New Host Plant Species of Grapevine Virus A Identified with Vector-Mediated Infections

Grapevine virus A (GVA) is an economically important virus and a member of the genus Vitivirus (family Betaflexiviridae) that causes a range of symptoms with qualitative and quantitative effects on grape production. Wild and domesticated species of Vitis, including hybrids used as rootstocks, are considered important natural hosts of GVA. Mechanical transmission to some herbaceous plant species, graft transmission, and vector transmission from grape to grape by various mealybugs and soft scale insects have been reported. Under laboratory and greenhouse conditions, this study demonstrates the transmission of GVA from grapes to alternative hosts by the vine mealybug (Planococcus ficus). Results of ELISA, end-point one-step RT-PCR, and real-time RT-PCR, and in some cases electron microscopy and genome sequencing, confirmed successful transmission to three new plant species commonly found in Croatian vineyards: velvetleaf (Abutilon theophrasti), redroot pigweed (Amaranthus retroflexus), and field poppy (Papaver rhoeas), along with Chenopodium murale and the previously known host Nicotiana benthamiana, with variable infection rates. Depending on the host species, symptoms in the form of leaf reddening, yellow spots, reduced growth of lateral shoots, systemic vein clearing, foliar deformation and rugosity, and dwarfism were observed in GVA-infected plants, whereas no symptoms were observed in infected plants of A. theophrasti. Reverse transmission from these new hosts to grapevines by Pl. ficus was not successful. These results confirm four new GVA host species and open new research venues.

Germination Response of Datura stramonium L. to Different pH and Salinity Levels under Different Temperature Conditions

Weeds can be one of the most severe threats to crop production, especially when they are widespread and highly adaptable. Part of the adaptive strategy of plants is the ability to germinate in different conditions. Germination is the first developmental phase of plant life and is fundamental for its establishment. In this work, the germination of two populations of Datura stramonium L. at two different sites in Croatia (one cropped, the other non-agricultural) was tested under a wide range of salinity stress, 4, 8, 12, and 16 dS/m, and pH stress, values 1-9, at two temperature ranges of 15-25 °C and 18-30 °C. The results show that this species can tolerate high salinity, with a high number of seeds germinating, even under the highest level of saline stress and especially at higher temperatures: 21.7% of seeds germinated at 15-25 °C and 51.2% at 18-30 °C. D. stramonium also appears to be quite acid tolerant, with a significant reduction in germination only at pH 2, and no germination only at pH 1. Germination was always higher at higher temperatures, independently of abiotic stress. Although there were some differences between the two populations in the final germination percentages, they were similar in their responses to the abiotic stresses.

Size-strain line-broadening analysis of anatase/brookite (TiO2)-based nanocomposites with carbon (C): XRPD and Raman spectroscopic analysis

A size-strain line-broadening analysis of the XRPD patterns and Raman spectra for two anatase/brookite (TiO₂)-based nanocomposites with carbon (C) was carried out and the results compared with those of a similar sample free of carbon. The crystal structures and microstructures of anatase and brookite, as well as their relative abundance ratio, have been refined from XRPD data by the Rietveld method (the low amount of carbon is neglected). The XRPD size-strain analysis resulted in reliable structure and microstructure results for both anatase and brookite. The experimental Raman spectra of all the samples in the region 100-200 cm^-1 are dominated by a strong feature primarily composed of the most intense modes of anatase (E_g) and brookite (A_1g). The anatase crystallite sizes of 14-17 nm, estimated by XRPD, suggest the application of the phonon confinement model (PCM) for the analysis of the anatase E_g mode, whereas the relatively large brookite crystallite size (27-29 nm) does not imply the use of the PCM for the brookite A_1g mode. Superposition of the anatase E_g mode profile, calculated by the PCM, and the Lorentzian shape of the brookite A_1g mode provide an appropriate simulation of the change in the dominant Raman feature in the spectra of TiO₂-based nanocomposites with carbon. Raman spectra measured in the high-frequency range (1000-2000 cm^-1) provide information on carbon in the investigated nanocomposite materials. The results from field-emission scanning electron microscope (SEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and nitrogen physisorption measurements support the XRPD and Raman results.

Selected Phenolic Acids Inhibit the Initial Growth of Ambrosia artemisiifolia L

This study aimed to investigate whether different doses of specific phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, and p-coumaric acid), alone or in combination, can inhibit the early growth of the common ragweed (Ambrosia artemisiifolia L., Asterales: Asteraceae). A seed bioassay was performed in Petri dishes and placed in a climate chamber to assess the effects of five dose levels of phenolic acids to radicle and shoot length, as well seedling biomass of A. artemisiifolia. The lowest dose of phenolic acid corresponded to the natural phenolic acid concentration previously reported in dry plant tissue samples from Brassicaceae cover crop plants. Results show that the inhibition of the early growth of A. artemisiifolia depends strongly on phenolic acid. Across different treatments, high doses of phenolic acids significantly shortened shoots and radicles, as well as reduced seedling biomass. Treating seeds with ferulic acid alone, vanillic acid alone, p-hydroxybenzoic acid alone, or a mixture of all phenolic acids significantly reduced all early growth parameters. The estimated effective dose for the 50% inhibition (ED50) of radicle growth in A. artemisiifolia seedlings was 368.39 ± 59.85 × 10−8 mol with ferulic acid, 135.41 ± 17.65 × 10−8 mol with p-coumaric acid, 810.36 ± 134.15 × 10−8 mol with p-hydroxybenzoic acid, and 160.11 ± 12.30 × 10−8 mol with the combination of all phenolic acids.

Inhibitory Effects of Brassicaceae Cover Crop on Ambrosia artemisiifolia Germination and Early Growth

Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations [0, 0.5, 1, 2.5, 5, 7.5 and 10% (w/v)] of Brassicaceae CCs (Sinapis alba, Raphanus sativus, Camellina sativa) and of the CCs Fagopyrum esculentum and Guizotia abyssinica on germination and early growth of Ambrosia artemisiifolia L. The allelopathic effects were species and concentration-dependent. C. sativa, for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas S. alba and R. sativus inhibited germination and early growth of A. artemisiifolia only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of F. escultneum and G. abyssinica were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in C. sativa. Our results suggest that C. sativa is the most allelopathic CCs and that the fruits of C. sativa are the plant organs richest in allelochemicals.

Growth Stage of Alopecurus myosuroides Huds. Determines the Efficacy of Pinoxaden

Alopecurus myosuroides Huds. is an important pinoxaden-resistant grass weed in many countries of Europe. Recently, the low efficacy of pinoxaden was reported in winter cereals in Croatia, but a preliminary dose-response trial showed no herbicide resistance for the investigated weed population. Therefore, a two-year experiment was conducted under greenhouse conditions to determine the efficacy of various pinoxaden doses (20, 40 and 80 g a.i. ha^-1) on weed visual injuries and biomass reduction after herbicide application at different growth stages. As expected, the maximum weed biomass reduction (97.3%) was achieved by applying the highest dose (80 g a.i. ha^-1) at the earliest growth stage (ZCK 12-14). A pinoxaden dose of 20 g a.i. ha^-1 resulted in satisfactory weed biomass reduction (88.9%) only when applied at ZCK 12-14. The recommended dose (40 g a.i. ha^-1) also provided sufficient weed control up to the growth stage ZCK 21-25. Slightly delayed (ZCK 31-32) application of the recommended dose brought about a low weed biomass reduction (60.1%). Double than the recommended dose also failed to provide satisfactory weed control at the advanced weed growth stages (ZCK 31-32 and ZCK 37-39). Thus, reported low efficacy of pinoxaden is most likely because of delayed herbicide application when A. myosuroides is overgrown.

Sensitivity of yellow foxtail (Setaria glauca L.) and barnyardgrass (Echinochloa crus-galli L.) to aqueous extracts or dry biomass of cover crops

BACKGROUND

The common weeds Echinochloa crus-galli L. and Setaria glauca L. were studied for their sensitivity to aqueous extracts or dry biomass of the following cover crops (CCs): Brassicaceae (Sinapis alba, Raphanus sativus var. Oleiformis, Camellina sativa), Fagopyrum esculentum and Guizotia abyssinica.

RESULTS

Treating E. crus-galli with aqueous extracts of mixed CCs or individual brassica CC significantly reduced germination. Treating S. glauca with aqueous extracts of C. sativa or G. abyssinicia reduced germination. Aqueous extracts of all CCs significantly reduced radicle length of E. crus-galli and S. glauca, with C. sativa and mixed CCs showing the greatest effect. Aqueous extracts of nearly all CCs delayed start and middle germination of E. crus-galli and S. glauca, with S. alba and R. sativus showing the strongest effects. Aqueous extracts of Brassicaceae leaf and flower significantly reduced germination, coleoptile length, radicle length and seedling biomass of E. crus-galli and S. glauca. Brassicaceae leaves and flowers contained higher phenolics than other tissues. Adding 4 or 8% S. alba and R. sativus dry powder to soil significantly reduced growth of E. crus-galli and S. glauca; even concentrations of 1% measurably slowed growth of E. crus-galli.

CONCLUSIONS

Brassicaceae may be allelopathic to S. glauca and E. crus-galli. Aqueous extracts of leaves and flowers showed greater phytotoxic activity than other tissues and also contained more phenolics. Therefore Brassicaceae CCs may be most effective against S. glauca and E. crus-galli if incorporated into soil during their flowering stage. © 2020 Society of Chemical Industry.

Raman spectroscopy of K x Co2-y Se2 single crystals near the ferromagnet-paramagnet transition

Polarized Raman scattering spectra of the K _x Co_2-y Se₂ single crystals reveal the presence of two phonon modes, assigned as of the A _1g and B _1g symmetry. The absence of additional modes excludes the possibility of vacancy ordering, unlike in K _x Fe_2-y Se₂. The ferromagnetic (FM) phase transition at [Formula: see text] K leaves a clear fingerprint on the temperature dependence of the Raman mode energy and linewidth. For [Formula: see text] the temperature dependence looks conventional, driven by the thermal expansion and anharmonicity. The Raman modes are rather broad due to the electron-phonon coupling increased by the disorder and spin fluctuation effects. In the FM phase the phonon frequency of both modes increases, while an opposite trend is seen in their linewidth: the A _1g mode narrows in the FM phase, whereas the B _1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B _1g mode is due to the coupling of spin fluctuations and vibration. Our density functional theory (DFT) calculations for the phonon frequencies agree rather well with the Raman measurements, with some discrepancy being expected since the DFT calculations neglect the spin fluctuations.

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

Polarized Raman scattering spectra of superconducting K(x)Fe(2-y)Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm(-1) in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy near T(C) was observed in K(x)Fe(2-y) Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.