Brown apical necrosis (BAN) of walnut (Juglans regia L.) causes premature fruit drop and yield losses and has been reported to be an important walnut production problem in Spain, Italy, France, and Turkey (1,2). A number of organisms have been associated with BAN on walnut: Xanthomonas arboricola pv. juglandis, Fusarium spp., and Alternaria spp. (3). Since the spring of 2007, BAN was observed in 50 to 60% of the trees in walnut orchards in Taian City and Laiwu City, Shandong Province, China. Surface-disinfested tissue from premature walnut fruits was placed onto potato dextrose agar. Alternaria spp., X. arboricola pv. juglandis, and Pantoea agglomerans (formerly Enterobacter agglomerans) were isolated 76, 35, and 45% of the time, respectively. The P. agglomerans cultures formed a yellow lawn and were rod shaped with the body length of 1.5 to 3.0 μm, width of 0.5 to 1.0 μm, and four to six flagella. In biochemical tests, these bacteria were gram negative, lactose positive, and indole negative. Genomic DNA was extracted from one HXJ isolate and the 16S rRNA gene sequence (GenBank Accession No. HM016799) was obtained using universal primers 27F and 1492R. HM016799 had 99% sequence identity with P. agglomerans accessions in GenBank (GU477762, GQ494018, FJ756355, and AB004757). To confirm pathogenicity, HXJ isolate (108 CFU·ml–1) was inoculated at the bottom of the stigma within 5 days after florescence (DAF) and in premature fruit wounded with a needle within 30 DAF in 2008 to 2010. Stigmas injected with only sterile water served as controls. The bacteria were inoculated into three replicate 9-year-old plants of the walnut cv. Xiangling. Forty nuts on each plant were inoculated. The plants were grown in Shandong Province, China (36°09′59″N, 117°13′30″E). Ten days after inoculation, typical internal BAN symptoms were observed on all treated nuts and the controls were still healthy. In the inoculated stigmas, necrosis of stigma and style spread to internal tissues and reached the kernel. In treated premature fruit, internal tissues became necrotic and blackish and eventually led to nut drop. The same bacterium was reisolated from the inoculated tissue. On the basis of morphological, physiological, and biochemical characteristics and sequencing of the 16S rRNA gene, the bacterium was identified as P. agglomerans. To our knowledge, this is the first report of P. agglomerans causing internal type BAN of walnut in China or worldwide. References: (1) A. Belisario et al. Plant Dis. 6:599, 2002. (2) G. Bouvet. Acta Hortic. 705:447, 2005. (3) C. Moragrega and H. Özaktan. J. Plant Pathol. 92:S1.67, 2010.
Wood has a highly complex and anisotropic structure. Its xylem characteristics are key in determining the hydraulic properties of plants to transport water efficiently and safely, as well as the permeability in the process of wood impregnation modification. Previous studies on the relationship between the xylem structure and hydraulic conductivity of conifer have mainly focused on tracheids and bordered pits, with only a few focusing on the conduction model of cross-field pits which connect tracheids and rays. This study takes the xylem structure of conifer as an example, drawing an analogy between water flow under tension and electric current, and extends the model to the tissue scale, including cross-field pits by establishing isometric scaling. The structure parameters were collected by scanning electron microscopy and transmission electron microscopy. The improved model can quantify the important hydraulic functional characteristics of xylem only by measuring the more easily obtained tracheid section size. Then, this model was applied to quantify the relationship between the xylem anatomical structure and hydraulic properties in the pine (Pinus sylvestris L. var. mongholica Litv.) and the spruce (Picea koraiensis Nakai), and also to evaluate the effects of the number and size of cross-field pits on xylem conduction. The results showed that the growth ring conduction value of the pine was more than twice that of the spruce for the two tree species with similar growth widths in this study. The tracheid wall resistance of the pine reflected the result of the interaction of the size and number of cross-field pits, in comparison, the wall resistance of the spruce was more sensitive to the number of cross-field pits. Finally, the calculation output of the new model was cross-validated with the literature, which verified the accuracy and effectiveness of the model. This study provides an effective and complete solution for xylem conductivity measurement and the study of wood ecophysiological diversity and processing.
The intermittent hole-digging tree-planting machine shows a periodic short-time peak load law in planting operation, and the operation process is “idling” for small loads most of the time, leading to large torque fluctuations in the transmission system, unscientific power matching, and high energy consumption. To solve the above problems, this article proposes to use a series of energy-saving flywheels in the transmission system of the tree planting machine. On the premise of obtaining holes that meet the target young tree planting requirements, the optimal power compensation strategy for the flywheel system of the tree planting machine is studied to reduce torque fluctuations in the power transmission system, use smaller power drive units, and save energy. Firstly, the nonlinear multi-body dynamics simulation model of soil cutting by the hole-digging component is established. The boundary and contact conditions are set to simulate the power consumption of the hole-digging component at three rotating speeds. Based on the simulation results, the flywheel power compensation strategy is discussed, and the torque fluctuation of the flywheel balance system is analyzed. The results showed that the higher the speed, the greater the power consumption. The power value suddenly increased from 17.82 kW (1.28 s) to 27.93 kW (1.43 s) when the speed was 220 r/min. Then, the power value rapidly decreased, and the power consumption presented a short-term peak feature. The transmission system’s maximum input power is determined as 17.82 kW according to the various simulated power consumption characteristics. The part exceeding the power consumption is compensated by the energy storage flywheel. The total compensation energy was 2382.5 J. After the flywheel system was involved, the maximum output power of the tractor power output shaft decreased by 36.2%, and the peak torque decreased from 445.7 N·m to 285.1 N·m. The power consumption obtained from the field test and simulation was similar, but the energy required to overcome peak load was jointly provided by the flywheel and the engine. The actual input power of the power output shaft during the energy release period of the flywheel system was 18.51 kW when the rotating speed of the hole-digging component was 220 r/min, and the relative error with the simulation value was 2.43%. The measured actual speed reduction of the flywheel system was 8.9%. After installing an energy storage flywheel in the transmission system of the tree planting machine, the output power of the power unit can be stabilized. Tree planting machines can be equipped with smaller power units, which can reduce energy consumption and exhaust emissions.
Fluid flow between adjacent tracheids is realized through bordered pits in the xylem of conifers. The pit has an extremely small size and a highly complex structure. This paper presents a mesoscopic analytical method for the relationship between the pit structure and its hydraulic characteristics through mathematical modeling using the lattice Boltzmann method (LBM) and curved boundary treatment. Mongolian Scots pine were selected as the research subject of this study, and the bordered pit structure parameters was collected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the original geometric features were maintained for direct modeling analysis. The model revealed the relationship between various components of the bordered pit and liquid flow velocity/resistance, indicating that margo is the main factor affecting flow resistance. Further anatomical investigation separately analyzed the influence of change in a single factor, including pit diameter, pit aperture diameter, pit depth, torus diameter, and margo thickness, on the overall flow and pressure drop to confirm the importance of various factors in this relationship. Additionally, the influence of pore size and pore location distribution in the margo on the flow rate and pressure drop was further analyzed quantitatively. The results showed that the flow rate through individual pores is the result of the combined effect of pore area and radial position of the pore in the margo. Our study promotes the research and application of the mesoscopic model LBM in simulating flow conditions in the complex flow field of pits, which realizes the numerical analysis of the flow field model based on individualized real bordered pits. In comparison with the classical macroscopic model, the accuracy and effectiveness of the proposed model are proved. This research can provide a promising method for analyzing the physiological and ecological functions of conifer and realizing the efficient utilization of wood resources.
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