Inferring the introduction history of the invasive apomictic grass Cortaderia jubata using microsatellite markers

Aim Reconstructing the introduction history of exotic species is critical to understanding ecological and evolutionary processes that underlie invasive spread and to designing strategies that prevent or manage invasions. The aims of this study were to infer the introduction history of the invasive apomictic bunchgrass Cortaderia jubata and to determine if molecular data support the postulated horticultural origin of invasive populations. Location Invaded areas in the USA (California, Maui) and New Zealand; native areas in Bolivia, Ecuador and Peru. Methods We used nuclear microsatellite markers to genotype 281 plants from invaded areas in California, Maui and New Zealand, and 77 herbarium specimens from native South America, and compared the genotypic and clonal variation of C. jubata from the invaded and native ranges. Clonal diversity was determined from genotypic diversity using two analytical methods. Results Invasive C. jubata from invaded regions in California, Maui and New Zealand consisted of the same single clone that probably originated from a single introduced genotype. In contrast, 14 clones were detected in herbarium specimens from the native areas of Bolivia, Ecuador and Peru. The invasive clone matched the most common clone identified in herbarium specimens from southern Ecuador where horticultural stock is presumed to have originated. Main conclusions The lack of clonal and genotypic diversity in invasive plants, but moderately high diversity detected in native plants, indicates a significant reduction in genetic variation associated with the introduction of C. jubata outside of its native range. Based on historical accounts of the horticultural introduction of C. jubata and the results of this study, a severe founder effect probably occurred during deliberate introduction of C. jubata into cultivation. Our results are consistent with the postulated horticultural origin of invasive C. jubata and point to southern Ecuador as the geographical source of invasive populations.     

Dormancy and germination characteristics of herbaceous species in the seasonally dry tropics of northern Australia

This study investigated changes in dormancy and germination over 8 months for 23 common species (annual and perennial grasses, legumes and other dicotyledons) from herbaceous communities in northern Australia. Seeds were exposed to three storage treatments: relatively constant laboratory conditions, an oven with fluctuating temperatures similar to those found on the soil surface (25/60°C), or exposed on the soil surface at Townsville. There were wide ranges of initial levels of dormancy (9–100%), rates of change of dormancy and response to the different storage conditions showing that species with several types of dormancy characteristics are able to coexist in these communities. The general trend in dormancy levels was a decline with time with the rate of decline greatest for seeds exposed on the soil surface and least for those stored in the laboratory. The species were divided into groups based on dormancy levels in seeds on the soil surface during the late dry and mid wet seasons. The dormancy characteristics of the groups were related to the ecology of the species in the groups. There was an approximately linear increase in germination rate (i.e. a decrease in the number of days to 50% of final germination) over time for all storage treatments; rates for seeds on the soil surface increased more rapidly than those of seeds in laboratory and oven samples.     

Root herbivore performance suppressed when feeding on a jasmonate‐induced pasture grass

1. Plants defend themselves from insect herbivore attack using a range of physical and chemical defences which are in many cases regulated by phytohormones such as jasmonates. While much more is known about how jasmonates regulate defence against above‐ground herbivores (e.g. herbivores of leaves), there is increasing interest in how they influence below‐ground defences. 2. For the Poaceae, most below‐ground studies focus on highly domesticated cereals. Here it is demonstrated how exogenous application of methyl jasmonate (MeJA) to the leaf blades of a non‐domesticated pasture grass (Microlaena stipoides) caused a more than two‐fold decrease in relative growth rate (RGR) of a root‐feeding chafer (Dermolepida albohirtum). MeJA treatment did not affect root consumption rates, but substantially reduced the efficiency of conversion of ingested food to body mass. 3. Non‐targeted metabolomics identified significant changes in the metabolome of MeJA‐induced plants, with three compounds (a galactolipid, a trihydroxy fatty acid and a lysophospholipid) found to be correlated with herbivore RGR, although their roles in herbivore defence remain uncertain. 4. This study suggests that an important Australian pasture grass can become better defended against root herbivores via enhanced jasmonate activity.     

Induction of morphogenically competent callus and suspension cell cultures from leaf explants and mature seeds ofDigitaria sanguinalis

Summary Digitaria sanguinalis (crabgrass) has recently been introduced as a high quality forage crop. We report here a tissue culture system showing a high level of regeneration developed to aid in a breeding program. Two morphologically distinct types of callus, compact opaque and friable translucent, were induced from leaf blade explants and mature seeds when cultured on MS medium containing 0.9 μM 2,4-dichlorophenoxyacetic acid. Proline (25 mM) inhibited induction of callus but was required for continued maintenance. Plants were readily regenerated from the compact opaque callus. Selectively subcultured friable translucent callus continued to produce colony sectors of the morphogenically competent compact opaque callus when transferred to regeneration medium. Suspension cell cultures derived from callus or directly from leaf blade explants also produced regenerable callus.     

A taxometric analysis of seed proteins in the genusBriza s. l. (Poaceae)

The species ofBriza L. s. l. are disjunctly distributed between Eurasia and South America. A taxometric analysis has been carried out, using data from electrophoresis of seed polypeptides and published morphological characters. Evidence from a cluster analysis of seed polypeptide data strongly supports the recognition of two different natural groups, a S. American group and a Eurasian group, and is consistent with karyotype data, but does not support the generic groupings of South American taxa derived from the morphological data.     

Digestibility of fractionated green biomass as protein source for monogastric animals

Globally, there is an increased demand for sustainable protein sources for animal feed. Grass and forage legumes have the yield potential to become such alternatives, but the protein needs to be separated from the fibres. Red clover, white clover, lucerne and perennial ryegrass were fractionated into a green juice and a fibrous pulp in a screw-press and protein was subsequently precipitated. The nitrogen (N) and amino acid composition of the produced fractions was analysed and the digestibility of dry matter (DM) and N was evaluated using a rat digestibility trial. The aim was to determine the effect of fractionation on composition and digestibility in order to evaluate the four plants as potential protein sources for monogastrics. Protein concentrates with CP concentrations of 240 to 388 g/kg DM and fibrous pulps with CP concentrations of 111 to 216 g/kg DM were produced. The sum of all analysed amino acids was highest in the protein concentrates corresponding to a low concentration of non-protein nitrogen ranging from 4.9% to 10.4%. Only small variations were seen in the amino acid compositions of the different plants and fractions. The concentration of the essential lysine and methionine in the protein concentrate ranged from 6.27 to 6.67 g/16 g N and 1.54 to 2.09 g/16 g N for lysine and methionine, respectively. For all plants species, total tract digestibility of DM and standardised N digestibility was significantly higher in the protein concentrates (60.8% to 76.5% and 75.4% to 85.0% for DM and N, respectively) compared to pulp (21.2% to 43.4% and 52.1% to 72.5% for DM and N, respectively). Digestibility of lucerne protein concentrate (76.5% and 85.0% for DM and N, respectively) was higher than of the unprocessed plant (39.6% and 74.9% for DM and N, respectively), whereas for red and white clover no difference was found. The amino acids methionine and cysteine were limiting for pigs and broilers in all fractions regardless of plant origin, and low scores were also found for lysine. The study demonstrated great potential of using green plants as a protein source for monogastrics because of high protein content, balanced amino acid composition and high digestibility of DM and N. The effects of processing and protein precipitation were pronounced in lucerne where significantly improved digestibility was observed in the protein concentrate. The results from the study provide valuable and enhanced knowledge to the production of alternative and sustainable protein sources for monogastric feed.     

Historical land-use legacy and Cortaderia selloana invasion in the Mediterranean region

Two major components of global change: land‐use changes and intentional or accidental species introduction are threatening the conservation of native species worldwide. In particular, Mediterranean coastal areas are highly susceptible to the invasion of alien species and they also have experienced major changes in land use such as agricultural abandonment and urbanization. However, there has been little research done which quantitatively links biological invasions and the components of land‐use changes (i.e. number, trajectory and direction of the changes). We analysed the current distribution and abundance of Cortaderia selloana (Schultes et Schultes fil.) Asch. et Graebner, an alien ornamental species, in 332 fields in Aiguamolls de l'Empordà (Catalonia, NE Spain) and related the patterns of invasion to spatiotemporal data on land‐use changes from 1956 to 2003. Our aim was to determine which land uses had been more susceptible to C. selloana invasion during the last 5 years and to find out which components of land‐use changes triggered invasion. We found that 22.30% of the fields are currently invaded. In the last 5 years, fields have triplicated the total density of C. selloana. The presence of C. selloana decreases with the distance from urban areas. Invasion is over‐represented in pastures and old‐fields, and it has increased with time since abandonment. The presence of C. selloana was also associated to fields that had experienced many changes in land use in the last 46 years. The most heavily invaded fields were those that were pastures in 1956 and are now old fields in 2003. On average, the largest plants are found in agricultural field margins and in fields that had a disturbed land use both in 1956 and in 2003. Furthermore, pastures had the lowest proportion of reproductive plants. Overall, current C. selloana patterns of invasion can be explained by the historical legacy of land‐use changes.     

Evolutionary significance of genotypic variation in developmental reaction norms for a perennial grass under competitive stress

The developmental reaction norm (DRN) represents the set of ontogenetic trajectories that can be produced by a genotype exposed to different environmental conditions. Genetic variation in the DRN for growth traits and in the patterns of biomass allocation is critical to phenotypic evolution in heterogeneous environments. The DRN and patterns of biomass allocation were investigated in 11 clones of the caespitose, corm-forming, perennial grass Phleum pratense in relation to competitive stress imparted by Lolium perenne in a 16 week glasshouse experiment. A separate experiment assessed the ability of basal buds flanking a corm to sprout and the relationship of corm mass to sprout mass for the same clones. Corm fresh mass varied among clones and was significantly correlated with the dry mass of the tillers that sprouted from basal buds. In the competition experiment, clones in competitive environments varied significantly from those in non-competetive environments in terms of their DRNs for number of tillers and shoot dry mass. Thus, selection of DRNs would favour different genotypes in the two environments and at different times. Significant negative genetic correlations were detected for tiller number and mean tiller mass in the noncompetitive, but not the competitive, environment. Biomass allocation to stem bases was significantly greater for clones under competitive stress. Allocation to storage tissues such as corms may be adaptive if it enhances persistence in the competitive field environments typically occupied by caespitose grasses. Root and shoot allocation showed a significant clone by competition interaction. For P. pratense, genotypic variation in growth trajectories plays an important role in determining variation in individual performance, a condition necessary for the continued evolution of the DRN.