block design of the sensory panels, coupled with best linear unbiased prediction, facilitated the evaluation of a large number of genotypes with small numbers of fruit per genotype while accounting for individual sensory panelist effects. Broad-sense heritability estimates exceeded 0.70 for all four traits. Principal component analysis, applied to the phenotypic data, characterized ‘Honeycrisp’ as having average crispness and low firmness (53rd percentile relative to its offspring) but also as being a relatively extreme example of high juiciness and low work to fracture (first percentile). The improved characterization of desired fruit texture phenotypes and the high levels of broad-sense heritability provide valuable tools for the further development of new, high-quality apple cultivars.

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Accessions of Vaccinium species (deliciosum, ovalifolium, membranaceum, parvifolium, scoparium) were evaluated for tolerance to higher pH in the root zone using an in vitro screening procedure. Seeds were germinated on media containing all essential nutrients with nitrogen in the nitrate form at pH 5 and pH 6 and evaluated for 21 weeks. Excess EDTA was used to buffer the micronutrients and pH was buffered by MES and succinic acid. Germination varied among species with V. ovalifolium being highest and V. parvifolium not germinating at all. Mortality was lower at pH 5. At pH 6, V. ovalifolium and V. membranaceum exhibited variation for growth while all other species suffered complete mortality.

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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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Runners from 318 plants representing 37 populations across the northern tier of US states, from Washington to New York, were collected and planted in two replications in a common greenhouse environment to assess morphological variation among octoploid strawberries (Fragaria chiloensis, F. virginiana spp. glauca and F. v. spp. virginiana). DNA was also extracted from these plants to determine molecular variation using RAPD's (Random Amplified Polymorphic DNA). Preliminary data suggest that the following morphological characters are useful traits in assessing diversity: flowering and runnering date; sex; petiole and peduncle hairs; petiole and peduncle color; leaf color, size, shape and density; and powdery mildew resistance. Preliminary RAPD data has revealed many useful molecular markers capable of detecting variability from the intrapopulation to interspecific level. Analysis of these data will determine relative genetic distances among the populations and provide a more complete understanding of the diversity available to the strawberry breeder in the octoploid taxa native to North America.

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