Leaching of unexpected cyazofamid degradation products into groundwater demonstrates gaps in current pesticide risk assessment.

To investigate the formation and leaching potential of degradation products N,N-dimethylsulfamide (DMS) and dimethylsulfamic acid (DMSA) from cyazofamid under real-world agricultural conditions, the fungicide cyazofamid was applied in a potato crop as part of the Danish Pesticide Leaching Assessment Programme (PLAP). Leaching of DMS, DMSA, 4-chloro-5-(4-methylphenyl)-1H-imidazole-2-carbonitrile (CCIM), and 4-chloro-5-(4-methylphenyl)-1H-imidazole-2-carboxylicacid (CTCA) was monitored in water from the variably saturated zone (suction cups) and groundwater for more than two years following the applications. In total, 424 samples were analyzed for the content of the four degradation products. An additional laboratory study was executed in parallel with the field monitoring study. Here, cyazofamid was applied to soil columns and leaching of the four degradation products was studied under controlled conditions. In the EFSA conclusion on cyazofamid, CCIM and CTCA are mentioned as major relevant metabolites; DMS is not mentioned in the risk assessment and DMSA is only included in acute oral toxicity studies and an in vitro bacterial mutation assay. In contrast to the EFSA conclusion on cyazofamid, our studies showed no leaching of the two major metabolites, CTCA and CCIM, but instead, major leaching of DMS and DMSA in both the field and laboratory studies was observed. That is, both DMS and DMSA leached to the groundwater in concentrations >0.1 µg/L for more than half a year. Based on this, we suggest improvements to the current pesticide risk assessment.

Spatiotemporal Winter Wheat Water Status Assessment Improvement Using a Water Deficit Index Derived from an Unmanned Aerial System in the North China Plain.

Agricultural droughts cause a great reduction in winter wheat productivity; therefore, timely and precise irrigation recommendations are needed to alleviate the impact. This study aims to assess drought stress in winter wheat with the use of an unmanned aerial system (UAS) with multispectral and thermal sensors. High-resolution Water Deficit Index (WDI) maps were derived to assess crop drought stress and evaluate winter wheat actual evapotranspiration rate (ETa). However, the estimation of WDI needs to be improved by using more appropriate vegetation indices as a proximate of the fraction of vegetation cover. The experiments involved six irrigation levels of winter wheat in the harvest years 2019 and 2020 at Luancheng, North China Plain on seasonal and diurnal timescales. Additionally, WDI derived from several vegetation indices (VIs) were compared: near-infrared-, red edge-, and RGB-based. The WDIs derived from different VIs were highly correlated with each other and had similar performances. The WDI had a consistently high correlation to stomatal conductance during the whole season (R2 between 0.63-0.99) and the correlation was the highest in the middle of the growing season. On the contrary, the correlation between WDI and leaf water potential increased as the season progressed with R2 up to 0.99. Additionally, WDI and ETa had a strong connection to soil water status with R2 up to 0.93 to the fraction of transpirable soil water and 0.94 to the soil water change at 2 m depth at the hourly rate. The results indicated that WDI derived from multispectral and thermal sensors was a reliable factor in assessing the water status of the crop for irrigation scheduling.

Water use efficiency and shoot biomass production under water limitation is negatively correlated to the discrimination against 13C in the C3 grasses Dactylis glomerata, Festuca arundinacea and Phalaris arundinacea.

Climate change impacts rainfall patterns which may lead to drought stress in rain-fed agricultural systems. Crops with higher drought tolerance are required on marginal land with low precipitation or on soils with low water retention used for biomass production. It is essential to obtain plant breeding tools, which can identify genotypes with improved drought tolerance and water use efficiency (WUE). In C3 plant species, the variation in discrimination against 13C (Δ13C) during photosynthesis has been shown to be a potential indicator for WUE, where discrimination against 13C and WUE were negatively correlated. The aim of this study was to determine the variation in the discrimination against 13C between species and cultivars of three perennial C3 grasses (Dactylis glomerata (cocksfoot), Festuca arundinacea (tall fescue) and Phalaris arundinacea (reed canary grass)) and test the relationships between discrimination against 13C, season-long water use WUEB, shoot and root biomass production in plants grown under well-watered and water-limited conditions. The grasses were grown in the greenhouse and exposed to two irrigation regimes, which corresponded to 25% and 60% water holding capacity, respectively. We found negative relationships between discrimination against 13C and WUEB and between discrimination against 13C and shoot biomass production, under both the well-watered and water-limited growth conditions (p < 0.001). Discrimination against 13C decreased in response to water limitation (p < 0.001). We found interspecific differences in the discrimination against 13C, WUEB, and shoot biomass production, where the cocksfoot cultivars showed lowest and the reed canary grass cultivars highest values of discrimination against 13C. Cocksfoot cultivars also showed highest WUEB, shoot biomass production and potential tolerance to water limitation. We conclude that discrimination against 13C appears to be a useful indicator, when selecting C3 grass crops for biomass production under drought conditions.

Low-temperature leaf photosynthesis of a Miscanthus germplasm collection correlates positively to shoot growth rate and specific leaf area.

BACKGROUND AND AIMS: The C4 perennial grass miscanthus has been found to be less sensitive to cold than most other C4 species, but still emerges later in spring than C3 species. Genotypic differences in miscanthus were investigated to identify genotypes with a high cold tolerance at low temperatures and quick recovery upon rising temperatures to enable them to exploit the early growing season in maritime cold climates. Suitable methods for field screening of cold tolerance in miscanthus were also identified. METHODS: Fourteen genotypes of M. sacchariflorus, M. sinensis, M. tinctorius and M. × giganteus were selected and grown under warm (24 °C) and cold (14 °C) conditions in a controlled environment. Dark-adapted chlorophyll fluorescence, specific leaf area (SLA) and net photosynthetic rate at a photosynthetically active radiation (PAR) of 1000 µmol m(-2) s(-1) (A1000) were measured. Photosynthetic light and CO2 response curves were obtained from 11 of the genotypes, and shoot growth rate was measured under field conditions. KEY RESULTS: A positive linear relationship was found between SLA and light-saturated photosynthesis (Asat) across genotypes, and also between shoot growth rate under cool field conditions and A1000 at 14 °C in a climate chamber. When lowering the temperature from 24 to 14 °C, one M. sacchariflorus exhibited significantly higher Asat and maximum photosynthetic rate in the CO2 response curve (Vmax) than other genotypes at 14 °C, except M × giganteus 'Hornum'. Several genotypes returned to their pre-chilling A1000 values when the temperature was increased to 24 °C after 24 d growth at 14 °C. CONCLUSIONS: One M. sacchariflorus genotype had similar or higher photosynthetic capacity than M × giganteus, and may be used for cultivation together with M × giganteus or for breeding new interspecies hybrids with improved traits for temperate climates. Two easily measured variables, SLA and shoot growth rate, may be useful for genotype screening of productivity and cold tolerance.

Cytosolic glutamine synthetase is important for photosynthetic efficiency and water use efficiency in potato as revealed by high-throughput sequencing QTL analysis.

KEY MESSAGE: WUE phenotyping and subsequent QTL analysis revealed cytosolic GS genes importance for limiting N loss due to photorespiration under well-watered and well-fertilized conditions. Potato (Solanum tuberosum L.) closes its stomata at relatively low soil water deficits frequently encountered in normal field conditions resulting in unnecessary annual yield losses and extensive use of artificial irrigation. Therefore, unraveling the genetics underpinning variation in water use efficiency (WUE) of potato is important, but has been limited by technical difficulties in assessing the trait on individual plants and thus is poorly understood. In this study, a mapping population of potatoes has been robustly phenotyped, and considerable variation in WUE under well-watered conditions was observed. Two extreme WUE bulks of clones were identified and pools of genomic DNA from them as well as the parents were sequenced and mapped to reference potato genome. Following a novel data analysis approach, two highly resolved QTLs were found on chromosome 1 and 9. Interestingly, three genes encoding isoforms of cytosolic glutamine synthase were located in the QTL at chromosome 1 suggesting a major contribution of this enzyme to photosynthetic efficiency and thus WUE in potato. Indeed, Glutamine synthetase enzyme activity of leaf extracts was measured and found to be correlated with contrasting WUE phenotypes.

Can the exceptional chilling tolerance of C4 photosynthesis found in Miscanthus × giganteus be exceeded? Screening of a novel Miscanthus Japanese germplasm collection.

BACKGROUND AND AIMS: A clone of the hybrid perennial C4 grass Miscanthus × giganteus (Mxg) is known for achieving exceptionally high rates of leaf CO2 uptake during chilling. This is a requisite of success in the early spring, as is the ability of the leaves to survive occasional frosts. The aim of this study was to search for genotypes with greater potential than Mxg for photosynthesis and frost survival under these conditions. METHODS: A total of 864 accessions representing 164 local populations of M. sacchariflorus (Msa), M. sinensis (Msi) and M. tinctorius (Mti) collected across Japan were studied. Accessions whose leaves survived a natural late frost in the field were screened for high maximum photosystem II efficiency (Fv/Fm) following chilling weather, as an indicator of their capacity for light-limited photosynthesis. Those showing the highest Fv/Fm were transferred to a high-light-controlled environment and maintained at chilling temperatures, where they were further screened for their capacities for high-light-limited and light-saturated leaf uptake of CO2 (ΦCO2,max and Asat, respectively). KEY RESULTS: For the first time, relatives of Mxg with significantly superior capacities for photosynthesis at chilling temperatures were identified. Msa accession '73/2' developed leaves in the spring that survived night-time frost, and during growth under chilling maintained a statistically significant 79 % higher ΦCO2,max, as a measure of light-limited photosynthesis, and a 70 % higher Asat, as a measure of light-saturated photosynthesis. A second Msa accession, '73/3' also showed significantly higher rates of leaf uptake of CO2. CONCLUSIONS: As remarkable as Mxg has proved in its chilling tolerance of C4 photosynthesis, this study shows that there is still value and potential in searching for yet more superior tolerance. Msa accession '73/2' shows rates of light-limited and light-saturated photosynthesis at chilling temperatures that are comparable with those of the most cold-tolerant C3 species. This adds further proof to the thesis that C4 photosynthesis is not inherently limited to warm climates.