Variation in barley yellow dwarf virus transmission efficiency by Rhopalosiphum padi (Homoptera: Aphididae) after acquisition from transgenic and nontransformed wheat genotypes

The effects of different acquisition access periods (AAPs) and inoculation access periods (IAPs) on the transmission efficiency of barley yellow dwarf luteovirus (BYDV) by Rhopalosiphum padi (L.) (Homoptera: Aphididae) after feeding on transgenic or nontransformed wheat, Triticum aestivum L., genotypes were studied. Three wheat genotypes were tested as virus sources: virus-susceptible 'Lambert' and 'Lambert'-derived transgenic lines 103.1J and 126.02, which express the BYDV-PAV coat protein gene. Lower virus titers were measured in BYDV-infected transgenic plants compared with Lambert. No significant differences in transmission efficiency were detected for R. padi after varying IAPs, regardless of genotype. Transmission efficiency increased with an increase in AAP in all genotypes tested. However, AAPs ranging from 6 to 48 h on Lambert resulted in significantly greater transmission efficiency than similar periods on transgenic 103.1J. Maximum transmission efficiency (70%) was observed after a 48-h AAP on Lambert, whereas the same AAP on 103.1J and 126.02 resulted in a significantly lower transmission efficiency (57%). Contrasts were used to compare the rates of transmission and the theoretical maximum transmission percentage among the different wheat genotypes serving as virus sources. Both parameters were significantly different among genotypes, indicating that viral acquisition from each genotype resulted in a unique pattern of virus transmission by R. padi. The lowest rate of virus transmission after an AAP was observed on 103.1J compared with 126.02 or Lambert. This is likely associated with a lower virus titer in 103.1J. This is the first report of transgenic virus resistance in wheat affecting the transmission efficiency of a virus vector.     

Life history of the bird cherry-oat aphid, Rhopalosiphum padi, on transgenic and non-transformed wheat challenged with Wheat streak mosaic virus

The life history of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), was studied via laboratory assays on Wheat streak mosaic virus (WSMV)-infected and non-infected transgenic and non-transformed wheat [ Triticum aestivum L. (Poaceae)]. Although R. padi is not a WSMV vector, it is known to colonize WSMV-infected wheat plants. Two transgenic soft white winter wheat genotypes, 366-D03 and 366-D8, that express the WSMV coat protein gene, and the WSMV-susceptible non-transformed cultivar Daws were tested. All genotypes showed disease symptoms when infected with WSMV. Whereas plant height was significantly reduced on virus-infected compared to non-infected plants of all genotypes, virus-infected transgenic plants exhibited lower virus titer and lower disease rating scores than Daws. No significant effects of WSMV infection or genotypes were observed on the length of R. padi nymphal development period, nor on their pre-, and post-reproductive periods. Rhopalosiphum padi reproductive period was significantly longer on Daws infected with WSMV than on non-infected plants of this cultivar. In contrast, there were no significant differences in length of R. padi reproductive period between virus-infected and non-infected transgenic plants within a genotype. Rhopalosiphum padi daily fecundity was significantly lower and adult longevity significantly longer on virus-infected than on non-infected plants of all genotypes. Total aphid fecundity and intrinsic rate of increase were not significantly different among treatments. The percentage of winged aphids that developed was greater on WSMV-infected compared to non-infected plants within a genotype. Results indicate that both virus infection status of plants and wheat genotype influence the life history of R. padi.     

取食感染大麦黄矮病毒的小麦后介体麦长管蚜和非介体禾谷缢管蚜体内抗氧化酶和解毒酶活性的变化

【目的】小麦黄矮病［病原为大麦黄矮病毒(barley yellow dwarf virus, BYDV)］是危害小麦生产的主要病害之一,GAV是BYDV在我国的主流株系,且其在田间与介体麦长管蚜 Sitobion avenae 和非介体禾谷缢管蚜Rhopalosiphum padi同时发生,对小麦产量造成严重影响。本研究旨在探究大麦黄矮病毒胁迫下介体和非介体蚜虫体内重要保护酶和解毒酶活性变化规律,为揭示病毒 蚜虫互作生理生化机理提供参考。【方法】利用生化方法测定取食健康小麦(空白对照组),取食前期经无毒麦二叉蚜Schizaphis graminum 3龄若蚜为害72 h的小麦(条件对照组)及取食前期经携带BYDV-GAV麦二叉蚜3龄若蚜为害72 h的小麦(处理组)7 d后,介体麦长管蚜与非介体禾谷缢管蚜成蚜体内过氧化物酶(POD)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)等重要保护酶及乙酰胆碱酯酶(AchE)、酸性磷酸酶(ACP)和碱性磷酸酶(AKP)等重要解毒酶活性变化。【结果】取食前期经BYDV-GAV感染的麦二叉蚜3龄若蚜为害的小麦7 d后,介体麦长管蚜成蚜体内POD, SOD和AKP活性比空白对照组显著上升,但与条件对照组相比无显著差异;且条件对照组比空白对照组显著上升。取食经BYDV-GAV感染的麦二叉蚜3龄若蚜为害的小麦7 d后,非介体禾谷缢管蚜成蚜体内SOD,AKP和AchE活性比空白对照组显著下降,ACP活性显著上升,但与条件对照组相比仅ACP活性显著上升;且条件对照组禾谷缢管蚜体内AKP和AchE比空白对照组显著下降,ACP活性显著上升。【结论】取食感染BYDV-GAV小麦后介体麦长管蚜成蚜体内POD, SOD和AKP酶活性升高是前期蚜虫的为害造成,与BYDV-GAV无关;非介体禾谷缢管蚜成蚜体内AKP和AchE酶活性下降是前期蚜虫为害引起,SOD酶活性下降是前期蚜虫为害和BYDV-GAV的综合作用,而BYDV-GAV和前期蚜虫为害均能使禾谷缢管蚜体内ACP酶活性上升。     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

The effect of natural enemies on the spread of barley yellow dwarf virus (BYDV) by Rhopalosiphum padi (Hemiptera: Aphididae)

The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) transmitted by the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) were studied under laboratory conditions. Predators or parasitoids were introduced to trays of durum wheat seedlings and the patterns of virus infection were observed after two, seven and 14 days of exposure. More plants were infected with BYDV in control trays without A. rhopalosiphi than in trays with the parasitoid present, both seven and 14 days after the introduction of parasitoids. Patterns of virus infection were found to be similar over time in trays with a parasitoid present and in control trays. More plants were infected in trays with C. septempunctata present than in control trays, both two and seven days after the introduction of the coccinellid. The spread of virus infections progressed differently over time for the two treatments (predator and parasitoid), differences between treatments being most marked after two days and seven days, when more plants exposed to predators but fewer exposed to parasitoids were infected with BYDV compared to their respective controls. However, by the 14th day 88% of all plants were infected and there was no significant difference between the two treatments. The role of natural enemies in spread of BYDV is discussed.     

小麦品种对麦蚜主要生命参数影响的研究

选用经田间鉴定抗蚜性表现不同的１０个小麦品种,在室内外较系统地研究了其对禾谷缢管蚜和麦长管蚜存活、生长发育和生殖的影响,分析了室内外试验结果的相关性．结果表明,小麦品种的抗生性并不能造成若蚜个体的直接死亡,但对若蚜发育历期、成蚜寿命和产仔数影响显著,差异均达极显著水平或显著水平．其中对两种蚜虫若蚜发育历期的影响室内外表现了较好的一致性,可作为小麦品种抗蚜性鉴定的主要指标;其次是对成蚜产仔数的影响,禾谷缢管蚜室内外试验结果比较的吻合性也较好     

Screening for Barley Yellow Dwarf Luteovirus Resistance in Barley on the Basis of Virus Movement

The movement of barley yellow dwarf luteovirus (BYDV) was evaluated in susceptible and resistant barley and bread wheat genotypes. After leaf inoculation, the virus infected the root system and the growing point of susceptible earlier than resistant, barley genotypes. No difference in virus movement occurred in resistant and susceptible wheat genotypes. It was possible to reliably differentiate susceptible from resistant genotypes when root extracts of 41 barley genotypes were tested by DAS-ELISA 3 or 4 days after inoculation at the oneleaf stage. When barley plants inoculated at the two- or three-leaf stage were assayed by tissue-blot ELISA on nitrocellulose membrane, virus was detected in the phloem vessels of the growing points of the susceptible, but not of the resistant genotype, 4–6 days after inoculation. Our results thus suggest that screening for BYDV resistance in barley could be done quickly and cheaply especially when assays are made by the tissue-blot test.     

Growth Regulators and the Effect of Barley Yellow Dwarf Virus on Barley (Hordeum vulgare L.)

Estimation of cell number in the third leaf of barley (Hordeumvulgare L. C I 666) infected with barley yellow dwarf virus(BYDV) showed a marked decrease in the mitotic activity of theinfected plants Assay of endogenous gibberellins revealed adecrease in the level of a substance corresponding to gibberellicacid (GA₃) in BYDV-infected plants No significant differencein the level of endogenous auxins was observed Application ofgibberellic acid to infected plants reversed the dwarfing effectbut the response was not significantly different from the responseof healthy plants and was found to be due to increased cellelongation. It is suggested that the dwarfing of BYDV-infectedplants is a result of reduced mitotic activity This may be relatedto the reduced level of endogenous gibberellins.     

High Levels of Resistance in Agropyron Species to Barley Yellow Dwarf and Wheat Streak Mosaic Viruses

Several Agropyron species were tested for new sources of resistance to barley yellow dwarf virus (Bydv ) and wheat streak mosaic virus (WSMV). With BYDV strain PAV, 11 of the 17 Agropyron species showed no virus transmission when plants were given access feed by viruliferous Rhopalosiphum padi. Similar trials with BYDV strain RMV (vectored by R. maidis) indicated that all plants, except susceptible control plants, remained virus free. Virus status was confirmed by enzyme-linked immunosorbent assays. When plants were mechanically inoculated with WSMV, 11 Agropyron species failed to express symptoms, while five other species showed a segregating response or had some accessions segregating and some resistant. Test results suggest that resistance to BYDV and WSMV in Agropyron species does not appear to be correlated with any specific genome of Agropyron species although most of the Agropyron species containing S genome were resistant to BYDV and WSMV.     

Ultrastructural and Immunocytochemical Studies on Effects of Barley Yellow Dwarf Virus – Infection on Fusarium Head Blight, Caused by Fusarium graminearum, in Wheat Plants

The interactions between barley yellow dwarf virus (BYDV) and Fusarium head blight (FHB), caused by Fusarium graminearum, were studied in the two winter wheat cultivars (cvs.), Agent (susceptible to FHB) and Petrus (moderately resistant to FHB), using ultrastructural and immunocytochemical methods. Infections of wheat plants of both cvs. by BYDV increased susceptibility to FHB. BYDV infection caused numerous cytological changes in lemma tissue of both cvs. such as formation of vesicles in the cytoplasm, degradation of fine structures of chloroplasts of both cvs. and accumulation of large starch grains in the chloroplasts. Electron microscopical studies showed that the development of F. graminearum on spike surfaces was not affected in BYDV‐infected plants. After penetration and intercellular growth in lemma tissue, defence responses to Fusarium infections were markedly reduced in BYDV‐diseased plants compared to the tissue of virus‐free plants. At sites of contact of fungal cells with host tissue, depositions of cell wall material were distinctly less pronounced than in tissues of virus‐free plants of cv. Petrus. Detection of β‐1,3‐glucanases and chitinases in lemma tissue of cv. Agent revealed no appreciably increased accumulation of both defence enzymes in F. graminearum‐infected virus‐free and BYDV‐infected tissues compared to the non‐infected control tissue. On the other hand, in cv. Petrus, infection with F. graminearum induced a markedly enhanced activity of both enzymes 3 days after inoculation. The increase of both enzyme activities was less pronounced in BYDV‐infected plants than in tissue exclusively infected with F. graminearum. Cytological studies suggest that in contrast to the susceptible cv. Agent postinfectional defence responses may play still an important role in the resistance of the moderately resistant cv. Petrus to FHB.     

Virus disease in wheat predicted to increase with a changing climate

Current atmospheric CO₂ levels are about 400 μmol mol^?1 and are predicted to rise to 650 μmol mol^?1 later this century. Although the positive and negative impacts of CO₂ on plants are well documented, little is known about interactions with pests and diseases. If disease severity increases under future environmental conditions, then it becomes imperative to understand the impacts of pathogens on crop production in order to minimize crop losses and maximize food production. Barley yellow dwarf virus (BYDV) adversely affects the yield and quality of economically important crops including wheat, barley and oats. It is transmitted by numerous aphid species and causes a serious disease of cereal crops worldwide. This study examined the effects of ambient (aCO₂; 400 μmol mol^?1) and elevated CO₂ (eCO₂; 650 μmol mol^?1) on noninfected and BYDV‐infected wheat. Using a RT‐qPCR technique, we measured virus titre from aCO₂ and eCO₂ treatments. BYDV titre increased significantly by 36.8% in leaves of wheat grown under eCO₂ conditions compared to aCO₂. Plant growth parameters including height, tiller number, leaf area and biomass were generally higher in plants exposed to higher CO₂ levels but increased growth did not explain the increase in BYDV titre in these plants. High virus titre in plants has been shown to have a significant negative effect on plant yield and causes earlier and more pronounced symptom expression increasing the probability of virus spread by insects. The combination of these factors could negatively impact food production in Australia and worldwide under future climate conditions. This is the first quantitative evidence that BYDV titre increases in plants grown under elevated CO₂ levels.     

Barley yellow dwarf virus, wheat, and Sitobion avenae: a case of trilateral interactions

We analysed interactions in the system of two Barley Yellow Dwarf Virus (BYDV) strains (MAV and PAV), and wheat (cv. Tinos) as host plant for the virus, and the cereal aphid Sitobion avenae (F.) as vector, in particular whether or not infection by the virus might alter host plant suitability in favour of vector development. By measuring the amino acid and sugar content in the phloem sap of infected and non‐infected wheat plants we found a significant reduction in the concentration of the total amount of amino acids on BYDV‐infected plants. Qualitative and quantitative analysis of honeydew and honeydew excretion indicated a lower efficiency of phloem sap utilisation by S. avenae on infected plants. In addition, S. avenae excreted less honeydew on infected plants. Both BYDV strains significantly affected aphid development by a reduction in the intrinsic rate of natural increase. Hence, infection by the virus reduced the host suitability in terms of aphid population growth potential on BYDV‐infected plants. However, more alate morphs developed on virus‐infected plants. These findings are discussed in relation to the population dynamics of S. avenae, and, as a consequence, the spread of BYDV.     

Influence of aphid species and barley yellow dwarf virus on soft red winter wheat yield

Yield loss in soft red winter wheat, Triticum aestivum L., caused by aphid-transmitted barley yellow dwarf virus (family Luteoviridae, genus Luteovirus, BYDV) was measured over a 2-yr period in central Missouri. Rhopalosiphum padi (L.) was the most common and economically important species, accounting for > 90% of the total aphids. Schizaphis graminum (Rondani), Rhopalosiphum maidis (Fitch), and Sitobion avenae (F.) made up the remainder of the aphids. Aphid numbers peaked at wheat stem elongation in 2003 with 771 R. padi per meter-row. In the 2003-2004 growing season, aphid numbers averaged seven aphids per meter-row in the fall and peaked at 18 aphids per meter-row at jointing. Wheat grain yield was reduced 17 and 13% in 2003 and 2004, respectively. Thousand kernel weights were reduced 10 and 5% in the untreated plots compared with the treated control in 2003 and 2004, respectively. Padi avenae virus was the predominate strain, accounting for 81 and 84% of the symptomatic plots that tested positive for BYDV in 2003 and 2004. Our results indicate that economic thresholds for R. padi are 16 aphids per meter-row in the fall and 164 aphids per meter-row at jointing.     

Interaction Of Barley Yellow Dwarf Virus and Fusarium culmorum (W. G. Sm.) Sacc. in Winter Wheat

The barley yellow dwarf virus (BYDV) epidemics, which occurred predominantly in northern Germany in 1988–90 and caused unusual yield losses of wheat, prompted our study on interactions of BYDV and Fusarium culmorum. At the late stages of plant development (EC 55/65) infections with BYDV resulted in a lower yield reduction of wheat plants than infections with F. culmorum. Combined infections at flowering resulted in severer yield reduction, indicating additive effects of the two pathogens. However, if wheat infected by BYDV at stage EC 25/35 was secondarily inoculated with the fungus at EC 55/65 the yield was less reduced than in combined infections at EC 55/65. Our results proved that the susceptibility of wheat plants to F. culmorum is increased when infection by BYDV takes place during the late stages of growth. These results correspond to observations during 3 years of the epidemic in Germany. In these years BYDV was spread mainly during the late spring, resulting in a severe secondary infection by the fungus. From the results of these investigations it may be concluded that during the years of BYDV epidemic the yield of wheat was reduced to an economically important extent because of the fungal infection, which was favoured by the virus infection.     

Influence of rice black streaked dwarf virus on the ecological fitness of non-vector planthopper Nilaparvata lugens （Hemiptera： Delphacidae）

Rice black streak dwarf virus （RBSDV） is transmitted by the small brown planthopper （SBPH）, Laodelphax striatellus （Fallen）. Non-vector rice brown planthopper （BPH）, Nilaparvata lugens （Stal）, shares the same host rice plants with SBPH in paddy fields. The changes in nutritional composition of rice plants infected by RBSDV and the ecological fitness of BPH feeding on the infected plants were studied under both artificial climate chamber and field conditions. Contents of 16 detected amino acids and soluble sugar in RBSDV infected rice plants were higher than those in the healthy ones. On the diseased plants BPH had significantly higher nymphal survival rates, nymphal duration of the males, weight of the female adults, as well as egg hatchability compared to BPH being fed on healthy plants. However, there was no obvious difference in female nymph duration, longevity and fecundity. Defense enzymes （superoxidase dismutase, SOD and catalase, CAT） and detoxifying enzymes （carboxylesterase, CAE and glutathione S-transferase, GST） in BPH adults fed on diseased plants had markedly higher activities. The results indicate rice plants infected by RBSDV improved the ecological fitness of the brown planthopper, a serious pest but not a transmitter of the RBSDV virus.     

Interaction between crown rust (Puccinia coronata) and two viruses of ryegrass

In Lemtal Italian and S.24 perennial ryegrass plants, two isolates of ryegrass mosaic virus (RMV) suppressed the amount of crown rust emerging on leaves inoculated with Puccinia coronata uredospores by up to 75% compared with the amount on virus-free plants. Severity of rust infection on barley yellow dwarf virus (BYDV) infected plants generally did not differ significantly from that on virus-free plants. When both RMV and BYDV were present, rust was restricted in Lemtal plants to a level intermediate between those occurring on plants infected by either virus alone, and in S.24 plants to a level below that obtained with either virus alone. The mean water soluble carbohydrate (WSC) content of Lemtal plants was reduced more than 20% by RMV, but was not significantly altered by BYDV. In S.24 plants the WSC content was increased by 10% by RMV and by 60% by BYDV. Rust reduced the WSC content of healthy and virus-infected plants, the reduction being positively correlated with the level of rust on the sampled leaves. In plants of Lemtal, but not of S.24, the degree of rust infection was positively correlated with the WSC content of leaves from rust-free control plants.     

A single wheatgrass chromosome reduces the concentration of barley yellow dwarf virus in wheat

Seedlings of a series of addition or substitution lines of wheat containing different Thinopyrum intermedium chromosomes were inoculated with the PAV and RPV serotypes of barley yellow dwarf virus (BYDV). Reduced virus titres in infected plants were ascribed to a single pair of homoeologous group 7 chromosomes from Th. intermedium in the disomic addition lines L1 and TAF 2. The group 7 chromosome is associated with red pigmentation of coleoptiles, which was also observed in two lines ditelosomic for the α arm of the chromosome. However, when infected with the PAV serotype of BYDV, the ditelosomic lines had normal virus titres and it is concluded that potential determinants of BYDV resistance are located on the β arm of the Group 7 chromosome.     

Winter wheat (Triticum aestivum) response to Barley yellow dwarf virus at various nitrogen application rates in the presence and absence of its aphid vector,Rhopalosiphum padi

Barley yellow dwarf (BYD) is one of the most common diseases of cereal crops, caused by the phloem‐limited, cereal aphid‐borne Barley yellow dwarf virus (BYDV) (Luteoviridae). Delayed planting and controlling aphid vector numbers with insecticides have been the primary approaches to manage BYD. There is limited research on nitrogen (N) application effects on plant growth, N status, and water use in the BYDV pathosystem in the absence of aphid control. Such information will be essential in developing a post‐infection management plan for BYDV‐infected cereals. Through a greenhouse study, we assessed whether manipulation of N supply to BYDV‐infected winter wheat, Triticum aestivum L. (Poaceae), in the presence or absence of the aphid vector Rhopalosiphum padi L. (Hemiptera: Aphididae), could improve N and/or water uptake, and subsequently promote plant growth. Similar responses of shoot biomass and of water and N use efficiencies to various N application rates were observed in both BYDV‐infected and non‐infected plants, suggesting that winter wheat plants with only BYDV infection may be capable of outgrowing infection by the virus. Plants, which simultaneously hosted aphids and BYDV, suffered more severe symptoms and possessed higher virus loads than those infected with BYDV only. Moreover, in plants hosting both BYDV and aphids, aphid pressure was positively associated with N concentration within plant tissue, suggesting that N application and N concentration within foliar tissue may alter BYDV replication indirectly through their influence on aphid reproduction. Even though shoot biomass, tissue N concentration, and water use efficiency increased in response to increased N application, decision‐making on N fertilization to plants hosting both BYDV and aphids should take into consideration the potential of aphid outbreak and/or the possibility of reduced plant resilience to environmental stresses due to decreased root growth.     

Long-term changes of aphid vectors of Barley yellow dwarf viruses in north-eastern Italy (Friuli-Venezia Giulia)

Migrations of aphid vectors of Barley yellow dwarf viruses (BYDV) were monitored using a Rothamsted Insect Survey suction trap in Friuli-Venezia Giulia (north-eastern Italy). Catches from 1983 to 2002 were studied for trends, correlations of total catches of each year with those of previous years, correlations between the autumn and the spring + summer catches of the same year and between spring + summer catches of one year with catches of the previous autumn. Infectivity of autumn alates was studied using biological tests, and infectivity indexes were calculated for all vector species and for Rhopalosiphum padi alone. Colonisation of barley and proportion of infected plants were checked in a field close to the suction trap from 1992 to 2002 and related to trap catches. Catches were also correlated to acreage dedicated to cereal and fodder crops in the region. During the 20 years, 15 BYDV vector species were caught in the trap, but only five species were found consistently colonising barley plants during autumn. R. padi was the most numerous species in catches, while Sitobion avenae was the predominant colonising species in the barley field. Relatively to R. padi , S. avenae colonies were about six times more numerous than expected from catches. The yearly abundance of catches of most species did not change significantly during the 20 years, with a few exceptions, significantly correlated to changes in the acreage dedicated to cereal and fodder crops. There was a significant decrease of the autumn catches of both R. padi and the total of BYDV vectors.     

转病毒来源发夹RNA小麦表现对大麦黄矮病毒的抗性

将大麦黄矮病毒GPV株系的复制酶基因片段和CP基因片段构建成可在植物细胞内表达含有双链复制酶RNA(茎)和反义CP RNA(环)的复合发夹RNA结构, 希望能够诱发植物体针对病毒的RNA干扰作用, 从而达到抗病毒目的。利用基因枪法将该结构导入小麦幼胚愈伤组织细胞后, 通过在幼苗再生阶段进行以叶片为模板的快速PCR来加速阳性植株的筛选过程, 最终共获得基因组整合有外源基因的小麦再生植株21株。对再生植株接种不同剂量的病毒, 其中9株对BYDV-GPV有低度抗性, 表现在低接毒量时无症状, 接毒量提高时发病且严重; 6株具中度抗性, 表现在低接毒量时无症状, 接毒量提高时局部有不严重症状; 6株具高度抗性, 两种情况下均无症状。抗性实验结果表明, hpRNA介导对BYDV的抗性可能受到BYDV含量的影响, 具有剂量效应的特点。