Poplars (Populus spp.) are widely used in the pulp and paper industry and as bioenergy resources. Poplars require a large amount of water for biomass accumulation and lack of water is a limiting factor for poplar growth. Arbuscular mycorrhizal (AM) fungi have been previously reported to afford some plant species with greater resistance to drought stress. However, the effects of AM fungi on hybrid poplar under drought stress and recovery have not been studied. The main aim of this study was to evaluate the effects of the AM fungus, Rhizophagus irregularis, on the growth, water status, chlorophyll (Chl) content and fluorescence, and photosynthesis of poplar seedlings. The experiment was divided into three stages. At each stage of the experiment, the seedlings were subjected to a different watering regime: well-watered (prior stress), drought, and then rewatering (recovery). Measurements were taken at the end of each stage of the experiment. The results showed that mycorrhizal plants had a higher net photosynthetic rate and Chl fluorescence compared with nonmycorrhizal plants, regardless of the stage. Mycorrhizal and nonmycorrhizal plants showed different responses to drought stress: mycorrhizal plants showed better water-use efficiency and water uptake under drought stress conditions. In general, the poplar seedlings that formed the AM symbiosis with R. irregularis showed enhanced growth and reduced loss of biomass during the drought stress compared with the nonmycorrhizal seedlings.

Significance and Impact of the Study: The semi-nested PCR assay may provide researchers and laboratory technologists a tool to rapidly detect C. lunata, which causes maize Curvularia leaf spot, compared with histological examination. AbstractCurvularia lunata (Wakker) Boed, the causative agent of Curvularia leaf spot in maize, was determined according to conidiophore and conidium morphology in a previous study. In the current study, a sensitive polymerase chain reaction assay was developed for the detection of C. lunata. Two specific forward (ClgD1/ClgD2) and one reverse primers (ClgD3) were designed based on a Ras-related (Clg2p) gene. Eight C. lunata isolates that represent different virulent strains in maize, six other Curvularia spp., and 22 fungal plant pathogens were used to test the specificity of the primers. PCR amplification using ClgD1/ClgD3 as the first-round primers resulted in an 870-bp band from the C. lunata isolates. The detection sensitivity using ClgD1/ClgD3 was 100 pg of genomic DNA. In the second round of PCR, a 1 : 50 dilution of the firstround PCR products was used as a template with the ClgD2/ClgD3 primer pair, which increased the detection sensitivity to 1 fg. This semi-nested PCR procedure could also be used to detect C. lunata from infected maize leaves. The proposed PCR-based assay may be used for diagnosing and monitoring maize Curvularia leaf spot.

Short-wavelength mid-infrared (2–2.5 μm wave band) silicon photonics has been a growing area to boost the applications of integrated optoelectronics in free-space optical communications, laser ranging, and biochemical sensing. In this spectral region, multi-project wafer foundry services developed for the telecommunication band are easily adaptable with the low intrinsic optical absorption from silicon and silicon dioxide materials. However, light coupling techniques at 2–2.5 μm wavelengths, namely, grating couplers, still suffer from low efficiencies, mainly due to the moderated directionality and poor diffraction-field tailoring capability. Here, we demonstrate a foundry-processed blazed subwavelength coupler for high-efficiency, wide-bandwidth, and large-tolerance light coupling. We subtly design multi-step-etched hybrid subwavelength grating structures to significantly improve directionality, as well as an apodized structure to tailor the coupling strength for improving the optical mode overlap and backreflection. Experimental results show that the grating coupler has a recorded coupling efficiency of − 4.53    dB at a wavelength of 2336 nm with a 3-dB bandwidth of ∼ 107    nm . The study opens an avenue to developing state-of-the-art light coupling techniques for short-wavelength mid-infrared silicon photonics.

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