Leguminous cover crop and living mulch species show not only great potential for providing multiple beneficial services to agro-ecosystems, but may also present pathological risks for other crops in ...rotations through shared pathogens, especially those of the genus Fusarium. Disease severity on roots of subterranean clover, white clover, winter and summer vetch grown as cover crop and living mulch species across five European sites as well as the frequency, distribution and aggressiveness to pea of Fusarium spp. recovered from the roots were assessed in 2013 and 2014. Disease symptoms were very low at all sites. Nevertheless, out of 1480 asymptomatic roots, 670 isolates of 14 Fusarium spp. were recovered. The most frequently isolated species in both years from all hosts were F. oxysporum and F. avenaceum accounting for 69% of total isolation percentage. They were common at the Swiss, Italian and German sites, whereas at the Swedish site F. oxysporum dominated and F. avenaceum occurred only rarely. The agressiveness and effect on pea biomass were tested in greenhouse assays for 72 isolates of six Fusarium species. Isolates of F. avenaceum caused severe root rot symptoms with mean severity index (DI) of 82 and 74% mean biomass reduction compared to the non-inoculated control. Fusarium oxysporum and F. solani isolates were higly variable in agressiveness and their impact on pea biomass. DI varied between 15 and 50 and biomass changes relative to the non-inoculated control -40% to +10%. Isolates of F. tricinctum, F. acuminatum and F. equiseti were non to weakly agressive often enhancing pea biomass. This study shows that some of the major pea pathogens are characterized by high ecological plasticity and have the ability to endophytically colonize the hosts studied that thus may serve as inoculum reservoir for susceptible main legume grain crops such as pea.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Living mulch gives many benefits to agro-ecosystems such as erosion control, nitrogen fixation and nutrient recycling, increasing of organic matter, weed and pest control, and increasing of soil ...organism. The experiment, carried out in Puglia, Southern Italy on transplanted broccoli raab (cv. Grossa fasanese), evaluated four soil management systems (SMSs):
and
used as living mulch, undisturbed weedy, and conventional tillage. For each SMS, four rates of nitrogen and phosphorous (NP0, NP1, NP2, and NP3) were supplied, using an organic fertilizer. The following data were collected: weed infestation, leaf chlorophyll in the plants (as SPAD units), weight, diameter, and colour of the inflorescences, anion and Mg, Fe, Na, K, Ca content. Fertilization showed prominent effects on most of parameters evaluated. The Sufficient Index of broccoli raab plants was higher in fertilized plots. With the increasing of fertilization rates, weight of primary inflorescences and the marketable yield linearly increased, confirming the great influence of nitrogen fertilization on the yield of
vegetables and highlighting the importance of combining living mulch and fertilization. By increasing fertilization rates, some elements, such as Mg and Fe, increased, whereas a decrease of Na, K, and Ca was observed. The nitrate content in the inflorescences was different only between the fertilized and unfertilized plots, although it was very low. In NP2 and NP3 a greener colour was found. Living mulch did not clearly affect quality and yield of broccoli raab but was effective in weed control. Results show the positive effects of living mulch and organic fertilization in the sustainable production of broccoli raab.
In vitro germination tests were performed at 11 constant temperatures (range 2.5-35°C) to quantify the maximum germination percentage and germination rate of four subterranean clover cultivars ...('Antas', 'Denmark', 'Monti' and 'Narrikup'). These were used to estimate their cardinal temperatures, base (T
b
), optimum (T
opt
) and maximum (T
max
) and the thermal time requirements for seed germination. Germination percentages were ≥ 88% in the 5-25°C temperature range for all cultivars. The time to reach 50% of final germination (T
50
) decreased from 12 to 2 days as the temperature increased from 2.5 to 17.5°C. The determined T
opt
were 16°C for 'Monti' and 'Narrikup' and 22°C for 'Antas' and 'Denmark'. At a common T
b
of 0°C the thermal time requirements for T
50
were 32 ± 1°Cd for 'Antas' and 'Denmark' and 39 ± 1°Cd for 'Narrikup' and 'Monti'. 'Antas' and 'Denmark' (both from Italy) germinated at the widest range of temperatures.
Subterranean clover (
) is the most widely grown annual pasture legume in southern Australia. With the advent of advanced sequencing and genome editing technologies, a simple and efficient gene ...transfer protocol mediated by
was developed to overcome the hurdle of genetic manipulation in subterranean clover. In vitro tissue culture and
transformation play a central role in testing the link between specific genes and agronomic traits. In this paper, we investigate a variety of factors affecting the transformation in subterranean clover to increase the transformation efficiency. In vitro culture was optimised by including cefotaxime during seed sterilisation and testing the best antibiotic concentration to select recombinant explants. The concentrations for the combination of antibiotics obtained were as follows: 40 mg L
hygromycin, 100 mg L
kanamycin and 200 mg L
cefotaxime. Additionally, 200 mg L
cefotaxime increased shoot regeneration by two-fold. Different plant hormone combinations were tested to analyse the best rooting media. Roots were obtained in a medium supplemented with 1.2 µM IAA. Plasmid pH35 containing a hygromycin-resistant gene and
gene was inoculated into the explants with
strain AGL0 for transformation. Overall, the transformation efficiency was improved from the 1% previously reported to 5.2%, tested at explant level with Cefotaxime showing a positive effect on shooting regeneration. Other variables in addition to antibiotic and hormone combinations such as bacterial OD, time of infection and incubation temperature may be further tested to enhance the transformation even more. This improved transformation study presents an opportunity to increase the feeding value, persistence, and nutritive value of the key Australian pasture.
A field-experiment (2004/2005 and 2005/2006 seasons) was conducted in the coastal plain of south-eastern Sicily (37°03′N, 15°18′E, 15 m a.s.l.), on a Calcixerollic Xerochrepts soil, aimed at ...quantifying the effect of shading on chlorophyll (Chl) content, Chl fluorescence, photosynthesis and growth of subterranean clover. Four levels of photosynthetically active radiation reduction (from 0 % to 90 %) were tested on Trifolium brachycalycinum cv. ‘Clare' and Trifolium subterraneum ecotype ‘Ragalna'. In both species shading progressively increased Fv/Fm, internal CO₂ concentration, diffusive leaf resistance and specific leaf area (up to 8 %, 34 %, 18 % and 68 %, respectively), and decreased Chl content, Tmax, photosynthetic rate and plant dry weight (up to 9 %, 24 %, 79 % and 39 %, respectively). As plants aged, characteristic bell-shaped trends were evident for photosynthetic parameters, with Fv/Fm increasing up until the onset of flowering, and thereafter declining. This implies that Fv/Fm may be a useful indicator of earliness in subterranean clover genotypes. The aboveground dry biomass response to shading was both genotype- and season-dependent, but was predictable from the measurement of relative leaf Chl content. Moreover, our results suggest that an improvement in the interaction between host-rhizobium may represent a major potential breeding target for enhancing subterranean clover tolerance to shading.
Background and Aims: The structures of arbuscular mycorrhizal (AM) fungi (hyphae, arbuscules, vesicles, spores) are used to make inferences about fungal activity based on stored samples, yet the ...impact of storage method has not been quantified, despite known effects of temperature and host condition on AM fungal colonisation. Methods: We measured how four storage treatments (cool or ambient conditions, with and without plant shoots attached, i.e. n = four treatment combinations) affected AM fungal colonisation of subterranean clover (Trifolium subterraneum L.) after 0, 2, 6 and 10 days of storage. Roots were assessed for colonisation of fine root endophyte and coarse AM fungi. Results: For coarse AM fungi, total colonisation was unaffected, but arbuscules were reduced at Day 6 and increased again by Day 10, except Ambient-Minus-Shoots. There was a loss of vesicles in all treatments at Day 2, and an increase in spore number at Day 6 within Cool-Plus-Shoots. In contrast, for fine root endophyte, total colonisation was greatly reduced at Day 6 but increased again at Day 10, in all except the Cool-Plus-Shoots treatment. Conclusions: Our data demonstrate that AM fungal activity is not suspended in commonly used plant storage conditions. Storage method and time impacted AM fungal colonisation, particularly for fine root endophyte. We recommend samples are processed within 2 days of harvest.
Aims: Trifolium subterraneum L. is the predominant annual pasture legume in southern Australia. Cultivars with improved phosphorus (P) foraging ability would improve the P-use efficiency of ...agricultural systems. We therefore investigated variation in root traits related to Puptake among six cultivars. Methods: Micro-swards were grown at six levels of P in field soil with indigenous arbuscular mycorrhizal (AM) fimgi for six weeks. Dry matter yield, tissue P concentration, rhizosphere carboxylates, AM fungal colonisation and root morphological traits were measured. Results: The cultivars showed similar shoot and root yield responses to P supply. Average root diameter did not change, specific root length (SRL) increased and root tissue density (RTD) decreased with increased P supply. Amounts of total rhizosphere carboxylates were low (<1.2 nmol cm⁻¹ root). The percentage of root length colonised by AM fungi was greatest (29-43 %) at an intermediate level (8 mg kg⁻¹ dry soil) of P supply. Conclusions: Most differences among cultivars were reasonably consistent across P supply levels, indicating greater numbers of lines could be screened reliably at a single P level. Low colonisation by AM fungi at low P supply deserves consideration when selecting soils for cultivar comparisons. Increased SRL and decreased RTD at high P supply likely result from self-shading within the micro-swards and warrant further investigation.
Nitrogen fixation from pasture legumes is a fundamental process that contributes to the profitability and sustainability of dryland agricultural systems. The aim of this research was to determine ...whether well-managed pastures, based on aerial-seeding pasture legumes, could partially or wholly meet the nitrogen (N) requirements of subsequent grain crops in an annual rotation. Fifteen experiments were conducted in Western Australia with wheat, barley or canola crops grown in a rotation that included the pasture legume species French serradella (Ornithopus sativus), biserrula (Biserrula pelecinus), bladder clover (Trifolium spumosum), annual medics (Medicago spp.) and the non-aerial seeded subterranean clover (Trifolium subterraneum). After the pasture phase, five rates of inorganic N fertilizer (Urea, applied at 0, 23, 46, 69 and 92 kg/ha) were applied to subsequent cereal and oil seed crops. The yields of wheat grown after serradella, biserrula and bladder clover, without the use of applied N fertilizer, were consistent with the target yields for growing conditions of the trials (2.3 to 5.4 t/ha). Crop yields after phases of these pasture legume species were similar or higher than those following subterranean clover or annual medics. The results of this study suggest a single season of a legume-dominant pasture may provide sufficient organic N in the soil to grow at least one crop, without the need for inorganic N fertilizer application. This has implications for reducing inorganic N requirements and the carbon footprint of cropping in dryland agricultural systems.
Aims
To examine the legacy of pasture drill rows sown to various configurations of subterranean clover (
Trifolium subterraneum
L.), lucerne (
Medicago sativa
L.) and phalaris (
Phalaris aquatica
...L.), on soil chemical characteristics and wheat (
Triticum aestivum
L.) production in the year following pasture removal.
Methods
A field experiment comparing 10 pasture species combination treatments conducted on a Red Kandosol soil in a semi-arid environment in south-eastern Australia was monitored from the end of the pasture phase until harvest of the first wheat crop. Quadrats were fixed to the soil surface to mark previous pasture drill rows. Soil within and between rows was sampled to 0.6 m at three times and analysed for mineral nitrogen (N), pH, total carbon (C) and available macro-nutrients, and related to wheat growth rate and yield.
Results
Significantly higher total C, mineral N and plant-available potassium (K), and lower sulphur (S) concentrations, were still evident in the original pasture drill row after grain harvest compared to the inter-row area, four years after pastures were sown. Grain yield was 11% greater in wheat growing on the original pasture drill row compared to between rows. Pure lucerne swards had less mineralised N than mixed lucerne swards associated with reduced water in the soil profile.
Conclusions
This study establishes the enduring legacy of pasture drill rows observed up to 14 months post-removal and highlights the opportunity to improve soil fertility through manipulation of pasture sowing configurations in a cropping field in south-eastern Australia.
Background and aims Endophytic actinobacteria are known to benefit their hosts by improving plant growth and by reducing the severity of soil borne diseases. In this study, their role in enhancing ...the growth of lucerne and their interaction with its rhizobial symbiosis is examined Comparison is made between endophytic actinobacteria isolated from wheat plants and isolates from the roots and nodules of four different legume species: lucerne (Medicago sativa L.), field pea (Pisum sativum L.), subterranean clover (Trifolium subterraneum L.) and burr medic (Medicago polymorpha L.). Methods Two hundred and twenty five isolates of actinobacteria were recovered from the legumes. Five selected legume isolates were compared to five wheat isolates for their effects on rhizobial growth on agar and on the early nodulation and growth of lucerne plants inoculated with Sinorhizobiwrn meliloti strain RRI 128. Results Co-inoculation with lucerne isolates Streptomyces spp. LuP30 and LuP47B, increased lucerne shoot dry weight at 7 weeks after inoculation by 25 to 35 %, and shoot nitrogen content by 22 to 28 % respectively, compared to plants treated with Sinorhizobium meliloti RRI 128 alone. Conclusions This study shows that some endophytic actinobacteria have the potential to enhance the lucerne - rhizobia symbiosis.
PDF
