Grass Flower Research Articles

Influence of season of fire on flowering of wet prairie grasses in south Florida, USA

We measured the effects of prescribed fire during January (dormant season) and May (growing season) on flowering of three perennial grasses, muhly (Muhlenbergia capillaris), gulfdune paspalum (Paspalum monostachyum), and south Florida bluestem (Schizachyrium rhizomatum), which are dominant grasses in wet prairies of south Florida, USA. Flowering was promoted by growing season fire but not by dormant season fire. Flowering was significantly greater for all species following prescribed fire conducted during May compared with areas burned during January of the same calendar year. The strong positive effect of growing season fire on flowering of all three species decreased after the first growing season. We rejected the hypothesis that season of fire did not influence flowering. Our results indicated that flowering by these dominant, wet prairie grasses is promoted by early growing season fire, which corresponds to historical patterns of lightning-ignited fire in south Florida.

A genomic approach to elucidating grass flower development

In sugarcane (Saccharum sp) as with other species of grass, at a certain moment of its life cycle the vegetative meristem is converted into an inflorescence meristem which has at least two distinct inflorescence branching steps before the spikelet meristem terminates in the production of a flower (floret). In model dicotyledonous species such successive conversions of meristem identities and the concentric arrangement of floral organs in specific whorls have both been shown to be genetically controlled. Using data from the Sugarcane Expressed Sequence Tag (EST) Project (SUCEST) database, we have identified all sugarcane proteins and genes putatively involved in reproductive meristem and flower development. Sequence comparisons of known flower-related genes have uncovered conserved evolutionary pathways of flower development and flower pattern formation between dicotyledons and monocotyledons, such as some grass species. We have paid special attention to the analysis of the MADS-box multigene family of transcription factors that together with the APETALA2 (AP2) family are the key elements of the transcriptional networks controlling plant reproductive development. Considerations on the evolutionary developmental genetics of grass flowers and their relation to the ABC homeotic gene activity model of flower development are also presented.

The Grasses: A Case Study in Macroevolution

▪ Abstract Macroevolution in the grasses has often involved change in the position (heterotopy) of developmental programs, possibly via ectopic gene expression. Heterotopy apparently has been involved in the evolution of unique epidermal morphology in the grasses and their sister genus, Joinvillea; in the origin of the grass flower and possibly in the spikelet as well; in the formation of unisexual flowers in the panicoid grasses, and in the repeated origin of C4 photosynthesis. Change in timing of development (heterochrony) may explain the novel morphology of the grass embryo. Changes in the structure and size of the nuclear genome correlate with phylogenetically informative cytogenetic characteristics. Most of the 10,000 species of grasses evolved tens of millions of years after the common ancestor of the family, indicating that the origin of novel morphologies did not lead to immediate radiation.

The blooming of grass flower development

The past half decade has provided a wealth of information concerning the molecular and genetic control of floral organ and meristem identity in dicotyledonous plants. Comparatively little is understood about these processes in grass species in spite of the importance that these species play in human agriculture. The isolation of grass genes that are homologous to dicot floral homeotic genes in combination with recent advances in reverse genetic technology and improvements in cereal transformation opens the door for understanding molecular mechanisms of grass flower development. Such information will also focus attention on the evolutionary relationships between grass and dicot flowers and the degree to which the developmental pathways leading to reproductive organ development in divergent angiosperms have utilized conserved mechanisms.

The Mechanics of the Grass Flower: Anther Dehiscence and Pollen Shedding in Maize

In this paper on the flower mechanics of the grasses, the opening mechanism of the maize anther is studied. Both the septum between each two locules and the stomium of these porate-dehiscing anthers appear to be opened due to lysis of the middle lamellae of their cells. Additional mechanical force of the expanding pollen might be necessary to completely dissociate the parenchyma cells of the septum. A number of hours before anthesis the anther is structurally able to dehisce. At anthesis the dehydrating endothecium cells bend the locule walls bordering the pore in outward direction. Presumably evaporation is not the only cause for this dehydration.

The Mechanics of the Grass Flower: The Extension of the Staminal Filaments and the Lodicules of Maize

The Mechanics of the Grass Flower: The Extension of the Staminal Filaments and the Lodicules of Maize

The Mechanics of the Grass Flower: The Extension of the Staminal Filaments and the Lodicules of Maize

In this paper on the flower mechanics of the grasses, the morphological and cytological processes leading to flower opening and anther exsertion are studied. At anthesis synchronous cell extension in both the lodicules and the filaments open the flower and exsert the anthers, respectively. In the lodicules all the cells extend, except the vascular tissues. In the filaments extension is limited to the epidermis and one or two subepidermal cell layers, whereas the more centrally located parenchyma and the vascular tissues are disrupted. Ultrastructural aspects of the rapid vacuolations, necessary for these extensions, are studied using comparisons between TEM and high-resolution SEM.

A national survey of airborne pollen and grass flowering in New Zealand, with implications for respiratory disorder

Airborne pollen and spore levels were monitored at seven sites in New Zealand using the Intermittent Cycling Rotorod sampler during the summer of 1988/1989. Grasses formed the major component of atmospheric pollen levels during spring and summer at every locality. Peak levels of grass and total pollen occurred during December or late November, with a slight latitudinal lag apparent at the more southern sites. Highest levels were recorded at the smaller rural centres of Gore and Kaikohe and the lowest at the larger urban centres of Auckland, Christchurch and Wellington. We make a first approximation of the likely risk to hayfever and allergic asthma patients at each of the seven centres. For example, significantly higher grass pollen levels were experienced at Kaikohe on 44% and 65% of days during November and December, compared with just 15% and 8% at Auckland. By recording the flowering seasons of the principal allergenic grass species at each locality, we determined the potentially allergenic grasses contributing to peak pollen levels, the most ubiquitous being tall fescue (Festuca arundinacea Schreb.), ryegrass (Lolium perenne L.,L. multiflorum Lam.), cocksfoot (Dactylis glomerata L.), Yorkshire fog (Holcus lanatus L.) and sweet vernal (Anthoxanthum odoratum L.).

Red and far-red light influence carbon partitioning, growth and flowering of bahia grass (Paspalum notatum)

SUMMARYBahia grass (Paspalum notatum Flugge) plants were grown in growth chambers at Gif, France, and at Gainesville in Florida, demonstrating that the species is a long-day plant and greatly influenced by light quality during the photosynthetic period. Flowering occurred in all instances when the middle of the dark period was interrupted with red or red + far-red light. With nightly interruptions of farred light, flowering occurred only when a sufficient quantity of far-red was present during the photosynthetic period. Plants grown under short days with nightly interruptions of red, far-red or red + far-red light had less starch accumulation and greater leaf growth and dry weight than plants grown without nightly light interruptions, whatever the light quality during the photosynthetic period. The treatments did not affect the partitioning of assimilates and flowering in the same way.

Control of flowering and reproduction in temperate grasses.

Temperate grasses of the subfamily Festucioideae can be grouped into two main categories according to their environmental control of flowering, species with regular long day (LD) induction, and those with dual induction requirements. The former group includes the temperate annual crosses and a few perennial species such as Phleum pratense and Poa nemoralis. These species base no winter requirement and require only LD to flower. Most temperature perennial grasses have a dual induction requirement for flowering, a primary induction which is brought about by low temperature (vernalization) and/or short days (SD), and a secondary induction which requires a transition to long days and is enhanced by moderately high temperatures. In most dual induction species SD and low temperature are interchangeable and independently able to fulfil the primary induction requirement. Yet, they are highly interactive in this process. Commonly the plants become day neutral at low temperature (0-6 °C) and primary induction takes place in both SD and LD. Primary induction is then identical with the common vernalization response. At higher temperatures induction becomes increasingly dependent on SD. until a critical temperature is reached, usually c. 12-18 °C, at which primary induction cannot take place regardless of the photoperiod. In a few species, e.g, Bromus inermts, Phalaris arundinacea and to some extent Dactylis glomeratca, the SD response predominates while low temperature induction is weak or absent. Critical temperatures and photoperiods for primary induction vary greatly among species and, within the species, among ecotypes of different geographical origin. Critical exposure time may vary from 3-4 wk in arctic-alpine Poa species to 20 wk in some Festuca species. Generally, ecotypes from high latitudes and especially arctic-alpine ones, have wider temperature and daylength limits and require fewer inductive cycles for primary induction than their low-latitude counterparts. In some grasses, especially- arctic-alpine species, initiation of inflorescence primordia takes place during SD primary induction, in others it requires a transition to LD. In the former group, primordia are initiated in the autumn, an important adaptation to arctic-alpine conditions. Critical photoperiods for secondary induction vary from 9-10 h in Mediterranean ecotypes to more than 16 h, and the critical number of LD cycles from four to eight, whereas 12-16 LD cycles are needed for the full saturated response. Generally, high-latitude ecotypes have longer critical photoperiods and require more LD cycles for secondary induction than do those from lower latitudes. Culm elongation, heading and inflorescence development are all promoted by LD. The more inductive cycles given and the more favourable their daylength, the greater is the response. Grasses also have efficient vegetative means of reproduction which are also environmentally controlled. Vegetative proliferation of inflorescences or 'vivipary' is readily induced in habitually seminiferous grasses of both LD and dual induction types, by marginal LD induction of flowering. On the other hand, a high proportion of normal flowering can be obtained in habitually viviparous species and ecotypes by optimal primary and secondary Moral induction. Thus, sexuality is by no means entirely suppressed in viviparous species but is under environmental control. In the high-latitude environment the primary induction requirements are met: by the decreasing daylength and temperature of autumn and winter, while the increasing daylength and temperature of spring and early summer fulfil the secondary induction requirements. Thus, the dual Horal induction control system of the temperate perennial grasses provides an efficient and important mechanism for fitting their life cycles to the dramatic seasonal changes of the high-latitude environment in which they live.

Plant demographic responses to mycorrhizal symbiosis in tallgrass prairie

The effects of mycorrhizal symbiosis on seedling emergence, flowering and densities of several grasses and forbs were assessed in native tallgrass prairie and in sown garden populations at the Konza Prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed with the fungicide benomyl. Flowering and stem densities of the cool-season grass, Dichanthelium oligosanthes, sedges (Carex spp.), and the forb Aster ericoides were higher in non-mycorrhizal (benomyl-treated) than in mycorrhizal plots and the magnitude of these differences was significantly affected by burning. Mycorrhizae significantly enhanced flowering of the warmseason grasses Andropogon gerardii and Sorghastrum nutans in burned prairie, but not in unburned sites. These patterns suggest that mycorrhizal effects on the dynamics of cool-season graminoid and forb populations are likely to be mediated indirectly through effects of the symbiosis on the competitive dominance of their neighbors. Seedling emergence rates of the cool-season C3 grasses Elymus canadensis and Koeleria cristata were significantly reduced in the benomyl-treated plots, whereas benomyl treatment had no significant effect on seedling emergence of the warm-season C4 grasses A. gerardii and Panicum virgatum. The forbs showed variable responses. Seedling emergence of Liatris aspera was greater under mycorrhizal conditions, but that of Dalea purpurea was unaffected by mycorrhizal treatment. These results show that effects of mycorrhizal symbiosis on the population dynamics of co-occurring prairie plants vary significantly both among species and among different life history stages within species. The results also indicate that mycorrhizas and fire interact to influence competitive interactions and demographic patterns of tallgrass prairie plant populations.

Mineral nutritional status and botanical composition of pastures. II. Effects on nitrogen concentration and digestibility of herbage

To study the effects of herbage nutritional status and botanical composition on herbage nitrogen content and digestibility, we carried out an experiment in which : (i) four plots had similar herbage nutritional status (N and P), but different botanical compositions, (ii) three pairs of plots each with similar botanical composition but different herbage nutritional status. Nitrogen content and digestibility patterns were studied from the start of vegetative growth to the time of flowering of the main grasses. To explain variation in nitrogen content and in vitro organic matter digestibility (IVOMD), we studied the leaf-stem ratio and the percentage of senescent material in the herbage.At the start of vegetative growth, the IVOMD was stable but it was lower for P deficient plots in relation to botanical composition (plots dominated by Festuca rubra). However, the temporal decrease of IVOMD was less rapid in these plots because they had a higher leaf-stem ratio and a lower percentage of senescent material. Thus, at the flowering stage of grasses, the IVOMD was the highest for P deficient plots.At the beginning of spring, the nitrogen content of the plot with non-limiting P herbage nutritional status was the highest, but it became the lowest after the heading stage of the main grasses. Differences between plots were related to P herbage nutritional status rather than to botanical composition : before stem elongation of the grasses, deficiency of P reduced N absorption, subsequently the rate of decrease in nitrogen concentration of the herbage was educed.

Gloeotinia granigena . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Gloeotinia granigena . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Chief host: Lolium perenne , but also infects other pasture grasses including Lolium multiflorum, Lolium temulentum, Bromus spp., Elytrigia spp., Festuca spp., Secale cereale . DISEASE: Blind seed disease of ryegrass and other grasses. Once the grass flower is infected the endosperm is permeated by the fungal mycelium and the embryo is frequently killed, resulting in failure to germinate. GEOGRAPHICAL DISTRIBUTION: Australasia: Australia (NSW, SA, Tas., Vic.), New Zealand; Europe: Denmark, Eire, England, France, Germany, The Netherlands, Northern Ireland, Norway, Scotland, Sweden, USSR, Wales, North America: Canada (Quebec), USA (OR) (see CMI Distribution Maps of Plant Diseases , No. 315). TRANSMISSION: Fungus overwinters in fallen infected seed; apothecia produced in spring coincidentally with flowering of host plant; ascospores forcibly discharged and carried by air currents to open flowers. Macroconidia may also infect additional flowers.

The Grass Flower: Suggestions on its Origin and Evolution

Summary Analysing a large number of different grass flowers, a hypothesis is proposed to explain the floral variation found in the family. It is postulated that the interaction of the palea with the floral apex generates an area of inhibition wich substantially affects the floral apex. Depending on the mode of action in the reduction process, together with an independent phenomenon which affects the gynoecial organization, four major evolutionary patterns are recognized. The form of grass flower which has been most successful appears to be the bi-lodiculate, tri-staminate and bi-stigmatic, with the stamens belonging to two different cycles – the frontal from the outer whorl and the two lateral from the inner whorl.

Grass flowers in the diet of Megaloceraea recticornis (Heteroptera: Miridae): plant structural defences and interspecific competition reviewed

ABSTRACT. 1. Megaloceraea recticornis (Geoffroy) is the most common of seven species of stenodemine bugs on a calcareous grassland in Oxfordshire. Previous work indicated that it competed with a related species, Notostira elongata Geoffroy, by behavioural interference at the feeding site. Both bugs were thought to eat only grass leaves.2. The importance of grass flowers in the diet of M.recticornis was studied in the laboratory. This bug completes its development only by feeding on grass flowers; grass leaves do not suffice.3. M.recticornis is unusual among phytophagous insects in that its later instars can eat flowers of the grass Brachypodium pinnatum L. The hard lemma and palea surrounding these flowers inhibit feeding by young bugs. The age of the flowers also affect bug feeding success.4. The result of field experiments, which previously appeared to show competition between M.recticornis and N.elongata, are discussed in the light of the present findings. It now seems that M.recticornis may not suffer from competition with N.elongata.

Cleistogamy in Grasses

Grasses display an extraordinary diversity of breeding systems-inbreeding and most forms of monoecism, dioecism, and apomixis are well represented (49, 50). Self-fertility and inbreeding are important in limiting the gene flow between populations and producing ecogenetic differentiation (2, 4, 27, 97, 159); preserving gene combinations that confer high fitness in a local environment (2, 72, 90); permitting fruit to be set after long-distance dispersal or when conditions for pollination are adverse (11, 90, 145, 162); and reducing or eliminating the costs of sex, while maintaining an adaptive advantage over asexuality (140). Cleistogamy (CL)-i.e. self-fertilization in an enclosed flower-intensifies these potential advantages of inbreeding; it may also be important in altering seed size, germinability, dispersibility, and susceptibility to fire and animal predation (27, 57, 133, 164). CL is an evolutionarily derived and complex syndrome of morphological, developmental, genetic, and environmental components. The variability in the expression of CL in grasses may be considered from the perspective of any one component or a combination of them. The structures adapted for the protection of aerially exposed, chasmogamous (CH) spikelets, florets, and fruits and for fruit dispersal are often either reduced in size and/or number or lost altogether. CL grass flowers often mature precociously, although the developmental or physiological basis for this heterochrony is generally unknown. Mendelian inheritance of structural differences that lead to CL flowering has been demonstrated in two cases (10, 129), and Clay (39) has shown that variations in the flowering mode in Danthonia are at least partly genotypic. At the same time, environmental variables such as the photoperiod (76, 77, 93), level of soil

A survey of grass weeds in cereals in central southern England

SummaryA survey of grass weeds in cereals in nine areas of central southern England was made in summer 1981 with the primary purpose of determining the importance of Bromus sterilis. A total of 1477 fields of winter wheat, 715 of winter barley and 434 of spring barley were assessed by visually scoring the whole field for grass flower heads. In all, 19 species were found; their levels of infestation were scored. In winter cereals the most frequent species were Avena spp. in 32% of fields. Agropyron repens in 24%, Poa trivialis in 22% and Alopecurus myosuroides in 19%. Bromas sterilis was next most frequent in 9%. In spring barley the two most frequent species were Agropyron repens in 53% of the fields and Avena spp. in 52%. The third most frequent was Alopecurus myosuroides in 1 1%. Bromus sterilis was recorded in 12% of winter wheat and 4% of winter barley crops, but did not occur in spring barley. Of the 206 fields where it was present it occurred throughout the field in only 82 and it was confined to the headlands in the remainder.

Evolution of Reproductive Systems in the Gramineae

From a simple hermaphrodite flower, and from a complex incompatibility system unique among the flowering plants, several breeding systems have evolved in the Gramineae. Self-compatibility is the most commonplace variant and following this mutation, habitual or facultative cleistogamy is a simple evolutionary step. Separation of the sexes to different plants as in dioecism is relatively uncommon (ca. 20 genera), and gynodioecism is much less frequent still (3-4 genera). Both are seen as escape pathways from self-compatibility; the development of such pathways is discussed. Separation of the sexes to separate flowers as in monoecism is relatively common and with the variants andromonoecism and gynomonoecism is the most substantial departure from hermaphroditism in the family. These states are also interpreted as responses to self-compatibility; and though they do not generate cross-fertilization, they assist its evolution. Pathways for the evolution of these breeding systems are described. Apomixis and the breeding system best suited are discussed.I Reproductive biology in the Gramineae begins at the transition in the shoot apex from leaf production to the initiation of inflorescence primordia and the later development of floral structures. These have been well described for numerous grasses (Barnard, 1955, 1957, 1964; Bonnett, 1966; Sharman, 1960), and are mediated by photoperiod. The review of Evans (1964) elegantly reveals data on the interplay of daylength, temperature, and vernalization on inflorescence development. Floral induction and initiation may occur in the season of flowering (Evans, 1964), or in the season preceding inflorescence emergence (Mark, 1965; Hodgson, 1966). Inflorescence emergence is temperature or daylength dependent (Cooper, 1952; Connor, 1963; Heslop-Harrison, 1961). Temperature also controls anthesis, and later the release of pollen from anthers. Photoperiod, however, has other effects on the reproductive cycle. It may, for example, affect the frequency of cleistogamy in facultatively cleistogamous grasses (Langer & Wilson, 1965), or in a facultative apomict the frequency of apomictic or sexual embryo sacs (Knox, 1967; Knox & Heslop-Harrison, 1966), or depress maleness (Heslop-Harrison, 1959), or reduce the number of florets in the male inflorescence of Zea mays (Moss & Heslop-Harrison, 1968), or control protandry and protogyny (Emerson, 1924). Although these environmental influences are considerable, genetic influences may cause transient male and female sterility, or restore lost fertility in part or in whole, or promote redistribution of the sex-forms. A combination of both genetic and physiological factors may introduce difficulties into an interpretation of the breeding system of any grass. At the International Symposium on Reproduction in Flowering Plants held at Christchurch, New Zealand, in 1979, I presented a survey of the breeding systems known in the Gramineae (Connor, 1980). This present paper is complementary 1 J am grateful to colleagues and friends in several countries for helpful discussion, and especially to D. W. Clayton, Kew, T. R. Soderstrom, Smithsonian Institution, Ana M. Anton, Universidad Nacional de C6rdoba, Elizabeth Edgar and C. J. Webb, Botany Division, DSIR. 2 Botany Division, Department of Scientific and Industrial Research, Christchurch, New Zealand. ANN. MISSOURI BOT. GARD. 68: 48-74. 1981. 0026-6493/81/0048-0074/,$2.85/0 This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 05:44:04 UTC All use subject to http://about.jstor.org/terms 1981] CONNOR-REPRODUCTIVE SYSTEMS IN THE GRAMINEAE 49 to that; the bibliographies of both papers supplement each other. Here, as there, I follow the organization of tribes proposed by Hubbard (1973) for the grasses. THE FLOWER, THE SPIKELET, AND THE INFLORESCENCE The primitive grass flower is postulated as having three bracts and lodicules, six stamens, and a 1or 3-locular tristigmatic gynoecium (Schuster, 1910; Arber, 1934; Clifford, 1961). The spikelet is considered to have been many flowered, and the inflorescence is thought to have comprised many of these spikelets in a simple moreor less-branched, terminal panicle. Associated with these characteristics is the further postulate of entomophily (Schuster, 1910; Clifford, 1961; Stebbins,

Dynamics of microbiological processes in conservation of leguminous grasses with the use of bacterial preparations of complex action

Purpose. To determine the course of accumulation of fermentation metabolites when preparing silage from the wilted mass of legumes with the introduction of bacterial preparations based on lactic acid microorganisms and to substantiate modern technological schemes of wilting grasses by machine-tractor units equipped with devices for green mass conditioning. Methods. Field experiment with elements of chronometry of technological processes and laboratory chemical analysis of feed quality. Results. Dynamics of accumulation of the main strains of the desired micro-flora during inoculation of leguminous mass with osmotolerant microorganisms was determined. On the basis of which the technological operations of preparing haylage and silage from wilted mass of alfalfa, sainfoin and deer vetch with the study of microbial composition of feed have been improved. Studies have determined the effectiveness of ensiling and nutritional value of feed from the dried mass of legumes. Conclusions. Intensification of sugar fermentation processes under the action of polybacterial preservatives of complex action occurs during the first 12-15 days of haylage and during 20-30 days of ensiling. Legumes (alfalfa, sainfoin, deer vetch) due to the increased buffer capacity prolong CO2 emissions for 24-30 days, which increased the risk of biochemical protein loss due to the formation of NH3. The decrease in osmotic pressure in the plant cell during deep flowering of grasses was accompanied by a decrease in the colony-forming ability of bacteria when treated with biological preservatives, in particular rod-shaped forms of Lactobaccillus brevis and Lactobaccillus plantarum.

Flowering in pasture Grasses

Flowering in pasture Grasses