Study on the inhibitory mechanism of fig leaf extract against postharvest Fusarium in melon

The objective of this study was to explore the fungistatic mechanism of fig leaf extract against Fusarium and to provide a theoretical basis for the development of new plant-derived fungicides. Methods The fungistaticity of fig leaf extract were analyzed by the ring of inhibition method. Fusarium equiseti was selected as the target for analyzing its fungistatic mechanism in terms of mycelial morphology, ultrastructure, cell membrane permeability, membrane plasma peroxidation, reactive oxygen species (ROS) content and changes in the activity of protective enzymes. The effect of this extract was verified in melon, and its components were determined by metabolite analysis using ultraperformance liquid chromatography‒mass spectrometry (UPLC‒MS). Results Fig leaf extract had an obvious inhibitory effect on Fusarium, and the difference was significant (P < 0.05) or highly significant (P < 0.01). Scanning and transmission electron microscopy revealed that F. equiseti hyphae exhibited obvious folding, twisting and puckering phenomena, resulting in an increase in the cytoplasmic leakage of spores, interstitial plasma, and the concentration of the nucleus, which seriously damaged the integrity of the fungal cell membrane. This phenomenon was confirmed by propidium iodide (PI) and fluorescein diacetate (FAD) staining, cell membrane permeability and malondialdehyde (MDA) content. Fig leaf extract also induced the mycelium to produce excessive H2O2,which led to lipid peroxidation of the cell membrane, promoted the accumulation of MDA, accelerated protein hydrolysis, induced an increase in antioxidant enzyme activity, and disrupted the balance of ROS metabolism; these findings showed that fungal growth was inhibited, which was verified in melons. A total of 1,540 secondary metabolites were detected by broad-targeted metabolomics, among which the fungistatic active substances flavonoids (15.45%), phenolic acids (15%), and alkaloids (10.71%) accounted for a high percentage and the highest relative content of these substances 1,3,7,8-tetrahydroxy-2- prenylxanthone, 8-hydroxyquinoline and Azelaic acid were analysed for their antimicrobial, anti-inflammatory, antioxidant, preventive effects against plant diseases and acquisition of resistance by plants. This confirms the reason for the fungicidal properties of fig leaf extracts. Conclusion Fig leaf extract has the potential to be developed into a plant-derived fungicide as a new means of postharvest pathogen prevention and control in melon

Effects of Low-Light Stress on Physiological Characteristics of Fruits of Different Muskmelon Varieties

【Objective】The study aims to explore the effects of low-light stress on the main quality characteristics of fruits of different muskmelon varieties.【Method】The content changes of carbohydrates, carotenoids and chlorophyll in different fruit positions (pedicle, areola and pulp) of three varieties (Xizhoumi No. 1, Zaohuanghou and Jiashi) of muskmelon under different light intensities (100%, 42% and 23% transmittance) at different development stages (0, 3, 7, 14, 21, 35, 40, 60 d after blooming) were investigated.【Result】Results showed that contents of fruit starch, sucrose and reducing sugar all increased continuously during fruit development and the highest contents exhibited at mature stage (35 d), and Xizhoumi No. 1 had the highest starch content (10.835%), while Jiashi had the lowest starch content (8.342%). The pulp and areola of the fruits of three varieties showed higher sucrose content than that in pedicle, but no difference in reducing sugar content. The contents of carotenoid and chlorophyll increased during fruit development but decreasedat full ripe stage (60 d after blooming). Low-light stress significantly reduced the carbohydrate content, increased carotenoid and chlorophyll contents, and most significant effect was found under transmittance 23% treatment, under which the contents of starch, sucrose and reducing sugar in Xizhoumi No. 1 muskmelon reduced by 32.3%, 29.87% and 28.02%, while contents of carotene and chlorophyll increased by 19.47% and 13.98%, respectively. The contents of starch, sucrose and reducing sugar in Zaohuanghou muskmelon reduced by 32.63%, 25.09% and 20.24%, and the contents of carotene and chlorophyll increased by 54.74% and 21.06%, respectively. The contents of starch, sucrose and reducing sugar in Jiashi muskmelon reduced by 41.08%, 32.39% and 39.1%, and the contents of carotene chlorophyll increased by 55.20% and 31.79%, respectively. Compared with Xizhoumi No. 1 and Zaohuanghou muskmelons, the Jiashi muskmelon showed the lowest starch and chlorophyll contents and the highest sucrose and reducing sugar contents, and exhibited the most significant decline of starch, sucrose and reducing sugar contents, and increase of carotenoid and chlorophyll contents, indicating that the Jiashi muskmelon was affected most significantly by low-light stress and showed poorest low-light tolerance.【Conclusion】The low-light stress reduces the commercial quality of muskmelon fruits, and the quality is worse when the light transmittance is lower. Jiashi muskmelon is most sensitive to low-light stress

Manipulating Picosecond Photoresponse in van der Waals Heterostructure Photodetectors

Self-powered ultrafast 2D photodetectors have demonstrated great potential in imaging, sensing, and communication. Understanding the intrinsic ultrafast charge carrier generation and separation processes is essential for achieving high-performance devices. However, probing and manipulating the ultrafast photoresponse is limited either by the temporal resolution of the conventional methods or the required sophisticated device configurations. Here, van der Waals heterostructure photodetectors are constructed based on MoS2/WSe2 p–n and n–n junctions and manipulate the picosecond photoresponse by combining photovoltaic (PV) and photothermoelectric (PTE) effects. Taking time-resolved photocurrent (TRPC) measurements, a TRPC peak at zero time delay is observed with decay time down to 4 ps in the n–n junction device, in contrast to the TRPC dip in the p–n junction and pure WSe2 devices, indicating an opposite current polarity between PV and PTE. More importantly, with an ultrafast photocurrent modulation, a transition from a TRPC peak to a TRPC dip is realized, and detailed carrier transport dynamics are analyzed. This study provides a deeper understanding of the ultrafast photocurrent generation mechanism in van der Waals heterostructures and offers a new perspective in instruction for designing more efficient self-powered photodetectors.Comprehensive understanding of interaction between photovoltaic and photothermoelectric effects is demonstrated via a time-resolved photocurrent (TRPC) measurement technique. Compared to MoS2/multilayer WSe2 p–n junction having a conventional TRPC dip, MoS2/1L WSe2 n–n junction processes a distinct TRPC peak, which is attributed to the opposite polarity between photovoltaic and photothermoelectric currents and can be further modulated via an external bias.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/173088/1/adfm202200973_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/173088/2/adfm202200973-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/173088/3/adfm202200973.pd