Citral (Eo) exhibits excellent fungicidal activities. However, it is difficult to maintain long-term fungicidal activity due to its strong volatility. Herein, a controlled-release strategy by using biomass-derived porous carbon (BC) was developed to overcome the drawback of Eo. New composite materials were prepared by loading Eo on tea stem porous carbon (BC@Eo), and their controlled-release fungicidal activity against Exobasidium vexans was assessed. BC with a large specific surface area of 1001.6 m 2 /g and mesoporous structure was fabricated through carbonization temperature of 700°C. The BC@Eo materials were characterized using Fourier-transform infrared spectroscopy and X-ray powder diffraction. The results suggested that chemical and physical interactions occurred in BC@Eo. The Eo release profile suggested a biphasic pattern with an initial fast release on days 1-14 and a subsequent controlled phase on days 14-30. The in vitro cumulative release percentage of Eo from BC@Eo was 51% during one month, and this result was significantly lower than that from free Eo (cumulative release percentage of Eo of 82% in one week). The antifungal activities of Eo and BC@Eo against E. vexans were determined using the inhibition zone method. The results indicated that Eo and BC@Eo formed large inhibition zones of 19.66 ± 0.79 and 21.92 ± 0.77 mm, respectively. The influence on the hyphal structure of E. vexans was observed by scanning electron microscopy on day 30. The hyphal structure of E. vexans treated with BC@Eo was more shrunken than that treated with Eo at 30 days, suggesting that BC@Eo prolongs the fungicidal activity against E. vexans. This study demonstrated that the encapsulation of Eo in BC for developing the BC@Eo materials could be a promising strategy to inhibit volatility and maintain the fungicidal activity of Eo and provide a potential alternative for the reuse of abundant tea biomass waste resources.
Plants produce and emit a large variety of volatiles that have multiple defense-related functions in response to abiotic or biotic stresses. In comparison with studies on plant volatile–herbivore interactions, little research has been carried out on plant volatile–microbe interactions. In the present paper, tea volatile–Colletotrichum camelliae interactions were studied. The results of emitted volatiles following infection with C. camelliae in “Baiye No. 1” showed that healthy tea plants contained 68 kinds of volatiles, while infected tea plants contained 76 kinds of volatiles. Five volatiles, namely, geraniol, linalool, methyl salicylate, (E)-3-hexen-1-ol, and α-farnesene, were found to have a relatively large content variation in infected tea plants, with increments of 7.903%, −2.247%, 2.770%, −6.728%, and 3.848%, respectively. The fungicidal activity results of the five volatiles against C. camelliae showed that geraniol had the best activity, with MIC and MBC values of 0.5 and 1 mg·mL−1, respectively. Thus, geraniol was selected for subsequent studies. The effects of geraniol on the mycelia and cell structures of C. camelliae were investigated by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results showed that the mycelia were significantly disrupted, and the cell structures were damaged. The effects of geraniol on the related enzymes of C. camelliae were assessed. The results showed that cellulase activity increased, malondialdehyde content increased, and the activity of defense enzymes was inhibited, thereby inhibiting the growth of pathogens. This study provides the first evidence that geraniol is a defense-related function volatile of “Baiye No. 1” in response to C. camelliae stress. It also provides valuable information and enriches the chemical ecology of tea plant diseases for the research field on defensive substances of microbe-induced plant volatiles.
A compound aircraft with a collectible rotor has the ability of vertical takeoff and landing (VTOL), high-speed flight and long-range cruising. Compared to systems in other compound aircraft, the collectible rotor can work as a conventional rotor in helicopter mode and can be gathered into a disk in the center in fixed-wing mode, thereby relieving the rotor's limitations pertaining to forward flight performance. The collectible rotor is a key component in the design and realization of a compound aircraft. Based on a 35-kg-level prototype, in this study, the principle of a folding rotor is proposed, a dynamic model of the rotor is established considering the complex nonlinear compound motion of rotation and folding, and the aerodynamic and dynamic characteristics are analyzed considering the coupling of different speeds of the rotor and folding strategies for the folding process. According to the above research, a complete rotor system, including an unconventional rotor structure, closed-loop real-time control system, and high-torque driving system, is designed. A demonstration model was constructed to verify the feasibility of the folding rotor. Finally, through an on-board test, the folding rotor system was verified in a simulated real flight state. This paper provides a theoretical basis for folding rotor design and proposes a set of design methods and research concepts.
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