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Seed Source Affects Flowering and Growth of Container-Grown Black-Eyed Susan (Rudbeckia hirta L.)
Abstract
Rudbeckia hirta, black-eyed susan, is a popular container-produced native wildflower. However, there is a growing demand for regionally adapted selections because of ecological and sustainability issues. In separate studies in 2001 and 2002, seed from three sources — north Florida (NFL), central Florida (CFL), and Texas (TEX)—were sown in the greenhouse in mid-January. Seedlings were transplanted to cell packs in early February. In early April, liners were potted in 2.5 liter (0.66 gal) containers and placed on an outdoor production bed under full sun. Full bloom occurred about 21.5 to 23 weeks after sowing. TEX achieved full bloom 10 days earlier than NFL or CFL. Except for CFL in 2001, most plants were of a commercially acceptable height. The most uniform growth or flowering trait based on coefficients of variation was date of full bloom, with date of first bloom just slightly more variable. Other growth and flowering traits were moderately to highly variable.
Growth, flowering, and survival of black-eyed susan (Rudbeckia hirta L.) from three seed sources - Northern Florida (NFL), central Florida (CFL), and Texas (TEX) - Were evaluated under low input conditions for one growing season at four sites in Florida. Two sites were in American Horticultural Society (AHS) Heat Zone 9 while the other two were in AHS Heat Zones 10 and 11. Growth, onset date of flowering, and number of flowers at peak flowering varied by site. With few exceptions, plants tended to reach peak flowering at about the same time. Flower diameter varied by seed source with TEX>NFL>CFL. While TEX plants were perceived as the showiest, NFL and CFL plants persisted longer under the low input conditions in Florida, and hence provided some evidence of adaptation to regional site conditions.
Fifty-two populations of fifty species of wildflowers characteristic of either field or deciduous forest were analyzed to determine pattens of biomass allocation to component organs. These populations' allocation patterns were used to determine generalized allocation patterns of the herb component of earlier (field) and later (deciduous forest) secondary successional communities. The following patterns were determined: (1) The proportion of dry matter allocated to seed reproductive organs was greater in field populations than in woods populations; (2) The herbs of woodland habitats allocated a greater proportion of their resources to leaves and belowground organs than field habitat herbs; (3) The field annuals allocated a greater proportion of their resources to reproduction than field perennials; (4) Introduced species showed a higher reproductive allocation than native species of fields; (5) Regression analysis showed strong correlations of component organ biomass to total biomass and belowground biomass to shoot biomass.
Phenotypic plasticity is an important means by which individual plants respond to environmental heterogeneity. Relative plasticities were compared for three species of annual Phlox grown in a set of six environmental treatments. Two measures of plasticity were computed for 18 characters per species: the Coefficient of Variation to measure amounts of plasticity and a new measure, the correlation of responses between species, which compares patterns of plasticity. Three hypotheses concerning the species’ amounts and patterns of plasticity were examined. The heterozygosity hypothesis states that levels of heterozygosity and amounts of plasticity should be inversely related. The relatedness hypothesis states that more distantly related species should have less similar patterns and amounts of plasticity. The ecological hypothesis states that species from similar habitats should have more similar amounts and patterns of plasticity than species which evolved under differing conditions. The results suggest that heterozygosity, relatedness, and ecology may all affect patterns and amounts of plasticity, and that no single hypothesis is sufficient to explain the observed results. Some data from previous studies are examined in relation to the proposed hypotheses.
Survival of black-eyed susan (Rudbeckia hirta) from three regional seed sources was evaluated after inoculation with the pathogenic fungus Fusarium oxysporum in the greenhouse, and after they were planted in fumigated or nonfumigated and irrigated or nonirrigated field plots. The three seed sources were northern Florida (NFL), central Florida (CFL), or Texas (TEX). Plants from the three seed sources were inoculated individually under greenhouse conditions with four isolates of F. oxysporum originally isolated from the roots of diseased black-eyed susan grown in ecotype trials near Monticello, Fla. About 20% of the inoculated plants developed symptoms similar to those observed in the field, but no consistent ecotype or isolate effects were observed. In the field trial, planting beds were fumigated with methyl-bromide and chloropicrin and irrigated with drip irrigation (high input), not fumigated and irrigated, fumigated and not irrigated, or not fumigated and not irrigated (low input). During the first month of the trial, treatment and seed source had a significant effect on survival due to the low initial survival of NFL in the nonfumigated-nonirrigated plots. After the first month, only seed source had a significant effect on survival, with TEX decreasing rapidly and the NFL population decreasing to a lesser degree. The decline of TEX could not be directly attributed to pests or climatic effects.
Progenies from nine populations of six species of Clarkia, including the new species C. calientensis, were compared using a similarity index based on the sum of significant differences for 22 morphological and developmental traits. The two most similar populations were conspecific. Other populations of different species were more similar to each other than to respective conspecific populations. Characteristics associated with pollination tend to have low plasticity and high interpopulation differences, suggesting rigorous selection for precisely integrated systems. Extremely plastic traits, such as the time to first flower and the number of seeds per capsule, result from a series of morphogenetic events, each of which in itself, may be highly plastic. Despite continuous adjustment, these highly plastic traits are efficient and consistent in differentiating between populations. A group of populations in woodland habitats and another in grassland habitats both show intragroup similarity in a number of characteristics, which indicate common adaptations, and some differences, which probably reflect a mode of isolation. Sympatric populations often have similar vegetative and developmental characteristics but different breeding-system characteristics; usually some characteristics of each system differentiate sympatric or adjacent populations. The greatest similarities occur in sympatric or environmentally equivalent situations, emphasizing the importance of environmental selection.
Genetic variability and mating system were investigated quantitatively in Collinsia heterophylla from three different localities in central California. Seed parents were chosen from two sites within each locality, and the progenies of these plants were grown in a replicated field planting at Davis, California. Individual plants were scored for two monogenic color characters and measured for eight quantitative characters related to plant size and rate of development. Estimates of percentage of outcrossing based on the monogenic characters and occurrence of moderate inbreeding depression for the quantitative characters indicate that the species is predominantly outcrossing. Three sources of genetic variability for the quantitative characters could be distinguished and measured: differences between localities, differences between sites within localities, and plant-to-plant differences within sites. The means of localities were found to differ for all characters measured. The most striking differences were those involving mature plant size. For seven of the quantitative characters, statistically significant differences were found between the means of progenies within sites. Estimates of the genetic variability within sites were made from the between progenies components of variance. The results confirm previous observations that substantial quantitative genetic variability exists in outbred plant populations. Distinct genetic differentiation between sites occurred in one of the localities. Ecological differences and genetic isolation between the sites suggested that this locality had the most favorable structure for such differentiation. For most characters the magnitude of the difference between the two sites of this locality was significant in comparison with both the differences between the means of the three localities and the magnitude of the genetic variation within sites. It thus appears that genetic differentiation over very short distances can contribute appreciably to both the genetic variability within one locality and the genetic variation observed over large geographical areas.
Plantings of six native wildflower species—Cassia fasciculata Michx. (partridge-pea), Coreopsis ianceoiata L. (lanceleaf coreopsis), Gaillardia pulchella Foug. (blanketflow er), Ipomopsis rubra(L.) Wherry (standing cypress), Rudbeck ia hirta L. (black-eyed susan), and Salvia lyrata L. (lyreleaf sage) —were established during winter 1997 at five sites in Jef ferson County, Florida. Seeds of each species were derived from native populations (local ecotype) and purchased from commercial sources outside of Florida (nonlocal ecotype). Plantings were irrigated as needed up until early April to en sure germination but received no supplemental fertilizer. No pesticides were applied except to control weeds on the perim eter of the plantings and fireants; plots were handweeded as necessary. Plants were evaluated once per month from June to October 1997. It was clearly evident from these evaluations that the local ecotypes generally were better adapted to north Florida conditions than were the nonlocal ecotypes. The most noteworthy differences were as follows: 1) local ecotypes of black-eyed susan and blanketflower had longer flowering peri ods than their nonlocal counterparts; 2) the local ecotype of lanceleaf coreopsis flowered profusely while flowering of the nonlocal ecotype was sparse; 3) the local ecotypes of lanceleaf coreopsis and lyreleaf sage had less disease incidence than nonlocal ecotypes; 4) flower color and blooming date of stand ing cypress ecotypes varied substantially.
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