Ruellia Humilis Research Articles

Drought reduces productivity and anti-herbivore defences, but not mycorrhizal associations, of perennial prairie forbs.

During drought, plants allocate resources to aboveground biomass production and belowground carbohydrate reserves, often at the expense of production of defence traits. Additionally, drought has been shown to alter floral resources, with potential implications for plant-pollinator interactions. Although soil symbionts, such as arbuscular mycorrhizal (AM) fungi, can alleviate drought stress in plants, certain levels of drought may negatively impact this relationship, with potential cascading effects. Because of their importance to plant and animal community diversity, we examined effects of drought on biomass production, physical defence properties, nectar production, and associated AM fungal abundance of five common prairie forb species in a greenhouse study. Reduced soil moisture decreased vegetative biomass production. Production of trichomes and latex decreased under drought, relative to well-watered conditions. Ruellia humilis flowers produced less nectar under drought, relative to well-watered conditions. Intra-radical AM fungal colonization was not significantly affected by drought, although extra-radical AM fungal biomass associated with S. azurea decreased following drought. Overall, grassland forb productivity, defence, and nectar production were negatively impacted by moderate drought, with possible negative implications for biotic interactions. Reduced flower and nectar production may lead to fewer pollinator visitors, which may contribute to seed limitation in forb species. Reduced physical defences increase the likelihood of herbivory, further decreasing the ability to store energy for essential functions, such as reproduction. Together, these results suggest drought can potentially impact biotic interactions between plants and herbivores, pollinators, and soil symbionts, and highlights the need for direct assessments of these relationships under climate change scenarios.

Relative Energetic Economy of Cleistogamous Selfing in Three Populations of the Perennial Ruellia humilis

Relative Energetic Economy of Cleistogamous Selfing in Three Populations of the Perennial <i>Ruellia humilis</i>

Can heterosis and inbreeding depression explain the maintenance of outcrossing in a cleistogamous perennial?

What maintains mixed mating is an evolutionary enigma. Cleistogamy-the production of both potentially outcrossing chasmogamous and obligately selfing cleistogamous flowers on the same individual plant-is an excellent system to study the costs of selfing. Inbreeding depression can prevent the evolution of greater selfing within populations, and heterosis in crosses between populations may further tip the balance in favor of outcrossing. Few empirical estimates of inbreeding depression and heterosis in the same system exist for cleistogamous species. We investigate the potential costs of selfing by quantifying inbreeding depression and heterosis in three populations of the cleistogamous perennial Ruellia humilis Nutt (Acanthaceae). We performed three types of hand-pollinations-self, outcross-within, and outcross-between populations-and measured seed number, germination, total flower production, and estimated cumulative fitness for the resulting progeny in a greenhouse experiment. We found moderate inbreeding depression for cumulative fitness (<30%) in two populations, but outbreeding depression for crosses within a third population (-26%). For between-population crosses, there was weak to modest heterosis (11-47%) in two of the population combinations, but modest to strong outbreeding depression (-21 to -71%) in the other four combinations. Neither inbreeding depression nor heterosis was of sufficient magnitude to explain the continued production of chasmogamous flowers given the relative energetic advantage of cleistogamous flowers previously estimated for these populations. Outbreeding depression either within or between populations makes the maintenance of chasmogamous flowers even harder to explain. More information is needed on the genetic basis of cleistogamy to resolve this conundrum.

The potential for floral evolution in response to competing selection pressures following the loss of hawkmoth pollination in Ruellia humilis.

In the absence of hawkmoth pollinators, chasmogamous (CH) flowers of Ruellia humilis self-pollinate by two secondary mechanisms. Other floral visitors might exert selection on CH floral traits to restore outcrossing, but at the same time preferential predation of CH seeds generates selection to increase the allocation of resources to cleistogamous (CL) flowers. To assess the potential for an evolutionary response to these competing selection pressures, we estimated additive genetic variances ( ) and covariances for 14 reproductive traits and three fitness components in a Missouri population lacking hawkmoth pollinators. We found significant for all 11 floral traits and two measures of resource allocation to CL flowers, indicating the potential for a short-term response to selection on most reproductive traits. Selection generated by seed predators is predicted to increase the percentage of CL flowers by 0.24% per generation, and mean stigma-anther separation is predicted to decrease as a correlated response, increasing the fraction of plants that engage in prior selfing. However, the initial response to this selection is opposed by strong directional dominance. The predicted evolutionary decrease in the number of CH flowers available for potential outcrossing, combined with the apparent preclusion of potential diurnal pollinators by the pollen-harvesting activities of sweat bees, suggest that 100% cleistogamy is the likely outcome of evolution in the absence of hawkmoths. However, rare mutations with large effects, such as delaying budbreak until after sunrise, could provide pathways for the restoration of outcrossing that are not reachable by gradual quantitative-genetic evolution.

The Impact of Fire on Nectar Quality and Quantity for Insect Pollinator Communities

Grassland insect pollinators have undergone population declines due to habitat loss and degradation. Patch-burning is a management method used to reduce woody plant encroachment and maintain grassland habitats. However, the impacts of fire on the quality and quantity of floral resources (nectar volume, total sugar, and sucrose concentration) available to insect pollinators are understudied. Evaluating how time since last fire and season of fire impact nectar quality and quantity is vital to understanding the overall impact of fire on insect pollinator communities. For this study, 10 flowering forb species (Asclepias viridis, Baptisia alba, Cirsium undulatum, Desmodium canadense, Monarda citriodora, Monarda fistulosa, Oenothera speciosa, Penstemon tubaeflorus, Ruellia humilis, Spiranthes cernua) were selected in The Nature Conservancy's Joseph H. William's Tallgrass Prairie Preserve in an area managed with patch-burning and cattle grazing. Study sites were burned in spring 2018, summer 2018, summer 2019, and spring 2020, with three replicates of each treatment (for 12 total burn units). In each unit, we collected nectar from flowering individuals of each plant species with microcapillary tubes to measure standing crop or the nectar in flowers at any given time that is available to insect pollinators. Total volume of nectar and sucrose concentration were recorded, and total mg of sugar was calculated. Desmodium canadense flowering individuals were only located in units burned the previous spring, whereas P. tubaeflorus flowering individuals were only located in units burned the previous summer. For the eight remaining species, total volume of nectar, total mg of sugar, and sucrose concentration varied with different burn regimens for different species. Cirsium undulatum inflorescences with crab spiders (Thomisidae) had higher volumes of nectar and higher amounts of sugar available. This study highlights how a patch-burn approach with different fire return intervals may benefit insect pollinators at the community level by providing a wide range of nectar qualities and quantities to support insect pollinators with different nutritional needs.

DOES CLEISTOGAMOUS SELF-FERTILIZATION PROVIDE REPRODUCTIVE ASSURANCE AGAINST SEED PREDATION IN RUELLIA HUMILIS?

Mixed mating is thought to be adaptive in many species of flowering plants because self-fertilization provides reproductive assurance when pollinator densities are low. In species with dimorphic flowers, automatic self-fertilization by small cleistogamous (CL) flowers might also provide reproductive assurance by avoiding floral herbivory. We tested this hypothesis by quantifying flower production, seed production, and seed predation across an entire reproductive season within a Missouri population of Ruellia humilis, a species with mixed mating enforced by dimorphic flowers. The production of CL flowers was delayed relative to the production of open-pollinated chasmogamous (CH) flowers, consistent with the hypothesis of reproductive assurance. The rate of seed predation by larvae of the Noctuid moth Tripudia rectangula was much higher for fruits produced by CH flowers (69%) than by CL flowers (18%). Thus, although CH flowers self-pollinate in the absence of outcross pollen, CL flowers are a much more economical source of selfed seeds, not only because they require fewer resources but also because they experience much lower levels of seed predation. Seed predation by Tripudia is common in many other cleistogamous species of Ruellia native to the southern United States and Mexico and might have played a significant role in the evolution of CL flowers in this large genus.

Anthropogenic and soil environmental drivers of arbuscular mycorrhizal community composition differ between grassland ecosystems

Interactions between arbuscular mycorrhizal fungi (AMF) and plants are sensitive to a myriad of underlying factors, including soil chemistry and land-use disturbances. Here we address how two grassland ecosystems (Ozark glades vs. tallgrass prairies) in south-central USA have been impacted by legacy effects from land-use disturbances (e.g., fire suppression in glades and tillage, fertilizer, row cropping, and grazing in prairies) and geological substrate (acidic versus calcareous bedrock). We surveyed AMF on the roots of two native generalist host species [Ruellia humilis Nutt. and Schizachyrium scoparium (Michx.) Nash] as well as plants randomly selected from the plant community. Glades on calcareous bedrock had a higher pH than those on acidic bedrock, and AMF communities on all three root sample types varied between acidic and calcareous bedrock locations. In prairies, both bedrock types had a similar soil pH, and AMF communities on all three root sample types varied across remnant and disturbed prairies. Shifts in AMF composition across land-use history included shifts in dominant AMF genera, and some unique rare AMF taxa were restricted to only calcareous glades or remnant prairies. Our findings suggest that reseeding prairie plant communities on cultivated lands does not restore AMF communities. Restoration projects need to address the soil environment and community.

Genetic and environmental integration of the hawkmoth pollination syndrome in Ruellia humilis (Acanthaceae).

The serial homology of floral structures has made it difficult to assess the relative contributions of selection and constraint to floral integration. The interpretation of floral integration may also be clouded by the tacit, but largely untested, assumption that genetic and environmental perturbations affect trait correlations in similar ways. In this study, estimates of both the genetic and environmental correlations between components of the hawkmoth pollination syndrome are presented for chasmogamous flowers of Ruellia humilis , including two levels of control for serial homology. A greenhouse population for quantitative genetic analysis was generated by a partial diallel cross between field-collected plants. An average of 634 chasmogamous flowers were measured for each of eight floral traits that contribute to the hawkmoth syndrome. Genetic correlations (across parents) and environmental correlations (across replicate flowers) were estimated by restricted maximum likelihood. Stigma height, anther height and floral tube length were very tightly integrated in their responses to both genetic and environmental perturbations. The inclusion of floral disc width as a control for serial homology suggests this integration is an adaptive response to correlational selection imposed by pollinators. In contrast, integration of non-homologous traits was low. Furthermore, when comparisons between the dimensions of serially homologous structures were excluded, the genetic and environmental correlation matrices showed little congruence. The results suggest that hawkmoths have imposed strong correlational selection on floral traits involved in the deposition and removal of pollen, and that this is a consequence of stabilizing selection on the relative positions of stigmas and anthers in the face of substantial flower size variation. Low integration of other floral traits, and conflicting patterns of genetic and environmental correlations among these traits, suggest weak or no correlational selection within the range of variability expressed within a population.

Determinants of taxonomic composition of plant viruses at the Nature Conservancy's Tallgrass Prairie Preserve, Oklahoma.

The role of biotic and abiotic factors in shaping the diversity and composition of communities of plant viruses remain understudied, particularly in natural settings. In this study, we test the effects of host identity, location, and sampling year on the taxonomic composition of plant viruses in six native plant species [Ambrosia psilostachya (Asteraceae), Vernonia baldwinii (Asteraceae), Asclepias viridis (Asclepiadaceae), Ruellia humilis (Acanthaceae), Panicum virgatum (Poaceae) and Sorghastrum nutans (Poaceae)] from the Nature Conservancy’s Tallgrass Prairie Preserve in northeastern Oklahoma. We sampled over 400 specimens of the target host plants from twenty sites (plots) in the Tallgrass Prairie Preserve over 4 years and tested them for the presence of plant viruses applying virus-like particle and double-stranded RNA enrichment methods. Many of the viral sequences identified could not be readily assigned to species, either due to their novelty or the shortness of the sequence. We thus grouped our putative viruses into operational viral taxonomic units for further analysis. Partial canonical correspondence analysis revealed that the taxonomic composition of plant viruses in the target species had a significant relationship with host species (P value: 0.001) but no clear relation with sampling site or year. Variation partitioning further showed that host identity explained about 2–5 per cent of the variation in plant virus composition. We could not interpret the significant relationship between virus composition and host plants with respect to host taxonomy or ecology. Only six operational viral taxonomic units had over 5 per cent incidence over a 4-year period, while the remainder exhibited sporadic infection of the target hosts. This study is the first of its kind to document the dynamics of the entire range of viruses in multiple plant species in a natural setting.

Vascular Flora of Buettner Xeric Limestone Prairies, Monroe County, Illinois

Xeric limestone prairies occur in southwestern and southern Illinois. These small grassland communities are present on thin soil and commonly have relatively extensive areas of exposed rock. Warm-season clump grasses, primarily Schizachyrium scoparium and Bouteloua curtipendula, are dominant along with a mixture of prairie and open-forest species. The vascular flora of two xeric limestone prairies, located near the bluff line of the Mississippi River on the property of Mr. and Mrs. Ralph Buettner in Monroe County, Illinois, were surveyed in 2011. A total of 174 vascular plant species were recorded from the two prairies, with 60 species present in survey plots. Bouteloua curtipendula dominated the East prairie followed by Schizachyrium scoparium, Andropogon gerardii, and Ruellia humilis. Andropogon gerardii dominated the West prairie followed by Bouteloua curtipendula, Solidago ulmifolia, Aster oblongifolius, Tridens flavus, and Schizachyrium scoparium. Vegetation covers 38.0% and 33.5% of the surface in these two prairies, while exposed rock was between 17% and 19%, and bare ground and litter was from 40% to 44%.

Effects of Temperature on Seed Viability of Six Ozark Glade Herb Species and Eastern Redcedar (Juniperus virginiana)

Although prescribed fires are commonly used in management, little is known about how temperatures generated during fires affect the seed viability of species of conservation concern. We measured seed viability of six herbaceous forbs native to Ozark glade ecosystems and the glade-invading shrub Juniperus virginiana (eastern redcedar) after exposure to four temperature treatments for 15 min: 24 C, 50 C, 100 C and 150 C. Viability of Allium canadense and Ruellia humilis was reduced to near zero after exposure to temperatures of 100 or 150 C, whereas viability of Echinacea simulata and J. virginiana was only significantly reduced at 150 C. Lespedeza virginica, Oenothera macrocarpa, and Silphium terebinthinaceum maintained substantial viability after exposure to 150 C, with the proportion of viable seeds ranging from 0.3–0.5. Our results suggest that interspecific differences in tolerance to heat-related mortality of seeds may be an important factor mediating post fire patterns of plant regeneration.

Monitoring Change in a Central U.S. Calcareous Glade: Resampling Transects Established in 1993

Vegetation monitoring transects established in calcareous glade habitats in 1993 at Chickamauga and Chattanooga National Military Park were resampled in 2006 and 2008. Data showed an increase in woody cover and a correlated decrease in density of herbaceous plants characteristic of this habitat. The average percent cover of woody species increased from 35.9% in 1993 to 64.3% in 2006/2008 for the 11 glades sampled. Nearly all woody species showed an increase in percent cover with Juniperus virginiana var. virginiana (Eastern red-cedar) increasing the most in percent cover (11% increase in cover, a 57% change). The non-native invasive shrub Ligustrum sinense (Chinese privet) ranked second in increase in cover (4.63%) and is now the third most abundant woody species in the glades. In addition, transects showed a decrease in the density of herbaceous plants characteristic of these calcareous glades ranging from 35% to 100%, including Pediomelum subacaule, Viola egglestonii, Dalea gattingeri, Ruellia humilis, Hypericum dolabriforme, Ratibida pinnata, Scutellaria leonardii, Silphium pinnatifidum, Packera paupercula, Leavenworthia exigua var. exigua, and Delphinium carolinianum ssp. calciphilum. The evidence from this study strongly suggests a decline in the natural integrity of these glade communities over a 15-year period and an increase in the natural rate of ecological succession with the invasion of a non-native species. Our management recommendations focus on two equally important actions: the targeted removal of Ligustrum sinense and the re-introduction of fire into the forest/woodland environment surrounding the glades.

A “Cyclops” of the Bee Lasioglossum (Dialictus) bruneri (Hymenoptera: Halictidae)

This note reports striking morphological aberrations of the compound eye, vertex and ocelli of a bee belonging to the genus Lasioglossum. Morphological aberrations of various kinds occur throughout the bees. Mitchell (1929), Michener (1943), Sivik (1962), Knerer and Atwood (1964), Wcislo et al. (2004), and Engel (2007) have reported sex anomalies, true gynandromorphs, antennal anomalies and metanotal anomalies. These reported aberrations primarily include changes in antennae, shape of the metasoma, genitalic structures, pollen collecting structures and the metanotum. Salt (1927) described the many external and internal changes in aculeate Hymenoptera caused by strepsipterous parasitism. Outside of Hymenopterans, Byers (1992) gave an account of distinct deformities of the head of a single individual of the scorpionfly Panorpa helena Byers, which had only a single normal compound eye and a single antenna both located on the right side of the head. However, no such dramatic aberrations of the head have previously been reported in bees. The ‘‘cyclops’’ bee described here, identified as a female of Lasioglossum (Dialictus) bruneri (Crawford), is therefore of some interest. I collected this unusual specimen on 13 July 2005 during a study conducted along roadsides in northeastern Kansas. The specimen was collected between the hours of 10:15 and 13:15 in a florescent yellow 16 oz. pan trap raised 70 cm above the ground, in the right-of-way along Highway 177 south of Cottonwood Falls in Chase County, Kansas. The most abundant forb in bloom in the area was Dalea purpurea Vent. (Fabaceae), with Ruellia humilis Nutt. (Acanthaceae), Dalea candida Michx. ex Willd. (Fabaceae), Amorpha canescens Pursh (Fabaceae) and Desmodium illinoense Gray (Fabaceae) present in smaller numbers. Land adjacent to the right-of-way was primarily rangeland grazed by cattle. Numerous Lasioglossum (Dialictus) spp. individuals were collected at this site prior to and after the collection of this specimen, although this individual was the only L. bruneri collected, and the only abnormal individual. The bee will be deposited in the Snow Entomological Collection, Division of Entomology, University of Kansas Natural History Museum, with the label J.L. Hopwood 2006 voucher. The bee has morphological aberrations of the head conspicuous enough to be seen without the aid of a microscope (Figs. 1–3). The size of the head is 75% of that of a typical specimen, with head width particularly reduced. Most readily noticeable is the fusion of the compound eyes at the vertex, which somewhat resembles the holoptic condition of honey bee drones and other insects such as syrphid flies, but instead results in a continuous, single compound eye (Fig. 1). This single compound eye extends completely over the vertex from either side of the head; thus a true vertex is lost and the ocelli are displaced. The remaining vertex is uniquely sculptured, with striations extending from the midline away from the occipital carina, along the gena (Fig. 2). The ocelli, normally located on the vertex, are situated on the frons just above the antennae. The sizes of the ocelli are highly reduced, as is the interocellar distance, and the ocelli are surrounded by an unusual and strong carina (Fig. 3). There are no other evident deformities of this individual. The mesosoma, wings, legs and metasoma are typical in appearance, with the exception of the presence of a female strepsipteran under the fourth tergum of the metasoma. While the morphological alterations of the head described above cannot definitively be attributed to stylopization, a noticeable decrease in head size has been described as an effect of stylopization (Salt, 1927). An extreme reduction in head size could account for the fusion of the compound eyes and the subsequent alteration of the vertex and ocelli. In any case, this individual has deformities 1 Current address: 33 Bessey Hall, Iowa State University, Ames, IA 50010, e-mail address:

A COMPARISON OF THE VEGETATION OF THREE LIMESTONE GLADES IN CALHOUN COUNTY, ILLINOIS

Three limestone glades in Calhoun County, Illinois were studied. These relatively rare herbaceous plant communities are dominated by grasses of the tallgrass prairie that grow where limestone is at or near the surface and the shallow soils do not support much woody vegetation. Occasionally associated with hill prairies on the bluffs of the Illinois and Mississippi Rivers, the thin soil and bare rock prevent the growth of many hill prairie species. Vascular plant species found included three ferns, one gymnosperm, 33 monocots, and 87 dicots for a total of 124 taxa. Thirteen alien taxa were encountered (10%). Juniperus virginiana (eastern red cedar) was common on and around the glade edges. The common grasses were Schizachyrium scoparium (little bluestem), and Bouteloua curtipendula (sideoats grama), while Andropogon gerardii (big bluestem) and Sorghastrum nutans (Indian grass) were occasionally found in crevices. Common forbs included Hedyotis nigricans (narrow-leaved bluets), Ruellia humilis (wild Petunia), and Croton capitatus (capitate croton).

Effects of grazing intensity on growth, reproduction, and abundance of three palatable forbs in Kansas tallgrass prairie

The effects of different intensities of cattle grazing on theaboveground growth, reproduction, and abundances of three palatable forbs werestudied in native tallgrass prairie. Populations of Asterericoides, Ruellia humilis, andAmorpha canescens were sampled at peak flowering duringthe1993–1995 growing seasons in four annually-burned sites varying incattle stocking density [ungrazed, low, moderate, high]. The threeforbs exhibited reduced shoot growth and/or reproduction under moderate toheavy grazing, and in no case did grazing increase any measure of plantperformance. Ruellia showed reduced shoot height andbiomass, percentage of stems flowering, and reproductive biomass in response tograzing. Aster showed decreases in shoot biomass andheightwith grazing. Amorpha showed no change in shoot orreproductive biomass, but a decrease in percent of flowering stems and inreproductive allocation with grazing. Patterns in the percentage of stemsgrazedindicated generally high but variable palatability among these species. Bycontrast, the three species showed inconsistent population response to grazing.Abundance (frequency) of all three species indicated no short-term changebetween years in response to grazing intensity. Responses of these speciesdiffer considerably from those of most other perennial tallgrass prairie forbsthat are unpalatable, unconsumed, and increase in performance (e.g. size,abundance) due to release from competition from the dominant grasses underungulate grazing. The results demonstrate that immediate aboveground growth andreproductive responses of established adults to grazing are not good predictorsof grazer effects on population abundances in tallgrass prairie.

Quantum yields for uptake of carbon dioxide in C3 vascular plants of contrasting habitats and taxonomic groupings

The maximum quantum yields (ϕa,c) for CO2 uptake in low-oxygen atmospheres were determined for 11 species of C3 vascular plants of diverse taxa, habitat and life form using an Ulbricht-sphere leaf chamber. Comparisons were also made between tissues of varied age within species. The species examined were Psilotum nudum (L.) P. Beauv., Davallia bullata Wall. ex Hook., Cycas revoluta Thunb., Araucaria heterophylla (Salisb.) Franco, Picea abies (L.) Karst., Nerium oleander L., Ruellia humilis Nutt., Pilea microphylla (L.) Karst., Beaucarnea stricta Lem., Oplismenus hirtellus (L.) P. Beauv. and Poa annua L. Quantum yields were calculated from the initial slopes of the response of CO2 uptake to the quantity of photons absorbed in conditions of diffuse lighting. Regression analysis of variance of the initial slopes of the response of CO2 uptake to photon absorption failed to show any statistically significant differences between age classes within species or between the mature photosynthetic organs of different species. The constancy of ϕa,c was apparent despite marked variation in the light-saturated rates of CO2 uptake within and between species. The mean ϕa,c was 0.093±0.003 for 11 species. By contrast, surface absorptance varied markedly between species from 0.90 to 0.60, producing proportional variation in the quantum yield calculated on an incidentlight basis. The ratio of variable to maximum fluorescence emission at 695 nm for the same tissues also failed to show any statistically significant variation between species, with a mean of 0.838±0.008. Mean values of ϕa,c reported here for C3 species, in the absence of photorespiration, are higher than reported in previous surveys of vascular plants, but consistent with recent estimates of the quantum yields of O2 evolution.

Growth of Ruellia humilis Plants from Embryos of Chilled, GA3-Treated, and Laboratory-Stored Seeds

Growth and development to maturity of plants of Ruellia humilis from excised embryos of GA3-treated, chilled, and laboratory-stored seeds were compared. Young plants from GA3-treated seeds had longer cotyledon petioles, longer and narrower blades of the first leaves, and longer first internodes than plants from chilled or laboratory-stored seeds, but these morphological differences did not persist beyond the first pair of leaves. Plants from GA3-treated seeds initially had the highest growth rate, based on dry weight and energy accumulation, but the average growth rate for the 109-day period from May 1 to September 19, 1972, when most of the growth occurred, was the same for plants in all three treatments. Flowering in plants from the three treatments commenced at approximately the same time. Throughout most of the growing period only minor differences in allocation of dry weight and energy to roots, stems, leaves, and reproductive parts occurred between the three treatments. However, during the latter part of the growth period plants from chilled seeds allocated relatively more dry weight and energy to roots and less to stems, leaves, and reproductive parts than did plants in the other two treatments. Either GA3 treatment or chilling is required to break dormancy in intact seeds of R. humilis, but otherwise neither is required for normal growth and development and completion of the life cycle.

Effect of chilling and gibberellic acid on growth potential of excised embryos of Ruellia humilis

Dormancy in intact seeds of Ruellia humilis is broken by chilling or by treatment with gibberellic acid (GA3). Embryos are nondormant and will grow when the seed coat is removed completely. Embryos from chilled or GA3-treated seeds have more growth potential than embryos from nontreated seeds. Dormancy is ascribed to the mechanical restriction of the embryo by the seed coat. Chilling and treatment with GA3 break dormancy by increasing the expansive force of the embryo; thus, chilled or GA3-treated embryos exert enough expansive force to break through the seed coat, whereas nontreated embryos do not.

Replacement of chilling requirement in seeds of Ruellia humilis by gibberellic acid

Gibberellic acid (GA3) completely replaced the chilling requirement of intact, dormant seeds of Ruellia humilis. At 30° 100 and 1000 mg/l completely replaced the chilling requirement, while in seeds germinated at 25° 100 mg/l GA3 was ineffective but 1000 mg/l entirely replaced the after-ripening requirement at low temperature.