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Christopher S. Cramer and Todd C. Wehner

Recurrent selection has been used as a breeding method to improve traits having low heritability such as fruit yield, earliness, and fruit shape. The objective of this study was to measure the progress of recurrent selection in four slicing cucumber populations in terms of hybrid performance when crossed with a common tester. The four populations, North Carolina wide-base slicer (NCWBS), medium-base slicer (NCMBS), elite slicer 1 (NCES1), and Beit Alpha 1 (NCBA1) populations, which differed in their genetic diversity and mean performance, were developed using modified intrapopulation half-sib recurrent selection to improve fruit yield and quality. Eleven S0 families were taken randomly from each of three selection cycles (early, intermediate, and advanced) from each population. Those families were self-pollinated to form S1 families, and the S1 families were crossed to `Poinsett 76', a popular slicing cucumber cultivar. The experiment was a splitplot treatment arrangement in a randomized complete-block design with 22 replications per population, with the four populations as whole plots and the three cycles as subplots. When 10% of fruit were oversized (>60 mm in diameter), plants were sprayed with paraquat to defoliate them for once-over harvest. Plots were evaluated for total, early, and marketable yield and fruit shape. Recurrent selection for improved fruit yield and shape per se resulted in improved hybrid performance of the NCWBS and NCBA1 populations for fruit yield and shape rating when tested in the selected or nonselected environment. The NCWBS population had the largest gain (21%) in hybrid performance averaged over all traits. In addition, early yield was improved an average of 18% from early to late cycles for each population. Even though the fruit yield and shape rating of `Dasher II' was greater than the hybrid performance of each population mean for the same traits, several F1 families within each population exceeded the fruit yield of `Dasher II'.

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Christopher S. Cramer and Todd C. Wehner

The relationships between fruit yield and yield components in several cucumber (Cucumis sativus L.) populations were investigated as well as how those relationships changed with selection for improved fruit yield. In addition, the correlations between fruit yield and yield components were partitioned into partial regression coefficients (path coefficients and indirect effects). Eight genetically distinct pickling and slicing cucumber populations, differing in fruit yield and quality, were previously subjected to modified half-sib family recurrent selection. Eight families from three selection cycles (early, intermediate, late) of each population were evaluated for yield components and fruit number per plant in four replications in each of two testing methods, seasons, and years. Since no statistical test for comparing the magnitudes of two correlations was available, a correlation (r) of 0.7 to 1.0 or –0.7 to –1.0 (r 2 ≥ 0.49) was considered strong, while a correlation of –0.69 to 0.69 was considered weak. The number of branches per plant had a direct positive effect on, and was correlated (r = 0.7) with the number of total fruit per plant over all populations, cycles, seasons, years, plant densities, and replications. The number of nodes per branch, the percentage of pistillate nodes, and the percentage of fruit set were less correlated (r < |0.7|) with total fruit number per plant (fruit yield) than the number of branches per plant. Weak correlations between yield components and fruit yield often resulted from weak correlations among yield components. The correlations among fruit number traits were generally strong and positive (r ≥ 0.7). Recurrent selection for improved fruit number per plant maintained weak path coefficients and correlations between yield components and total fruit number per plant. Selection also maintained weak correlations among yield components. However, the correlations and path coefficients of branch number per plant on the total fruit number became more positive (r = 0.67, 0.75, and 0.82 for early, intermediate, and late cycles, respectively) with selection. Future breeding should focus on selecting for the number of branches per plant to improve total fruit number per plant.

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Christopher S. Cramer and Joe N. Corgan

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Christopher S. Cramer and Joe N. Corgan

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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 Mark P. Bridgen

Mussaenda, a tropical ornamental shrub developed in the Philippines is being examined as a potential greenhouse potted crop in the United States. Showy sepals of white, picotee, pink or red and fragrant, yellow flowers make Mussaenda an attractive patted plans however, the profuse upright growth habit of some Mussaenda cultivars is undesirable for pot plant culture. With this in mind experiments were conducted to determine the effects of three growth regulators at two concentrations each, as well as the application method and the number of applications on Mussaenda plant height.

Three growth regulators, daminozide (B-Nine), ancymidol (A-Rest), and paclobutrazol (Bonzi) were applied at two commercially recommended rates and two application methods (spray or drench). The treatment were daminozide at 2500 ppm and 5000 ppm (spray), ancymidol at 33 and 66 ppm (spray) and at 0.25 and 0.50 mg/pot (drench), and paclobutrazol at 25 and 50 ppm (spray) and at 0.125 and 0.25 mg/pot (drench). In subsequent experiments, the same growth regulators were applied with an increase in concentration and either two or three applications. The treatments were daminozide at 5000 ppm (spray), ancymidol at 66 and 132 ppm (spray) and at 0.50 and 1.0 mg/pot (drench), and paclobutrazol at 50 and 100 ppm (spray) and at 0.25 and 0.50 mg/pot (drench).

The most attractive potted plants were produced with two applications of daminozide at 5000 ppm or two applications of ancymidol at 0.5 mg/pot (drench). Higher concentrations or additional applications excessively reduced plant height. Three spray applications of 132 ppm ancymidol also produced an attractive potted plant. Paclobutrazol sprays or drenches at any concentration or application number were ineffective for reducing Mussaenda `Queen Sirikit' plant height.

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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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Parminder Singh Multani and Christopher S. Cramer

Identification of resistant cultivars offers the best control for Iris yellow spot virus (IYSV), a new onion disease vectored by Thrips tabaci. In this study, 18 spring-seeded onion cultivars were screened for IYSV. Each alternate plot in the field was planted with infected bulbs from the previous year to serve as a source of virus inoculum and thrips. With increased thrips population and temperature over time, straw-colored, necrotic lesions typical to IYSV infection were observed on plant leaves. Plants were analyzed by enzyme linked immunosorbant assay to confirm the IYSV infection and determine the virus titer. Ten randomly selected plants from each plot were rated for IYSV symptoms on a scale of 1 to 9, with 1 representing no symptomatic tissue and 9 representing more than 50% tissue damage. Starting 1 June, disease ratings were collected each week until 13 July. Nearly all cultivars showed similar disease symptoms when rated on 1 June. By 29 June, NMSU 03-52-1 exhibited some tolerance to IYSV as fewer symptoms were observed. By 13 July, NMSU 03-52-1 exhibited fewer disease symptoms than most of the other cultivars tested, while `Caballero' showed the highest IYSV symptoms. All other cultivars showed low to high susceptibility for IYSV. The increase in disease severity was accompanied by a relative increase in the virus titer of plants over time. However, virus titer poorly correlated with the amount of disease symptoms in different cultivars. The most tolerant cultivar, NMSU 03-52-1, had higher virus titer than many susceptible cultivars but still performed well. Conversely, some cultivars with low virus titer were susceptible and developed more symptoms. This indicates a difference in the capabilities of different cultivars to resist IYSV.

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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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Troy A. Larsen* and Christopher S. Cramer

Current onion varieties that are grown in New Mexico were developed for hand harvesting and not for mechanical harvesting. In order for onion production in New Mexico to remain a viable commodity, firmer onion varieties need to be developed for mechanical harvesting. In this study, bulb firmness of onions was examined in short and intermediate-day onion entries comparing a qualitative `finger pressure' method with a digital FFF-series durometer. After harvesting and curing of the onion bulbs, dry outer scales were removed before durometer measurements were taken at two perpendicular points on the vertical center axis of the bulb. Following the durometer measurements, bulb firmness was rated by `finger pressure' applied to multiple points on the vertical center axis. For intermediate and late-maturing entries, durometer measurements and firmness rating were positively correlated in a strong fashion (r = 0.77 to 0.87). Early maturing entries, NMSU 02-25 and NMSU 02-03 both had high durometer averages and firmness ratings. `NuMex Crimson' and `NuMex Crispy' had the highest durometer averages and firmness ratings among intermediate maturing entries while `NuMex Solano' and NMSU 01-06 had the highest among late maturing entries. From our results, the durometer can be useful in providing a quantifiable measure of bulb firmness.