Alleviating eutrophication by reducing the abundance of Cyanophyta due to dissolved inorganic carbon fertilization: Insights from Erhai Lake, China.

The eutrophication of lakes is a global environmental problem. Regulating nitrogen (N) and phosphorus (P) on phytoplankton is considered to be the most important basis of lake eutrophication management. Therefore, the effects of dissolved inorganic carbon (DIC) on phytoplankton and its role in mitigating lake eutrophication have often been overlooked. In this study, the relationships between phytoplankton and DIC concentrations, carbon isotopic composition, nutrients (N and P), and hydrochemistry in the Erhai Lake (a karst lake) were investigated. The results showed that when the dissolved carbon dioxide (CO2(aq)) concentrations in the water were higher than 15 µmol/L, the productivity of phytoplankton was controlled by the concentrations of TP and TN, especially by that of TP. When the N and P were sufficient and the CO2(aq) concentrations were lower than 15 µmol/L, the phytoplankton productivity was controlled by the concentrations of TP and DIC, especially by that of DIC. Additionally, DIC significantly affected the composition of the phytoplankton community in the lake (p<0.05). When the CO2(aq) concentrations were higher than 15 µmol/L, the relative abundance of Bacillariophyta and Chlorophyta was much higher than those of harmful Cyanophyta. Thus, high concentrations of CO2(aq) can inhibit harmful Cyanophyta blooms. During lake eutrophication, when controlling N and P, an appropriate increase in CO2(aq) concentrations by land-use changes or pumping of industrial CO2 into water may reduce the proportion of harmful Cyanophyta and promote the growth of Chlorophyta and Bacillariophyta, which may provide effectively assist in mitigating water quality deterioration in surface waters.

A Novel Cooperative Localization Method Based on IMU and UWB.

In this paper, a range-based cooperative localization method is proposed for multiple platforms of various structures. The localization system of an independent platform might degrade or fail due to various reasons such as GPS signal-loss, inertial measurement unit (IMU) accumulative errors, or emergency reboot. It is a promising approach to solve this problem by using information from neighboring platforms, thus forming a cooperative localization network that can improve the navigational robustness of each platform. Typical ranging-based ultra-wideband (UWB) cooperative localization systems require at least three auxiliary nodes to estimate the pose of the target node, which is often hard to meet especially in outdoor environment. In this work, we propose a novel IMU/UWB-based cooperative localization solution, which requires a minimum number of auxiliary nodes that is down to 1. An Adaptive Ant Colony Optimization Particle Filter (AACOPF) algorithm is customized to integrate the dead reckoning (DR) system and auxiliary nodes information with no prior information required, resulting in accurate pose estimation, while to our knowledge the azimuth have not been estimated in cooperative localization for the insufficient observation of the system. We have given the condition when azimuth and localization are solvable by analysis and by experiment. The feasibility of the proposed approach is evaluated through two filed experiments: car-to-trolley and car-to-pedestrian cooperative localization. The comparison results also demonstrate that ACOPF-based integration is better than other filter-based methods such as Extended Kalman Filter (EKF) and traditional Particle Filter (PF).

Low Temperature Storage of Southern Rice Black-Streaked Dwarf Virus-Infected Rice Plants Cannot Sustain Virus Transmission by the Vector.

Southern rice black-streaked dwarf virus (SRBSDV) is a novel virus transmitted by white-backed planthopper Sogatella furcifera (Hováth) (Hemiptera: Delphacidae). Due to low virus transmission efficiency by the planthopper, researchers are frequently confronted with shortage of viruliferous vectors or infected rice plants, especially in winter and the following spring. To find new ways to maintain virus-infected materials, viral rice plants were stored at -80°C for 45 or 140 d and evaluated as virus sources in virus transmission by the vector. SRBSDV virions were not degraded during storage at -80°C as indicated by reverse transcription-polymerase chain reaction and reverse transcription real-time PCR detection. The planthopper nymphs fed on the infected thawed plants for 48 h survived at about 40% and showed positive detection of SRBSDV, but they lost the virus after feeding for another 20 d (the circulative transmission period) on noninfected plants. Transmission electron microscope images indicated broken capsid of virions in infected thawed leaves in contrast to integrity capsid of virions in infected fresh leaves. These results show that low temperature storage of SRBSDV-infected rice plants cannot sustain virus transmission by white-backed planthopper.

A Novel Zero Velocity Interval Detection Algorithm for Self-Contained Pedestrian Navigation System with Inertial Sensors.

Zero velocity update (ZUPT) plays an important role in pedestrian navigation algorithms with the premise that the zero velocity interval (ZVI) should be detected accurately and effectively. A novel adaptive ZVI detection algorithm based on a smoothed pseudo Wigner-Ville distribution to remove multiple frequencies intelligently (SPWVD-RMFI) is proposed in this paper. The novel algorithm adopts the SPWVD-RMFI method to extract the pedestrian gait frequency and to calculate the optimal ZVI detection threshold in real time by establishing the function relationships between the thresholds and the gait frequency; then, the adaptive adjustment of thresholds with gait frequency is realized and improves the ZVI detection precision. To put it into practice, a ZVI detection experiment is carried out; the result shows that compared with the traditional fixed threshold ZVI detection method, the adaptive ZVI detection algorithm can effectively reduce the false and missed detection rate of ZVI; this indicates that the novel algorithm has high detection precision and good robustness. Furthermore, pedestrian trajectory positioning experiments at different walking speeds are carried out to evaluate the influence of the novel algorithm on positioning precision. The results show that the ZVI detected by the adaptive ZVI detection algorithm for pedestrian trajectory calculation can achieve better performance.

Effects of carbon limitation and carbon fertilization on karst lake-reservoir productivity.

Nitrogen and phosphorus are universally recognized as limiting elements in the eutrophication processes affecting the majority of the world's lakes, reservoirs, and coastal ecosystems. However, despite extensive research spanning several decades, critical questions in eutrophication science remain unanswered. For example, there is still much to understand about the interactions between carbon limitation and ecosystem stability, and the availability of carbon components adds significant complexity to aquatic resource management. Mounting evidence suggests that aqueous CO2 could be a limiting factor, influencing the structure and succession of aquatic plant communities, especially in karstic lake and reservoir ecosystems. Moreover, the fertilization effect of aqueous CO2 has the potential to enhance carbon sequestration and phosphorus removal. Therefore, it is important to address these uncertainties to achieve multiple positive outcomes, including improved water quality and increased carbon sinks in karst lakes and reservoirs.

Control of carbon dioxide exchange fluxes by rainfall and biological carbon pump in karst river-lake systems.

As an important component of inland water, the primary factors affecting the carbon cycle in karst river-lake systems require further investigation. In particular, the impacts of climatic factors and the biological carbon pump (BCP) on carbon dioxide (CO2) exchange fluxes in karst rivers and lakes deserve considerable attention. Using quarterly sampling, field monitoring, and meteorological data collection, the spatiotemporal characteristics of CO2 exchange fluxes in Erhai Lake (a typical karst lake in Yunnan, SW China) and its inflow rivers were investigated and the primary influencing factors were analyzed. The average river CO2 exchange flux reached 346.80 mg m-2 h-1, compared to -6.93 mg m-2 h-1 for the lake. The carbon cycle in rivers was strongly influenced by land use within the basin; cultivated and construction land were the main contributors to organic carbon (OC) in the river (r = 0.66, p < 0.01) and the mineralization of OC was a major factor in CO2 oversaturation in most rivers (r = 0.76, p < 0.01). In addition, the BCP effect of aquatic plants and the high pH in karst river-lake systems enhance the ability of water body to absorb CO2, resulting in undersaturated CO2 levels in the lake. Notably, under rainfall regulation, riverine OC and dissolved inorganic carbon (DIC) flux inputs controlled the level of CO2 exchange fluxes in the lake (rOC = 0.78, p < 0.05; rDIC = 0.97, p < 0.01). We speculate that under future climate and human activity scenarios, the DIC and OC input from rivers may alleviate the CO2 limitation of BCP effects in karst eutrophication lakes, possibly enabling aquatic plants to convert more CO2 into OC for burial. The results of this research can help advance our understanding of CO2 emissions and absorption mechanisms in karst river-lake systems.

High stability of autochthonous dissolved organic matter in karst aquatic ecosystems: Evidence from fluorescence.

Biological carbon pump (BCP) in karst areas has received intensive attention for years due to their significant contribution to the global missing carbon sink. The stability of autochthonous dissolved organic matter (Auto-DOM) produced by BCP in karst aquatic ecosystems may play a critical role in the missing carbon sink. However, the source of dissolved organic matter (DOM) in inland waters and its consumption by planktonic bacteria have not been thoroughly examined. Recalcitrant dissolved organic matter (RDOM) may exist in karst aquatic ecosystem as in the ocean. Through the study of the chromophoric dissolved organic matter (CDOM) and the interaction between CDOM and the planktonic bacterial community under different land uses at the Shawan Karst Water-carbon Cycle Test Site, SW China, we found that C2, as the fluorescence component of Auto-DOM mineralised by planktonic bacteria, may have some of the characteristics of RDOM and is an important DOM source in karst aquatic ecosystems. The stability ratio (Fmax(C2/(C1+C2))) of Auto-DOM reached 89.6 ± 6.71% in winter and 64.1 ± 7.19% in spring. Moreover, correlation-based network analysis determined that the planktonic bacterial communities were controlled by different fluorescence types of CDOM, of which C1 (fresh Auto-DOM), C3 (conventional allochthonous DOM (Allo-DOM)) and C4 (the Allo-DOM mineralised by bacteria) were clustered in one module together with prevalent organic-degrading planktonic bacteria; C2 was clustered in another tightly combined module, suggesting specific microbial utilization strategies for the C2 component. In addition, some important planktonic bacterium and functional genes (including chemotrophic heterotrophs and photosynthetic bacteria) were found to be affected by high Ca2+ and dissolved inorganic carbon (DIC) concentrations in karst aquatic ecosystems. Our research showed that Auto-DOM may be as an important carbon sink as the Allo-DOM in karst ecosystems, the former generally being neglected based on a posit that it is easily and first mineralized by planktonic bacteria.

Silicon amendment to rice plants reduces the transmission of southern rice black-streaked dwarf virus by Sogatella furcifera.

BACKGROUND: Plant viruses are transmitted mainly by piercing-sucking herbivores, and viral disease management relies on chemical control of vectors. Southern rice black-streaked dwarf virus (SRBSDV) is transmitted by the white-backed planthopper (WBPH), Sogatella furcifera. This study aimed to evaluate the potential of silicon (Si) amendment for reducing SRBSDV transmission. RESULTS: The settling and ovipositional preferences of WBPH females decreased significantly by 14.6-43.7% for plants treated with either 0.16 g or 0.32 g SiO2  kg-1 soil during SRBSDV acquisition and by 26.2-28.3% for plants treated with 0.32 g SiO2  kg-1 soil during SRBSDV inoculation, compared with controls. Adding either 0.16 or 0.32 g SiO2  kg-1 soil significantly reduced SRBSDV inoculation rate by 31.3% and 45.3%, respectively, and acquisition rate by 25.5% and 66.0%, respectively. Silicification was intensified more in plants treated with 0.32 g SiO2  kg-1 soil than in controls. The nonprobing (np) duration increased, and the phloem sap ingestion (N4-b) duration decreased significantly in the WBPHs feeding on high-rate-Si-supplemented plants compared with control plants during both inoculation and acquisition access. CONCLUSION: This study showed that Si amendment to rice plants decreased the WBPH settling and ovipositional preference and the SRBSDV acquisition and inoculation rates, thereby reducing SRBSDV transmission. The intensified plant silicification and the altered WBPH feeding behaviors (i.e. prolonged np and shortened N4-b) may explain the reduced SRBSDV transmission in Si-amended plants. © 2021 Society of Chemical Industry.

Composition and Distribution of Aliphatic Hydrocarbon Compounds and Biomarkers in Seafloor Sediments from Offshore of the Leizhou Peninsula (South China).

The offshore of Leizhou Peninsula (LP, China), which contains unique ecosystems such as mangroves, seagrass beds, and coral reefs, is an environmentally sensitive area. For this reason, the levels of aliphatic hydrocarbon including biomarkers (hopanes, steranes) in the offshore seafloor sediments were analyzed in terms of their composition, distribution, and input sources and aimed to evaluate the extent of possible petroleum hydrocarbon contamination in the sediments of coastal areas. The total aliphatic hydrocarbons (TAH) fraction, the content of total n-alkanes (nC14-nC37) (∑n-alkanes), and content of hopane + sterane are in the range of 13.76-99.53, 1.22-8.33, and 0.02-0.23 µg/g dw, respectively. The presence of unresolved complex mixture (UCM) hydrocarbons hump and petrogenic steranes and hopanes in these seafloor sediments suggest that petrogenic sourced hydrocarbon inputs were present. The stations on the peninsula's southwest side had the lowest values of UCM/resolved aliphatic compounds (UCM/R) and UCM/n-alkanes. These findings suggest that seafloor sediments from the southwest offshore of the peninsula were likely contaminated by recently inputted petroleum hydrocarbons. The presence of relatively high ∑n-alkanes content in seafloor sediments from southwest offshore of the LP, combined with relatively low natural n-alkane ratios (NARs), indicates an increased influence of petrogenic hydrocarbons. The elevated levels of recent petrogenic hydrocarbon contamination in the sediments from the LP's southwestern offshore were likely related to petroleum exploitation in the Beibu Gulf's Maichen and Wushi sags.

Silicon-mediated rice plant resistance to the Asiatic rice borer (Lepidoptera: Crambidae): effects of silicon amendment and rice varietal resistance.

The Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is one of the most destructive pests in rice, Oryza sativa L., throughout Asian countries. The aim of this study was to investigate the potential of applied silicon in mediating rice plant resistance to C. suppressalis in a susceptible (Shanyou63) and a moderately resistant (Yanfeng47) rice cultivar. Silicon-treated plants showed significant increases in silicon content compared with the control. Silicon addition significantly decreased borer penetration, weight gain, and stem damage, and it prolonged penetration duration and larval development; some of the effects were manifested more strongly in the susceptible rice cultivar compared with the moderately resistant cultivar. Therefore, silicon amendment may contribute to the suppression of C. suppressalis directly through reduced feeding damage and performance and indirectly through increased exposure time of young larvae to natural enemies and control measures.

Plant-Mediated Horizontal Transmission of Asaia Between White-Backed Planthoppers, Sogatella furcifera.

Asaia is a bacterial symbiont of sugar-feeding insects that has been shown to be vertically transmitted by maternal transmission and paternal transmission mechanism, and to be horizontally transmitted via co-feeding artificial diet and venereal routes. Here, the first case of plant-mediated horizontal transmission of Asaia between white-backed planthoppers (WBPH), Sogatella furcifera, was reported. In Asaia-infected WBPH, Asaia was detected mostly in salivary glands and to a less extent in stylets. The rice leaf sheaths fed by Asaia-infected WBPH for 12 h were all positive with Asaia, where Asaia persisted for at least 30 d but was localized in the feeding sites only. When confined to Asaia-infected leaf sheaths for 7 d at the sites pre-infested by the Asaia-infected WBPH, all Asaia-free WBPH became infected with Asaia and the acquired Asaia could be vertically transmitted to their offspring. Phylogenetic analysis confirmed an identical Asaia strain in the Asaia-infected donor WBPH, the Asaia-infected leaf sheaths, and the newly infected recipient WBPH. Our findings provide direct evidence for the first time that rice plant can mediate horizontal transmission of Asaia between WBPH, which may contribute to the spread of Asaia in the field WBPH populations.

Seasonal changes in supercooling points and glycerol content in overwintering larvae of the asiatic rice borer from rice and water-oat plants.

The Asiatic rice borer Chilo suppressalis (Walker) occurs mainly on rice Oryza sativa L. and water-oat Zizania latifolia (Turcz). Certain ecological and physiological differentiations between rice and water-oat populations have been shown. To determine whether there is host-associated differentiation in supercooling capacity, seasonal changes in supercooling points, glycerol content, and other physiological parameters of naturally occurring C. suppressalis larvae overwintering in rice and water-oat plants were compared over the winter. Supercooling points were low in the winter (November and December), significantly higher in March, and significantly lower in the water-oat population than in the rice population in the winter. Larvae from the water-oat population experienced a significant weight loss from December to March and were heavier than those from the rice population in the winter. Body water content (percentage of fresh weight) was low in the winter and increased significantly in March; no population differences were detected. Hemolymph glycerol content was high in the winter and dropped significantly in March; interpopulation differences were significant in December. Hemolymph trehalose content increased in the winter, and no population differences were detected. Whole body glucose and lipid content varied differently between the rice and the water-oat populations over the winter. It was found that variations in hemolymph glycerol content were responsible for the host-associated seasonal changes in supercooling capacity of overwintering larvae of the Asiatic rice borer.

Rapid Cold Hardening Confers a Transient Increase in Low Temperature Survival in Diapausing Chilo suppressalis Larvae.

The striped stem borer, Chilo suppressalis (Walker), overwinters as a diapausing larva. The diapausing larvae were tested for a rapid cold hardening (RCH) response and its role in the insect’s survival of sub-zero temperatures. When laboratory-reared diapausing larvae were transferred directly from the rearing temperature of 25 °C to −14 °C and maintained there for 2 h, 21% survived. Acclimation of diapausing larvae for 4 h at 5 °C before their exposure for 2 h to −14 °C increased survival to approximately 41%, indicating an RCH response. Durability of RCH effects on low temperature survival was less than 1 h. Although transient in the test, the increased survival acquired through rapid cold hardening may play a role in preparing the diapausing larvae for abrupt temperature drops in the field that would otherwise be lethal.

Resistance to Nilaparvata lugens in rice lines introgressed with the resistance genes Bph14 and Bph15 and related resistance types.

Crop resistance is a cost-effective and environmentally friendly strategy for pest management. The brown planthopper (BPH, Nilaparvata lugens) is a devastating rice insect pest due to its ability to rapidly overcome plant resistance and the lack of sufficient resistance resources. BR4831 (a rice breeding line derived from the pyramiding of two BPH resistance genes, Bph14 and Bph15, into the elite rice variety Huang-Hua-Zhan, HHZ) and two single-gene introgression lines (HF106, carrying Bph14, and C602, carrying Bph15, in the elite rice cultivar 9311) were evaluated for their resistance to BPH using a standard seed box screening test coupled with field tests. The related resistance types were determined using laboratory assays. The seed box test and laboratory biological assays showed that BR4831 exhibited strong antibiotic resistance, and the behavioral assay showed that this line also exhibited strong antixenotic resistance, while both HF106 and C602 exhibited only weak antibiosis and no antixenotic resistance. Field tests showed significantly improved resistance in BR4831 compared to that of its recipient parent HHZ and slightly increased resistance in HF106 and C602 in comparison with their recipient parent 9311. These results demonstrate that the rice line BR4831, with pyramided resistance genes, exhibits higher resistance than the monogenic lines HF106 and C602 and highlight the benefits of combining the seed box seedling test, field tests and laboratory assays to thoroughly analyze plant resistance types.

Cross-Resistance and Baseline Susceptibility of Brown Planthopper Nilaparvata lugens (Hemiptera: Delphacidae) From China to Cycloxaprid.

The brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a serious pest of rice. At present, the application of chemical insecticides is the main control option for this pest. BPH has evolved resistance to various classes of insecticides. Cycloxaprid, a new oxabridged cis-configuration neonicotinoid insecticide, is a (nitromethylene) imidazole analog of imidacloprid. This study focused on the baseline susceptibility to cycloxaprid of 18 field samples of N. lugens collected from nine geographical locations in China, as well as possible cross-resistances between cycloxaprid and other important neonicotinoids in one laboratory-selected resistant strain of N. lugens to imidacloprid. The median lethal concentration (LC50) of cycloxaprid for the 18 samples ranged from 1.26 to 14.90 mg/liter. Furthermore, the cross-resistance studies showed that the imidacloprid-resistant strain exhibited a 27.63-fold resistance to imidacloprid and lower levels of cross-resistance to acetamiprid (16.64-fold), thiacloprid (12.64-fold), and nitenpyram (16.90-fold); however, there was no cross-resistance to cycloxaprid (1.92-fold). These results indicate that cycloxaprid could be an effective alternative insecticide for the management of N. lugens, which is urgently needed to prevent or delay further increases in insecticide resistance in N. lugens.

Silicon amendment to rice plants impairs sucking behaviors and population growth in the phloem feeder Nilaparvata lugens (Hemiptera: Delphacidae).

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a migratory and destructive sucking insect pest of rice. Silicon (Si) amendment to plants can confer enhanced resistance to herbivores and is emerging as a novel approach for pest management. In the present study, we tested the effects of Si addition at 0.16 (low) and 0.32 (high) g Si/kg soil on sucking behaviors and population growth in BPH. Si amendment increased Si content in rice stems and extended non-probing event and phloem puncture followed by sustained phloem ingestion over that in the no-Si-addition control. High Si addition rate prolonged the stylet pathway and the time needed to reach the first phloem puncture, shortened durations of phloem puncture and phloem ingestion, and decreased the proportion of individuals that produced sustained phloem ingestion. BPH female feeding on and preference for plants with the high Si addition rate were also reduced. As a result, Si application significantly decreased BPH population growth rates while increased population doubling time. These results indicate that Si amendment, especially at the high rate, confers enhanced rice plant resistance to BPH through impairment of BPH feeding. Our results highlight the potential of Si amendment as an alternative for BPH management.

Silicon amendment is involved in the induction of plant defense responses to a phloem feeder.

Plant resistance to herbivores is a key component in integrated pest management. In most cases, silicon (Si) amendment to plants enhances resistance to herbivorous insects. The increase of plant physical barrier and altered insect behaviors are proposed as mechanisms for the enhanced resistance in Si-amended plants, but our understanding of the induced mechanisms involved in Si-enhanced plant resistance to phloem-feeding insects remains unclear. Here, we show that Si amendment to rice (Oryza sativa) plants impacts multiple plant defense responses induced by a phloem-feeder, the brown planthopper (Nilaparvata lugens, BPH). Si amendment improved silicification of leaf sheaths that BPH feed on. Si addition suppressed the increase of malondialdehyde concentration while encouraged increase of H2O2 concentration in plants attacked by BPH. Higher activities of catalase and superoxide dismutase were recorded in Si-amended than in non-amended BPH-infested plants. BPH infestation activated synthases for secondary metabolites, polyphenol oxidase and pheny-lalanine ammonia-lyase, and ß-1,3-glucanase, but the activation was greater in Si-amended than in non-amended plants. Taken together, our findings demonstrate that Si amendment interacts with BPH infestation in the induction of plant defense responses and consequently, to confer enhanced rice plant resistance.

Luminescence and white-light emitting luminescent sensor of tetrafluoroterephthalate-lanthanide metal-organic frameworks.

Two types of sixteen complexes 1-16, namely, {[Ln(TFBDC)1.5(H2O)]·2H2O}n [Ln = Pr (1) and Nd (2)] and {[Ln(TFBDC)1.5(H2O)2]·H2O}n [Ln = Ce (3), Pr (4), Nd (5), Sm (6), Eu (7), Gd (8), Tb (9), Dy (10), Ho (11), Er (12), Yb (13) and Lu (14)], {[Dy0.281Eu0.719(TFBDC)1.5(H2O)2]·H2O}n (15) and {[Gd0.871Eu0.103Tb0.026(TFBDC)1.5(H2O)2]·H2O}n (16), were isolated by the reaction of LnCl3·6H2O with 2,3,5,6-tetrafluoroterephthalic acid (H2TFBDC). X-ray crystallographic analysis revealed that 1 and 2 exhibit 3D network structures and complexes 3-14 feature 2D network structures formed via three different coordination modes of the ligand. Luminescence spectra revealed that these complexes exhibit broad-spectrum luminescence from the visible to the near-infrared (NIR) region. Unexpectedly, complex 1 exhibits a unique NIR luminescence pattern and the longest lifetime among reported molecular praseodymium complexes. White-light emission was realized via three approaches using the single-component complex 6 (Sm), the two-component complex 15 (Eu and Dy) and the three-component complex 16 (Eu, Tb and Gd). Complex 9 exhibits high sensitivity and selectivity in its luminescence response to benzaldehyde, which provides a promising luminescent sensor for the detection of benzaldehyde.

Defense Responses in Rice Induced by Silicon Amendment against Infestation by the Leaf Folder Cnaphalocrocis medinalis.

Silicon (Si) amendment to plants can confer enhanced resistance to herbivores. In the present study, the physiological and cytological mechanisms underlying the enhanced resistance of plants with Si addition were investigated for one of the most destructive rice pests in Asian countries, the rice leaf folder, Cnaphalocrocis medinalis (Guenée). Activities of defense-related enzymes, superoxide dismutase, peroxidase, catalase, phenylalanine ammonia-lyase, and polyphenol oxidase, and concentrations of malondialdehyde and soluble protein in leaves were measured in rice plants with or without leaf folder infestation and with or without Si amendment at 0.32 g Si/kg soil. Silicon amendment significantly reduced leaf folder larval survival. Silicon addition alone did not change activities of defense-related enzymes and malondialdehyde concentration in rice leaves. With leaf folder infestation, activities of the defense-related enzymes increased and malondialdehyde concentration decreased in plants amended with Si. Soluble protein content increased with Si addition when the plants were not infested, but was reduced more in the infested plants with Si amendment than in those without Si addition. Regardless of leaf folder infestation, Si amendment significantly increased leaf Si content through increases in the number and width of silica cells. Our results show that Si addition enhances rice resistance to the leaf folder through priming the feeding stress defense system, reduction in soluble protein content and cell silicification of rice leaves.

Asymmetric Spread of SRBSDV between Rice and Corn Plants by the Vector Sogatella furcifera (Hemiptera: Delphacidae).

Plant viruses are mostly transmitted by sucking insects via their piercing behaviors, which may differ due to host plant species and their developmental stages. We characterized the transmission of a fijivirus, southern rice black-streaked dwarf virus (SRBSDV), by the planthopper vector Sogatella furcifera Horváth (Hemiptera: Delphacidae), between rice and corn plants of varying developmental stages. SRBSDV was transmitted from infected rice to uninfected corn plants as efficiently as its transmission between rice plants, while was acquired by S. furcifera nymphs at a much lower rate from infected corn plants than from infected rice plants. We also recorded a high mortality of S. furcifera nymphs on corn plants. It is evident that young stages of both the virus donor and recipient plants added to the transmission efficiency of SRBSDV from rice to corn plants. Feeding behaviors of the vector recorded by electrical penetration graph showed that phloem sap ingestion, the behavioral event that is linked with plant virus acquisition, was impaired on corn plants, which accounts for the high mortality of and low virus acquisition by S. furcifera nymphs on corn plants. Our results reveal an asymmetric spread of SRBSDV between its two host plants and the underlying behavioral mechanism, which is of significance for assessing SRBSDV transmission risks and field epidemiology, and for developing integrated management approaches for SRBSDV disease.