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.

Policy shock effect of SDP on environmental total factors productivity: 53 coal cities versus 165 non-resource-based cities.

The trend of economic decline for coal cities is a serious threat to the high-quality development of China's economy, and how to improve the environmental total factor productivity (ETFP) has become an urgent issue. Based on the framework of data envelopment analysis (DEA), this paper estimates ETFP using the global Malmquist-Luenberger productivity index (GMLPI). We decompose GMLPI into environmental technical efficiency change (ETEC) and the best practice gap change (BPGC). Then, the difference-in-difference (DID) model combining propensity score matching (PSM) method is used to investigate the effect of the Sustainable Development Plan of National Resource-based Cities (2013-2020) (SDP) aiming to improve ETFP. The results indicate that (1) On average, the GMLPI and BPGC are rising, while the ETEC is decreasing in the observed sample period; the western regions have the biggest BPGC, while the eastern regions have the biggest ETEC; (2) The SDP significantly improves the GMLPI and BPGC but has little effect on the ETEC; Coal cities located in eastern and central regions have policy effect, while the western regions do not have. (3) The SDP affects ETFP through slowing down the economic growth rate and reducing population agglomeration, but promoting the optimization of industrial structure. Those findings have policy implications for improving ETFP and promoting the industrial upgrade of coal cities.