Assessing Seed Longevity of the Invasive Weed Navua Sedge (Cyperus aromaticus), by Artificial Ageing

Navua sedge (Cyperus aromaticus (Ridley) Mattf. & Kukenth) is a significant agricultural and environmental weed found in tropical island countries including north Queensland, Australia. It is a prolific seed producer and consequently forms a high-density seedbank, and therefore understanding the longevity and persistence of the seeds can provide critical information required for the management of this species. A laboratory-controlled artificial ageing experiment was conducted where the seeds were exposed to a temperature of 45 °C and 60% relative humidity for 125 days. Seeds were removed at various times (1, 2, 5, 9, 20, 30, 50, 75, 100 and 125 days) and their viability determined through standard germination tests. It took 20 days in the artificial ageing environment for the seeds to decline to 50% viability which indicates that Navua sedge has relatively short-lived persistent seeds. These findings will assist in developing a better understanding of the seedbank dynamics of this invasive species, allowing managers to tactically implement control strategies and prepare budgets for ongoing treatments, and have implications for the duration and success of management programs

Germination Biology of Three Populations of Navua Sedge (Cyperus aromaticus)

Navua sedge [Cyperus aromaticus (Ridley) Mattf. & Kük.] is an aggressive perennial sedge native to equatorial Africa that has become problematic in many Pacific islands and wet, tropical Queensland, Australia. It has had a significant impact on the livestock-grazing industry, sugarcane (Saccharum officinarum L.) and banana (Musa acuminata Colla) plantations, and various other ecosystems. A laboratory-based research investigation was conducted to understand germination and emergence requirements under various environmental conditions of three geographically varied populations sourced from South Johnstone (SJ), Mackay (M) and Nyleta Creek (NC) in Queensland. Germination was identified to be stimulated by light, with no germination recorded under darkness. Populations SJ and NC had optimal germination at alternating temperatures of 25/15, 30/20, and 35/25 C, whereas population M had optimal germination at 25/15 and 30/20 C. All populations recorded greater than 85% germination at all pH levels tested. Seeds of population SJ were more sensitive to salinity compared with populations M and NC, with SJ showing no germination at 100 mM, whereas populations M and NC had 23% and 9% germination, respectively. An inverse relationship was observed between osmotic potential and germination, with no germination recorded at osmotic potentials below –0.8 MPa in any population, indicating moisture availability is a critical requirement for germination. Exposing seeds to 120 C radiant heat completely inhibited germination in populations M and NC, whereas 3% of population SJ germinated following a 180-s exposure at 120 C. Seedling emergence decreased as planting depth increased. Emergence was greatest for seeds on the soil surface or at 0.5-cm burial depth, consistent with germination being stimulated by light. Knowledge of these biological characteristics of C. aromaticus seed germination will assist in investigation of suitable control actions for this species, particularly in the early stage of its invasion into new areas, and will contribute to significant reduction in the soil seedbank

Biology, Ecology and Management of the Invasive Navua Sedge (Cyperus aromaticus)—A Global Review

Navua sedge (Cyperus aromaticus (Ridley) Mattf. & Kukenth) is an invasive perennial sedge, native to tropical Africa, which is threatening many natural ecosystems and agroecosystems, especially in northern Queensland, Australia. Crop and pasture production have been impacted by Navua sedge and it is also directly causing reductions in dairy and beef production in affected regions. This review documents the biology, ecology and potential management options to minimise the spread and impact of Navua sedge. The weed reproduces both sexually (seeds) and vegetatively (via underground rhizomes). Its tiny seeds can be spread easily via wind, water, vehicles, farm machinery and animals, whilst the rhizomes assist with establishment of dense stands. The CLIMEX model (which uses distribution and climate data in native and novel ranges) indicates that in Australia, Navua sedge has the potential to spread further within Queensland and into the Northern Territory, New South Wales and Victoria. Several management strategies, including mechanical, chemical and agronomic methods, and their integration will have to be used to minimise agricultural production losses caused by Navua sedge, but most of these methods are currently either ineffective or uneconomical when used alone. Other management approaches, including biological control and mycoherbicides, are currently being explored. We conclude that a better understanding of the interaction of its physiological processes, ecological patterns and genetic diversity across a range of conditions found in the invaded and native habitats will help to contribute to and provide more effective integrated management approaches for Navua sedge

Annual ryegrass (Lolium rigidum Gaud) competition altered wheat grain quality: a study under elevated atmospheric CO2 levels and drought conditions

Annual ryegrass is one of the most serious, costly weeds of winter cropping systems in Australia. To determine whether its competition-mediated plant defence mechanisms effect on wheat grain quality, wheat (cv. Yitpi) and annual ryegrass were grown under two levels of CO (400 ppm; (a[CO]) vs 700 ppm; (e[CO]), two levels of water (well-watered vs drought) and two types of competition (wheat only; (W), and wheat × annual ryegrass; (W × R) with four replicates. The competition × [CO] interaction had a significant effect on wheat grain protein content, where it was increased in W × R under both e[CO] (+17%) and a[CO] (+21%). Grain yield, total grain reducing power and phenolic content were significantly affected by [CO] × drought × competition. In a summary, annual ryegrass competition significantly altered the wheat grain quality under both [CO] levels (depending on the soil water level), while also decreasing the grain yield

Ecology of Eucalyptus victrix in grassland in the floodplain of the Fortescue River.

The WA coolibah tree, Eucalyptus victrix L. Johnson & K. Hill forms an unique and pristine woodland in the Fortescue Valley, in the Pilbara district of Western Australia. Until recently, no research had been done on E. victrix ecology and concern had been expressed by pastoral managers and others about the condition of the woodland occupied by this species. This research was an attempt to understand the ecology of coolibah using a multi-disciplinary approach.A population demographic study of stands in E. victrix woodland reveals that the present tree populations occupy larger areas than saplings and seedlings. Soil moisture and warm summer temperatures are believed to be stimulating factors for seedling recruitment of E. victrix. Different size classes (height/diameter) reflect different recruitment events and these reflect past availability of seeds and adequate soil moisture in that particular area of the woodland. Occasional grasshopper outbreaks and drought cause canopy shrinkage. Presence of hollow boles, restrict dendrochronological examination of tree ages.An important population study was of a post-seedling cohort at Roy Hill, where height distribution reflected a typical single recruitment event. In subsequent years (1995 - 1998) height measurement showed several peaks, suggesting that seedlings were now growing at different rates. Uniform and steady height growth was observed on saplings found at the edges of gilgai. During May 1998 several saplings flowered, it was assumed that E. victrix attained its reproductive maturity at mean height of 2.50 m and with a stem diameter of 50 mm.Seedling recruitment and subsequent growth mainly depend on heavy rainfall flooding events. Seedling recruitment occurs only from current seed rain. Seed longevity reduces after 54 days of burial at 50 mm depth. Mortality (4 - 6 leaf stage) of newly recruited seedlings during subsequent dry months is very high. Furthermore, allelopathic effects (root competition from established grass and insect herbivory) are additional causes of seedling mortality in the years of recruitment.Seedlings recruited at a burnt (disturbed) site, grew faster compared with undisturbed sites with less mortality. This suggested that fire created a suitable condition by reducing root competition, increasing soil nutrients and also creating a gap which providing sufficient solar radiation for seedlings to establish and develop into a healthy population. It is suggested that once newly recruited seedlings overcome the first summer, mortality rates during subsequent years are drastically reduced.Long-term waterlogging of E. victrix seedlings significantly increases seedling stem diameter. Large numbers of adventitious roots are developed and lenticels proliferate on the submerged portion of the stem. Flooding reduces each photosynthesis, transpiration and stomatal conductance. Flooding does not increase shoot fresh or dry weight on 4-, 8- or 17- week old seedlings. Leaf emergence may be stimulated on flooded seedlings compared with unflooded seedlings. While root dry weight is greater in 17-week old flooded plants than 13 - week seedlings, this difference is not significant. It is suggested that maintenance of a high root/shoot ratio is a drought adaptation. Furthermore, comparative study of flood tolerance in semi-arid eucalypt species suggests that those species intolerant of flooding seldom express morphological adaptations and fail to recover from physiological damage.The annual grass Setaria dielsii occurs under the canopy of mature E.victrix trees of the coolibah woodland. This species has probably displaced more palatable perennial grasses. Soil moisture under trees is slightly higher and soil temperatures are less extreme than away from the canopy. Growth of S. dielsii appears to be more associated with soil nutrient status. Levels of total N, Mg, K, and of electrical conductivity (EC) under trees are significantly higher than those away from the tree. Levels of Ca, Na, Fe, and organic carbon do not differ. The under story sub-shrub Malvastrum americanum is an important competitor with S. dielsii. Light availability may determine relative biomass contributions of the two species.The effect of the density of grass species, growing space and time of establishment on E. victrix seedlings (inter-specific competition), and the effect of density and growing space within E. victrix seedling populations (intra-specific competition) were studied under controlled conditions. Results indicate resources necessary for growth of individual E. victrix seedlings were more limiting under increase density of neighbouring grass species than under intra-specific competition. In particular photosynthetic area was drastically reduced in mixed culture.Lack of ground cover beneath the canopy of isolated E. victrix trees was ascribed to toxic or phenolic substances present in leaf, bark and leaf litter of E. victrix. Lactuca sativa seed germination subjected to extracts and leachate demonstrate that the fresh leaf of E. victrix possesses toxic substances which cause deleterious effects on both germination and radicle development. Similarly, increasing concentrations of leaf and bark leachate show reduced germination percentage of L. sativa seeds. Shoot and root biomass of grass and eucalyptus treated with leaf leachate were reduced. E. victrix leaf leachate significantly reduced shoot and root biomass of its own seedlings. High Performance Liquid Chromatogram (HPLC) analysis separated 11 and 8 possible toxic substances from leaf and bark extract respectively

Responses of the weed Parthenium hysterophorus (Asteraceae) to the stem gall-inducing weevil Conotrachelus albocinereus (Coleoptera : Curculionidae)

A stem-galling weevil Conotrachelus albocinereus Fiedler 1940 from Argentina is being field released to regulate populations of the weed Parthenium hysterophorus in Queensland, Australia since 1995. In this paper we report the tissue and metabolic responses in P hysterophorus in the context of the biology and feeding behaviour of the weevil. C albocinereus induces elliptical galls often on the main shoot axes and rarely on the terminal and axillary meristems of the host plant. From oviposition through gall maturation, the structure and metabolism of the host-plant tissues. especially at the gall region, change continuously to accommodate pressure inflicted by the feeding larva. The host plant shows re-direction of its vital metabolites to the gall, and to the metaplasied cells of nutrition in particular. In mature galls. the pith parenchyma elements tum lignified. Larval feeding fractures the vertical continuity of vascular tissues, which affects the host plant's overall metabolism. As the larva tunnels the shoot column, it places the frass at the fissured vascular sites. That activity initiates necrosis and eventual death of the living cells of the vascular tissue complex. Such a development induces water-logging stress in the gall and the evapo-transpirational system displays contrasting responses. Permanently closed stomatal apertures and abnormally inflated substomatal chambers indicate that P hysterophorus suffers moisture-stress with cecidogenesis. The larval performance triggers moisture inundation in the galled shoot and this appears to be an advantage in using this weevil in the control of P hysterophorus

Influence of selected environmental factors on seed germination and seedling emergence of Dinebra panicea var. brachiata (Steud.)

Dinebra panicea var. brachiata (Steud.) is related to genus Leptochloa., some species of which are significant rice crop weeds However, little is known about how D. panicea responds to various environmental cues. This study investigates the effects of temperature, light, salt stress, moisture stress, pH, heat shock, smoke, and burial depth on seeds collected in successive years (2015 and 2016) from Queensland, Australia. Seed germination was higher overall for older seeds (2015) compared to younger (2016) at 30/20 degrees C and 25/15 degrees C, but there was less difference between light treatments (12 L/D, 24D) in both temperature ranges for older seeds compared to younger. Increasing moisture and salt stress gradually reduced germination, germination was high over the pH range from pH 4 to pH 10, short term (three minutes) heat exposure to 80 degrees C or less did not inhibit germination, but there was no significant difference between years for any of these environmental cues. Germination was greatly reduced at 100 degrees C and eliminated at 120 degrees C. Smoke significantly inhibited germination. Seeds from both years germinated on the soil surface and emerged from 0.2 cm, with no emergence from deeper than 0.5 cm. The data collected from this study may assist land managers to manage infestations of this weed

Effect of Rhizome Fragment Length and Burial Depth on the Emergence of a Tropical Invasive Weed <i>Cyperus aromaticus</i> (Navua Sedge)

Cyperus aromaticus (Navua sedge) is a problematic perennial weed in pastures and crops including sugarcane, banana, rice, and fruits and vegetables in tropical climates. It reproduces both via rhizomes and seeds. As a regenerative and storage organ, these rhizomes play an important part in the invasion, establishment, and persistence of this weed. To eliminate their regenerative ability, it is important to understand the regrowth potential with respect to rhizome fragment size and burial depth. This study evaluated the emergence of C. aromaticus from rhizomes in a controlled condition. Three different sizes of rhizome fragments were buried at seven depths of up to 20 cm in two soil types. The experimental measurements included (i) the time for tillers to emerge, (ii) the cumulative emergence of tillers, recorded weekly, and (iii) the number of underground emerging tillers. The cumulative shoot emergence and the number of underground tillers produced were found to be positively correlated with the initial length of the rhizome fragments and negatively correlated with the burial depth. The time for the emergence of the tillers was negatively correlated with the burial depth, and soil type had no significant effect on any of the parameters recorded. There was no emergence recorded from rhizomes buried at 15 cm depth and deeper, irrespective of their size. Our results indicate that the combination of the fragmentation of rhizomes into small pieces and a deep burial, below 15 cm, is an important aspect to control the regeneration of C. aromaticus from rhizomes, if tillage is carried out, and can therefore form a part of an integrated weed management strategy for this troublesome weed

Response of glyphosate-resistant and -susceptible biotypes of annual sowthistle (Sonchus oleraceus) to increased carbon dioxide and variable soil moisture

The growth response of annual sowthistle (Sonchus oleraceus\ua0L.) to anticipated future climate conditions is currently unknown, and thus, two parallel studies were conducted dealing with glyphosate-resistant (GR) and glyphosate-susceptible (GS) biotypes of\ua0S. oleraceus. The glyphosate efficacy study was conducted using different doses of glyphosate [0 (control), 180, 360, 720 (recommended dose) and 1440 g a.e. ha-1] at two different moisture levels (well-watered and water-stressed). In the second study, the growth and seed production of these biotypes were studied under different atmospheric carbon dioxide (CO2) concentrations (450 and 750 ppm) and under well-watered (100% field capacity) and water-stressed (50% field capacity) conditions. Results showed that the GR biotype survived (>68%) at 1440 g ha-1, but for the GS biotype, no plant survived, and both biotypes were slightly (38% taller and produced >44%, >18% and >21% more leaves, buds, and seeds, respectively, compared with the ambient CO2\ua0concentration under both moisture regimes. The biomass also increased by 27% in comparison with the ambient CO2\ua0concentration. For the GR biotype, plants at the elevated CO2\ua0level, whilst they also grew 38% taller in comparison with the ambient CO2\ua0concentration, the number of leaves, buds, seeds, and biomass was not affected by this increase in CO2. Results showed that there were minimal changes in response to glyphosate for GR and GS biotypes of\ua0S. oleraceus\ua0with or without moisture stress. Our study suggests that future climate change with elevated CO2\ua0levels can affect the response of\ua0S. oleraceus\ua0to glyphosate and such knowledge will be helpful for weed management in the future

Factors affecting seed germination of feather fingergrass (Chloris virgata)

Laboratory experiments were carried out to determine the effect of several environmental factors on seed germination of feather fingergrass, one of the most significant emerging weeds in warm regions of the world. Seed germination occurred over a broad range of temperatures (17/7, 25/10, and 30/20 C), but germination being highest at alternating temperatures of 30/20 C under both 12 h light/12 h dark and 24 h dark conditions. Although seed germination was favored by light, some seeds were capable of germinating in the dark. Increasing salt stress decreased seed germination until complete inhibition was reached at 250-mM sodium chloride. Germination decreased from 64 to 0.7% as osmotic potential decreased from 0 to -0.4 MPa, and was completely inhibited at -0.6 MPa. Higher seed germination (>73%) was observed in the range of pH 6.4 to 8 than the other tested pH levels. Heat shock had a significant effect on seed germination. Germination of seeds placed at 130 C for 5 min was completely inhibited for both dry and presoaked seeds. The results of this study will help to develop protocols for managing feather fingergrass, and to thus avoid its establishment as a troublesome weed in economically important cropping regions