Assessment of Transmission Ability of Barley Yellow Dwarf Virus-PAV Isolates by Different Populations of Rhopalosiphum padi and Sitobion avenae

Populations of two aphid species from different geographic regions of Morocco were tested for their ability to transmit five barley yellow dwarf virus-PAV (BYDV-PAV) type isolates using Clintland 64 oat as the test plant. Transmission efficiencies were determined for 10 sub-populations of Rhopalosiphum padi and 12 sub-populations of Sitobion avenae. After a short acquisition access period (AAP) of 4h, all populations transmitted the virus but with different efficiencies. R. padi (Rp-S) and S. avenae (Sa-S) collected in the Settat region were the most efficient vectors, with transmission rates of 38% and 27%, respectively. R. padi (Rp-C) collected at Chaouen and S. avenae (Sa-B) at Berkane, were poor transmitters with respective vectoring abilities of 20% and 16%. These four sub-populations were chosen to study the acquisition of BYDV-PAV and the retention of virus within aphids in more detail. The transmission after two AAPs of 4h and 48h were compared. Starved aphids given a 4h AAP had significantly higher transmission efficiencies than non-starved aphids. However, after a 48h AAP, no difference was observed in the transmission between starved and non-starved aphids. Intraspecific variability was also detected by means of serial transfers of individual aphids after the given AAP. Following the first day of serial transfers, no differences were observed in transmission efficiency and virus titers for sub-populations within each species acquiring the virus during 48h, but there was significant variation when the virus was acquired in 4h. The levels of PAV antigen retained by aphids fed on healthy plants declined rapidly during the first day after acquisition, but remained fairly constant during the next 5–7 days depending on the length of the AAP. Virus antigen could be detected by ELISA in Rp-S and Sa-S for up to 11 days of serial transfer, but it was shown that aphids could retain and transmit BYDV-PAV for at least 3 weeks.     

Analyzing and Modeling Temporal Disease Progress of Barley yellow dwarf virus Serotypes in Barley Fields

ABSTRACT Population dynamics of Padi avenae (PAV), Macrosiphum avenae (MAV), and Rhopalosiphum padi (RPV) virus serotypes of Barley yellow dwarf virus (BYDV) and of their main aphid vectors were studied in winter barley (Hordeum vulgare) fields for three successive years in western France. An epidemiological model of the spread of viruses in the field was developed based on vector populations as forcing variables and the population dynamics of each virus serotype. This model accurately simulated the kinetics of the epidemic for PAV serotypes, which are the most common ones. For RPV and to some extent for MAV, the results were less satisfactory. The occurrence and spread of PAV and MAV serotypes in the field was clearly and easily related to that of their main vector species. Conversely, the spread of RPV serotypes showed no consistent relationships with the dynamics of their vectors. Incidence of PAV in 1989 to 1990 and 1990 to 1991 showed a bimodal distribution, with maximums in fall (December) and spring (May) that were linked to fall infestations by R. padi and spring infestations by three (R. padi, Sitobion avenae, and Metopolophium dirhodum) or two (S. avenae and M. dirhodum) aphid species. In 1991 to 1992, the PAV infection curve was monomodal and mainly due to a primary spread of the virus by very large populations of alate R. padi. MAV incidence was low in fall and winter and reached a maximum in spring 1990 and 1991 related to the occurrence of S. avenae and M. dirhodum. RPV incidence was low every year, despite the abundance of its vector, R. padi. Mixed infections were more frequent than expected by chance and were assumed to be partly related to heterologous encapsidation. The occurrence of each serotype is discussed in relation to the time of crop infection and possible damage.     

The Effect of Temperature on Variation in Transmission of a BYDV PAV-like isolate by Clones of Rhopalosiphum Padi and Sitobion Avenae

The efficiencies of seven clones of Rhopalosiphum padi and five clones of Sitobion avenae (originating from Greece and the United Kingdom) as vectors of barley yellow dwarf virus (PAV-like isolate) were evaluated at 5, 10 and 15°C. When inoculation took place at 5 or 10°C, clones of R. padi differed in their ability to transmit. At 15°C there were no differences in the vectoring ability of different clones. For S. avenae, there were no interclonal differences in the transmission efficiency at any of the temperatures. The epidemiological consequences of differences in virus transmission at different temperatures are discussed.     

大麦黄矮病毒-GAV在燕麦植株体内运动规律的初步研究

 利用RT-PCR方法研究了大麦黄矮病毒-GAV在燕麦植株内的移动规律。先将介体麦二叉蚜(Schizaphis graminum)在BYDV-GAV新鲜病叶上饲毒,再将获毒蚜虫放置到二叶期的健康燕麦植株接种48h,随后分期提取接种植株的第1~6片叶和根组织的总RNA,利用特异引物扩增BYDV-GAV的外壳蛋白(CP)基因以检测病毒在燕麦植株内的复制和移动。结果表明,在接种5d后,接种叶片(第2片叶)呈现阳性,接种7d后,植株新生的第4片叶被侵染,接种9d后,部分的第3片叶呈现阳性,至接种16d,几乎所有的叶片均呈现阳性。仅在接种的第5、7和9d收集的根组织呈现阳性,而所有的第1片叶均为阴性,可能是由于这些组织内病毒含量太低所致。本研究初步揭示了BYDV-GAV长距离运动的规律并且发现该病毒在燕麦根部从接种到系统发病都没有进行大量增殖,为今后进一步研究病毒运动机制选取适当的植物材料提供了基本信息。     

Aphid Transmission Alters the Genomic and Defective RNA Populations of Citrus tristeza virus Isolates

ABSTRACT A total of 14 Spanish isolates of Citrus tristeza virus (CTV) and 1 isolate from Japan were transmitted by Aphis gossypii, and the subisolates obtained were compared with the source isolates for symptom expression and double-stranded RNA (dsRNA) pattern. Of the 14 Spanish isolates, 9 showed altered dsRNA patterns after aphid transmission but only minor variations in the intensity of symptoms induced on Mexican lime. Northern blot hybridization with complementary DNA (cDNA) probes corresponding to both the 5' and the 3' termini of the CTV genomic RNA (gRNA) showed that the dsRNA bands that could be used to discriminate between the dsRNA pattern of the source and the aphid-transmitted isolates were the replicative forms of defective RNAs (D-RNAs). Conversely, the Japanese isolate and two subisolates obtained from it by aphid transmission had the same dsRNA pattern, but one of the subisolates induced milder symptoms in several hosts. Dot-blot hybridization with cDNA probes representing several regions of the gRNA showed that most of the aphid-transmitted isolates differed from the corresponding source isolate by their hybridization pattern. Our results indicate that aphid transmission often sorts the populations of gRNA variants and D-RNAs present in CTV isolates.     

我国不同地区麦蚜携带BYDV-GAV比率的差异

为了研究我国不同地区麦蚜携带大麦黄矮病毒麦二叉蚜麦长管蚜非专化性株系(BYDV GAV)比率的差异,采用RT-PCR技术,对BYDV-GAV的传毒介体麦蚜带毒情况进行检测.所用方法具有较高的灵敏度和特异性,测定样本用量可少至1/200头蚜虫;对采自我国主要麦区的蚜虫样本进行分子检测,山西、甘肃、青海、陕西11个小麦黄矮病重病区蚜虫样本带毒率为56％～91.5％,而河北、河南两省4个非重病区蚜虫样本带毒率为2.5％～33％.通过试验证实,我国不同地区麦蚜携带BYDV-GAV比率存在差异,小麦黄矮病重病区山西、甘肃、青海、陕西等地的麦蚜带毒率高,而非重病区河北、河南等地的麦蚜带毒率低.     

A comparative study of the Barley yellow dwarf virus species PAV and PAS: distribution,accumulation and host resistance

This study investigated the distribution and characteristics of the Barley yellow dwarf virus (BYDV) species BYDV‐PAS, which was recently separated from BYDV‐PAV, the most commonly studied BYDV species. Throughout 3 years of experimental monitoring of BYDV incidence, PAS was the most frequently occurring species infecting cereals and grasses in the Czech Republic. Furthermore, Rhopalosiphum maidis and Metopolophium dirhodum were recorded as BYDV‐PAS vectors, even though M. dirhodum does not usually transmit BYDV‐PAV. In field experiments with barley and wheat, where virus accumulation, symptoms and effect on the yield were tested, BYDV‐PAV was more severe than PAS. Infection with the BYDV‐PAV isolate resulted in greater expression of symptoms and also in a greater reduction in plant height and grain weight per spike than BYDV‐PAS. In a sensitive cultivar of barley (Graciosa), the amount of viral RNA of BYDV‐PAV was also significantly higher than that of BYDV‐PAS. In a tolerant line (Wbon‐123), however, no such differences were found. In conclusion, although BYDV‐PAS seems to be dominant in the Czech Republic, BYDV‐PAV has the potential to cause more significant crop losses in barley and wheat.     

Barley yellow dwarf viruses in Japanese pasture grasses and lack of correlation with the presence of fungal endophytes

Pasture grasses from temperate Japan were tested for infection with barley yellow dwarf viruses (BYDVs) and fungal endophytes. BYDVs from both the MAV and RPV subgroups were detected, but no symptoms attributable to BYDV infection were observed. Not all isolates from the MAV subgroup could be clearly discriminated as MAV or PAV solely on ELISA results, and may have been intermediate serotypes or mixed infections. BYDVs were found to infect fescue ( Festuca arundinacea : 17%), ryegrass ( Lolium perenne : 41%), timothy ( Phleum pratense : 94%) and Poa spp. (20%). Fescue and ryegrass were predominantly infected with RPV and PAV, respectively. The small collections of Poa spp. were only infected with PAV, while timothy was only tested for MAV subgroup viruses. In fescue 26% of tillers were infected with Acremonium coenophialum , and 60% of ryegrass tillers from an ecotype collection were infected with Acremonium lolii. There was no correlation between BYDV infection and the presence of endophytes for the above species or for Epichloe typhina -infected (50%) timothy. An ELISA test for A. lolii did not detect A. coenophialum in fescue or E. typhina in timothy but showed good agreement with epidermal staining of A. lolii in ryegrass leaf sheaths.     

大麦黄矮病毒GPV株系ORF4基因在大肠杆菌中的表达及特异抗血清的制备

 根据已报道的大麦黄矮病毒GPV株系(BYDV-GPV)相关基因序列设计合成引物,利用RT-PCR方法获得ORF4基因,并将其克隆到原核表达载体pET-5a中。经IPTG诱导、SDS-PAGE分析,结果表明:ORF4基因在大肠杆菌BL21(DE3) pLysS中获得了高效表达,分子量为17 kDa。以回收的表达产物为抗原免疫家兔,制备了BYDV-GPV 17kDa蛋白的特异性抗血清。Western blot检测结果,制备的抗血清可用于检测BYDV-GPV侵染后在燕麦体内表达的17 kDa蛋白。     

小麦禾谷缢管蚜的危害损失和防治指标研究

禾谷缢管蚜种群数量和危害历期是造成小麦产量损失的主要因素。采用累积虫日作为危害量指标 ,建立了蚜虫危害量与小麦产量损失的回归模型 ,即Y₁=1.4250+5.3529×10^-4X₁,Y₂=1.1780+0.0106X₂ ,确定了禾谷缢管蚜的动态防治指标     

Rate of Tomato yellow leaf curl virus Translocation in the Circulative Transmission Pathway of its Vector, the Whitefly Bemisia tabaci

ABSTRACT Whiteflies (Bemisia tabaci, biotype B) were able to transmit Tomato yellow leaf curl virus (TYLCV) 8 h after they were caged with infected tomato plants. The spread of TYLCV during this latent period was followed in organs thought to be involved in the translocation of the virus in B. tabaci. After increasing acquisition access periods (AAPs) on infected tomato plants, the stylets, the head, the midgut, a hemolymph sample, and the salivary glands dissected from individual insects were subjected to polymerase chain reaction (PCR) without any treatment; the presence of TYLCV was assessed with virus-specific primers. TYLCV DNA was first detected in the head of B. tabaci after a 10-min AAP. The virus was present in the midgut after 40 min and was first detected in the hemolymph after 90 min. TYLCV was found in the salivary glands 5.5 h after it was first detected in the hemolymph. Subjecting the insect organs to immunocapture-PCR showed that the virus capsid protein was in the insect organs at the same time as the virus genome, suggesting that at least some TYLCV translocates as virions. Although females are more efficient as vectors than males, TYLCV was detected in the salivary glands of males and of females after approximately the same AAP.     

Role of acquisition and inoculation time in the expression of clonal variation for BYDV-PAV transmission in the aphid species Rhopalosiphum padi

Vector efficiency of 20 Rhopalosiphum padi clones, originating from Europe, North America and North Africa and exhibiting different types of life cycle, was evaluated by transmitting a French BYDV-PAV isolate to barley plants under five different acquisition/inoculation sequences (AAP/IAP). Differences between clones in transmission efficiency were found only when a short AAP was followed by a long IAP (6 h/120 h) and, to some extent, when a long AAP (48 h) was followed by a short IAP (6 h), but no differences were found when the conditions for virus transmission were optimal, i.e. long AAP followed by long IAP (48 h/120 h). There were no differences in transmission rates by clones of different geographical origins and with different life cycles. As a consequence, clonal variation is probably of little importance in the vector aspects of the epidemiology of PAV serotypes transmitted by R. padi , but the availability of a range of clones exhibiting transmission differences under limiting AAP or IAP conditions could be of interest for studies of virus–vector relationships.     

BYDV PREDICTOR: a simulation model to predict aphid arrival, epidemics of Barley yellow dwarf virus and yield losses in wheat crops in a Mediterranean-type environment

BYDV PREDICTOR, a simulation model, was developed to forecast aphid outbreaks and Barley yellow dwarf virus (BYDV) epidemics in wheat crops in the grainbelt region of southwest Australia, which has a Mediterranean-type climate. The model used daily rainfall and mean temperature to predict aphid ( Rhopalosiphum padi ) buildup in each locality before the commencement of the cereal-growing season in late autumn, and to forecast the timing of aphid immigration into crops. The introduction of BYDV by aphid immigrants, aphid buildup within the crop, spread of BYDV, and yield losses were predicted for different sowing dates. The model simulations were validated with 10 years' field data from five different sites in the grainbelt, representing a wide range of scenarios. When first aphid arrival dates ranging from 1 June to 2 September were compared with predictions, 65% of the variation between sites and years was explained. Progress curves for the predicted percentage of plants infected with the serotype BYDV-PAV closely resembled the starting point and shape of those recorded in 14 out of 18 scenarios. Sensitivity analysis confirmed that the combination of a high proportion of immigrants vectoring BYDV, early sowing of crops and early start to aphid arrival relative to sowing date led to the most BYDV spread and greatest yield loss. The model was incorporated into a decision support system used by farmers in targeting sprays against aphids to prevent virus spread in autumn and winter. BYDV PREDICTOR could serve as a template for modelling similar virus/aphid vector pathosystems in other regions of the world, especially those with Mediterranean-type climates.     

蚕豆蚜日龄、翅型和寄生对其共生菌胞变化的影响

初生内共生菌与宿主蚜虫的营养代谢密切相关.本文观察了蚕豆蚜Aphis fabae不同翅型的共生菌胞随宿主蚜虫生长发育的变化规律,以及饥饿和混合柄瘤蚜茧蜂Lysiphlebus confusus寄生对共生菌胞的影响.菌胞数量和体积随发育进程和翅型的变化而呈现有规律的变化:随若蚜发育而逐渐增大,然后随胎生蚜产生而逐渐减少;无翅蚜的菌胞数量和体积均显著大于有翅蚜.随饥饿时间的延长,菌胞数量和体积迅速直线下降,而重新取食后又可迅速恢复.蚕豆蚜被混合柄瘤蚜茧蜂寄生后的第3d,菌胞数量显著多于未寄生蚜虫,此后则明显少于未寄生蚜虫,从第4d的119个·头-1降至第6d的46个·头-1.研究结果说明,蚜虫共生菌胞的变化与宿主蚜虫翅型、发育、外源营养以及蚜茧蜂寄生等密切关联.     

Genetic Regulation of Polerovirus and Luteovirus Transmission in the Aphid Schizaphis graminum

ABSTRACT Sexual forms of two genotypes of the aphid Schizaphis graminum, one a vector, the other a nonvector of two viruses that cause barley yellow dwarf disease (Barley yellow dwarf virus [BYDV]-SGV, luteovirus and Cereal yellow dwarf virus-RPV, polerovirus), were mated to generate F1 and F2 populations. Segregation of the transmission phenotype for both viruses in the F1 and F2 populations indicated that the transmission phenotype is under genetic control and that the parents are heterozygous for genes involved in transmission. The ability to transmit both viruses was correlated within the F1 and F2 populations, suggesting that a major gene or linked genes regulate the transmission. However, individual hybrid genotypes differed significantly in their ability to transmit each virus, indicating that in addition to a major gene, minor genes can affect the transmission of each virus independently. Gut and salivary gland associated transmission barriers were identified in the nonvector parent and some progeny, while other progeny possessed only a gut barrier or a salivary gland barrier. Hemolymph factors do not appear to be involved in determining the transmission phenotype. These results provide direct evidence that aphid transmission of luteoviruses is genetically regulated in the insect and that the tissue-specific barriers to virus transmission are not genetically linked.     

Transmission Efficiency of 'Candidatus Liberibacter solanacearum' and Potato Zebra Chip Disease Progress in Relation to Pathogen Titer, Vector Numbers, and Feeding Sites

ABSTRACT With diseases caused by vector-borne plant pathogens, acquisition and inoculation are two primary stages of the transmission, which can determine vector efficiency in spreading the pathogen. The present study was initiated to quantify acquisition and inoculation successes of 'Candidatus Liberibacter solanacearum', the etiological agent of zebra chip disease of potato, by its psyllid vector, Bactericera cockerelli (Hemiptera: Triozidae). Acquisition success was evaluated in relation to feeding site on the host plant as well as the acquisition access period. Inoculation success was evaluated in relation to vector number (1 and 4) on the plants. Acquisition success was influenced by the feeding site on the plant. The highest acquisition success occurred when insects had access to the whole plant. The results of the inoculation study indicated that the rate of successfully inoculated plants increased with the vector number. Plants inoculated with multiple psyllids had higher bacterial titer at the point of inoculation. Although disease incubation period was significantly shorter in plants inoculated with multiple psyllids, this effect was heterogeneous across experimental blocks, and was independent of pathogen quantity detected in the leaflets 3 days postinoculation. Disease progress was not affected by bacterial quantity injected or psyllid numbers.     

Occurrence of barley yellow dwarf virus in cereals and grasses of the low-rainfall wheatbelt of South Australia

South Australia is in the dry temperate zone where most cereal crops are grown in an area of low rainfall, with a crop-free season from December to April. The incidence of barley yellow dwarf virus (BYDV) was assessed by ELISA from 1989 to 1991 in wheat crops and irrigated pastures of South Australia. The incidence of BYDV was low in most wheat crops of the low-rainfall area in 1989 and 1990 (less than 1% of plants infected), but moderate levels of infection (1–10%) were observed in some early-sown crops. BYDV infection was more widespread in the high-rainfall area (south east of South Australia). A high incidence of BYDV was observed in the irrigated pastures of the three areas surveyed (4–86%). Of the five previously described strains, the Rhopalosiphum padi/Sitobion avenae strain (PAV) was the most common in wheat samples (> 90%). PAV and the R. padi-specific strain (RPV) were found in pasture grasses, alone or in mixed infection. Virus incidence was greater in Festuca spp. (56%) and Lolium perenne (30%) than in other species (2-–9%).