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  • Author or Editor: D. Richards x
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Abstract

Plant height and lateral shoot growth of Camellia × Williamsii ‘Waterlily’ and ‘Debbie’ were controlled effectively by foliar sprays or media drenches of paclobutrazol. A single foliar application of 500 mg·liter–1 paclobutrazol reduced height of both cultivars by ≈30%, and plants were considered commercially acceptable. The response did not carry over into subsequent years. Some rates of paclobutrazol increased the total number of open flowers, but there was a varied effect on flower abscission. Paclobutrazol treatment could prove a useful technique for the commercial production of camellias for temporary use as indoor flowering pot plants before subsequent planting in the landscape. Chemical name used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol, ICI-PP333).

Open Access

Shoot extension of Rhododendron `Sir Robert Peel' was reduced, but flowering was more precocious after treatment of plants with paclobutrazol. All of the drench rates tested (0.05 to 0.4 g a.i./pot) proved excessive and resulted in prolonged shoot growth reduction but greatly increased the number of flowers. However, flowers produced at the higher drench rates were grossly malformed and unacceptable. Foliar spray treatments (250 to 2000 mg a.i./liter) were less inhibitory than drenches, and a single spray of 500 mg·liter-1 was considered an appropriate commercial application rate. Paclobutrazol application could thus prove to be a useful technique in producing compact flowering plants of Rhododendron hybrids for improved retail sales. Chemical name used: β-[(4∼chlorophenyl) methyl] (1,1-dimethylethl)-1H-l,2,4-triazole-l-ethano1 (paclobutrazol, ICI-PP333).

Free access

Abstract

Plant height of potted Bouvardia humboldtii Hort. was controlled effectively by foliar or drench applications of paclobutrazol. Three foliar applications of 250 mg·liter−1 paclobutrazol or a drench of 2 mg/100-mm-diameter pot reduced plant height by≈30% and increased the total number of flowers per plant by ≈35%. Overall, paclobutrazol significantly reduced total plant dry weight, and sprays were more inhibitory than drenches. Paclobutrazol altered the shoot : root ratio in favor of the shoot. Foliar sprays of daminozide (5000 mg·liter−1) or chlormequat (2000 mg·liter−1) were ineffective in controlling growth or flowering. It is concluded that paclobutrazol application may be a useful technique in the commercial production of Bouvardia as a flowering pot plant. Chemical name used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-l-ethanol [paclobutrazol (ICI-PP333)].

Open Access

A freestone, nonmelting flesh peach would offer the opportunity to transport freestone peaches to distant markets, and so open lucrative export opportunities. Peach [Prunus persica (L.) Batsch.] germplasm segregating for semi-freestone and clingstone has been identified among the nonmelting flesh, open-pollinated progeny of the Univ. of Florida selection, Fla. 9-20C. The segregation approached a 1 : 1 ratio. No significant differences were detected between the two categories for titratable acidity, soluble solids concentration, or skin color. However, the semi-freestone progeny had significantly softer flesh than their clingstone siblings, although not soft enough to justify reclassification of the flesh texture. No simple genetic model can be proposed for the inheritance of this new phenotype. The semi-freestone, nonmelting germplasm represents a step towards a less perishable, freestone cultivar for the fresh market, as well as an opportunity to study the reason for the rarity of the freestone/nonmelting phenotype among peaches.

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Garlic (Allium sativum L.) has been clonally propagated for thousands of years because it does not produce seed under standard cultivation conditions. A single garlic accession frequently displays a high degree of phenotypic plasticity that is likely to be dependent upon soil type, moisture, latitude, altitude, and cultural practices. The diversity observed by collectors has occasionally led to the renaming of varieties as they are exchanged among growers and gardeners. As a result, there are numerous garlic varieties available both commercially and within the USDA National Plant Germplasm System (NPGS) that may be identical genotypically, yet have unique cultivar names. To address this possibility, we performed amplified fragment-length polymorphism (AFLP) analysis on a comprehensive selection of 211 Allium sativum and Allium longicuspis accessions from NPGS and commercial sources. We used several statistical approaches to evaluate how these clonal lineages are genetically differentiated and how these patterns of differentiation correspond to recognized phenotypic classifications. These data suggest that while there are extensive duplications within the surveyed accessions, parsimony and distance based analyses reveal substantial diversity that is largely consistent with major phenotypic classes.

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The interspecific and intergeneric relationships of eight species of Juglans (walnuts) and three other members of Juglandaceae were investigated. The following species were included: the American J. australis Griseb., J. neotropica Diels., J. olanchana Standl. et L.O. Williams, J. nigra L., and Carya illinoensis (Wang.) K. Koch.; two Juglans from South China, namely, J. sigillata Dode and an unidentified J. sp; an Engelhardia also from China and the Asian J. ailantifolia Carr., Pterocarya stenoptera var. tonkinensis Franchet and the Eurasian J. regia L. Cladistic analysis of 27 multistate morphological characters showed that the juvenile J. ailantifolia possessed similar physical traits to that of the juvenile American Juglans species. The chloroplast DNA in the trnL-trnF region indicated a close relationship between Juglans species. Pterocarya put the root of the cpDNA network among the American species. RAPD analysis was performed using eight primers. A total of 138 fragments were generated but only 78 clearly defined bands were used in the analysis. All the DNA data grouped the tropical/subtropical American Juglans with J. nigra, and the two new Asian species with J. ailantifolia and J. regia. The American species were closely related, more so than their Asian counter parts. The closeness of the investigated species predicts interspecific graft compatibility not only within the Asian and American groups, but also between them.

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There are several Central Asian Malus species and varieties in the USDA-ARS National Plant Germplasm System (NPGS) apple collection. Malus sieversii is the most comprehensively collected species native to Central Asia. Other taxa such as M. sieversii var. kirghisorum, M. sieversii var. turkmenorum, M. pumila, and M. pumila var. niedzwetzkyana have primarily been donated to the collection by other institutions and arboreta. We sought to determine if genetic and/or phenotypic differences among the individuals that make up the gene pools of these taxa in the NPGS exhibit unique characteristics. Genetic data, based on microsatellite analyses, suggested that the diversity within each taxa is significantly greater than that among taxa. Trait data also revealed very few differences among taxa, the primary characteristic being the dark red fruit coloration and tinted flesh color of the accessions assigned to M. pumila var. niedzwetzkyana resulting from a known single-gene mutation in anthocyanin production. We found that M. sieversii is a highly diverse species with a range in genetic and phenotypic trait variation that includes the characteristics of the other Central Asian taxa of interest. We conclude that the gene pools that comprise the accessions within the NPGS Central Asian Malus collection are highly overlapping with respect to both phenotypic traits and genotypic characters.

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The genetic diversity of a wild Malus population collected in the Kyrgyz Republic was compared with seedlings of Malus sieversii collected in Kazakhstan. Based on microsatellite marker results, we conclude that the population of 49 individuals collected in the Kyrgyz Republic includes private alleles and this population is assigned to a common genetic lineage with M. sieversii individuals found in the Karatau Mountain range of Kazakhstan. We recommend that a subset of these individuals be included in the National Plant Germplasm System Malus collection so they may be made available to breeders, physiologists, and other scientists for further examination.

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Edible european pears (Pyrus communis L. ssp. communis) are derived from wild relatives native to the Caucasus Mountain region and eastern Europe. Microsatellite markers (13 loci) were used to determine the relationships among 145 wild and cultivated individuals of P. communis maintained in the National Plant Germplasm System (NPGS). A Bayesian clustering method grouped the individual pear genotypes into 12 clusters. Pyrus communis ssp. caucasica (Fed.) Browicz, native to the Caucasus Mountains of Russia, Crimea, and Armenia, can be genetically differentiated from P. communis ssp. pyraster L. native to eastern European countries. The domesticated pears cluster closely together and are most closely related to a group of genotypes that are intermediate to the P. communis ssp. pyraster and the P. communis ssp. caucasica groups. Based on the high number of unique alleles and heterozygosity in each of the 12 clusters, we conclude that genetic diversity of wild P. communis is not fully represented at the NPGS. Additional diversity may be present in seed accessions stored in the NPGS and more pear diversity could be captured through supplementary collection trips to eastern Europe, the Caucasus Mountains, and the surrounding countries.

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The development of a crop production system that can be used on the International Space Station, long-duration transit missions, and lunar or Mars habitats, has been a part of NASA's Advanced Life Support (ALS) research efforts. Crops that can be grown under environmental conditions that might be encountered in the open cabin of a space vehicle would be an advantageous choice. The production efficiency of the system would be enhanced by growing these crops in a mixed-crop arrangement. This would also increase the variety of fresh foods available for the crew's dietary supplementation. Three candidate ALS salad crops, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber with baseline environments maintained at 22 °C, 50% RH, 17.2 mol·m-2·d-1 light intensity and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Tests were carried out at three different CO2 concentrations: 400, 1200, and 4000 μmol·mol-1. Weekly time-course harvests were taken over 28 days of growth, and fresh mass, dry mass, and harvest index were determined. Results showed that none of the species experienced negative effects when grown together under mixed-crop conditions compared to monoculture growth conditions under the range of environmental conditions tested.

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