Lack of synergistic effects in tomato plants co-infected with tomato severe rugose virus and tomato chlorosis virus

The begomovirus Tomato severe rugose virus (ToSRV) and the crinivirus Tomato chlorosis virus (ToCV), in single and co-infections, are very common in tomato crops in Brazil. Both viruses are transmitted by the whitefly Bemisia tabaciMEAM1 (biotype B). The objective of this study was to analyse the interaction between ToSRV and ToCV in tomato plants of cultivars Santa Clara and Kada. Plants at 15, 30 and 45 days after emergence were inoculated with 30 viruliferous B. tabaci per plant. The following treatments were compared: plants inoculated with ToSRV, ToCV, ToSRV + ToCV, and healthy (control). The interaction between these viruses was analysed by measuring the virus titre by qPCR and the fresh and dry weights of the aerial parts of the tomato plants. Based on two independent assays, no significant effects for co-infection of ToSRV and ToCV on virus titres and plant development were observed compared to single infections. The dry weight of tomato plants of both cultivars infected with ToSRV, ToCV, or co-infected did not differ significantly. However, the dry weight of Santa Clara tomato plants infected with ToSRV, ToCV and ToSRV + ToCV showed mean reductions of 21.5%, 25.5% and 32%, respectively, compared to healthy plants, and mean reductions for Kada were 31.7%, 37.5% and 38%, respectively.     

Differential reaction of sweet pepper to infection with the crinivirus tomato chlorosis virus probably depends on the viral variant

The tomato chlorosis virus (ToCV), transmitted by whitefly species of the genera Bemisia and Trialeurodes in a semipersistent manner, causes significant losses in solanaceous crops including tomato (Solanum lycopersicum) and sweet pepper (Capsicum annuum). Worldwide reports of natural and experimental infection of sweet pepper plants with ToCV are contradictory, raising the question of whether the critical factor determining infection is related to the susceptibility of sweet pepper cultivars or the genetics of virus isolates. In this work, ToCV isolates obtained from different hosts and geographical origins were biologically and molecularly analysed, transmitted by B. tabaci MEAM1 and MED, and the reaction of different sweet pepper cultivars was evaluated under different environmental conditions. Brazilian ToCV isolates from tomato, potato (S. tuberosum), S. americanum, and Physalis angulata did not infect plants of five sweet pepper cultivars when transmitted by B. tabaci MEAM1. Temperatures did not affect the sweet pepper susceptibility to tomato-ToCV isolates from São Paulo, Brazil, and Florida, USA. However, sweet pepper-ToCV isolates from Spain and São Paulo, Brazil, were transmitted efficiently to sweet pepper plants by B. tabaci MEAM1 and MED. Although the results indicated that ToCV isolates from naturally infected sweet pepper plants seem to be better adapted to plants of C. annuum, phylogenetic analyses based on the complete nucleotide sequences of RNA1 and RNA2 as well as the p22 gene did not reveal significant nucleotide differences among them. Additional studies are needed to identify intrinsic characteristics of ToCV isolates that favour infection of sweet pepper plants.     

Panel of real‐time PCRs for the multiplexed detection of two tomato‐infecting begomoviruses and their cognate whitefly vector species

A new approach for the simultaneous identification of the viruses and vectors responsible for tomato yellow leaf curl disease (TYLCD) epidemics is presented. A panel of quantitative multiplexed real‐time PCR assays was developed for the sensitive and reliable detection of Tomato yellow leaf curl virus‐Israel (TYLCV‐IL), Tomato leaf curl virus (ToLCV), Bemisia tabaci Middle East Asia Minor 1 species (MEAM1, B biotype) and B. tabaci Mediterranean species (MED, Q biotype) from either plant or whitefly samples. For quality‐assurance purposes, two internal control assays were included in the assay panel for the co‐amplification of solanaceous plant DNA or B. tabaci DNA. All assays were shown to be specific and reproducible. The multiplexed assays were able to reliably detect as few as 10 plasmid copies of TYLCV‐IL, 100 plasmid copies of ToLCV, 500 fg B. tabaci MEAM1 and 300 fg B. tabaci MED DNA. Evaluated methods for routine testing of field‐collected whiteflies are presented, including protocols for processing B. tabaci captured on yellow sticky traps and for bulking of multiple B. tabaci individuals prior to DNA extraction. This work assembles all of the essential features of a validated and quality‐assured diagnostic method for the identification and discrimination of tomato‐infecting begomovirus and B. tabaci vector species in Australia. This flexible panel of assays will facilitate improved quarantine, biosecurity and disease‐management programmes both in Australia and worldwide.     

山东寿光地区Q型烟粉虱对番茄褪绿病毒的传播

为明确山东寿光地区Q型烟粉虱对番茄褪绿病毒(Tomato chlorosis virus,To CV)感病流行的影响及其传毒特性,于2014年调查了该地区设施番茄上烟粉虱种群动态与To CV发病情况,利用特异引物对烟粉虱体内To CV进行了RT-PCR检测;并在室内测定了带毒Q型烟粉虱取食时间和种群数量对To CV感病株率的影响。结果表明,在番茄发病植株上采集的烟粉虱种群体内可检测到To CV;春茬番茄To CV发病株率随烟粉虱种群数量增加而逐渐升高,4—6月是To CV发生高峰期,6月22日发病株率达100%;秋茬番茄烟粉虱种群数量从10月下旬明显下降,而To CV发病株率升高,11月12日发病株率达100%;室内试验表明,To CV感病株率随着带毒Q型烟粉虱数量与取食时间的增加而明显升高。研究表明,Q型烟粉虱能有效传播To CV,且其种群数量对To CV发病株率存在显著影响,可通过防控烟粉虱以控制To CV的危害。     

日光温室番茄褪绿病毒病的发生规律及其与Q型烟粉虱种群动态关系

为有效控制日光温室番茄褪绿病毒病,于2014—2015年通过RT-PCR检测方法研究了济南市日光温室番茄褪绿病毒(Tomato chlorosis virus,ToCV)的发生规律、其与Q型烟粉虱Bemisia tabaci种群动态的关系及防虫网对该病毒病的防控效果。结果表明,春季日光温室番茄植株上Q型烟粉虱成虫数量呈增长趋势,5月下旬最高达到0.10头/叶,秋季日光温室番茄植株上Q型烟粉虱成虫数量9月上旬达最高7.42头/叶,后逐渐下降;日光温室Q型烟粉虱带毒率随着定植时间的延长而逐渐上升,之后维持相对稳定状态,即春季为20.00%~24.14%,秋季为30.00%~40.00%。日光温室ToCV发生与Q型烟粉虱成虫数量和带毒率密切相关,春季番茄最高发病率为12.00%;秋季番茄植株最高发病率为93.02%。番茄育苗和生长期用100目防虫网隔离可显著降低番茄植株带毒率。因此,秋季是日光温室ToCV防控关键期,覆盖防虫网阻隔烟粉虱可有效防治ToCV,推荐在日光温室使用。     

Evidence of no horizontal or vertical transmission of tomato severe rugose virus by Bemisia tabaci MEAM1

Bemisia tabaci is important in agriculture worldwide, mainly because it is a vector of numerous plant viruses, probably the most important of which are members of the genus Begomovirus. Dozens of begomoviruses have been reported to infect tomato plants in Brazil, although tomato severe rugose virus (ToSRV) predominates in tomato crops. ToSRV, found so far only in Brazil, is efficiently transmitted by B. tabaci MEAM1. However, no studies have assessed the occurrence of vertical and horizontal transmission of the virus in the insect, which may have epidemiological consequences affecting disease management. This study evaluated the possibility of transmission of ToSRV between whiteflies during copulation and transovarial transmission from viruliferous females of B. tabaci MEAM1 to their progeny. Transmission of ToSRV did not occur during mating between males and females of B. tabaci MEAM1. Aviruliferous males and females confined with viruliferous insects of the opposite sex were also unable to transmit the virus to tomato plants. ToSRV was detected, by PCR, in the ovaries of viruliferous females of B. tabaci MEAM1 but not in eggs, nymphs, or adults of the progeny of viruliferous females. Adult progeny of viruliferous females also did not transmit ToSRV to tomato plants. Together, the results indicate that vertical and horizontal transmission of ToSRV by B. tabaci MEAM1 is unlikely. Sustainable management of the tomato golden mosaic disease caused by ToSRV should continue to focus on using resistant varieties, managing sources of inoculum around tomato fields, and rational chemical control of the vector.     

烟粉虱传播的番茄褪绿病毒和番茄黄化曲叶病毒对不同番茄品种的复合侵染

为明确烟粉虱传播的番茄褪绿病毒(Tomato chlorosis virus,ToCV)与番茄黄化曲叶病毒(Tomato yellow leaf curl virus,TYLCV)对不同番茄品种的复合侵染情况,于2015年11月在山东省寿光市温室内采集13个番茄品种共390份疑似发病植株叶片,对不同番茄品种的TYLCV抗性和2种病毒的复合侵染以及温室内发病番茄植株上烟粉虱成虫的带毒率进行检测。结果表明,采集的13个番茄品种经分子标记检测鉴定均为TYLCV杂合抗性;不同番茄品种ToCV与TYLCV的复合侵染率存在明显差异,大果番茄粉宴和贝瑞上复合侵染率最高可达73.3%,而樱桃番茄八喜上未检测到这2种病毒的复合侵染。此外,在发病番茄植株上采集的烟粉虱成虫体内可检测到2种病毒,其中烟粉虱ToCV带毒率为90.7%,TYLCV带毒率为80.0%,同时检测到ToCV与TYLCV的概率为71.3%。表明ToCV和TYLCV的复合侵染在山东省番茄生产中普遍发生,烟粉虱可同时携带这2种病毒并广泛传播。     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

Tomato chlorosis virus in pepper: prevalence in commercial crops in southeastern Spain and symptomatology under experimental conditions

Tomato chlorosis virus (ToCV), a member of the genus Crinivirus (family Closteroviridae), has been present in Spain since at least 1997, causing annual epidemics of yellowing in protected tomato crops. In 1999, sweet pepper plants exhibiting stunting and symptoms of interveinal yellowing and mild upward curling in the leaves, were found to be infected with ToCV in a greenhouse heavily infested with the whitefly Bemisia tabaci in the province of Almería, southeastern Spain. This study investigated the prevalence of ToCV in tomato and pepper crops in the major growing areas of southeastern Spain (Murcia, Almería and Málaga provinces) over a 3‐year period. In addition, an experimental system was developed for ToCV inoculation using B. tabaci as a vector, which allowed analysis of susceptibility of different pepper cultivars to the virus. The disease syndrome and yield losses induced by ToCV in pepper were also studied under experimental conditions, confirming severe yield reduction in infected plants.     

Arabidopsis thaliana,an experimental host for tomato yellow leaf curl disease‐associated begomoviruses by agroinoculation and whitefly transmission

Tomato yellow leaf curl disease is one of the most devastating viral diseases affecting tomato crops worldwide. This disease is caused by several begomoviruses (genus Begomovirus, family Geminiviridae), such as Tomato yellow leaf curl virus (TYLCV), that are transmitted in nature by the whitefly vector Bemisia tabaci. An efficient control of this vector‐transmitted disease requires a thorough knowledge of the plant–virus–vector triple interaction. The possibility of using Arabidopsis thaliana as an experimental host would provide the opportunity to use a wide variety of genetic resources and tools to understand interactions that are not feasible in agronomically important hosts. In this study, it is demonstrated that isolates of two strains (Israel, IL and Mild, Mld) of TYLCV can replicate and systemically infect A. thaliana ecotype Columbia plants either by Agrobacterium tumefaciens‐mediated inoculation or through the natural vector Bemisia tabaci. The virus can also be acquired from A. thaliana‐infected plants by B. tabaci and transmitted to either A. thaliana or tomato plants. Therefore, A. thaliana is a suitable host for TYLCV–insect vector–plant host interaction studies. Interestingly, an isolate of the Spain (ES) strain of a related begomovirus, Tomato yellow leaf curl Sardinia virus (TYLCSV‐ES), is unable to infect this ecotype of A. thaliana efficiently. Using infectious chimeric viral clones between TYLCV‐Mld and TYLCSV‐ES, candidate viral factors involved in an efficient infection of A. thaliana were identified.     

Severe outbreaks of late blight on potato and tomato in South India caused by recent changes in the Phytophthora infestans population

Late blight, caused by Phytophthora infestans, has emerged as the most destructive disease of potato and tomato in South India since 2008. One hundred and fifty‐seven isolates of Phytophthora infestans, 63 from potato and 94 from tomato, were collected from major potato and tomato production areas of South India between 2010 and 2012. Their phenotypic and genotypic characteristics were determined and compared with reference isolates. Isolates were characterized based on mating type, in vitro metalaxyl sensitivity, mitochondrial DNA haplotype, RG57 DNA fingerprinting patterns, SSR markers and aggressiveness on potato and tomato, in order to monitor population changes in P. infestans. All isolates were A2 mating type, metalaxyl resistant, mtDNA haplotype Ia and had RG57 and SSR fingerprints almost identical to the 13_A2 clonal lineage reported in Europe. Variation at the D13 and SSR4 loci allowed discrimination of minor variants, designated as 13_A2_3, 13_A2_3b, 13_A2_3c and 13_A2_1. A comparison of the lesion diameters caused by 157 isolates on detached leaflets of three potato and tomato cultivars showed all isolates to be equally aggressive, confirming that the same clonal population is infecting both hosts. This study demonstrates that the 13_A2 lineage was responsible for severe late blight outbreaks on potato and tomato in South India and has replaced the prior population represented by the US‐1 and other genotypes. Revised management strategies will be required to combat this destructive 13_A2 clonal lineage and monitoring of the population across other potato‐ and tomato‐growing regions of India is warranted.     

沼泽红假单胞菌PSB-06菌剂对番茄褪绿病的防效及其作用机制

为明确沼泽红假单胞菌Rhodopseudomonas palustris PSB-06菌剂对番茄褪绿病毒（tomato chlorosis virus,ToCV）的抑制作用,连续3年在田间进行沼泽红假单胞菌PSB-06菌剂对ToCV的药效试验,并在室内研究其抗病毒的作用机制。田间试验结果显示,PSB-06菌剂处理能降低ToCV的发生,植株发病率均低于50%,均显著低于清水和氨基寡糖素处理;室内试验结果显示,PSB-06菌剂处理能抑制病毒传播,喷施PSB-06菌剂后的感病番茄的SA含量达532.67 mg/g,PI II和NPR1基因表达量也相对上升;同时,健康番茄与感病番茄的叶绿素含量均明显升高;经PSB-06喷施后番茄植株上的烟粉虱Bemisia tabaci生存数量降低。蛋白组学分析结果表明,PSB-06处理促使植物代谢及防御的相关蛋白均上调。表明沼泽红假单胞菌PSB-06菌剂能增强植物免疫和防御烟粉虱的能力,从而有效地控制ToCV的发生及传播。     

Resistance to Xanthomonas perforans race T4 causing bacterial spot in tomato breeding lines

Tomato (Solanum lycopersicum) is the second most important vegetable crop in the world. Bacterial spot (BS) of tomato, caused by four species of Xanthomonas: X. euvesicatoria, X. vesicatoria, X. perforans and X. gardneri, results in severe loss in yield and quality due to defoliation and formation of lesions on fruits, respectively. Currently management practices do not offer effective control under conditions of high disease pressure. Thus, developing BS resistance is a critical priority for tomato growers in order to minimize crop losses. Sixty‐three advanced tomato breeding lines, heirlooms and wild tomato lines with diverse genetic backgrounds were screened under greenhouse and field conditions for BS resistance using X. perforans race T4, which was found to be a prevalent race in North Carolina. Race T4 isolate 9 was used to inoculate the plants by spraying, and disease severity was measured using the Horsfall–Barratt scale. Tomato lines 74L‐1W(2008), NC2CELBR, 081‐12‐1X‐gsms, NC22L‐1 (2008) and 52LB‐1 showed resistance to BS in the field and/or greenhouse trials. These lines were derived from S. pimpinellifolium L3707. Screening L3707 followed by development of a mapping population and mapping resistance genes might be useful for breeding resistance against BS in future breeding programmes.     

Potato, an experimental and natural host of the crinivirus Tomato chlorosis virus

Tomato chlorosis virus (ToCV, genus Crinivirus, family Closteroviridae) causes yellowing of tomatoes in many countries worldwide. Symptoms of ToCV infections in tomatoes include inter-veinal yellow chlorotic areas that develop first on lower leaves and then advance towards the upper part of the plant. ToCV is transmitted in nature by the whiteflies Bemisia tabaci, Trialeurodes vaporariorum, and Trialeurodes abutilonea in a semi-persistent manner. In the summer of 2006, a few potato (Solanum tuberosum) volunteer plants heavily infested with the whitefly B. tabaci were found growing within a pepper crop in the province of Málaga, southern Spain. Leaf samples from volunteer plants were tested for the presence of ToCV by molecular hybridization and RT-PCR, and were shown to be infected. Furthermore, potato plants were readily infected by ToCV after experimental transmission using B. tabaci biotype Q as vector. ToCV was also detected in the tubers from infected plants that subsequently produced infected plants. Potato also served as virus source for tomato infection via B. tabaci transmission.     

SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.     

Evaluation of Datura stramonium and Nicandra physaloides as reservoirs of tomato severe rugose virus and whiteflies

Tomato severe rugose virus (ToSRV) is the most important begomovirus transmitted and spread by the whitefly Bemisia tabaci in tomato crops in Brazil. Cultural practices are being adopted, along with insecticides, for controlling this virus. However, little is known about the importance of weeds in the pathosystem, which can contribute to the failure of these practices. This work aimed to evaluate the role of Datura stramonium and Nicandra physaloides as alternative hosts of ToSRV and verify the viral influence on the biological performance of Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) cryptic species. N. physaloides was a better alternative host for ToSRV when combined with MEAM1 whiteflies, while D. stramonium was mostly a good host for whitefly reproduction. Viral infection improved MEAM1 performance on both host plants but affected MED performance negatively. These data suggest that both weeds can be of some importance for the pathosystem, and their control should be included in management programmes.     

Situation of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum in protected tomato crops in Algarve (Portugal)*

Protected tomato is the most important horticultural crop in the Algarve (south of Portugal). However, the growing area has decreased by almost 48% since 1995, mainly as a result of the pests Bemisia tabaci and Trialeurodes vaporariorum and the epidemics of Tomato yellow leaf curl virus (TYLCV), a Begomovirus transmitted by B. tabaci. Both whiteflies are vectors of economically important viruses. Recently, Tomato chlorosis virus (ToCV), a member of the genus Crinivirus, transmitted by both B. tabaci and T. vaporariorum, was reported infecting tomato crops in Algarve. A study was carried out to evaluate the dynamics of whitefly populations on tomato crops in Algarve. Population counts of B. tabaci were high in the first months of autumn, then decreased until January, when numbers of T. vaporariorum became higher. Counts of B. tabaci then increased again.     

Biological characterization of Tomato leaf curl New Delhi virus from Spain

Tomato leaf curl New Delhi virus (ToLCNDV; family Geminiviridae, genus Begomovirus) is an emerging virus in horticulture crops in Asia, and has recently been introduced in Spain, Tunisia and Italy. No betasatellite DNA was detected in infected tomato and zucchini squash samples from Spain, and agroinoculated viral DNA‐A and DNA‐B were sufficient to reproduce symptoms in plants of both crop species. Infected tomato and zucchini squash plants also served as inoculum sources for efficient transmission either mechanically or using Bemisia tabaci whiteflies. Cucumber, melon, watermelon, zucchini squash, tomato, eggplant and pepper, but not common bean, were readily infected using viruliferous whiteflies and expressed symptoms 8–15 days post‐inoculation. New full‐length sequences from zucchini squash and tomato indicated a high genetic homogeneity (>99% sequence identity) in the ToLCNDV populations in Spain, pointing to a single recent introduction event.     

<Emphasis Type="Italic">Bemisia tabaci</Emphasis> Biotype Q is present in Costa Rica

Whiteflies are an insect group that comprises multiple species and biotypes, capable of affecting crops by phloem feeding, virus transmission and promotion of fungal colonization. The distribution of these pests is worldwide. In Costa Rica, a country located in the tropics, the most problematic whiteflies are Bemisia tabaci biotype B and Trialeurodes vaporariorum. In September 2009, two greenhouses in the Alfaro Ruiz region, northwest of the country’s capital, San Jose, were surveyed as part of a larger effort to determine the occurrence of species and races of whiteflies in this agronomically important region. In addition, the insect samples were analyzed to determine the presence of Tomato chlorosis virus (ToCV), a yield-affecting crinivirus transmitted by whiteflies. The results revealed the presence of the Q biotype of B. tabaci, and important invasive species, as well as the expected T. vaporariorum. Viral detection assays identified potentially viruliferous individuals for Tomato chlorosis virus. These results identified a new pest capable of harbouring plant viruses has been identified, as well as a viral agent (ToCV) in a region where it was not reported, and which might cause significant yield losses.