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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Michael J. Havey

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Christopher S. Cramer and Todd C. Wehner

The combining ability (hybrid performance) of breeding lines is often determined to measure selection progress for yield. Plant breeders utilize this information to develop breeding lines with higher combining ability. The objectives of this study were to measure the specific combining ability for yield traits over three selection cycles from four pickling cucumber populations with Gy 14, a popular pickling cucumber inbred; and to determine the change in specific combining ability for yield traits in four populations improved through recurrent selection. Four pickling cucumber populations, North Carolina wide base pickle (NCWBP), medium base pickle (NCMBP), elite pickle 1 (NCEP1), and hardwickii 1 (NCH1), were developed and improved through modified half-sib selection from 1983 to 1992 to improve yield per se and fruit quality in each population. Eleven families were randomly selected from each of 3 selection cycles (early, intermediate, advanced) from each populations and were hybridized to Gy 14. Plants were sprayed with Paraquat to defoliate them and to simulate once-over harvest. The experiment was a randomized complete-block design with 22 replications per population arranged in a split plot with the four populations as whole plots and the three cycles as subplots. The combining ability for fruit quality rating of NCWBP and NCMBP increased as the number of selection cycles increased. Conversely, selection for higher yield per se decreased the combining ability of the NCEP1 population for improved fruit quality. In most instances, the combining ability of each population exhibited a constant response over selection cycles for each measured yield trait.

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Christopher S. Cramer and Todd C. Wehner

Plant breeders often measure selection progress for yield by measuring the hybrid performance (combining ability) of a breeding line. This information is used to develop breeding lines with higher combining ability. The objectives of this study were to measure the specific combining ability for yield traits over three selection cycles from four slicing cucumber populations with `Poinsett 76', a popular slicing cucumber cultivar; and to determine the change in specific combining ability for yield traits in four populations improved through recurrent selection. Four slicing cucumber populations, North Carolina wide base slicer (NCWBS), medium base slicer (NCMBS), elite slicer 1 (NCES 1), and Beit Alpha 1 (NCBA1), were developed and improved through modified half-sib selection from 1983 to 1992 to improve yield per se and fruit quality in each population. Eleven families were randomly selected from each of three selection cycles (early, intermediate, advanced) from each population and were hybridized to `Poinsett 76'. Twenty-three seeds from each cross were planted in 1.2-m plots in Spring and Summer 1995. When 10% of fruit were oversized (>50 mm in diameter), plants were sprayed with paraquat to defoliate them and to simulate once-over harvest. The experimental design was a randomized complete block with 22 replications per population arranged in a split plot with the four populations as whole plots and the three cycles as subplots. The combining ability for early and marketable yield of NCWBS and NCBA1 increased as the number of selection cycles increased. Conversely, selection for higher yield per se decreased the combining ability of the NCES 1 population for early and marketable yield. The NCBA1 population exhibited the largest gain (131.2%) from cycle 0 to 8 averaged over all traits. Early yield exhibited the largest gain (60.8%) averaged over all populations.

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Christopher S. Cramer and Todd C. Wehner

Currently, both hybrid and inbred pickling cucumber cultivars are being grown commercially in the United States. Heterosis for yield in pickling cucumber has been previously reported. However, heterosis has not been repeatable in other studies. The objective of this study was to determine the existence of heterosis and inbreeding depression for yield in pickling cucumber. Six pickling cucumber inbreds (`Addis', `Clinton', M 12, M 20, `Tiny Dill', `Wisconsin SMR 18') were hybridized to form four F1 hybrid families (`Addis × M 20, `Addis' × `Wis. SMR 18', `Clinton' × M 12, M 20 × `Tiny Dill'). Within each family, F2, BC1A and BC1B generations were also formed. Thirty plants of each generation within each family were grown in 3.1-m plots for four replications in the spring and summer seasons of 1996 at the Horticultural Crops Research Station in Clinton, N.C. Data were collected at once-over harvest for total, marketable, and early yield in terms of number (1000 fruit/ha) and weight (Mg/ha). In addition to yield, a fruit shape rating was collected for each plot. High parent heterosis for yield (total and marketable fruit weight) was only observed for `Addis' × `SMR 18' grown in the summer season. The three other families did not exhibit heterosis for total, marketable, and early yield. Heterosis for shape rating was not observed for any family. `Addis' × `Wis. SMR 18' also exhibited inbreeding depression for total fruit weight, marketable fruit weight, early fruit number, and early fruit weight during the spring season and for marketable fruit number and marketable fruit weight during the summer season.

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Christopher S. Cramer and Mark P. Bridgen

Mussaenda, a tropical, hybrid ornamental plant from India and the Philippines, is being evaluated as a potential greenhouse ported crop in the united States. Showy sepals of white, picotee (White with rosy edges), light pink, dark pink, or red complemented by fragrant, yellow flowers and dark green, pubescent foliage make Mussaenda a very attractive potted plant. However, sometimes the height of Mussaenda is unsuitable for pot plant culture. With the use of chemical growth regulators. plant height is reduced thus making Mussaenda a more feasible potted crop.

In the summer of 1992, a growth regulator study was conducted to evaluate three growth regulators and concentrations capable of reducing plant height in Mussaenda. Daminozide (B-Nine SP), ancymidol (A-Rest), or paclobutrazol (Bonzi) was applied at two concentrations each. Daminozide was tested as a spray at 2500 ppm and 5000 ppm. Ancymidol was applied as a spray at 33 ppm and 66 ppm or as a drench at 0.25 mg/pot and 0.50 mg/pot. Paclobutrazol was tested as a spray at 25 ppm and 50 ppm or as a drench at 0.125 mg/pot and 0.25 mg/pot. Growth regulators were applied as a single application or a double application with two weeks separating applications.

Daminozide at 2500 ppm and 5000 ppm was most effective in controlling plant height. Ancymidol as a drench at 0.25 mg/pot and 0.50 mg/pot was also effective in plant height control. Two applications of these growth regulators were more effective in controlling plant height than a single application.

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Christopher S. Cramer and Mark P. Bridgen

Disinfected midrib sections of Mussaenda `Queen Sirikit' ≈3 to 4 mm in size were cultured on a basal medium of Murashige and Skoog salts and vitamins, 87.7 mm sucrose, and 5 g Sigma agar/liter supplemented with several concentrations of indole-3-acetic acid (IAA) (0, 5.0, 10.0, 20.0 μm) and 6-benzylaminopurine (BAP) (0, 0.5, 1.0, 2.5, 5.0, 10.0, 25.0, 50.0 μm). Cultures were subculture onto the same treatment after 5 weeks and observed weekly for 15 weeks for the presence of somatic embryos. As somatic embryos were produced, they were subculture onto basal medium supplemented with 0.5, 1.0, 2.5, or 25.0 μm BAP. Callus was first observed at 2 weeks in cultures grown on basal medium supplemented with 5.0–20.0 μm IAA and 0–50.0 μm BAP. Somatic embryos were observed at 8 weeks on basal medium supplemented with 5.0–10.0 μm IAA and 2.5–5.0 μm BAP. Callus cultured on 0–10 μm IAA and 5.0–10.0 μm BAP produced the greatest number of somatic embryos by 15 weeks. Somatic embryos subculture to basal medium supplemented with 25.0 μm BAP proliferated shoots, while eliminating BAP from the medium resulted in root and callus production. Shoots and entire plants were removed from in vitro conditions and successful] y acclimated to greenhouse conditions. Somatic embryo-derived plants flowered sporadically 25 to 35 weeks after removal from in vitro conditions. Variations in sepal number and leaf number per node were observed at 1% to 5%.

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Christopher S. Cramer and Larry D. Robertson

Numerous short-day onion accessions maintained at the Plant Genetic Resources Unit (PGRU) of Geneva, N.Y., were in danger of being lost from the U.S. germplasm collection due to sub-standard viability and low seed supply of those accessions. Seed regeneration of short-day onions at Geneva, N.Y., has been difficult because of improper daylengths and environmental conditions. A project was initiated in Sept. 2001 between PGRU and the onion breeding program at New Mexico State University to regenerate 75 accessions that were in the most danger of being lost from the collection. Even though germination rates were low for most accessions, plants were recovered from 72 accessions. Two accessions did not produce bulbs as it was likely they were long-day accessions. Of the remaining accessions, two accessions produced bulbs but did not produce seed. Several accessions bolted during bulb production and plants were covered with crossing cages, crosses were made, and seed was collected. Seed of 54 accessions were sent to PGRU to be incorporated back into the collection and to become available for distribution. Seventeen accessions produced less than 35 g of seed and were retained in order to produce additional seed in a second regeneration step. Some of the short-day accessions that have become available include `Amarela Globular Rio Grande', `Babosa', `Baia Performe Sintese No. 22', `Beth Alpha', `Burgundy', `California Early Red', `Dehydrator No. 5', `Early Crystal', `Eclipse L303', `Imperial 48', `New Mexico Yellow Grano', `Pusa Red', `Red Bermuda', `Red Creole', `Red Grano', `Red Patna', and `Rio Grande'.

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Todd C. Wehner and Christopher S. Cramer

Fruit yield, earliness, and quality have low to moderate heritability, but are traits of major importance in cucumber (Cucumis sativus L.). The objective of this study was to determine the changes made in those traits using recurrent selection in three slicing cucumber populations (NCMBS, NCES1, and NCBA1). During population improvement, one or two replications of 200 to 335 half-sib families were evaluated in the spring season for five traits: total, early, and marketable fruit per plot, fruit shape rating, and a simple weighted index (SWI = 0.2(total yield)/2 + 0.3(early yield) + 0.2(% marketable)/10 + 0.3(fruit shape). Families from each population were intercrossed in an isolation block during the summer season using remnant seeds of the best 10% selected using the index. Response was evaluated using a split-plot treatment arrangement in a randomized complete block design with 32 replications in each of two seasons (spring and summer). Whole plots were the three populations, and subplots were the 11 cycles (cycles 0 to 9 plus checks). We measured improvement in performance of the populations in a selected (spring) and unselected environment (summer). Significant gains were made for all traits in all populations over the 9 to 10 cycles of recurrent selection. Greatest progress was made for the NCMBS population, with an average of 37% gain from cycle 0 to 9 over all five traits. The trait where most progress was made was early yield, with an average of 63% gain from cycle 0 to 9 over the three populations.

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Christopher S. Cramer and Todd C. Wehner

Increased fruit yield in slicing cucumber (Cucumis sativus L.) has been difficult to achieve since yield is quantitatively inherited with low heritability. From 1981 to 1993, four slicing cucumber populations differing in their genetic diversity (wide, medium, elite, and `Beit Alpha') were advanced through six to ten cycles of modified half-sib recurrent selection. The objectives of this research were to determine 1) the fruit yield and yield component means; 2) the correlations between yield components, between yield traits, and between components and yield; and 3) the change in means and correlations with selection for improved yield of four slicing cucumber populations. In 1994 and 1995, four families were randomly selected from three cycles (early, intermediate, and late) from each population and self-pollinated. Thirty plants from each S1 family were evaluated in 3.1-m plots in Spring and Summer 1995 and 1996 at the Horticultural Crops Research Station in Clinton, N.C. Plants were harvested and data were collected on number of branches per plant and nodes per branch, proportion of pistillate nodes, fruit set and shape, and total, early, and marketable yield. When averaged over all populations, seasons, and years, fruit yield and quality increased with selection while yield components remained unchanged with selection. Fruit yield and components differed between populations, seasons, and years. Most correlations between yield components and between yield components and fruit yield were weak, and strong correlations varied between populations, seasons, and yield components. Indirect selection of proportion of pistillate nodes has potential for improving yield for certain population-season combinations. Selection weakened many strong correlations between yield components and between yield and components. Changes in correlations often did not correspond with changes in trait means. Based on this research, selection for yield components would not be advantageous for improving fruit yield in all slicing cucumber populations. Additional yield components, yield component heritability, and better component selection methods need to be determined before component selection can be used to improve fruit yield.