Comparing the plant virus spread patterns of non-persistently transmitted virus and persistently transmitted virus using an individual-based model

To compare the spread patterns between two types of plant viruses, non-persistent virus (NPV) and persistent virus (PV), we developed a spatially-explicit individual-based model. Our probability-based model is driven by the actions of insect vectors that are affected by interactions with host plants and plant viruses, considering both biological and behavioral components of their relationship. As a model system, we used potato virus y and potato leafroll virus, respectively for NPV and PV, potato for host plant, and Myzus persicae for the insect vector; empirical results from previous studies were acquired and adjusted to be used as our parameter values. Our simulation results showed that initial infection of PV in the field resulted in over 1.3 times greater number of insect vectors while causing approximately 7 times greater number of virus-infected plants compared to NPV by the end of simulation. Furthermore, spatial analysis showed that PV-infected plants showed greater aggregation in the field, forming larger patches compared to NPV-infected plants. Our results demonstrated the importance of host plant and insect vector manipulation by plant viruses as well as biological properties such as infectious period in the insect on the difference in overall spread pattern.     

The pollen virome: A review of pollen-associated viruses and consequences for plants and their interactions with pollinators

The movement of pollen grains from anthers to stigmas, often by insect pollinator vectors, is essential for plant reproduction. However, pollen is also a unique vehicle for viral spread. Pollen-associated plant viruses reside on the outside or inside of pollen grains, infect susceptible individuals through vertical or horizontal infection pathways, and can decrease plant fitness. These viruses are transferred with pollen between plants by pollinator vectors as they forage for floral resources; thus, pollen-associated viral spread is mediated by floral and pollen grain phenotypes and pollinator traits, much like pollination. Most of what is currently known about pollen-associated viruses was discovered through infection and transmission experiments in controlled settings, usually involving one virus and one plant species of agricultural or horticultural interest. In this review, we first provide an updated, comprehensive list of the recognized pollen-associated viruses. Then, we summarize virus, plant, pollinator vector, and landscape traits that can affect pollen-associated virus transmission, infection, and distribution. Next, we highlight the consequences of plant–pollinator–virus interactions that emerge in complex communities of co-flowering plants and pollinator vectors, such as pollen-associated virus spread between plant species and viral jumps from plant to pollinator hosts. We conclude by emphasizing the need for collaborative research that bridges pollen biology, virology, and pollination biology.     

Plant virus ecology and epidemiology: historical perspectives,recent progress and future prospects

After clarifying the relationship between the closely related concepts of ecology and epidemiology as they are used in plant virology, this article provides a historical perspective on the subject before discussing recent progress and future prospects. Ecology focuses on virus populations interacting with host populations within a variable environment, while epidemiology focuses on the complex association between virus and host plant, and factors that influence spread. The evolution and growth of plant virus ecology and epidemiology since its inception to the present day, and the major milestones in its development, are illustrated by examples from influential historical reviews published in the Annals of Applied Biology over the last 100 years. Original research papers published in the journal are used to illustrate important ecological and epidemiological principles and new developments in both fields. Both areas are multifaceted with many factors influencing host plants, and virus and vector behaviour. The highly diverse scenarios that arise from this process influence the virus population and the spatiotemporal dynamics of virus distribution and spread. The review then describes exciting progress in research in the areas of molecular epidemiology and ecology, and understanding virus–vector interactions. Application of new molecular techniques has greatly accelerated the rate of progress in understanding virus populations and the way changes in these populations influence epidemics. Viruses cause direct and plant‐mediated indirect effects on insect vectors by modifying their life cycles, fitness and behaviour, and one of the most fascinating recent fields of research concerns plant‐mediated indirect virus manipulation of insect vector behaviour that encourages virus spread. Next, the review describes the current state of knowledge about spread of plant viruses at the critical agro‐ecological interface between managed and natural vegetation. There is an urgent need to understand how viruses move in both directions between the two and be able to anticipate these kinds of events. To obtain an understanding of, and ability to foresee, such events will require a major research effort into the future. The review finishes by discussing the implications of climate change and rapid technological innovation for the types of research needed to avoid virus threats to future world food supplies and plant biodiversity. There has been lamentably little focus on research to determine the magnitude of the threat from diseases caused in diverse plant virus pathosystems under different climate change scenarios. Increasing technological innovation offers many opportunities to help ensure this situation is addressed, and provide plant virus ecology and epidemiology with a very exciting future.     

媒介昆虫-病毒-植物互作对生物入侵的影响

媒介昆虫-病毒-植物互作关系复杂多样。虽然相关的研究较多, 然而有关三者互作对于生物入侵的影响还知之甚少。已有证据表明, 寄主植物对病毒的敏感性和对媒介昆虫的适合性、媒介昆虫对寄主的适应能力等因素影响三者互作关系。当寄主植物易感病并且对媒介昆虫的适合性低, 而媒介昆虫对寄主植物的适应能力强时, 媒介昆虫与植物病毒之间很可能建立间接互惠关系, 这种互惠可促进媒介昆虫入侵和病毒病流行。此外, 媒介昆虫与植物病毒之间中性或偏害的互作关系对于外来生物入侵的促进作用也不容忽视。鉴于三者互作对于生物入侵的重要性, 今后需要对不同物种所组成的多种组合进行比较研究, 并采用多种方法揭示互作的生理和分子机制。     

Survival and Transmission of Potato Virus Y,Pepino Mosaic Virus,and Potato Spindle Tuber Viroid in Water

Hydroponic systems and intensive irrigation are used widely in horticulture and thus have the potential for rapid spread of water-transmissible plant pathogens. Numerous plant viruses have been reported to occur in aqueous environments, although information on their survival and transmission is minimal, due mainly to the lack of effective detection methods and to the complexity of the required transmission experiments. We have assessed the role of water as a source of plant infection using three mechanically transmissible plant pathogens that constitute a serious threat to tomato and potato production: pepino mosaic virus (PepMV), potato virus Y (PVY), and potato spindle tuber viroid (PSTVd). PepMV remains infectious in water at 20 ± 4°C for up to 3 weeks, PVY (NTN strain) for up to 1 week, and PSTVd for up to 7 weeks. Experiments using a hydroponic system show that PepMV (Ch2 genotype) and PVY (NTN strain) can be released from plant roots into the nutrient solution and can infect healthy plants through their roots, ultimately spreading to the green parts, where they can be detected after a few months. In addition, tubers developed on plants grown in substrate watered with PSTVd-infested water were confirmed to be the source of viroid infection. Our data indicate that although well-known pathways of virus spread are more rapid than water-mediated infection, like insect or mechanical transmission through leaves, water is a route that provides a significant bridge for rapid virus/viroid spread. Consequently, water should be taken into account in future epidemiology and risk assessment studies.     

植物病原-媒介昆虫互作:研究进展与展望

大多数植物病毒及一些植物病原细菌由介体昆虫传播。植物病原与介体昆虫关系的研究有助于找到防控介体传播病原的关键环节,因此植物病原与介体昆虫的互作关系是植物病原传播机理研究中的核心问题。本文概述了国内外在植物病原与介体昆虫互作研究的最新进展,推介了本专辑论文的主要内容,并在此基础上,从生态和进化的角度提出了在植物病原-媒介昆虫互作研究中以下3个值得关注的研究方向:(1)植物病原与介体昆虫互作对生态系统的影响;(2)昆虫介体传播植物病毒的不同方式之间的关联性以及病毒、介体和植物之间的协同进化关系;(3)自然条件下植物病原-媒介昆虫互作的机理。植物病原与媒介昆虫互作的研究,既是生态和进化的理论问题,也和植物病原及其介体昆虫的绿色防控密切相关。     

Characteristics and drivers of plant virus community spatial patterns in US west coast grasslands

The spatial distribution of disease risk caused by multi‐pathogen infections is not frequently characterized, limiting understanding of the drivers of infection and thwarting prediction of future risk in a changing environment. Further complicating this predictive understanding is that interactions among multiple pathogens within a host commonly alter transmission success, infection risk, and disease dynamics. By characterizing spatial patterns of Barley and Cereal Yellow Dwarf Virus (B/CYDV) infections that range from the scale of an individual plant to thousands of neighboring plants, we examined the contributions of spatial processes to the distribution of disease risk. In a two‐year field experiment, we planted grass hosts of B/CYDVs into fertilized plots of US west coast grasslands. We determined how vector‐sharing, environmental conditions and spatial variation in host quality affected spatial patterns of single viruses, pairs of viruses and the whole virus community across out‐planted grass hosts. We found that single viruses and virus communities were spatially random, indicating that infection does not solely spread through the community in a wave‐like manner. On the other hand, we found that pairs of viruses, especially those that share a vector species, were aggregated spatially. This suggests that if within‐host competition exists, it is not strong. Aggregation in one pair of viruses was more frequent due to environmental conditions and spatial variation in out‐planted host quality, measured as vector preference. These results highlight the importance of insect vectors for predicting the spatial distribution of coinfection risk by B/CYDVs.     

Virus infection decreases the attractiveness of white clover plants for a non-vectoring herbivore

Plant pathogens and insect herbivores are prone to share hosts under natural conditions. Consequently, pathogen-induced changes in the host plant can affect herbivory, and vice versa. Even though plant viruses are ubiquitous in the field, little is known about plant-mediated interactions between viruses and non-vectoring herbivores. We investigated the effects of virus infection on subsequent infestation by a non-vectoring herbivore in a natural genotype of Trifolium repens (white clover). We tested whether infection with White clover mosaic virus (WClMV) alters (1) the effects of fungus gnat feeding on plant growth, (2) the attractiveness of white clover for adult fungus gnat females, and (3) the volatile emission of white clover plants. We observed only marginal effects of WClMV infection on the interaction between fungus gnat larvae and white clover. However, adult fungus gnat females clearly preferred non-infected over WClMV-infected plants. Non-infected and virus-infected plants could easily be discriminated based on their volatile blends, suggesting that the preference of fungus gnats for non-infected plants may be mediated by virus-induced changes in volatile emissions. The compound β-caryophyllene was exclusively detected in the headspace of virus-infected plants and may hence be particularly important for the preference of fungus gnat females. Our results demonstrate that WClMV infection can decrease the attractiveness of white clover plants for fungus gnat females. This suggests that virus infections may contribute to protecting their hosts by decreasing herbivore infestation rates. Consequently, it is conceivable that viruses play a more beneficial role in plant-herbivore interactions than generally thought.     

Mammalian Herbivores Alter the Population Growth and Spatial Establishment of an Early-Establishing Grassland Species

Plant-herbivore interactions influence the establishment context of plant species, as herbivores alter the community context in which individual species establish, and the spatial relationship between individuals and their source population as plants invade. This relationship can be described using an establishment kernel, which takes into account movement through seed dispersal, and subsequent establishment of adults. Mammalian herbivores are hypothesized to influence plant population growth and establishment through a combination of consumption of seeds and seedlings, and movement of seeds. While the movement abilities of plants are well known, we have very few empirical mechanistic tests of how biotic factors like mammalian herbivores influence this spread potential. As herbivores of all sizes are abundant on the landscape, we asked the question, how do mammalian herbivores influence the population growth, spatial establishment, and the community establishment context of an early-recruiting native prairie legume, Chamaecrista fasciculata? We planted C. fasciculata in source populations within a four-acre tallgrass prairie restoration in plots with and without herbivores, and monitored its establishment with respect to distance from the source populations. We found that herbivores decreased population growth, and decreased the mean and range establishment distance. Additionally, C. fasciculata established more often without herbivores, and when surrounded by weedy, annual species. Our results provide insight into how the interactions between plants and herbivores can alter the spatial dynamics of developing plant communities, which is vital for colonization and range spread with fragmentation and climate change. Mammalian herbivores have the potential to both slow rates of establishment, but also determine the types of plant communities that surround invading species. Therefore, it is essential to consider the herbivore community when attempting to restore functioning plant communities.     

Evaluation of barrier plants for the cultural control of tomato yellow leaf curl disease

Barrier cropping plays an essential role in controlling insect pests and insect-transmitted diseases in cultural control. It has been proven efficient in suppressing the spread of nonpersistently transmitted viruses. For suppressing the spread of persistently transmitted viruses, barrier cropping is not considered an effective control strategy because barrier plants cannot act as a virus sink to purge the virus in the vector. However, few successful cases of barrier cropping suppressing the spread of persistently transmitted viruses have been reported. The objectives of the present study were to screen candidates (cucumber, okra, Chinese kale, soybean, and corn) for potential barrier plants to control tomato yellow leaf curl Thailand virus (TYLCTHV) and examine whether prefeeding on these plants can reduce the virus titer in its vector, Bemisia tabaci, thus reducing TYLCTHV transmission. The results revealed that nonviruliferous whiteflies preferred cucumber and okra to tomato, whereas viruliferous whiteflies preferred cucumber to tomato. Although prefeeding on cucumber, okra, and Chinese kale did not reduce the titer of TYLCTHV in viruliferous whiteflies, the vector transmission rate decreased after the whiteflies fed on Chinese kale. It implies that planting Chinese kale as a barrier plant for tomato cultivation may reduce the incidence of TYLCTHV. In addition, the preference to cucumber plants may reduce the incidence of whiteflies acquiring TYLCTHV from virus-infected tomato plants and of viruliferous whiteflies inoculating the virus into healthy tomato plants, thereby reducing the disease incidence. Further field trials of barrier cropping using the candidate plants are warranted.     

Global warming and the disruption of plant-pollinator interactions

Anthropogenic climate change is widely expected to drive species extinct by hampering individual survival and reproduction, by reducing the amount and accessibility of suitable habitat, or by eliminating other organisms that are essential to the species in question. Less well appreciated is the likelihood that climate change will directly disrupt or eliminate mutually beneficial (mutualistic) ecological interactions between species even before extinctions occur. We explored the potential disruption of a ubiquitous mutualistic interaction of terrestrial habitats, that between plants and their animal pollinators, via climate change. We used a highly resolved empirical network of interactions between 1420 pollinator and 429 plant species to simulate consequences of the phenological shifts that can be expected with a doubling of atmospheric CO₂. Depending on model assumptions, phenological shifts reduced the floral resources available to 17–50% of all pollinator species, causing as much as half of the ancestral activity period of the animals to fall at times when no food plants were available. Reduced overlap between plants and pollinators also decreased diet breadth of the pollinators. The predicted result of these disruptions is the extinction of pollinators, plants and their crucial interactions.     

植物病毒病媒介昆虫的传毒特性和机制研究进展

植物病毒病是农作物的“癌症”, 至今缺少有效的防治方法。目前已知80%的植物病毒病依赖于媒介昆虫传播, 而媒介昆虫对植物病毒的传播是一个昆虫、 病毒、 寄主植物互作的过程, 历经获毒、 持毒和传毒等多个阶段, 昆虫体内一系列病毒受体或蛋白参与了这个过程。昆虫传播病毒的方式有口针携带式、 前肠保留式和体内循环式3类, 它们各自对应的持久性为非持久性、 半持久性和持久性, 不同昆虫获取这3类病毒的获毒时间、 在体内存留位置和传毒时间也各不相同。 这个过程受到媒介昆虫的性别及龄期、 寄主植物、 环境条件、 昆虫体内共生菌等多种因素的影响。与之相关的蛋白主要有病毒衣壳蛋白(CP)、 次要衣壳蛋白（CPm）、 GroEL蛋白、 辅助因子(HC)和下颚口针蛋白等。近年来对植物病毒基因组的研究也取得了很大的进展, 对昆虫传毒机制的研究正受到越来越广泛的关注。本文综述了近年来该领域内的相关研究进展, 包括昆虫传播植物病毒的传毒方式、 影响传毒效率的因素、 传毒机制特别是昆虫体内与病毒传播可能相关的受体等。     

昆虫介体行为与植物病毒的传播

大多数植物病毒都是依赖昆虫介体进行传播,其中超过80%的传毒介体昆虫都是属于半翅目同翅亚目。昆虫介体识别寄主植物和取食的过程与病毒的传播密切相关,本文主要综述了同翅亚目昆虫、蓟马等介体昆虫取食行为与植物病毒的相互作用方面的研究进展,着重于介绍昆虫不同取食阶段的行为对植物病毒传播的影响,病毒侵染对介体取食和识别寄主行为的影响。     

Winter climate change in plant–soil systems: summary of recent findings and future perspectives

The winter climate is changing in many parts of the world, and it is predicted that winter climate change will modify the structure and function of plant–soil systems. An understanding of these changes and their consequences in terrestrial ecosystems requires knowledge of the linkage between above- and below-ground components as well as the species interactions found in plant–soil systems, which have important implications for biogeochemical cycles. However, winter climate-change studies have focused on only a part of the ecosystem or ecological process. We summarize here recent findings related to the effects of winter climate and its changes on soil nitrogen (N) dynamics, greenhouse gas (N₂O) emissions from the soil, N use by individual plants, vegetation development, and interactions between vegetation and pollinators to generate an integrative understanding of the response of the plant–soil system to winter climate change. This review indicates that the net effects on plants, soil microbes, pollinators, and the associated biogeochemical cycles are balanced among several processes and are highly variable depending on the context, such as the target species/functional group, original winter condition of the habitat, and type of climate change. The consequences of winter climate change for species interactions among plants, associated animals, and biogeochemical cycles are largely unknown. For further research, a large-scale comparative study to measure ecosystem-level functions is important, especially in less-cold ecosystems.     

Exploring the diversity of plant DNA viruses and their satellites using vector-enabled metagenomics on whiteflies

Current knowledge of plant virus diversity is biased towards agents of visible and economically important diseases. Less is known about viruses that have not caused major diseases in crops, or viruses from native vegetation, which are a reservoir of biodiversity that can contribute to viral emergence. Discovery of these plant viruses is hindered by the traditional approach of sampling individual symptomatic plants. Since many damaging plant viruses are transmitted by insect vectors, we have developed "vector-enabled metagenomics" (VEM) to investigate the diversity of plant viruses. VEM involves sampling of insect vectors (in this case, whiteflies) from plants, followed by purification of viral particles and metagenomic sequencing. The VEM approach exploits the natural ability of highly mobile adult whiteflies to integrate viruses from many plants over time and space, and leverages the capability of metagenomics for discovering novel viruses. This study utilized VEM to describe the DNA viral community from whiteflies (Bemisia tabaci) collected from two important agricultural regions in Florida, USA. VEM successfully characterized the active and abundant viruses that produce disease symptoms in crops, as well as the less abundant viruses infecting adjacent native vegetation. PCR assays designed from the metagenomic sequences enabled the complete sequencing of four novel begomovirus genome components, as well as the first discovery of plant virus satellites in North America. One of the novel begomoviruses was subsequently identified in symptomatic Chenopodium ambrosiodes from the same field site, validating VEM as an effective method for proactive monitoring of plant viruses without a priori knowledge of the pathogens. This study demonstrates the power of VEM for describing the circulating viral community in a given region, which will enhance our understanding of plant viral diversity, and facilitate emerging plant virus surveillance and management of viral diseases.     

Settling preferences of the whitefly vector Bemisia tabaci on infected plants varies with virus family and transmission mode

Virus infection may change not only the host‐plant phenotypic (morphological and physiological) characteristics, but can also modify the behavior of their insect vector in a mutualistic or rather antagonistic manner, to promote their spread to new hosts. Viruses differ in their modes of transmission and depend on vector behavior for successful spread. Here, we investigated the effects of the semi‐persistently transmitted Tomato chlorosis virus (ToCV, Crinivirus) and the persistent circulative Tomato severe rugose virus (ToSRV, Begomovirus) on alighting preferences and arrestment behavior of their whitefly vector Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East Asia Minor 1 (MEAM1) on tomato plants (Solanum lycopersicum L. cv. Santa Clara, Solanaceae). The vector alighting preferences between infected and uninfected plants in choice assays were apparently influenced by the presence of ToCV and ToSRV in the whiteflies or by their previous exposure to infected plants. The observed changes in vector behavior do not seem to benefit the spread of ToCV: non‐viruliferous insects clearly preferred mock‐inoculated plants, whereas ToCV‐viruliferous insects landed on mock‐inoculated and ToCV‐infected plants, indicating a partial change in insect behavior – ToCV was able to directly affect the preference of its vector B. tabaci, but this change in insect behavior did not affect the virus spread because viruliferous insects landed on mock‐inoculated and infected plants indistinctly. In contrast, ToSRV‐viruliferous insects preferred to land on mock‐inoculated plants, a behavior that increases the probability of spread to new host plants. In the arresting behavior assay, the majority of the insects remained on mock‐inoculated plants when released on them. A greater number of insects moved toward mock‐inoculated plants when initially released on ToCV‐ or ToSRV‐infected plants, suggesting that these viruses may repel or reduce the nutritional quality of the host plants for B. tabaci MEAM1.     

气候变化下生物交互作用对树线生态过程的影响

树线交错带是具有强烈生物交互作用的高寒生态过渡带,生物互作与树线生态过程密切相关。本研究系统综述了气候变化下植物间、动植物间和微生物与植物间互作因子对树线生态过程的影响。植物间互利或竞争作用的强度调控变暖背景下树线生态过程的变化,目前尚缺少树轮生态学证据,且亟待检验高阶互作的适用性;动物采食活动、微生物与植物间互作可通过影响土壤状况、改变树木生长和更新等生态过程动态,增强或削弱树线与气候间耦合关系。迄今为止,地下与地上过程联系如何影响气候变暖下的树线动态尚不明晰,而营养级间互作可能调制树线生态过程对气候响应。青藏高原等高寒区具有开展此类研究的优势与潜力。     

Technical advancement in plant virus diagnosis – an appraisal

Plants infected by a wide range of viruses often cause important agronomic and economic losses worldwide. Detection of plant viruses is becoming more challenging as globalisation of trade, particularly the ornamental plants, and the potential effects of climate change facilitate movement of viruses and their vectors, thereby transforming the diagnostic landscape. Under such circumstances, detection of viruses at premature stages of infection by use of rapid, sensitive and accurate detection methods seems crucial to ensure safe and sustainable agriculture and as such reduces economic losses. For proper identification, detection technique needs to be rapid, most accurate and inexpensive, as it forms the key step in developing appropriate practical solutions to manage plant virus diseases that pose continuous threats to the viability of certain horticultural and agricultural industries. This review is concerned with the advancement in techniques in the diagnosis of viruses in plants.     

Herbicides and their potential to disrupt plant–insect chemical communication

Ecological interactions between plants and insects are of paramount importance for the maintenance of biodiversity and ecosystem functioning. Herbicides have long been considered a threat to plant and insect populations, but global increases in intensive agriculture and availability of herbicide-resistant crops have intensified concerns about their full impact on biodiversity. Here, we argue that exposure to sublethal herbicide doses has the potential to alter plant–insect interactions as a result of disruptions in their chemical communication. This is because herbicides interfere with biosynthetic pathways and phytohormones involved in the production of several classes of plant volatiles that mediate plant–insect chemical communication. Sublethal herbicide doses can modify the morphological and life-history plant traits and affect interactions with insects. However, the potential changes in plant volatiles and their consequences for plant–insect chemical communication have not yet received as much attention. We discuss how target-site (disruptors of primary metabolism) and non-target-site (synthetic auxins) herbicides could alter the production of plant volatiles and disrupt plant–insect chemical communication. We suggest research avenues to fill in the current gap in our knowledge that might derive recommendations and applied solutions to minimize herbicides' impacts on plant–insect interactions and biodiversity.     

Geminivirus genes and vectors

The geminiviruses are very small plant viruses with circular single-stranded DNA genomes. Recent advances have identified genes involved in replication, spread of virus or DNA in the plant, and insect transmission. Gene replacement experiments suggest that useful plant gene expression vectors can be constructed from these viruses.