Search Results
You are looking at 1 - 10 of 43 items for
- Author or Editor: Peter D. Ascher x
Abstract
Genotypes and pollination dates, but not cuttings, contributed significantly to variance in percent pseudo-self-compatibility (PSC) from self pollinations of F2 sibling Nemesia strumosa Benth. plants. Genotypes selected from different families which were self- and cross-pollinated on several dates in 4 locations having varying environmental conditions responded differently to environments. Correlations between seed set and daily temperatures were significant in only a few cases. Tests of the effect of plant age on seed set revealed that plants generally set fewer seeds following either self- or compatible-pollinations when old, but the ratio of self- to compatible-cross seed sets (percent PSC) varied with genotype.
Greenhouse and garden chrysanthemums are quantitative short-day (SD) plants for flower bud initiation (FBI) and qualitative (obligate) SD plants for flower bud development (FBD). Continuous or intermittent application of red light in the middle of the dark period (night), inhibits FBI. The chrysanthemum breeding program has been selecting for day-neutral (DN) types, i.e. that will undergo FBI and FBD under any photoperiod. The inheritance of DN was studied using six cultivars (n = 2 SD types, n = 4 DN types) that were crossed in a complete diallel over two crossing periods. Pollinations were replicated and ovules were counted. Histograms of self and cross seed set showed a distribution from 0% to 100%, with the majority of pollinations below 30%. Mean self seed set (2.6%) was less than the mean cross seed set (32.8%), indicating the presence of a self incompatibility system. Parents and F1 progeny were grown under LD conditions (red light, night interruption, 2200-0200 HR) and high temperatures (30 °C day/25 °C night, to screen for heat delay insensitivity). F2 progeny could not be generated due to self incompatibility. The fraction of flowering: non-flowering progeny and the number of days to first flower was recorded on the flowering individuals for comparison with the parents. Due to small progeny numbers, reciprocal crosses were bulked prior to Chi-square tests (1:1, 3:1, 1:3). The number of days to first flower ranged from 27 to 93+ in all progeny with significantly earlier and later outliers present. Most Chi-square tests were not significant, indicating that the inheritance of DN and heat delay insensitivity are not controlled by a single gene. Additive and epistatic effects may also be present.
Abstract
Dehiscence of a mature orchid fruit releases a multitude of seeds — more than a million per capsule in some species. Air currents carry the seeds, but few land on a site permitting germination; even fewer chance upon an environment suitable for development of a mature plant. The seed is microscopic and consists of the bare essentials: a seed coat modified for buoyancy, an embryo of from 8 to 100 cells, and, rarely, a small amount of undeveloped endosperm (2). All orchids require an external source of organic molecules for seed germination or seedling development. After germination, many exist for long periods, the entire life cycle in the case of true saprophytes, deriving carbohydrates and other organic molecules from exogenous sources. Various fungi, in mycorrhizal association with the orchid, provide these complex molecules.
It should be possible to maintain horticultural clones unchanged forever through asexual generations, as commercial propagators and clonal repositories maintain clonal integrity, disease-free stock plants, or remove mutations. However, unintentional selection for nonhorticultural traits could still be occurring. Accumulations of such traits would be due to the operation of Muller's ratchet and include fertility losses, increases in virus titer, and stunted growth habit. In chrysanthemums, Dendranthema grandiflora. clones separated from sexual cycles for generations become increasingly sterile. Seed set across years, using coefficients of crossability (FCC/MCC), was examined for garden clones (forced through sexual cycles annually) and greenhouse clones (asexual cycles only). Garden clones 40 years old (54-101-11) had only depressed levels of fertility. In other cases (77-AM 3-17), the ratchet was reversed >1 sexual cycle. Greenhouse clones were often completely sterile since their propagation is primarily asexual.
Commercial chrysanthemums are short day (SD) plants. Recently, several day neutral (DN) garden genotypes have been identified. Both glasshouse and garden cultivars vary in heat delay insensitivity (HDI). This research analyzed yield components (seed set, germination, yield potential) and tested a DN/HDI ideotype for its effectiveness. Progeny from a 6 × 6 diallel were embryo rescued, clonal ramats were grown in two environments (glasshouse—long days; field—long to short days) and evaluated for flowering, early flowering response groups, thermozero temperature response, low long day leaf number (LDLN), high leaf initiation rates, and low mean stem lengths of the terminal shoot. Self seed set ranged from 0% to 8% while outcross seed set was 0% to 92%. General and specific combining ability were highly significant for seed set, the reciprocals, and their interactions. Germination averaged 67%, while yield potential was 44%. Cotyledon pigmentation in embryo rescued seedlings was 7% albinos, 15% anthocyanin (transposable elements), and 78% normal (green). SD parents did not flower in either photoperiod although PPSL-10 carried alleles for DN. SD x DN crosses produced some DN progeny and fit a 1:3 chi square ratio (DN:SD), indicating DN to be recessive. However, DN x DN crosses also fit a 3:1 chi square ratio, due to HDI. No progeny flowered within the 3 to 6 week ideotype; visible bud date had a heritability of h 2 = 0.50. Most progeny were within the LDLN range (h 2 = 0.72). Several leaf initiation rates exceeded the ideotype (h 2 = 0.003); plant height also matched the ideotype (h 2 = 0.66). Both visible bud and flowering dates require significant improvement before progeny match the DN/HDI ideotype.
Commercial garden and greenhouse chrysanthemums [Dendranthema ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum xmorifolium Ramat.)] are facultative short-day plants for flower bud initiation, obligate short-day plants for flower bud development, and are categorized into short-day response groups. Flower initiation can be delayed by high night temperatures. Recent research has identified true day-neutral genotypes. The purpose of this investigation was to test environments for selecting genotypes that are both day-neutral and heat-delay insensitive. One greenhouse and 18 garden genotypes were selected. A series of environments were used to select for day-neutral genotypes and then differentiate between these genotypes for heat delay insensitivity: short days, long days/red light, long days/far red light and high temperatures, and natural day lengths under field conditions. Day-neutral selections from these environments were then grown in a fifth environment of long days/continuous far red and red light with high temperature. Data were collected on the number of days to first and third flower, long day leaf number, stem length, number of strap-shaped leaves subtending the terminal flower, internode lengths, number of nodes with axillary branching, and flower bud development of the first to the sixth flowers. Genotypes required 3 to 8 weeks for complete flower bud initiation/development. Flowering responses in the first four environments were highly significant for both the first and third flowers. Genotypes ranged from obligate short-day to day-neutral for the first six flowers. Three day-neutral genotypes were selected that differed significantly for all traits in the fifth environment; flower bud development with the first six flowers occurred with only one genotype, 83-267-3. Broad sense heritability estimates ranged from h2 = 0.75 for number of nodes with axillary branching, h2 = 0.79 for long day leaf number and number of strap-shaped leaves, to h2 = 0.91 for stem length. An ideotype for day-neutral and heat-delay-insensitive garden chrysanthemums was developed for use in breeding programs.
Male and female fertility, seed germination, and progeny fertility were used to determine cultivar fertility in species of Lythrum. One short-, 11 mid-, and six long-styled cultivars were included in this study. Duplicates of several cultivars from different nurseries and three unknown cultivars from Minnesota gardens were also collected. Plants from 17 Minnesota and one Wisconsin population of L. salicaria served as fertile male and/or female testers. Pollen stainability (usually 100%) showed low levels of male gamete abortion. Pollen size within and among anther type varied widely; possible 2n gametes were present in primarily the short- and mid-anther morphs. Seed production per capsule from legitimate cross-pollinations, using cultivars as male parents with Minnesota or Wisconsin female testers, averaged 48 ± 36 across style morphs. Cultivars differed as males, as did anther morphs. With female fertility tests, seed set per capsule ranged from zero to 152 and averaged 54 ± 40 in legitimate pollinations (i.e., pollinations between stamen and styles of the same length). Seed set for other crosses showed similar trends. Only `Morden Gleam' produced no seed with all legitimate pollinations, although illegitimate selfs or interspecific crosses produced seed. Seed from legitimate crosses of L. salicaria × cultivars had 30% to 100% germination. Common male and female parents within each legitimate crossing group were not significantly different. This study showed that the cultivars are highly fertile when used as male or female parents with wild purple loosestrife, native species (L. alatum Pursh.), or other cultivars. Thus, cultivars grown in gardens could serve as pollen or seed sources for the continued spread of purple loosestrife. The implications of cultivar fertility, especially interspecific F1 hybrids, is discussed in relation to the spread of noxious weeds in wetlands.
Chrysanthemum [Dendranthema ×grandiflora Tzvelv. (syn. Chrysanthemum ×morifolium Ramat.)] breeding programs have been selecting for reduced expression of self-incompatibility (via pseudo-self-compatibility) to create inbred families with selected genotypes to serve as parents for F1 hybrid chrysanthemum seed production. However, it is not known to what extent inbreeding is affecting fertility in this outcrossing, heterozygous species. The objective of this research was to assess male/female fertility changes (gain/loss) in successive inbred generations of chrysanthemums. Pseudo-self-compatible chrysanthemum parents (n = 41 inbred, noninbred, and recombinant inbred) were chosen for fertility analyses. As many as three generations of inbreds (I1, I2, and I3) from self-pollinations were created using rapid generation cycling. Female and male fertility levels of the parents and all derived inbred populations were assessed using outcross seed set and pollen stainability, respectively. Average seed set ranges were 0.3% to 96.1% (inbred parents), 24.5% to 38.5% (noninbred parents), and 0.9% to 85.1% (recombinant inbred parents); these began decreasing in the I1 and continued to decline steadily into the I3. Statistically significant (P < 0.05) decreases in seed set occurred in n = 23 (56.1%) inbred families; the remaining inbred families had similar or higher fertility than the parents. Pollen stainability was >50% for the parents, but began declining in some inbred families as inbreeding progressed. Fertility reductions were attributed to inbreeding depression. Lack of significant fertility losses in other inbred families demonstrates the opportunity of selection of fertile inbred parents for use in hybrid seed production.
Advanced, two-species CBC individuals were used to create the first-ever, three-species hybrids between P. acutifolius, P. coccineus and P. vulgaris. M6 (2 species) × H15 (3 species) is the only three-species hybrid to date that segregates for diagnostic traits. Three generations of M6 (F2, F3, F4,) were used to create the series. Hybrid breakdown was most severe with M6 F2 × H15, producing 100% cripples that died before anthesis. In M6 F3 × H15 hybrids, segregation for stigma position, flower color, germination type, growth habit, leaf length/width ratios, and seed morphology commenced in the F1 hybrid generation. F, phenotypes, with P. coccineus flowers & seeds and P. acutifolius leaves & growth habit, had severe hybrid breakdown with weak self compatibility; purple seed coats, with or without black circundatus markings, and new flower colors were also produced. F1's with P. vulgaris growth habits were self-fertile and ceased segregating after the F2.
The methods of Wall and York (1957) were used to measure cotyledon position in two populations of three species interspecific Phaseolus hybrids and in the single species cultivars and accessions of P. coccineus, P. acutifolius, and P. vulgaris used as parents. Cotyledon position was represented by the length of the epicotyl as a percentage of the total length of the seedling's stem from the first root initial to the base of the primary node. Progeny of interspecific crosses between P. coccineus and P. vulgaris have been shown to inherit the cotyledon position of the cytoplasmic parent. The objectives of this study were to determine if three species hybrids also inherited the cotyledon position of the cytoplasmic parent, and to determine if P. acutifolius could be distinguished from P. vulgaris by its cotyledon position. Results indicated that the cotyledon positions of the three species hybrids did not differ significantly from the cotyledon positions of cultivars of the species used as the cytoplasmic parent for both P. vulguris cytoplasm and P. coccineus cytoplasm. Further, the cotyledon position of the P. acutifolius accessions did differ significantly from the cotyledon positions of both the P. vulgaris cultivars and the three species hybrid with P. vulgaris cytoplasm. These results suggest that cotyledon position may indeed be a species-specific trait for Phaseolus in Lamprecht's sense of the term.