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Abstract

Recurrent half-sib selection within a heterogeneous population of cucumber (Cucumis sativus L.) was effective in improving germination at 15°C from 34.4% in cycle 0 to 92.4% in cycle 3. The linear regression coefficient indicated an average increase of 19.8% units per cycle of selection. Correlated responses to selection resulted in increased percentage of germination at 20° and 25° and decreased days to germination at 15°, 20°, and 25°.

Open Access

Abstract

Seed of four heterogeneous cucumber [Cucumis sativus (L.)] populations (C0-C3) that had undergone recurrent half-sib selection for improved germinability at 15°C were evaluated for seedling emergence and other horticultural characteristics under field conditions. Correlated responses to selection were observed for percent emergence 7 days after sowing and mean number of days to emergence. No correlated response to selection was observed for changes in sex expression, seedling vigor, or yield. These results suggest that selection for low temperature germinability at 15° did not result in any change in the horticulturally important characteristics monitored.

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The apple (Malus ×domestica Borkh.) cultivars Starkspur Supreme Delicious and Melrose were planted in 1987 on eight apomictic apple rootstock selections made in Germany by Dr. Hanna Schmidt and on M.7. Selections 2 [M. hupehensis (Pamp.) Rehd. parentage] and 8 [M. sieboldii (Regel) Rehd. parentage] were similar to M.7 in precocity, cumulative yield per tree, and yield efficiency, while the other selections with M. sargenti Rehd. in their parentage were slower to flower and had lower yields and yield efficiencies. Selections 2 and 8 tended to result in larger trees than M.7, while the selections with M. sargenti parentage were generally similar to M.7 in size. Except for trees on M.7 and selection 2, `Starkspur Supreme Delicious' developed more severe symptoms of internal bark necrosis (IBN) than did `Melrose', which normally does not show IBN. However, `Melrose' showed IBN symptoms on selections with M. sargenti parentage. IBN symptoms were positively correlated with leaf Mn concentrations. Influence of rootstocks on other nutrient elements, although significant, were small compared to the effect on Mn. A significant interaction occurred between cultivar and rootstock in their effects upon branch morphology, mostly because fewer flowering spurs and more vegetative spurs were observed on `Melrose' than on `Starkspur Supreme Delicious' when grafted on Selection 2. These apomictic selections offered no advantage over M.7 as rootstocks for apples.

Free access

In recent years, much emphasis has been placed on functional/antioxidant properties of various fruits and vegetables and their contribution to human health. Since average per capita consumption of potatoes in the United States is about 137 pounds, even moderate levels of antioxidants could be viewed as an important human health benefit. Variation in antioxidant activity has not been extensively investigated for colored potatoes (specialty selections). Therefore, the objective of this study was to evaluate antioxidant activity of specialty selections from the Texas Potato Variety Development Program and identify elite lines to use in breeding for improvement of this trait. Potato tubers were also assessed for their outer appearance, skin color, flesh color, spoilage and yield characteristics. Specialty potato selections (320 lines) were screened for total antioxidant activity using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay. After an initial screening, the top 10 % of selections were reevaluated in the following year. Significant (P ≤ 0.01) differences were found among selections and, for some selections, differences were found between seasons. Total antioxidant activity ranged from 27 μg/gfw to 832 μg/gfw. The specialty selection CO112F2-2 (purple flesh) had the highest antioxidant activity (832 μg/gfw) irrespective of season. In most cases, purple flesh selections produced the highest antioxidant activity, probably due to the presence of anthocyanins, followed by yellow selections.

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selecting for resistance to multiple pathogens ( Yang and Francis, 2005 ). Marker-assisted selection (MAS) offers an opportunity to overcome some of the problems associated with phenotypic selection and facilitates combining multiple resistance genes

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The pawpaw (Asimina triloba) is a new crop in the early stages of domestication. Recently commercialization has become feasible with the availability of high quality varieties. The history of pawpaw varieties is divided into three periods: 1900-50, 1950-85, and 1985 to the present. The history before 1985 was concerned primarily with the discovery of superior selections from the wild but experienced a serious break in continuity around 1950. The third period has been characterized by greater developmental activity. Larger breeding programs have been pursued, regional variety trials initiated, a germplasm repository established, and a formal research program at Kentucky State University (KSU) instituted. Future breeding will likely rely on dedicated amateurs with the education and means to conduct a 20-year project involving the evaluation of hundreds of trees. For the foreseeable future, governments and universities will not engage in long-term pawpaw breeding.

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Abstract

Studies were conducted on the feasibility of shortening the evaluation period of highbush blueberry (Vaccinium corymbosum L.) selections by propagating by softwood cuttings taken from each of the single-plant selections at the time of fruit evaluation row the following spring. Softwood cuttings were taken from a single plant of 5 early, 5 midseason, and 5 late ripening selections in June, July, and August. July cuttings (60%) rooted better than June (37%) and August (31%) cuttings. Early selections (34%) rooted about the same as midseason (32%) and late (35%) selections. The earlier the cuttings were potted, the larger the root system they developed before frost when grown in an unheated greenhouse. None of the rooted cuttings potted 30 Sept, developed root systems large enough to survive field planting. Supplemental heat and light after potting increased root growth of plants potted 25 Aug. but not those potted 10 Sept. Eighty percent of the plants transplanted to the field survived.

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Abstract

Mass selection for low oxidation of root flesh was initiated in the fourth generation of an open-pollinated sweetpotato [Ipomoea batatas (L.) Lam.] population. Two selection schemes were followed which provided different selection pressures by varying effective population sizes. In one (population A), selected plants were randomly intercrossed by insects each cycle. In the other (population D), approximately 10% of the randomly intercrossing population were selected each cycle and their true seed used to plant the next generation. After 2 cycles of selection in A and 3 in D, they were compared to appropriate generations of the base population. Results were in agreement with selection theory and closely paralleled those obtained with other crops. More rapid advance was made with A, which requires 2 seasons per cycle for any trait not measured in the seedling stage. Good advance was made with D, which allows 1 cycle per season. Study of 21 other traits indicated more changes in unselected traits in A than in D, thus favoring the method of D in early generations of mass selection in sweetpotato. The rapid increase of low oxidizing plants in this study suggests that selection for low oxidizing cvs. may reduce associated processing problems.

Open Access

Genetic variation in chilling requirement was investigated over three growth periods using clonal progenies of six apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] families derived from crosses of high and low chill requiring cultivars. Two quantitative measurements related to chilling requirement, viz., the time of initial budbreak (vegetative and reproductive) and the number of breaking buds over a specified time interval, were used as evaluation criteria. Genetic and environmental variances of the traits are presented as intra-class correlation coefficients for clones within and between families. For budbreak time, reproductive and vegetative, broad-sense heritability averaged around 75% and 69% respectively, indicating a high degree of genetic determination in this material. For budbreak number, moderate to low genetic determination was found with broad-sense heritabilities around 30%. Estimates of genetic components of variance between families were generally very low in comparison to the variance within families and predict potentially favorable responses to truncation selection on the traits within these progeny groups. Analysis of the data showed that distribution of budbreak time is typical of quantitative traits with means distributed closely around midparent values. Skewed distributions towards low budbreak number were obtained in varying degrees in all families.

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Abstract

The applicability of the method of correlated responses to selection of sweetpotatoes in a breeding program is illustrated by use of previously determined correlations between 21 traits Examples of the kinds of changes that might be expected due to correlated responses are pointed out. It is further demonstrated that knowledge of such responses can assist plant breeders in making prudent selections and in the design of improved breeding procedures. Agreement of predicted and realized correlated responses indicates that this technique is suited to use with the sweetpotato. Through mass selection procedures, cultivars with most any combination of traits desired should be possible.

Open Access