A Novel Real Time PCR Method for the Detection and Quantification of Didymella pinodella in Symptomatic and Asymptomatic Plant Hosts

Didymella pinodella is the major pathogen of the pea root rot complex in Europe. This wide host range pathogen often asymptomatically colonizes its hosts, making the control strategies challenging. We developed a real-time PCR assay for the detection and quantification of D. pinodella based on the TEF-1 alpha gene sequence alignments. The assay was tested for specificity on a 54-isolate panel representing 35 fungal species and further validated in symptomatic and asymptomatic pea and wheat roots from greenhouse tests. The assay was highly consistent across separate qPCR reactions and had a quantification/detection limit of 3.1 pg of target DNA per reaction in plant tissue. Cross-reactions were observed with DNA extracts of five Didymella species. The risk of cross contamination, however, is low as the non-targets have not been associated with pea previously and they were amplified with at least 1000-fold lower sensitivity. Greenhouse inoculation tests revealed a high correlation between the pathogen DNA quantities in pea roots and pea root rot severity and biomass reduction. The assay also detected D. pinodella in asymptomatic wheat roots, which, despite the absence of visible root rot symptoms, caused wheat biomass reduction. This study provides new insights into the complex life style of D. pinodella and can assist in better understanding the pathogen survival and spread in the environment.

Adsorption of Cadmium by Brassica juncea (L.) Czern. and Brassica pekinensis (Lour.) Rupr in Pot Experiment

Heavy metal pollution in farmland threatens human life. It is not clear whether crops can adsorb heavy metals. In this study, the cadmium accumulation and tolerance in Chinese cabbage Brassica pekinensis (cv. Xiaoza-56) and the known Cd-accumulator Brassica juncea in hydroponics and pot experiment were investigated. Furthermore, we evaluated their potential on the phytoextraction of Cd-contaminated soil. The hydroponics with 1–50 μM Cd concentrations showed that both B. juncea and B. pekinensis had high Cd accumulation and tolerance with translocation factor closed to 1 at Cd levels < 25 μM. The pot study conducted with 5 to 100 mg Cd kg−1 soil indicated that B. juncea showed less tolerance and accumulation to Cd than B. pekinensis, especially at higher Cd levels. The bioconcentration factor was much higher than 1 in both B. juncea and B. pekinensis grown in <40 mg Cd kg−1 soil without showing biomass reduction. In the model evaluation, the ability of B. juncea and B. pekinensis to reduce the initial soil Cd concentration of 20 and 5 mg kg−1 to specific targets with a lower or higher biomass of 4 or 20 t ha−1, respectively. The above results indicate that B. juncea and B. pekinensis (cv. Xiaoza-56), which the latter is a better candidate for Cd phytoextraction in moderated Cd-contaminated soil. The results provide a reference for Cd pollution control.

Effect of Salicylic Acid Foliar Application on Two Wheat Cultivars Grown under Zinc Stress

The aim of this study was to investigate the effect of foliar application of salicylic acid (SA) on alleviating Zn stress in young wheat plants. Two rigorous pot experiments were conducted with two spring wheat cultivars growing on soil artificially contaminated with Zn. The experimental design included three levels of soil contamination with Zn: 0, 300 and 700 mg kg−1, and three levels of SA concentration: 0, 0.5 and 1 mM. Foliar spray of SA was applied twice at an interval of two weeks. Wheat biomass was harvested two months after plant emergence. Both cultivars showed similar biomass reduction due to Zn phytotoxicity, but differed in the accumulation and distribution of this metal in the plant. The positive effect of SA foliar application was obtained only for one of the two tested cultivars, where a reduction in the Zn translocation from the roots to the aboveground part was observed. As a consequence, the decrease in biomass caused by the toxicity of Zn was limited. A greater positive effect of SA application on wheat biomass was observed at 700 than at 300 mg kg−1 Zn in soil. The different responses of the cultivars to the SA was probably related to their different defense mechanisms against Zn stress.

Management options for large plants of glyphosate-resistant feather fingergrass (Chloris virgata) in Australian fallow conditions

Chloris virgata has become one of the most difficult glyphosate-resistant (GR) grass weeds in summer fallows in the eastern region of Australia. It germinates in several cohorts following rainfall events; therefore, growers are often tempted to wait for most of the weeds to emerge before herbicide application. However, by that time, some seedlings have reached an advanced stage and there is limited information on the efficacy and reliability of alternate herbicides when targeting large plants of GR C. virgata. A series of experiments were conducted to determine the efficacy of alternate herbicides for the control of GR C. virgata. Haloxyfop (80 g a.i. ha-1) on its own, in mixtures, or sequential applications of haloxyfop and paraquat or glufosinate provided 97 to 100% mortality of the 8–10 leaf stage plants. Glufosinate (1500 g a.i. ha-1) also provided complete control of plants at this growth stage. For larger plants at the 24–28 leaf stage, glufosinate, with or without additional tank-mixed adjuvants, generally did not provide full control, however did show very high levels of biomass reduction and panicle suppression at application rates of 750 or 1500 g a.i. ha-1. Haloxyfop (40 to 160 g a.i. ha-1) and clethodim (180 g a.i. ha-1) on their own achieved 96 to 100% mortality at this growth stage. When applied to large plants (40–50 leaf stage), a tank-mix of isoxaflutole plus paraquat demonstrated significantly higher levels of plant mortality and biomass reduction than either herbicide used alone, and this mixture appears to be synergistic when tested via the Colby equation for synergy or antagonism. Plant mortality was greater (83%) when isoxaflutole (75 g a.i. ha-1) plus paraquat (300 g a.i. ha-1) was taken up through the foliage and soil, compared with the foliage alone. This study identified alternative herbicide options for large plants of GR C. virgata.

Combating Biofilm by Targeting Its Formation and Dispersal Using Gallic Acid against Single and Multispecies Bacteria Causing Dental Plaque

Exploring biological agents to control biofilm is a vital alternative in combating pathogenic bacteria that cause dental plaque. This study was focused on antimicrobial, biofilm formation and biofilm dispersal efficacy of Gallic acid (GA) against bacteria, including Proteus spp., Escherichia coli, Pseudomonas spp., Salmonella spp., Streptococcus mutans, and Staphylococcus aureus and multispecies bacteria. Biofilm was qualitatively and quantitatively assessed by crystal violet assay, florescence microscopy (bacterial biomass (µm2), surface coverage (%)) and extracellular polymeric substances (EPS). It was exhibited that GA (1–200 mg/L) can reduce bacterial growth. However, higher concentrations (100–200 mg/L) markedly reduced (86%) bacterial growth and biofilm formation (85.5%), while GA did not exhibit any substantial dispersal effects on pre-formed biofilm. Further, GA (20–200 mg/L) exhibited 93.43% biomass reduction and 88.6% (p < 0.05) EPS (polysaccharide) reduction. Microscopic images were processed with BioImageL software. It was revealed that biomass surface coverage was reduced to 2% at 200 mg/L of GA and that 13,612 (µm2) biomass was present for control, while it was reduced to 894 (µm2) at 200 mg/L of GA. Thus, this data suggest that GA have antimicrobial and biofilm control potential against single and multispecies bacteria causing dental plaque.

Effect of Soil Moisture Regimes on the Glyphosate Sensitivity and Morpho-Physiological Traits of Windmill Grass (Chloris truncata R.Br.), Common Sowthistle (Sonchus oleraceus L.), and Flaxleaf Fleabane [Conyza bonariensis (L.) Cronq.]

The glasshouse study was conducted with the objectives of (i) investigating the effect of soil moisture variations on the control efficiency of glyphosate on windmill grass (Chloris truncata R.Br.), common sowthistle (Sonchus oleraceus L.), and flaxleaf fleabane [Conyza bonariensis (L.) Cronq.], (ii) evaluating the tolerance of tested weed species under soil moisture variations, and (iii) determining the morphological and physiological characteristics of these species to partially explain herbicide tolerance under periods of reduced soil moisture availability (RSM). The species’ tolerance to glyphosate increased significantly under reduced soil moisture availability (p < 0.001). The lethal dose to cause herbicide injury or biomass reduction by 50% (LD50) and 80% (LD80) in relation to untreated control for water-stressed plants [i.e., moderate soil moisture availability (MSM) and RSM] was significantly higher than that of plants grown under high soil moisture availability (HSM). The tolerance factor (TF) for C. truncata, S. oleraceus, and C. bonariensis, in terms of biomass reduction under RSM, was 2.6, 2.4, and 2.6, respectively, as compared to HSM. The results showed that the glyphosate sensitivity, especially at the sub-lethal rates, of the three weed species under study decreased as soil moisture availability reduced (p < 0.01). Overall glyphosate efficacy, in relation to the recommended rate, was unaffected, except for C. truncata; the weed survived the highest tested glyphosate rate [750 g active ingredient (a.i.) ha−1] under RSM. There was significant interaction between weed species and soil moisture regimes for weed morpho-physiological traits (p < 0.001), with reduced soil moisture having a more influential impact on the growth of C. bonariensis and S. oleraceus compared to C. truncata. Changes in the leaf characteristics, such as increased leaf thickness, higher leaf chlorophyll content, reduced leaf area, and limited stomatal activity for all the tested weed species under MSM and RSM in relation to HSM, partially explain the tolerance of species to glyphosate at sublethal rates.

Mitotic-Inhibiting Herbicide Response Variation in Goosegrass (Eleusine indica) with a Leu136-Phe Substitution in α-Tubulin

Dithiopyr and dinitroanilines are preemergence-applied, mitotic-inhibiting herbicides used to control goosegrass [Eleusine indica (L.) Gaertn.]) in turfgrass. A suspected resistant E. indica population was collected from a golf course putting green and was evaluated for possible resistance to dithiopyr and prodiamine. After dose-response evaluation, the α-tubulin gene was sequenced for known target-site mutations that have been reported to confer resistance to mitotic-inhibiting herbicides. A mutation was discovered that resulted in an amino acid substitution at position 136 from leucine to phenylalanine (Leu136-Phe). Previous research has indicated that Leu136-Phe does confer resistance to dinitroaniline herbicides. The level of resistance indicated by regression models and I50 values indicates that there is a 54.1-, 4.7-, >100-, and >100-fold resistance to dithiopyr, prodiamine, pendimethalin, and oryzalin, respectively when compared to the susceptible population based on seedling emergence response and 88.4-, 7.8-, >100-, and >100-fold resistance to dithiopyr, prodiamine, pendimethalin, and oryzalin, respectively when compared to the susceptible population based on biomass reduction response. This is the first report of less resistance to prodiamine compared to pendimethalin or oryzalin due to a target-site α-tubulin mutation and the first report of a target-site α-tubulin mutation associated with dithiopyr resistance.

Urochloa brizantha cv. Marandu presents a better response to in vitro salt stress than other commercial cultivars

Urochloa brizantha is the main forage grass to raise cattle in Brazil, but salt stress can reduce yield. Physiological and molecular mechanisms of adaptation to salt stress remain poorly understood in this species. The objective of this study was to evaluate the responses of three cultivars of U. brizantha to in vitro salt stress. Seeds of three cultivars (Piatã, Marandu, and Xaraés) germinated in filter paper and then transferred to growth on culture media in vitro containing 0, 50, 100, and 200 mg L-1 of sodium chloride (NaCl). Biometric parameters and proline content were determined after 28 days. The data were subjected to analysis of variance and the separation of means was performed by the LSD test (p<0.05). Semi-quantitative expression of the Δ1-pyrroline-5-carboxylate synthase (P5CS1) gene was performed. In all cultivars, increase of NaCl concentration in the media affected roots and shoots growth. Xaraes cultivar presented the greater biomass reduction while Marandu cultivar was the least affected. Salt stress increased by approximated 0.6 folds transcription of the P5CS1 gene in all cultivars. However, Marandu cultivar presented a higher proline content and least biomass reduction suggesting a better response to in vitro to salt stress.

Opportunities for Improving Waterlogging Tolerance in Cereal Crops—Physiological Traits and Genetic Mechanisms

Waterlogging occurs when soil is saturated with water, leading to anaerobic conditions in the root zone of plants. Climate change is increasing the frequency of waterlogging events, resulting in considerable crop losses. Plants respond to waterlogging stress by adventitious root growth, aerenchyma formation, energy metabolism, and phytohormone signalling. Genotypes differ in biomass reduction, photosynthesis rate, adventitious roots development, and aerenchyma formation in response to waterlogging. We reviewed the detrimental effects of waterlogging on physiological and genetic mechanisms in four major cereal crops (rice, maize, wheat, and barley). The review covers current knowledge on waterlogging tolerance mechanism, genes, and quantitative trait loci (QTL) associated with waterlogging tolerance-related traits, the conventional and modern breeding methods used in developing waterlogging tolerant germplasm. Lastly, we describe candidate genes controlling waterlogging tolerance identified in model plants Arabidopsis and rice to identify homologous genes in the less waterlogging-tolerant maize, wheat, and barley.

Drought and Competition With Ivyleaf Morningglory (Ipomoea hederacea) Inhibit Corn and Soybean Growth

Agricultural impacts of climate change include direct effects on crop plants and indirect effects, such as changes to the distributions and competitiveness of weed species. In the northeastern United States, warming temperatures are likely to result in periods of soil moisture deficit and changes to weed communities. Ivyleaf morningglory (IMG, Ipomoea hederacea Jacq.) is a summer annual vine that competes with field crops and interferes with harvesting. Climate change may increase the competitive effects of IMG on northeastern U.S. field crops. We conducted a greenhouse study to evaluate the effects of IMG on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] under drought and non-drought conditions. The drought treatment was crossed against an IMG competition treatment with five levels: one crop plant without IMG plants, one crop plant with one, two, or three IMG plants, and one IMG plant without crop plants. Both drought and IMG (presence or biomass) reduced the biomass of corn and soybean (P &lt; 0.05). Drought and IMG (presence) reduced soybean pod production (P &lt; 0.001). IMG biomass was reduced by drought and the presence of corn (P &lt; 0.001). Across all competition treatments, drought reduced IMG biomass by 71% in the corn experiment and 79% in the soybean experiment, compared with a corn biomass reduction of 50% and a soybean biomass reduction of 58%. Well-designed management programs should mitigate the risks associated with stressors such as IMG and drought, which may threaten northeastern U.S. field crop production under climate change.