Occurrence of barley yellow dwarf virus in pastures of western France

As pasture grasses are preponderant in the agriculture of western France, their role as reservoirs of barley yellow dwarf virus (BYDV) and its aphid vectors has been studied from 1984 to 1986. Aphids were observed on most crops of five pasture grass species (brome grass, cocksfoot, tall fescue, Italian and perennial ryegrass) but in very low numbers. Rhopalosiphum padi was the most numerous species. The incidence of BYDV was high, with levels of infection ranging from 6 to 80% depending on the species of pasture grasses. Fescue pastures were highly infected with BYDV, whereas the virus was not detected in cocksfoot pastures. PAV-, RPV-, MAV-like isolates of BYDV were detected in pasture grasses, but RPV- and MAV-like isolates were only detected from ryegrass and brome grass, respectively. The role of these grasses as source of viruliferous aphids infecting cereals is discussed.     

The incidence of strains of barley yellow dwarf virus in perennial ryegrass crops in south-west and central Scotland

The incidence of barley yellow dwarf virus (BYDV) in perennial ryegrass ( Lolium perenne ) crops in four areas of south-west and central Scotland was investigated between March 1988 and February 1989. BYDV was detected in 93·8% of the grass swards using an indirect enzyme-linked immunosorbent assay (ELISA). This enabled the seasonal periodicity of the BYDV strains to be monitored over 12 months for the first time in Scotland. The incidence of the RPV, PAV and MAV strains of BYDV declined between March and July 1988, before gradually rising in August. Incidence increased markedly in September, especially of the RPV and MAV strains, and then gradually decreased over the winter months, before stabilizing in February 1989. The incidence of the different strains in perennial ryegrass leys varied between geographical areas and between fields within areas. Most ryegrass samples contained a mixture of the three strains of BYDV. RPV was the most common strain in Ayrshire, while the incidence of PAV was highest in Wigtownshire and that of MAV was highest in Dumfriesshire and Stirlingshire. The incidence of BYDV increased with the age of the sward. The role of perennial ryegrass as a source of virus for the infection of cereals is discussed.     

Effects of barley yellow dwarf and ryegrass mosaic viruses alone and in combination on the productivity of perennial and Italian ryegrasses

Moderately severe strains of barley yellow dwarf virus (BYDV) and ryegrass mosaic virus (RMV) significantly reduced the heights and yields of perennial ( Lolium perenne ) and Italian (L. multifiorum) ryegrasses. BYDV caused greater reductions in perennial ryegrass than in Italian, whereas the converse was true of RMV. Both viruses together rarely caused greater damage than the most damaging virus on its own. BYDV reduced the aggressiveness of perennial ryegrass more than of Italian, whereas with RMV the converse was true. In mixtures of perennial and Italian ryegrasses, the perennial was suppressed by the Italian when only BYDV was present, the Italian was suppressed by the perennial when only RMV was present, and the status quo was maintained when both viruses were present, even though they reduced the yield of the mixture by over 16%.     

Effects of barley yellow dwarf virus on some varieties of Italian, hybrid and perennial ryegrasses and their implication for grass breeders

With the exception of chlorotic streaks in a few plants, a severe strain of barley yellow dwarf virus (BYDV) transmitted by Rhopalosiplum padi caused no obvious foliar symptoms in 54 varieties of ryegrass when they were defoliated monthly. When defoliation ceased and yellow or red discoloration of the leaf tips was allowed to develop, it was a poor indicator of the seventy of disease effect on yield. Thus, some varieties which developed marked discoloration were less severely damaged than some with little or none While BYDV induced yield significant in some varieties of ryegrass, it increased it significantly in others. In some varieties these BYDV-induced yield increases occurred throughout the year, but in others they occurred in 1 month and were offset by a yield decrease in another. BYDV infection caused a greater yield reduction in roots than in shoots. Even varieties giving increased shoot yield gave decreased root yield. The possible disadvantages of the resulting increase in shoot to root ratio are discussed. It is concluded that breeding ryegrass for BYDV-induced yield increases may be easier and more rewarding than breeding for resistance or tolerance.     

The incidence of barley yellow dwarf virus isolates in perennial ryegrass (Lolium perenne) in south-western Victoria

Barley yellow dwarf virus (BYDV) was detected in perennial ryegrass cultivars examined from three sites in south-western Victoria (Balmoral, Mininera and Hamilton); the frequency of BYDV infection varied with cultivar. PAV-related isolates were prevalent at all sites, but the incidence of MAV- and RPV-related isolates varied with the site and cultivar. The PAV-related isolate was less frequent in cv. Ellett than in cv. Victorian at all sites. The implications for the epidemiology of the disease and its agronomic importance in Victoria are discussed.     

A simple test for evaluation of transmission efficiency of barley yellow dwarf virus by aphids

Barley yellow dwarf virus (BYDV) transmission test systems involve the use of clip-cages or of whole plants in cages, which are both labor-intensive methods and require large controlled environment units. Employing detached leaves for assessment of the inoculation efficiency of aphids proved reliable for assessing transmission of a BYDV PAV-like isolate byRhopalosiphum padi. One use of the system could be for the rapid determination of the infectivity of field-collected aphids, an essential part of any epidemiological study of BYDV. http://www.phytoparasitica.org posting Aug. 14, 2002.     

Occurrence of viruses in irrigated wheat in Zambia

Surveys were conducted during the cool-dry months of June–August 1997 and June–July 1998 for the presence of viruses in irrigated wheat in Central, Copperbelt, Lusaka and Southern Provinces of Zambia in 14 commercial farms and four wheat cultivar plots. Virus symptoms were observed on nine wheat cultivars ( Triticum aestivum 'Deka', 'Gamtoos', 'Lorie II', 'MM2', 'Nata', 'Nkwazi', 'P7', 'Scan' and 'Sceptre') of South African, Zambian and Zimbabwean origin. Several viruses were identified on the basis of field symptomatology, symptoms developing on mechanically inoculated indicator plant species or cultivars and serology (DAS-ELISA). The study revealed the occurrence of Brome mosaic virus (BMV), Barley stripe mosaic virus (BSMV), Barley yellow dwarf virus and its strains (BYDV-PAV and RPV), Soil-borne wheat mosaic virus (SBWMV), Wheat dwarf virus (WDV), Wheat streak mosaic virus (WSMV) and Wheat spindle streak mosaic virus (WSSMV). DSA-ELISA tests confirmed these identifications. The prevalence of viruses varied annually and from field to field. BSMV, BYDV-PAV, SBWMV, WDV, WSMV and WSSMV were found to be the most prevalent viruses. Viruses generally occurred in mixed infections of 3–6 viruses and the most common virus complex consisted of 4 viruses (50%), viz. BYDV, SBWMV, WDV and WSSMV. Five- and six-virus complexes were relatively less common (20% each) whereas 3-virus complex was noticed in only 10% cases. SBWMV and WSSMV have been found to be new to Africa and Zambia and are reportedly vectored by a fungal protist – Polymyxa graminis . BYDV strains MAV and SGV were also tested but gave negative results against their antisera.     

A South African isolate of ryegrasss mosaic virus

An isolate of ryegrass mosaic virus (RMV-SA) was found in Italian ryegrass plants in two areas in South Africa. Preliminary characterization indicated that the virus exhibited the same symptoms and host range as RMV strains previously found in Canada and the UK. The virus was transmitted by the eriophyid mite Abacarus hystrix. Particle structure and size were comparable to the USA and UK strains. The coat protein and RNA were found to be slightly larger than previously reported, being 32kDa and 2·8 × 10⁶, respectively. The virus exhibited serological cross-reactivity with antisera to RMV-Wales and RMV-Canada but was not serologically related to other Rymovirus members.     

小麦品种抗耐黄矮病性鉴定初步研究

1983—1987年田间人工鉴定4211份主要小麦品种资源材料,对黄矮病的反应虽有不同程度差异,但无免疫品种。症状表现最为抗病并且较为稳定的是远缘杂交小麦品种中4、中5、多年生1号及普通小麦品种复壮30号。小麦品种抗耐黄矮病性与其症状表现不一定一致,需结合被害损失综合鉴定。     

晋南冬麦区大麦黄矮病毒流行株系监测及防治策略探讨

连续5年(1996～2000年)采集晋南冬麦区小麦黄矮病标样,采用生物学和血清学(酶联免疫吸附法)相结合的诊断方法对该地区的大麦黄矮病毒流行株系进行了鉴别。结果表明,该小麦黄矮病流行区近五年以GAV株系为主流株系,兼有少量GPV、PAV和混合株系存在。同时对小麦抗黄矮病新品种“临抗1号”进行了GPV和GAV两种株系的抗性测定,明确了该品种兼抗GPV和GAV两种株系。根据小麦黄矮病发生现状,提出了一套以选育推广抗耐病品种为主,以药剂防治为辅的综合防治措施。以期为当地小麦生产服务。     

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.     

大麦黄矮病毒GPV与GAV株系间异源装配现象的初步研究

 以我国麦区的大麦黄矮病毒GPV、GAV株系为材料,利用它们的蚜传特异性,将由禾谷缢管蚜传播的GPV和由麦长管蚜传播的GAV混合侵染到岸黑燕麦上,并进行继代传毒。混合侵染后代蚜传表现型的变化初步表明存在异源装配现象,且表现型混合发生的比例较高。用DAS-ELISA和RT-PCR法对混合侵染后代进行了测定,进一步证明了异源包装现象的存在。部分基因的核苷酸序列分析初步显示所测定的混合侵染后代中没有发生基因重组。     

Genetics of Host Specificity in Epichloë typhina

ABSTRACT Epichlo? typhina perennially and systemically infects grass plants, causing choke disease in which maturation of host inflorescences is suppressed. In seedling-inoculation tests, isolate E8 from perennial ryegrass established and maintained infection in this host but not in orchardgrass. In contrast, isolates E469, E2466, and E2467 from orchardgrass varied in infection frequency and stability in orchardgrass, but all were unable to establish stable infections in perennial ryegrass. To investigate the genetics of host specificity, isolate E8 was crossed with each of the isolates from orchardgrass. Seedlings of parental host species were inoculated with F(1) progeny, and the frequencies of seedling infection and stability in adult plants were assessed. In the E8 x E2466 cross, the F(1) progeny exhibited a wide range of infection frequency and stability in each parental host. In crosses E8 x E469 and E8 x E2467, where the orchardgrass-derived parents infected 5 to 13% of inoculated perennial ryegrass seedlings, the distributions of infection frequencies for the F(1) progeny wereskewed toward levels comparable to that of the parent from perennial ryegrass. In all crosses, most progeny had low frequencies of infection in orchardgrass. However, transgression was evident in a cross of E8 with E469, an isolate that infected orchardgrass seedlings at a low frequency (2 to 3%). The E8 x E469 cross had a few F(1) progeny that infected orchardgrass at high efficiency (up to 81%). A Spearman rank correlation applied to the E8 x E2466 progeny indicated a significant negative correlation between infection frequencies in perennial ryegrass and orchardgrass. Also, there was a significant correlation of infection frequency and stability in perennial ryegrass but not in orchardgrass. To test whether only a few genes governed infection frequency in perennial ryegrass, an E8 x E2466 F(1) progeny (designated E386.04), which had intermediate compatibility with this host, was backcrossed to E8. The progeny of this backcross exhibited a distribution of infection frequencies in perennial ryegrass between that of E386.04 and the backcross parent, suggesting that multiple genes may determine compatibility at the seedling infection stage. The results of these experiments indicated multiple genetic determinants of compatibility or incompatibility with each host, with intermediate or high heritability.     

从麦类种质资源中筛选大麦黄矮病毒(BYDV)抗原

用 ELISA 法鉴定了小麦近缘种赖草属(Leymus)、披碱草属(Elymus)、鹅冠草属(Roegneria)3个属的21个种,其中17个种抗 BYDV。21145份小麦品种中筛选到症状轻、病毒含量高的耐病品种忻县冬麦、江西早等29份。3604份大麦品种中筛选到症状轻、病毒含量低的抗病品种C13208、小麦近缘种(Agropyronintemedium)和普通小麦杂交的异源八倍体中4无芒,中5,远中7,陇远45、46,远中1001,忻4079以及附加系 L1。现已获得抗 BYDV 的以中4无芒、L1为亲本的杂交后代。     

Reservoirs of plant virus disease: Occurrence of wheat dwarf virus and barley/cereal yellow dwarf viruses in Sweden

Non-crop plants such as grasses and volunteer plants are an inseparable part of the flora of crop fields and can influence virus incidence in crop plants. The presence of grasses as virus reservoirs can lead to a higher probability of virus incidence in crop plants. However, the role of reservoirs as an inoculum source in agricultural fields has not been well studied for many viral diseases of crops. Grasses have been found to constitute potential reservoirs for cereal-infecting viruses in different parts of the world. This study revealed that cereal-infecting viruses such as wheat dwarf virus (WDV), barley yellow dwarf viruses (BYDVs), and cereal yellow dwarf virus-RPV (CYDV-RPV) can be found among ryegrass growing in or around winter wheat fields. Phylogenetic analysis showed that a WDV isolate from ryegrass was a typical WDV-E isolate that infects wheat. Similarly, a ryegrass isolate of barley yellow dwarf virus-PAV (BYDV-PAV) grouped in a clade together with other BYDV-PAV isolates. Inoculation experiments under greenhouse conditions confirmed that annual ryegrass of various genotypes can be infected with WDV to a very low titre. Moreover, leafhoppers were able to acquire WDV from infected ryegrass plants, despite the low titre, and transmit the virus to wheat, resulting in symptoms. Information from the grass reservoir may contribute to improving strategies for controlling plant virus outbreaks in the field. Knowledge of the likely levels of virus in potential reservoir plants can be used to inform decisions on insect vector control strategies and may help to prevent virus disease outbreaks in the future.     

Expression of Thinopyrum intermedium-Derived Barley yellow dwarf virus Resistance in Elite Bread Wheat Backgrounds

ABSTRACT Resistance to Barley yellow dwarf virus (BYDV) is not found in wheat but is available in a Thinopyrum intermedium translocation (Ti) carried on chromosome 7DL of bread wheat recombinant lines. We used one of those lines (TC14/2*Spear) to introgress the Ti into bread wheat cultivars and to determine the influence of wheat backgrounds, with and without known tolerance to BYDV, on the expression of resistance. Two single and three backcross populations, segregating for the presence of the alien fragment, were tested under field conditions and artificial inoculation with BYDV isolates MAV-Mex and PAV-Mex. Lines containing the fragment were identified using the microsatellite marker gwm37. Tillering, biomass, grain yield, thousand-kernel weight, and seed quality were evaluated in inoculated and noninoculated plots. Resistance was assessed by enzyme-linked immunosorbent assay. In early generations, the alien fragment followed expected Mendelian segregation, whereas in the advanced ones a slight bias against its transmission was observed. No positive nor negative effects of Ti on agronomic performance and quality were found. A significant optical density reduction in individuals carrying the fragment was observed after PAV infection in crosses with lines Anza and Baviacora but not with Milan. In addition, the fragment was associated with a lower frequency of infected plants for both PAV and MAV isolates. The reduced yield loss associated with the presence of the translocation was due largely to the lower infection rate.     

Characterization of wheatgrass-derived barley yellow dwarf virus resistance in a wheat alien chromosome substitution line

ABSTRACT Wheatgrass (Thinopyrum intermedium) possesses a high level of resistance to barley yellow dwarf virus (BYDV) subgroup I and subgroup II strains. A wheat line (P29), in which the 7D chromosome has been substituted with a group 7 chromosome from T. intermedium, was examined for the level of resistance to two subgroup I and two subgroup II BYDV strains. In P29 plants inoculated with the subgroup I PAV strains, the titer of virus in leaf and stem tissue was typically reduced 42 to 52% when compared with the BYDV-susceptible cv. Abe. P29 and 'Abe' had the same content of PAV in roots. These results and the absence of detectable virus in inoculated T. intermedium plants indicate that the complete resistance to subgroup I possessed by the wheatgrass has not been introgressed into P29. In contrast, P29 was completely resistant throughout the plant to the subgroup II strains, NY-RPV and NY-RMV, demonstrating that the complete resistance to subgroup II in T. intermedium was incorporated into P29. Further analysis of this resistance to NY-RPV showed that NY-RPV can replicate in mesophyll protoplasts of P29 and 'Abe', suggesting that this resistance is not operating at the single-cell level. Molecular marker analysis confirmed that the T. intermedium chromosome present in P29 is a different group 7 wheatgrass chromosome than that present in L1, a wheat line with BYDV resistance properties similar to those of P29.     

Promotion of stomatal infiltration of glyphosate by an organosilicone surfactant reduces the critical rainfall period

The addition of the organosilicone surfactant ‘Silwet L77’ at 1-5 ml litre^?1 to formulated glyphosate gave complete surface wetting on application to the adaxial leaf surface of perennial ryegrass (Lolium perenne L.). The wetting characteristics of the solution were associated with rapid foliar uptake and near maximal uptake in 3 h compared to greater than 5 h in the absence of ‘Silwet L77’. Evidence is presented showing that solutions containing ‘Silwet L77’ rapidly infiltrate stomata. Rapid uptake did not occur after application to the astomatous abaxial surface of perennial ryegrass leaves. The rapid rate of glyphosate uptake reduced the critical rainfall period to 2 h or less, compared to up to 10 h in the absence of ‘Silwet L77’. The use of ‘Silwet L77’ has major practical implications for the use of glyphosate in regions with unpredictable rainfall or high rainfall frequency.     

Volunteer winter wheat: its effects and control in ryegrass seed production

The effects of different populations of volunteer winter wheal and their control with ethofumesate and TCA on growth, seed yield and yield components of S.24 perennial ryegrass were investigated in lield experiments in 1978 and 1979. Reductions in ryegrass seed yield due to the presence of wheat depended on the density of wheat and the number and dry weight of ryegrass tillers. The greatest percentage reduction in ryegrass seed yield occurred at high densities of wheat (300 plants m^?2) when the number of ear-bearing tillers and 1000 seed weight of ryegrass were reduced. When Ihe density of wheat was low (80 plants m^?2) a smaller reduction in ryegrass seed yield occurred and the number of live wheat plants remaining gradually decreased. Within the range of wheat densities in these experiments (0–300 plants m ^?2) a 1% loss in ryegrass seed yield occurred for every 10 wheal plants m^?2 present in the crop post winter. Both herbicides caused a reduction in number of ryegrass tillers during growth but, except where TCA was applied at 12 kg ha^?1 in November, ryegrass seed yields were not significantly reduced (in comparison with a wheat-free control) and were always greater than those obtained in the presence of wheat where no herbicides had been applied. Levels of volunteer infestation of 300 wheat plants m^?2 were controlled with minimum risk of crop damage by applications of 6 kg ha^?1 TCA in either October or November, or by application of 1–9 kg ha^?1 ethofumesate in November.     

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.