Dwarf Growth Habit Research Articles

Pyracantha × ‘Apache’

Abstract Pyracantha × ‘Apache’, the 5th U.S. National Arboretum introduction, combines disease resistance and compact dwarf growth habit. Pyracantha, commonly known as fire-thom, is a major nursery container-produced plant that is primarily grown for the spectacular fruit display. The four previously introduced cultivars are ‘Shawnee’, NA 28179 (1), ‘Mohave’, NA 32225 (2), ‘Navaho’, NA 38451, and ‘Teton’, NA 38450 (3).

Heritability of Fruit Quality Traits in Peach and Nectarine Breeding Stocks Dwarfed by the dw Gene

Abstract Means and heritabilities were estimated for the 2 fruit quality defects of dw/dw peach and nectarine [Prunus persica (L.) Batsch] genotypes that obstruct the commercial exploitation of the advantages inherent in their dwarf growth habit. The average dw/dw peach has substandard taste and too little blush for commercial acceptance. The average dw/dw nectarine also has substandard taste. In addition, it has substandard surface polish. The heritability of taste (as measured by percentage of soluble solids) in UCD's dwarf peach breeding stock was estimated to be 0.17 ± 0.04. The heritability of amount of surface blush was estimated to be 0.19 ± 0.04. The heritability of percentage of soluble solids in UCD's dwarf nectarine breeding stock was estimated to be 0.35 ± 0.04; of sweetness 0.19 ± 0.09; and of flavor 0.16 ± 0.06. The heritability of skin polish was estimated to be 0.24 ± 0.13. As expected, dw appears to have little or no effect on means or heritabilities of fruit weight, fruit firmness, or ripe date. The implications of these results are discussed.

Evaluation of potential genetic marker traits and estimation of outcrossing rate in Stylosanthes guianensis

The inheritance of flower, seed testa, and hypocotyl colour, and growth habit were studied in the F2 generation of biparental crosses between Stylosanthes guianensis accessions exhibiting contrasting phenotypes. Segregation ratios for flower colour in seven crosses and the pooled ratio supported a conclusion of single-gene inheritance, with yellow dominant to white. The data on seed colour (purple v. brown) gave inconsistent results in the two crosses evaluated. Neither red v. white hypocotyl colour nor normal v. dwarf growth habit appeared to be inherited monogenically, since a range of intermediate phenotypes was observed in the F2 populations examined. The open-pollinated progenies of 12 homozygous recessive (white-flowered) individuals within one F2 population contained yellow-flowered plants attributed to outcrossing. Overall outcrossing rate ( � s.e.) was estimated as 0.138�0.021. The proportion of yellow-flowered outcrosses in these 12 progenies was related to the number of yellow-flowered individuals adjacent to the F2 parent, indicating that pollen movement was limited within the F2 plot. Based on these findings a practical, recurrent population improvement scheme for S. guianensis is proposed.

‘Eskimo’ Viburnum11

Abstract ‘Eskimo’ establishes a landmark in the development of elite Viburnum cultivars as the first selection that combines the tubular V. carlesii-type flower in a snowball inflorescence, dwarf growth habit, and semi-evergreen foliage. This compact, slow-growing introduction is especially noteworthy since the majority of Viburnum species are too large and vigorous to be included in the modem home landscape. Not only does this cultivar fulfill the requirements of the home gardener, but also promotes commercial production and use by the nurserymen and landscape architects. ‘Eskimo’ is the 14th Viburnum cultivar introduced from the U.S. National Arboretum shrub breeding project (1, 2, 3, 4, 5).

Variability Observed in Centipedegrass Grown from 60Co Irradiated Seed1

AbstractCentipedegrass [Eremochloa ophiuroides (Munro) Hack.] has shown limited variability morphology and poor cold tolerance in the 64 years since its introduction into the United States. Variation in morphology and other parameters has been increased in other species by subjecting seed or vegetative parts to ionizing radiation. The purpose of this study was to observe and measure variation in morphology, cold tolerance, and growth habit of centipedegrass grown from irradiated seed. Centipedegrass selections grown from seed exposed to gamma radiation (0 to 80 kR) from a 80Co source were observed for variability in morphology, cold tolerance, and growth habit. No seedling emergence occurred at exposures greater than 40 kR. Irradiated plants had blade widths of 3.7 to 6.8 mm (controls 4.0 to 6.1 mm), blade length of 1.8 to 6.3 cm (controls 2.5 to 4.7 cm), and internode lengths of 0.6 to 4.1 cm (controls 2.0 to 4.1 un). Approximately 7% of the irradiated plants had a dwarfed growth habit, primarily due to shortened internode length. Environmental chamber tests indicated that several irradiated selections were equal or superior in cold tolerance to nonirradiated controls, and to ‘Oklawn’, ‘Tennessee Hardy’, ‘Mississippi 2’, and FC‐2. In field studies conducted on a Dothan sandy loam (Plinthic Paleudult), more than 40% of the irradiated plants had an establishment rate from sprigs equal to that of the controls; however, none was superior and 4% were inferior. Variability was also noted in turfgrass color and seedhead production among the irradiated selections. Seven percent produced no seedheads during the 2 years following establishment. Variability observed in these studies indicates the potential use of gamma radiation of seed to improve several turfgrass quality parameters in centipedegrass.

Mutation Induction in Melilotus Alba Annua by Chemical Mutagens1

Hydroxylamine (HA), 2‐aminopurine (AP), 5‐bromouracil (BU), and ethyl methanesulfonate (EMS) were tested for mutagenic activity on seeds of Melilotus alba annua. Mutants were classified into the following categories: o‐hydroxycinnamic acid (o‐HCA) content and β‐glucosidase activity, chlorophyll deficiency, dwarf growth habit, and miscellaneous morphological variations. Due to difficulties in classification, the o‐HCA and β‐glucosidase category and the dwarf category were unreliable for determining mutation rates. Based on the chlorophyll‐deficient and miscellaneous morphological categories, mutation rates for HA, AP, and BU treatments did not differ from the control rates, but EMS at 0.003M and 0.004M concentrations was highly effective in inducing mutations in these categories. Mutation rates based on chlorophyll deficiency were somewhat higher and more sensitive to EMS concentration than were mutation rates based on the miscellaneous category. Large numbers of chlorophyll, dwarf, and morphological variants, several more vigorous than the controls, were isolated from the EMS treatments, but no new o‐HCA or β‐glucosidase mutants were obtained.