Controlled Environment Studies Research Articles

Plant growth stage and Phoma medicaginis inoculum concentration together determine severity of Phoma black stem and leaf spot and consequent phytoestrogen production in annual Medicago spp.

AbstractPhoma black stem and leaf spot disease (Phoma medicaginis) not only destroys annual Medicago spp. forage and seed yield but also reduces herbage quality by consequent phytoestrogen production that reduces ovulation of grazing animals. Two controlled environment studies evaluated the effects of plant developmental stage in annual Medicago rugosa ‘Paraponto’ and M. scutellata ‘Sava’ and different inoculum concentrations of P. medicaginis in M. littoralis ‘Harbinger’ and M. polymorpha ‘Serena’ on disease development and coumestrol production. Disease incidence and severity and coumestrol production were dependent on plant developmental stage, cultivar and inoculum level (all p ≤ 0.001). Disease was least in 4‐week‐old plants; highest coumestrol was in inoculated 10‐week‐old Sava (1353 mg/kg) and least coumestrol in uninoculated 4‐week‐old Paraponto (87 mg/kg); and there was a positive correlation of disease incidence/severity factors with coumestrol across cultivars and plant growth stages (p < 0.001). Disease levels and coumestrol production were determined by inoculum concentration and cultivar (both p ≤ 0.001). Highest coumestrol was in Serena inoculated with 107 conidia/mL (265 mg/kg); lowest coumestrol was in uninoculated Harbinger (6 mg/kg); and there was a significant positive correlation of disease incidence/severity factors with coumestrol across cultivars and inoculum concentrations (p < 0.001). These studies emphasize both the opportunity for farmers to better use annual Medicago spp. stands for grazing reproducing animals early in the growing season when both disease and coumestrol levels are lowest, and the need for heightened farmer vigilance at later growth stages with greater disease and consequent phytoestrogen risk for grazing animals.

Inoculum threshold for stripe rust infection in wheat

Stripe rust (Puccinia striiformis f. sp. tritici (Pst)) and powdery mildew (Blumeria graminis f. sp. tritici (Bgt)) are important diseases of wheat in Canada and worldwide. Molecular detection methods permit spore detection of few spores; therefore, there is a need to determine initial inoculum thresholds for pathogens to cause disease under both controlled environments and in the field. Susceptible wheat cultivars ‘Avocet’ and ‘AC Barrie’ were inoculated with different quantities of spores (0, 103, 104, 105, 106, and 107) of Pst and Bgt. Disease incidence, severity and infection type were evaluated. Results of controlled environment studies showed that the minimum number of spores necessary to cause appreciable incidence and severity for Pst was at higher spore concentrations of 105–106 spores. Conversely, low incidence and severity levels were observed at 103–104 spores for Bgt. Despite occurrence of natural Pst infection, results of field studies in 2016 and 2017 in Southern Alberta demonstrated that significant increases in severity levels were observed following application of 1.2 × 107 spores. Collectively, these results demonstrated that stripe rust severities increased with increasing spore concentration only at high spore levels. In contrast, Bgt severity increased with spore concentration from 103 to 107 spores mL−1. In vitro and in vivo spore germination tests demonstrated germination rates of Pst spores were reduced at lower spore concentrations compared to germination rates at the higher concentrations. Understanding of minimum spore numbers required for disease development will be a prerequisite for predicting epidemics and devising fungicide control measures for future sustainable agricultural systems.

Development of Superabsorbent Polymer (SAP) Seed Coating Technology to Enhance Germination and Stand Establishment in Red Clover Cover Crop

Drought conditions after sowing threaten the seedling establishment of all seeds, including cover crops. Cover crops are commonly broadcast and, thus, are often susceptible to drought stress after sowing. Our hypothesis was that seed coating with superabsorbent polymers (SAPs) would enhance germination in the lab and stand establishment in the field by increasing water availability to single seeds. Red clover (Trifolium pratense L.) seeds were coated with the following selected SAP formulations at 2% of their seed weight: cross-linked potassium polyacrylate (PAL), cross-linked polyacrylamide-based polymer (PAM), PAM with graphite (PAM+G), and Starch-g-2-Propenoic acid (potassium salt) (STR). The water absorbency of each SAP formulation was >200 g water/g of polymer; STR had the greatest absorbency, at 352 g water/g of polymer. A seed coating method was developed, resulting in the uniform application of SAP from seed to seed. All SAP coating treatments increased germination compared to the 0% SAP coating in controlled environment studies in the lab. Three field trials were conducted for each seed coating treatment, providing a range of climatic soil conditions. Within each field trial, the STR with the greatest water absorbency had a higher stand for treatments sown by broadcasting followed by raking to incorporate seeds. The first two trials were conducted under more stressful conditions. PAM+G performed best in the first two trials by broadcasting seeds with no raking. Collectively, the selected SAP seed coating improved field stands compared to the non-treated controls.

Improving temperature‐based predictions of the timing of flowering in cotton

AbstractKey management recommendations for cotton (Gossypium hirsutum L.) management require estimates of the timing of crop phenology. Most commonly growing day degree (DD) (thermal time) approaches are used. Currently, across many cotton production regions, there is no consistent approach to predicting first square and flower timing. Day degree approaches vary considerably, with base thresholds different (12.0–15.6 °C) with no consistency using an optimum temperature threshold (i.e., temperature where development ceases to increase). As cotton is grown in variable and changing climates, and cultivars change, there is a need to ensure the accuracy of this approach for predicting timing of flowering for assisting cotton management. In this study new functions to predict first square and first flower were developed and validated using data collected in multiple seasons and regions (Australia and the United States). Earlier controlled environment studies that monitored crop development were used to assess in more detail how temperatures were affecting early cotton development. New DD functions developed predicted first square and first flower better than the existing Australian and U.S. approaches. The best performing functions had base temperatures like those of existing U.S. functions (15.6 °C) and an optimum threshold temperature of 32.0 °C. New universal DD targets for first square (343 DD [°C]) and first flower (584 DD) were developed. Controlled environment studies supported this base temperature outcome; however, it was less clear that 32.0 °C was the optimum threshold temperature from these data. Precise predictions of cotton development will facilitate accurate growth stage assessments and hence better cotton management decisions.

Integrating experiments to predict interactive cue effects on spring phenology with warming.

Climate change has advanced plant phenology globally 4-6 d °C-1 on average. Such shifts are some of the most reported and predictable biological impacts of rising temperatures. Yet as climate change has marched on, phenological shifts have appeared muted over recent decades - failing to match simple predictions of an advancing spring with continued warming. The main hypothesis for these changing trends is that interactions between spring phenological cues - long-documented in laboratory environments - are playing a greater role in natural environments due to climate change. Here, we argue that accurately linking shifts observed in long-term data to underlying phenological cues is slowed by biases in observational studies and limited integration of insights from laboratory studies. We synthesize seven decades of laboratory experiments to quantify how phenological cue-space has been studied and how treatments compare with shifts caused by climate change. Most studies focus on one cue, limiting our ability to make accurate predictions, but some well-studied forest species offer opportunities to advance forecasting. We outline how greater integration of controlled-environment studies with long-term data could drive a new generation of laboratory experiments, built on physiological insights, that would transform our fundamental understanding of phenology and improve predictions.

Lolium arundinaceum leaf and root developmental temperatures influence its allelopathic potency on Poa annua

AbstractAllelopathy is a commonly recognized but not fully understood method that could be utilized for weed management. Controlled environment studies in a growth chamber were conducted at Virginia Tech's Glade Road Research Facility in Blacksburg, VA, to determine whether aqueous leaf or root extracts from two Lolium arundinaceum (Schreb) Darbysh (tall fescue) cultivars grown under different growing temperature conditions affected the seed germination and growth of Poa annua L. (annual bluegrass). Two cultivars (‘Falcon III’ and ‘Kentucky 31’) of L. arundinaceum were maintained at cold (day/night 4.4:–1.1°C) or warm (day/night 32.2:26.7°C) conditions for 20 d. Leaf and root extracts were collected via destructive methods and applied to P. annua seed placed in petri dishes. The results indicated that aqueous leaf extracts of L. arundinaceum could inhibit P. annua seed germination, though there was no significant germination reduction with the root extract of L. arundinaceum. The results suggest that temperature may interact with other factors, such as L. arundinaceum cultivar, to influence its allelopathic potency on P. annua seed germination. These results further demonstrate that different cultivars of L. arundinaceum might have different allelopathic effects on P. annua germination.

Selection for early shoot vigour in wheat increases root hair length but reduces epidermal cell size of roots and leaves.

Six cycles of recurrent selection for early shoot vigour in wheat resulted in significant increases in leaf width and shoot biomass. Here, in replicated controlled-environment studies, the effect of early shoot vigour on root biomass, rhizosheath size, root hair length, and cell size in the roots and leaves was examined across different cycles of selection. Increased shoot vigour was associated with greater root biomass, larger rhizosheath size, and longer root hairs. Our findings demonstrate that rhizosheath size was a reliable surrogate for root hair length in this germplasm. Examination of the root epidermis revealed that the 'cell body' of the trichoblasts (hair-forming cells) and the atrichoblasts (non-hair-forming cells) decreased in size as shoot vigour increased. Therefore, in higher vigour germplasm, longer root hairs emerged from smaller trichoblasts so that total trichoblast volume (root hair plus cell body) was generally similar regardless of shoot vigour. Similarly, the sizes of the four main cell types on the leaf epidermis became progressively smaller as shoot vigour increased, which also increased stomatal density. The relationship between shoot vigour and root traits is considered, and the potential contribution of below-ground root traits to performance and competitiveness of high vigour germplasm is discussed.

Measuring Splash Dispersal of a Major Wheat Pathogen in the Field

Capacity for dispersal is a fundamental fitness component of plant pathogens. Characterization of plant pathogen dispersal is important for understanding how pathogen populations change in time and space. We devised a systematic approach to measure and analyze rain splash-driven dispersal of plant pathogens in field conditions, using the major fungal wheat pathogen Zymoseptoria tritici as a case study. We inoculated field plots of wheat ( Triticum aestivum) with two distinct Z. tritici strains. Next, we measured disease intensity as counts of fruiting bodies (pycnidia) using automated image analysis. These measurements characterized primary disease gradients, which we used to estimate effective dispersal of the pathogen population. Genotyping of reisolated pathogen strains with strain-specific PCR confirmed the conclusions drawn from phenotypic data. Consistently with controlled environment studies, we found that the characteristic scale of dispersal is tens of centimeters. We analyzed the data using a spatially explicit mathematical model that incorporates the spatial extent of the source, rather than assuming a point source, which allows for a more accurate estimation of dispersal kernels. We employed bootstrapping methods for statistical testing and adopted a two-dimensional hypotheses test based on kernel density estimation, enabling more robust inference compared with standard methods. We report the first estimates of dispersal kernels of the pathogen in field conditions. However, repeating the experiment in other environments would lead to more robust conclusions. We put forward advanced methodology that paves the way for further measurements of plant pathogen dispersal in field conditions, which can inform spatially targeted plant disease management. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Chickpea and lentil show little genetic variation in emergence ability and rate from deep sowing, but small-sized seed produces less vigorous seedlings

Context Germination and emergence are key to successful annual crop establishment. Emergence rate depends on germination rate, sowing depth, and rate of pre-emergent shoot elongation. The rate at which a shoot grows prior to emerging from the soil becomes significant when crops such as chickpea (Cicer arietinum L.) and lentil (Lens culinaris Medik.) are deep sown to utilise moisture below the conventional sowing zone. Aims In seeds of contrasting size, we aimed to compare the ability of chickpera and lentil varieties to emerge from deep sowing. Here we describe genetic variation for epicotyl growth rate, and phenotypic variation for epicotyl and root growth rates and biomass partitioning, of chickpea and lentil, as they relate to seed size. We further assess the impact of deep sowing and soil type on emergence, establishment and yield of the two species. Methods Epicotyl elongation rates, root growth and seedling biomass partitioning were determined in controlled environment studies, using soil tubes. Field trials were conducted on two different soil types at two sowing depths. Key results Most of the variance in epicotyl growth rate could be attributed to species rather than variety. Although epicotyl emergence was faster in lentil, chickpea epicotyl growth rates were higher than those in lentils and unrelated to seed size, whereas growth rates in lentils were weakly correlated to seed size (r = 0.31). Root development and epicotyl diameter appeared to be traded for maintenance of growth in smaller seeds of both species. In the field, sowing depth did not affect emergence, establishment or yield of chickpeas at either site. Deeper sowing resulted in minor reductions in emergence of lentil at one site, although biomass and yield were not affected. Conclusions Emergence of both crops was unaffected by deep sowing (to at least 200 mm) under controlled environment and sandy field conditions. There was minimal genetic variation for the measured parameters within a species. Seed size was of little importance for emergence rate; however, shoot growth rate from small seeds was maintained by reducing seedling vigour. Implications Seed size should be considered when deep sowing lentils in order to maintain high seedling vigour. Further work is needed to understand how environmental factors influence seedling emergence from depth.

Synergistic/antagonistic interactions between Neopseudocercosporella, Alternaria, Leptosphaeria, and Hyaloperonospora determine aggregate foliar disease severity in rapeseed

AbstractWhite leaf spot (Neopseudocercosporella capsellae), Alternaria leaf spot (Alternaria brassicae), blackleg (Leptosphaeria maculans), and downy mildew (Hyaloperonospora brassicae) commonly co‐occur on rapeseed (Brassica napus). In controlled environment studies, the synergistic/antagonistic interactions between these four pathogens were determined using two cultivars (Surpass 400, Thunder TT) with contrasting susceptibilities/resistances towards these pathogens. A spectrum of significant (p < 0.001) contrasting synergistic/antagonistic interactions between the four pathogens was observed and specific pathogen–pathogen interaction outcomes were determined by sequence of inoculation of different pathogens on each cultivar. On Thunder TT, Alternaria leaf spot was more severe (p < 0.001) when A. brassicae was applied prior to N. capsellae, but was reduced (p < 0.001) when A. brassicae was applied following N. capsellae. On Surpass 400, Alternaria leaf spot was enhanced (p < 0.001) when A. brassicae was applied following N. capsellae. For interactions involving H. brassicae on Thunder TT, downy mildew was reduced (p < 0.001) when co‐inoculated with N. capsellae, A. brassicae, or L. maculans, irrespective of co‐inoculating pathogen application sequence. This study highlights how disease severity of one or more co‐occurring pathogens is enhanced/decreased in the presence of other co‐occurring pathogens and emphasizes the importance of both pathogen inoculation sequence and relative host plant resistances/susceptibilities to different pathogens in together determining the total disease burden from these co‐occurring rapeseed diseases. Clearly, there is a need for rapeseed germplasm selection and breeding programmes to seriously consider the implications of co‐occurring pathogen complexes rather than solely relying upon single‐pathogen screening tests.

Use of rapid light curves to evaluate photosynthetic changes in turfgrasses exposed to low‐light conditions

AbstractShade is a widespread issue for turf areas that reduces turf quality, and the lack of light to drive photosynthetic processes is one major factor responsible for these declines. Maintaining a positive carbon balance is essential for plant survival under low‐light conditions, but large‐scale screening for photosynthetic performance can be a difficult task. Chlorophyll fluorescence rapid light curves (RLC) were used to understand difference in photosynthetic processes of hybrid bermudagrass ‘Tifway’ (Cynodon dactylon (L,) Pers. × C. transvaalensis Burtt Davy) and Japanese lawngrass ‘El Toro’ (Zoysia japonica Steud.) to high‐light (800 µmol m–2 s–1) and low‐light (200 µmol m–2 s–1) treatments in controlled environment studies. Measurement of maximum potential quantum yield (Fv/Fm) did not change over the course of the study but were significantly greater in El Toro. Tifway grown under high‐light treatment had greater maximum photosynthesis, and dark respiration rates compared to El Toro. The RLCs demonstrated that compared to hybrid bermudagrass in the low‐light treatment, Japanese lawngrass was more efficient at harvesting light at lower irradiance levels, but also reached saturation of light harvesting at lower irradiance levels. Differences in rapid light curves among plants grown under high‐light or low‐light treatments may be due to differences in photoacclimation. While rapid light curves should not be seen as a replacement for traditional light response curves based on CO2 flux, they did provide valuable information about acclimation of photosynthetic systems and warrant further testing in real‐world conditions.

Stomatal conductance limited the CO2 response of grassland in the last century

BackgroundThe anthropogenic increase of atmospheric CO2 concentration (ca) is impacting carbon (C), water, and nitrogen (N) cycles in grassland and other terrestrial biomes. Plant canopy stomatal conductance is a key player in these coupled cycles: it is a physiological control of vegetation water use efficiency (the ratio of C gain by photosynthesis to water loss by transpiration), and it responds to photosynthetic activity, which is influenced by vegetation N status. It is unknown if the ca-increase and climate change over the last century have already affected canopy stomatal conductance and its links with C and N processes in grassland.ResultsHere, we assessed two independent proxies of (growing season-integrating canopy-scale) stomatal conductance changes over the last century: trends of δ18O in cellulose (δ18Ocellulose) in archived herbage from a wide range of grassland communities on the Park Grass Experiment at Rothamsted (U.K.) and changes of the ratio of yields to the CO2 concentration gradient between the atmosphere and the leaf internal gas space (ca – ci). The two proxies correlated closely (R2 = 0.70), in agreement with the hypothesis. In addition, the sensitivity of δ18Ocellulose changes to estimated stomatal conductance changes agreed broadly with published sensitivities across a range of contemporary field and controlled environment studies, further supporting the utility of δ18Ocellulose changes for historical reconstruction of stomatal conductance changes at Park Grass. Trends of δ18Ocellulose differed strongly between plots and indicated much greater reductions of stomatal conductance in grass-rich than dicot-rich communities. Reductions of stomatal conductance were connected with reductions of yield trends, nitrogen acquisition, and nitrogen nutrition index. Although all plots were nitrogen-limited or phosphorus- and nitrogen-co-limited to different degrees, long-term reductions of stomatal conductance were largely independent of fertilizer regimes and soil pH, except for nitrogen fertilizer supply which promoted the abundance of grasses.ConclusionsOur data indicate that some types of temperate grassland may have attained saturation of C sink activity more than one century ago. Increasing N fertilizer supply may not be an effective climate change mitigation strategy in many grasslands, as it promotes the expansion of grasses at the disadvantage of the more CO2 responsive forbs and N-fixing legumes.

Clubroot resistance in canola and brassica vegetable cultivars in Ontario, Canada

Clubroot, caused by the obligate pathogen Plasmodiophora brassicae Woronin, has been present on brassica vegetables in Ontario for decades, but was only recently identified on canola (Brassica napus L.). Once P. brassicae is present in a field, eradication is difficult, but resistant cultivars can provide effective management. Pathotype 6 has been the predominant pathotype on vegetable crops for decades, but pathotype 2 is predominant in canola fields in Ontario. Field trials were used to assess the reaction of selected canola and vegetable Brassica cultivars to pathotype 2, and controlled environment studies were conducted to evaluate the reaction of the same cultivars to pathotypes 2 and 6. Four canola cultivars with putative clubroot resistance were compared with two cultivars that were expected to be susceptible and three susceptible control cultivars. Several brassica vegetables were assessed: cabbage, cauliflower, broccoli, napa cabbage, rutabaga, and Shanghai pak choi (a susceptible control). The canola cultivars marketed as resistant were highly resistant in both the field and growth room trials. The canola cultivars not marketed as resistant were susceptible to pathotype 2, as expected. All of the canola cultivars were resistant to pathotype 6. The vegetable cultivars marketed as resistant or tolerant were resistant to pathotype 6 and most were resistant to pathotype 2. A putative resistant cultivar of cabbage and one of broccoli were resistant to pathotype 6 but susceptible to pathotype 2. Clubroot consistently reduced fresh shoot weight in susceptible cultivars of canola and brassica vegetables relative to resistant cultivars.

First Report of Rhizoctonia solani AG 11 Causing Stem Rot of Phaseolus vulgaris in Idaho

In July 2018, bean plants (cv. Viva pink) at one location in south central Idaho were observed to have reduced growth with approximately 20% of the plants affected over 1 ha. Visual assessment showed that the below-ground parts of stems consistently displayed brown lesions up to 2 cm in length, which sometimes girdled the entire plant. To determine the causal agent, affected material (approximately 5 mm³) was surface disinfested in sodium hypochlorite (2%) for 30 s, rinsed twice in sterile water, and plated onto water agar medium amended with penicillin G (0.2 g/liter) and streptomycin sulfate (0.8 g/liter). After 3 days, colonies of Rhizoctonia solani were identified based on the presence of relatively broad (8 to 12 μm), septate hyphae with right-angle branching. Hyphal tips of R. solani colonies were transferred to potato dextrose agar (PDA) and grown for 2 weeks at 21°C. DNA was then extracted from hyphae taken from a single representative isolate (DB23). Anastomosis group (AG) was identified by ribosomal DNA ITS sequencing of isolate DB23. DNA was extracted and sequenced as previously described (Woodhall et al. 2013). The resulting sequence (GenBank no. MT256181) was over 99% identical with isolates previously identified as R. solani AG 11 (LC215403). To confirm pathogenicity, 2-week-old pinto bean plants (cv. Windbreaker) were each inoculated by placing a fully colonized 10-mm² plug taken from a 2-week-old PDA culture of isolate DB23 next to the stem 10 mm below the soil surface. Sterile PDA plugs were placed next to the stems of control plants. Each treatment was replicated five times. Plants were grown in a greenhouse at 21°C in potting compost (Scotts, Marysville, OH) under light for 16 h a day. After 5 weeks, each plant was assessed for disease using a previously described stem disease severity scale (Carling and Leiner 1990). No symptoms were present in the control plants. Plants inoculated with isolate DB23 had an average stem disease severity score of 2.6 (from a maximum of 4), and R. solani was consistently reisolated, thereby confirming Koch’s postulates. To our knowledge, this is the first report of R. solani AG 11 in Idaho on any host. Previously, R. solani AG 11 has been reported on Phaseolus vulgaris in Turkey (Eken and Demirci 2004) and on lily in Japan (Misawa et al. 2017). AG 11 has also been associated with soybeans in Arkansas (Ajayi-Oyetunde and Bradley 2017; Carling et al. 1994) and Illinois (Ajayi-Oyetunde and Bradley 2017). AG 11 has also been reported on rice in Arkansas (Carling et al. 1994; Spurlock et al. 2016) and sweet corn in New York (Ohkura et al. 2009). In western Australia, it was found on wheat and lupin, and these isolates were pathogenic to potatoes in controlled environment studies (Carling et al. 1994). Idaho is a major producer of wheat, potatoes, and dry beans; the presence of soilborne R. solani AG 11 also needs to be considered when diagnosing and managing Rhizoctonia diseases of these crops.

Agronomic Utilization of Precipitated Calcium Carbonate—Effect of PCC on Sugar Beet Root Aphid Control and Herbicide Dose Response of Kochia Grown on PCC Piles

Agricultural use of precipitated calcium carbonate (PCC), a byproduct of sugar clarification process, as a possible source of nutrients and pest and disease control in sugar beet (Beta vulgaris subsp. vulgaris.) needs a careful examination of the risk and benefit assessment at various levels of management and production. A series of controlled environment studies were conducted in Scottsbluff, NE, to assess the 1) effect of PCC on root aphids in sugar beet, and 2) risk of the weed kochia spreading by applying PCC to agricultural land and its chemical control strategy, by conducting various dose-response studies. A replicated lab study was conducted twice to determine the effect of PCC on root aphid in sugar beet using three rates of PCC (9, 18, and 27 Mg ha−1) and a control. The results showed that root aphid populations in all PCC-amended treatments were significantly reduced when compared to the control (p < 0.05). Two cycles of dose-response studies using the herbicides Roundup and Clarity at 6 concentrations revealed that kochia biotypes grown on PCC piles at three western sugar production locations were effectively controlled (LD50) with the current rate recommendations administered in this region for both herbicides. More field experiments are needed to confirm the results of these controlled environment studies.

Understanding Why Effective Fungicides Against Individual Soilborne Pathogens Are Ineffective with Soilborne Pathogen Complexes.

Annual forage legumes across southern Australia continue to be devastated by soilborne diseases. Nine fungicide seed treatments (thiram, metalaxyl, iprodione, phosphonic acid, propamocarb, fluquinconazole, difenoconazole + metalaxyl, ipconazole + metalaxyl, sedaxane + difenoconazole + metalaxyl) and four foliar fungicide treatments (phosphonic acid, metalaxyl, propamocarb, iprodione) were tested on four subterranean clover cultivars against individual oomycete soilborne pathogens Pythium irregulare, Aphanomyces trifolii, and Phytophthora clandestina and the fungal pathogen Rhizoctonia solani. Best treatments were then further tested across southern Australia in 2 years of field experiments. Under controlled conditions, seed treatment with thiram was best against damping-off caused by P. irregulare across the four cultivars (Woogenellup, Riverina, Seaton Park, Meteora), while metalaxyl was the most effective for maximizing root and shoot weights. Against A. trifolii, metalaxyl, iprodione, difenoconazole + metalaxyl, ipconazole + metalaxyl, and sedaxane + difenoconazole + metalaxyl, all reduced damping-off; sedaxane + difenoconazole + metalaxyl, fluquinconazole, and ipconazole + metalaxyl all reduced lateral root disease across two or more cultivars; while iprodione, thiram, and sedaxane + difenoconazole + metalaxyl increased shoot dry weight. Against P. clandestina, metalaxyl was the most effective in reducing tap and lateral root rot followed by ipconazole + metalaxyl or phosphonic acid for tap and lateral rot, respectively. Against R. solani, there were no effects of fungicides. For P. irregulare and P. clandestina, there were strong seed fungicide × cultivar interactions (P < 0.001). Under controlled conditions for foliar fungicide spray treatments, phosphonic acid was best at preventing productivity losses from A. trifolii, but was ineffective against P. clandestina, P. irregulare, or R. solani. Overall, controlled environment studies highlighted strong potential for utilizing seed treatments against individual pathogens to ensure seedling emergence and early survival, with seed and foliar sprays enhancing productivity by reducing seedling damping-off and root disease from individual pathogens. However, in field experiments over 2 years across southern Australia against naturally occurring soilborne pathogen complexes involving these same pathogens, only rarely did fungicide seed treatments or foliar sprays tested show any benefit. It is evident that currently available fungicide seed and/or foliar spray treatment options do not offer effective field mitigation of damping-off and root disease on annual forage legumes that underpin livestock production across southern Australia. The main reason for this failure relates to the unpredictable and ever-changing soilborne pathogen complexes involved, highlighting a need to now refocus away from fungicide options, particularly toward developing and deploying new host tolerances, but also in deploying appropriate cultural control options.

Contrasting Nitrogen Fertilisation Rates Alter Mycorrhizal Contribution to Barley Nutrition in a Field Trial.

Controlled environment studies show that arbuscular mycorrhizal fungi (AMF) may contribute to plant nitrogen (N) uptake, but the role of these near-ubiquitous symbionts in crop plant N nutrition under natural field conditions remains largely unknown. In a field trial, we tested the effects of N fertilisation and barley (Hordeum vulgare L.) cultivar identity on the contribution of AMF to barley N uptake using 15N tracers added to rhizosphere soil compartments. AMF were shown capable of significantly increasing plant 15N acquisition from root exclusion zones, and this was influenced by nitrogen addition type, N fertiliser application rate and barley cultivar identity. Our data demonstrate a previously overlooked potential route of crop plant N uptake which may be influenced substantially and rapidly in response to shifting agricultural management practices.

Tolerance and recovery of the annual pasture legumes Melilotus siculus, Trifolium michelianum and Medicago polymorpha to soil salinity, soil waterlogging and the combination of these stresses

This study evaluated the responses to and recovery from soil waterlogging, soil salinity and the combination of these stresses of the annual pasture legumes Melilotus siculus cv. Neptune, Trifolium michelianum cv. Frontier and Medicago polymorpha cv. Scimitar. The major aim was to test the tolerance of these plants to salinity and waterlogging in soil inoculated with rhizobia, adding to previous controlled-environment studies, which have used nutrient solution cultures, as well as to examine post-stress recovery. Plants were grown in pots of soil inoculated with their appropriate species-specific rhizobia. Drained non-saline controls, and waterlogged non-saline, drained saline (100 mM NaCl) and waterlogged saline treatments were imposed for 3 weeks, followed by a 4 week recovery period. In the waterlogged saline soil, shoot dry mass of M. siculus was 63% of the control, compared to 10% for T. michelianum and 5% for M. polymorpha, and after the recovery phase was 75% of the control for M. siculus, 58% for T. michelianum and 4% for M. polymorpha. Foliar Na+ concentrations of T. michelianum and M. polymorpha were 2.8-fold higher than for M. siculus. The greater tolerance of M. siculus can be attributed to regulation of leaf Na+ concentrations in saline conditions and the formation of aerenchymatous phellem to enhance O2 supply to roots in waterlogged soils. This controlled glasshouse study using pots of soil supports earlier nutrient solution experiments and field observations that M. siculus possesses greater tolerance of combined waterlogging and salinity, than T. michelianum and M. polymorpha.

Optimizing Pre-germination Techniques for Kentucky Bluegrass and Perennial Ryegrass1

Abstract Many intensively trafficked areas such as athletic fields and golf courses require constant overseeding to maintain suitable turfgrass cover. Rapid seed germination and development are critical to managing these high wear areas. The objectives of this research were to determine the effect of water aeration, seed soaking duration, and water temperature on mean germination time (MGT) and final germination percentage (FGP) of Kentucky bluegrass (Poa pratensis L., KBG) and perennial ryegrass (Lolium perenne L., PRG). Two separate controlled environment studies were conducted. PRG soaked in aerated water from 8 to 48 h had a 20% decrease in MGT compared to an untreated control, while treated KBG decreased MGT by only 10% compared to an untreated control. Soaking duration and water temperature had significant effects on KBG. KBG MGT was optimized at 20 C (68 F) water temperature with a soaking duration of 24 h. MGT of PRG was optimized when soaked for 8 h while water was aerated. There was no significant difference in FGP for any of the treatments tested. Index words: turfgrass, aeration, seed soaking. Species used in this study: Kentucky bluegrass (Poa pratensis L.); perennial ryegrass (Lolium perenne L.).

‘Collar propagation’ as an alternative propagation method for rhizomatous miscanthus

AbstractThe demand for perennial nonfood crops, such as miscanthus, is increasing steadily, as fossil resources are replaced by biomass. However, as the establishment of miscanthus is very expensive, its cultivation area in Europe is still small. The most common propagation method for miscanthus is via rhizomes, the harvesting of which is very labour‐intensive. Seed propagation is promising, but not suitable for sterile genotypes. In this study, a new vegetative propagation method, ‘collar propagation’, was tested in field and controlled environment studies. Collars are built at the junction between rhizome and stem. They can be harvested in a less destructive way than rhizomes by pulling out the stems from winter‐dormant miscanthus plants. One genotype of each of the species M. sacchariflorus, M. × giganteus, M. sinensis in combination with three fragment types (collars, rhizomes, collars + rhizomes) were tested for establishment success and plant performance. The performance (e.g. dry matter yield) of collar‐propagated plants was either better than or not significantly different from rhizome‐propagated plants. Pregrown plantlets transplanted into the field showed no significant differences in establishment success between the fragments within a genotype. When directly planted into the field however, the fragment ‘rhizome+collar’ had a significantly better establishment success than the other two. The winter survival rate of the fragment ‘rhizome+collar’ was 70% for M. sacchariflorus and 75% for M. × giganteus. Emergence success from collar‐derived plants was not affected by harvest date (harvested monthly from November to February). This study showed that miscanthus propagation via collars is feasible and a promising alternative to rhizome propagation, as the multiplication rate of collars is comparable to that of rhizome propagation. Collar propagation is the more suitable method for the tested genotypes of the species M. sachariflorus and M. × giganteus, but not for M. sinensis genotypes, which may be better propagated by seeds.