A tobamovirus infecting capsicum in Australia

A tobamovirus infection of Capsicum annuum is recorded for the first time in New South Wales, Australia. The causal virus is described and shown to differ from tobacco (TMV) and tomato (ToMV) mosaic viruses in its host reactions and serology. Seventeen capsicum cultivars were tested for reaction to the Australian isolate and ranked according to symptom severity. Field and glasshouse observations indicated that the virus causes a decrease in height and weight of plants, fruit malformation and leaf mosaic symptoms. It is proposed that the capsicum tobamovirus strains are sufficiently distinctive from TMV and ToMV to be grouped together and designated a separate virus: capsicum mosaic virus (CaMV).     

Detection of a Luteovirus in Groundnut Rosette Diseased Groundnuts (Arachis hypogaea) by Enzyme-linked Immunosorbent Assay and Immunoelectron Microscopy

In groundnut rosette diseased groundnut plants collected near Zaria, Nigeria, a luteovirus was detected by ELISA and ISEM. In ELISA only beet western yellows virus antiserum reacted, while in ISEM luteovirus particles were trapped by antisera beet western yellows virus, potato leafroll virus, pea leafroll virus and barley yellow dwarf virus. The data are in agreement with the interpretation that the assistor of groundnut rosette virus is possibly a member of the luteovirus group.     

Serological comparison of an Australian isolate of capsicum mosaic virus with capsicum tobamovirus isolates from Europe and America

A New South Wales isolate (Ca) of capsicum mosaic virus was tested against antisera to it and capsicum tobamovirus isolates from the Netherlands (P8, P11), USA (SL), Argentina (FO) and Sicily (PM). The comparison demonstrated that the four viruses Ca, P8, PM and SL are closely related to each other, forming a series of decreasing relationship to Ca in the above order. FO was related to these but insufficiently to be considered part of the group, and P11 was only slightly related to the others. The literature on serology of tobamoviruses in Capsicum spp. was collated and it is suggested that isolates from Sicily (pepper mild mottle), Australia (capsicum mosaic), The Netherlands (P8, P14) and USA (SL) be considered as strains of a virus distinct from both tobacco mosaic and tomato mosaic viruses and that these isolates all be referred to in future as strains of pepper mild mottle virus.     

Specificity of the effect of sap-transmissible viruses in increasing the accumulation of luteoviruses in co-infected plants

The concentration of potato leafroll luteovirus (PLRV) (c. 1300 ng/g leaf) in singly infected Nicotiana clevelandii plants was increased up to 10-fold in plants co-infected with each of several potyviruses, or with narcissus mosaic potexvirus, carrot mottle virus or each of three tobravirus isolates. With the tobraviruses, PLRV concentration was increased equally by co-infection with either NM-type isolates (coat protein-free cultures containing RNA-1) or M-type isolates (particle-producing cultures containing RNA-1 and RNA-2). In contrast, the accumulation of PLRV was not substantially affected by co-infection with either of two nepoviruses, cucumber mosaic cucumovirus, broad bean mottle bromovirus, alfalfa mosaic virus, pea enation mosaic virus or parsnip yellow fleck virus. The specificity of these interactions between PLRV and sap-transmissible viruses was retained in tests made in Nicotiana benthamiana and when beet western yellows luteovirus was used instead of PLRV.     

The prevalence and spatial distribution of viruses in natural populations of Brassica oleracea

We report a survey of four viruses (beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV), turnip mosaic potyvirus (TuMV), turnip yellow mosaic tymovirus (TYMV)) in five natural populations of Brassica oleracea in Dorset (UK). All four viruses were common; 43% of plants were infected with BWYV, 60% with CaMV, 43% with TuMV and 18% with TYMV. For each virus there were significant differences in the proportion of infected plants among populations, which were not completely explained by differences in the age of plants. Multiple virus infections were prevalent, with 54% of plants having two or more virus types. There were statistically significant associations between pairs of viruses. The CaMV was positively associated with the other three viruses, and BWYV was also positively associated with TuMV. There was no detectable association between BWYV and TYMV, whereas TuMV and TYMV were negatively associated. We suggest these associations result from BWYV, CaMV and TuMV having aphid vectors in common, as aphids are attracted to plants that already have a virus infection. Infected plants were distributed randomly or were very weakly aggregated within populations. The implications of widespread multiple virus infections in natural plant populations are discussed with respect to the release of transgenic plants expressing virus-derived genes.     

Increase in Cucurbit Aphid–Borne Yellows Virus Concentration by Co–infection with Sap–transmissible Viruses does not Increase its Aphid Transmissibility

The cucurbit aphid–borne yellows virus (CABYV) is a new tentative member of the luteovirus group which is transmitted persistently by Myzus persicae and Aphis gossypii.
In muskmelon plants, mixed infection with CABYV and zucchini yellow mosaic virus (ZYMV) induced an increase in CABYV concentration estimated by double antibody sandwich–enzyme linked immunosorbent assay (DAS–ELISA), which was maximum after 3 weeks, of co–infection.
Assays, conducted with other cucurbit hosts and sap–transmissible viruses showed that a similar increase occurred with most of the potyviruses tested. However, cucumber mosaic virus (CMV) and squash mosaic virus (SqMV) were inefficient for less efficient than potyviruses) in increasing CABYV concentration.
Aphid transmission experiments were conducted to check whether increased virus multiplication could either enhance transmission rates or modify the mode of CABYV acquisition by aphids. However, when A. gossypii was used, no increases in CABYV, transmissibility nor in its acquisition mode were detected.     

Purification of carrot red leaf virus and evidence from four serological tests for its relationship to luteoviruses

Carrot red leaf virus (CRLV) was purified from infected chervil by centrifuging whole plant extracts at low speed and incubating the resuspended pellets with Driselase; the digest was then treated with 1% (v/v) Triton X-100 and the virus concentrated by centrifugation twice at high speed through a layer of 20% sucrose. The preparations (about 1 μg virus/g tissue) contained isometric particles c. 25 nm in diameter which formed a single u.v.-absorbing component in sucrose density gradients. Chervil seedlings exposed to aphids (Cavariella aegopodii) that had been injected with or had fed on fractions from the u.v.-absorbing zone developed typical symptoms of infection with CRLV. CRLV particles had a sedimentation coefficient (s_20,w) of 104 S, buoyant density in CsCl of 1.403 g/cm³ and A₂₆₀/A₂₈₀ of 1.62. Antiserum with a gel-diffusion titre of 1/512 was obtained from a rabbit injected intradermally with 100 μg purified virus. CRLV was detected by immunosorbent electron microscopy and enzyme-linked immunosorbent assay in extracts of the petioles and leaf midribs of infected chervil and in groups of five to 20 viruliferous C. aegopodii. Analysis of antiserum/virus reactions by density gradient centrifugation showed that CRLV is distantly related to all luteoviruses tested; its relationships were closest to barley yellow dwarf virus (RPV strain), and perhaps also to beet western yellows virus, more distant to tobacco necrotic dwarf, potato leafroll and bean leafroll viruses, and very distant to barley yellow dwarf (MAV strain) and soybean dwarf viruses. Some of these relationships were detected by double diffusion in agarose gels and by electron microscopy of antiserum/virus mixtures. Immunosorbent electron microscopy detected all these relationships but suggested that CRLV was more closely related to tobacco necrotic dwarf and potato leafroll viruses than to barley yellow dwarf virus (RPV strain). The results show that CRLV should be considered a definitive member of the luteovirus group, and provide confirmation of recent evidence that potato leafroll virus is a luteovirus.     

Biometrical genetic analysis of luteovirus transmission in the aphid Schizaphis graminum

The aphid Schizaphis graminum is an important vector of the viruses that cause barley yellow dwarf disease. We studied the genetic architecture of virus transmission by crossing a vector and a non-vector genotype of S. graminum. F1 and F2 hybrids were generated, and a modified line-cross biometrical analysis was performed on transmission phenotype of two of the viruses that cause barley yellow dwarf: Cereal yellow dwarf virus (CYDV)-RPV and Barley yellow dwarf virus (BYDV)-SGV. Our aims were to (1) determine to what extent differences in transmission ability between vectors and non-vectors is due to net additive or non-additive gene action, (2) estimate the number of loci that determine transmission ability and (3) examine the nature of genetic correlations between transmission of CYDV-RPV and BYDV-SGV. Only additive effects contributed significantly to divergence in transmission of both CYDV-RPV and BYDV-SGV. For each luteovirus, Castle-Wright's estimator for the number of effective factors segregating for transmission phenotype was less than one. Transmission of CYDV-RPV and BYDV-SGV was significantly correlated in the F2 generation, suggesting that there is a partial genetic overlap for transmission of these luteoviruses. Yet, 63% of the F2 genotypes transmitted CYDV-RPV and BYDV-SGV at significantly different rates. Our data suggest that in S. graminum, the transmission efficiency of both CYDV-RPV and BYDV-SGV is regulated by a major gene or set of tightly linked genes, and the transmission efficiency of each virus is influenced by a unique set of minor genes.     

Relations of carrot red leaf and carrot mottle viruses with their aphid vector, Cavariella aegopodii

Studies with Scottish isolates of carrot red leaf (CRLV) and carrot mottle (CMotV) viruses confirmed the dependency of CMotV on CRLV for transmission by the aphid Cavariella aegopodii. CMotV was transmitted by aphids only when the two viruses were present in the same source plant, and its transmission was not assisted by anthriscus yellows virus, which acts as a helper for parsnip yellow fleck virus. Some test plants became infected with CRLV alone, and a few with CMotV alone. In winter, aphid transmission of CRLV and CMotV was greatly increased when the source plants received supplementary lighting whereas the CMotV infectivity of sap was not increased. C. aegopodii acquired CRLV and CMotV after minimum acquisition access times of 30 min and inoculated them after minimum inoculation access times of 2 min. There was a minimum latent period of 7–18 h. The viruses were retained by the aphid after moulting and are therefore circulative in the vector, but were not transmitted to progeny insects. Aphids allowed 24 h to acquire the viruses continued to transmit them for at least 12 days, but some aphids allowed 6 h or less for virus acquisition ceased to transmit after 3 or 4 days. CRLV is considered a tentative member of the luteovirus group.     

光呼吸条件下栾树和辣椒光合电子流的分配研究

用Li-6400光合仪同时测定了栾树和辣椒在温度为30℃、CO2浓度为380μmol·mol-1下的气体交换和叶绿素荧光数据。结果表明,栾树在饱和光合有效辐射时光合电子用于碳同化、光呼吸和其他途径的量分别为72.68、45.68和29.40μmol·m-2.s-1;辣椒在光合有效辐射为2000μmol·m-2.s-1时光合电子用于碳同化、光呼吸和其他途径的量分别为142.24、40.24和131.52μmol·m-2.s-1。揭示了在光呼吸条件下用Valentini和Epron等方法高估了辣椒和栾树的光合电子用于光呼吸的量,同时也高估了光呼吸在辣椒和栾树中的保护作用。     

海南黄灯笼椒与不同品种辣椒的辣椒素含量测定

目的:建立HPLC法测定海南黄灯笼椒等辣椒的辣椒素含量。方法:采用Diamonsil C18柱(4.6 mm×250mm,5μm),流动相为甲醇-水(体积比70∶30),流速为1.0 mL/min,检测波长为230 nm,柱温:30℃,外标法定量。结果:辣椒素的线性关系良好,线性范围2.0μg/mL～20.0μg/mL,r=0.9990;精密度、稳定性实验的RSD均低于2%;平均回收率100.8%(n=9),RSD=1.87%。对海南黄灯笼椒等7个品种辣椒的辣椒素含量进行测定,海南黄灯笼椒的辣椒素含量最高。结论:该方法简便快捷,可用于辣椒中辣椒素含量的测定;海南黄灯笼椒辣椒素含量最高,这些信息可为海南黄灯笼辣椒的研究开发提供参考。     

7株放线菌在辣椒根部定殖及对辣椒叶片PAL与PPO活性的影响

采用盆栽接种试验、平皿涂抹法测数及常规酶活测定法研究了7株拮抗性放线菌在辣椒根部的定殖能力及接种24d对辣椒叶片苯丙氨酸解氨酶（PAl。）与多酚氧化酶活性（PPO）的诱导效应。结果表明：（1）供试7株放线菌单独接种均不能在辣椒根内定殖,但与辣椒疫霉P3混合接种时有5株可定殖;供试放线菌在辣椒根部的定殖能力与其体外平皿试验中产生的的拈抗圈大小基本无关;可定殖放线菌的定殖密度随时间延长而降低,至40d时均无活菌检出。（2）在放线菌单接处理中,5株菌接种后可诱导辣椒叶片PAL,活性提高,全部供试菌均能诱导PPO活性提高,其中可使两种酶同步提高的有5株菌;在放线菌＋P3混接处理中,有6株接种后可诱导PAL,活性提高,5株菌能诱导PPO活性提高,其中可使两种酶同步提高的有4株菌;在接入放线菌时同时混接辣椒疫霉,能增强2株供试放线菌对辣椒叶片PAL活性及6株供试放线菌对辣椒叶片PPO活性的诱导作用;供试放线菌的定殖能力与辣椒叶片PAL及PPO活性变化无明显规律性关系。     

Capsicum ethanol extracts and capsaicin enhance interleukin-2 and interferon-gamma production in cultured murine Peyer's patch cells ex vivo

We investigated the effects of red pepper (Capsicum annuum Lin.) extracts (capsicum extract) and its main pungent capsaicin on T helper 1 (Th1) and 2 (Th2) cytokine production in cultured murine Peyer's patch (PP) cells in vitro and ex vivo. Direct administration of capsicum extract (1 and 10 mug/ml) and capsaicin (3 and 30 muM) resulted in suppression of interleukin (IL)-2, interferon (IFN)-gamma, IL-4 and IL-5 production. In an ex vivo experiment using PP cells removed from the mice after oral administration of capsicum extract (10 mg/kg/day for 4 consecutive days), IL-2, IFN-gamma and IL-5 increased in response to concanavalin A (Con A). Oral administration of 3 mg/kg/day capsaicin, one active constituent of the extract, also enhanced IL-2, INF-gamma and IL-4 production in response to Con A stimulation but did not influence the production of IL-5. Orally administered capsazepine (3 mg/kg/day), a selective transient receptor potential vanilloid 1 (TRPV1) antagonist, slightly enhanced IL-2 production also irrespective of Con A stimulation. The capsaicin-induced enhancement of both IL-2 and IFN-gamma production was not reduced by oral administration of capsazepine (3 mg/kg/day), suggesting a TRPV1 receptor-independent mechanism. Flow cytometric analysis revealed that the population of CD3(+) cells in the PP cells was significantly reduced while CD19(+) cells increased after oral administration of capsicum extract (1 and 10 mg/kg/day) and capsaicin (0.3 and 3 mg/kg/day). Capsazepine (3 mg/kg/day) weakly but significantly reversed these effects. Orally administered capsicum extract and capsaicin did not change the T cell subset (CD4(+) and CD8(+)), Th1 (IFN-gamma(+)) and T2 (IL-4(+)) ratio. These findings indicate that capsicum extract and capsaicin modulate T cell-immune responses, and their immunomodulatory effects on murine PP cells are partly due to both TRPV1-dependent and -independent pathway.     

幽影病毒属病毒的研究现状与展望

幽影病毒是一类较为特殊的植物病毒,其基因组不编码外壳蛋白,因此不形成通常的病毒粒体结构。这类病毒可以通过机械摩擦方式传播,在黄症病毒的帮助下也可以通过蚜虫传播。幽影病毒属病毒由7个确定种和3个暂定成员组成,烟草丛顶病毒是目前国内发现的幽影病毒属唯一成员。幽影病毒的寄主范围较窄,体外抗性也较差。幽影病毒感病组织中含有大量dsRNA。有些病毒还含有卫星RNA。幽影病毒的基因组为单分体的 ssRNA,编码4个非结构蛋白,其中的ORF3蛋白在病毒RNA的稳定性及寄主体内的长距离运输中起到非常重要的作用。文章综述了国内外幽影病毒的研究现状,并对未来的相关研究趋势和研究领域进行了展望。     

Evolutionary relationship between luteoviruses and other RNA plant viruses based on sequence motifs in their putative RNA polymerases and nucleic acid helicases

Comparative studies of sequence motifs in the RNA polymerases and nucleic acid helicases of positive-sense RNA plant viruses have provided a new scheme for the classification of these pathogens. We propose a new luteovirus supergroup which should be added to the already described Sindbisvirus-like and picornavirus-like supergroups. Sequence motifs of nucleic acid helicases and RNA polymerases which previously were considered to be specific for each of the two supergroups now occur together within this new supergroup. We propose that this new viral supergroup provides an evolutionary link between the other two supergroups.     

Mycoparasitism of Pythium ultimum by Antagonistic Binucleate Rhizoctonia Isolates in Agar Media and on Capsicum Seeds

Hyphal interactions between two antagonistic binucleate Rhizoctonia isolates (BNR) and the seedling dampingoff pathogen, Pythium ultimum var. sporangiiferum, were observed by both light-and scanning electron microscopy (SEM), on agar media and on capsicum seeds in sterilized potting mix. Both BNR isolates displayed similar mycoparasitic behaviour towards P. u. sporangiiferum on agar media. This included parallel growth along the pathogen hyphae, formation of hook-shaped hyphal tips and coils on the surface of P. u. sporangiiferum hyphae and penetration and growth within pathogen structures. Disruption of cytoplasmic streaming and disorganisation of pathogen cytoplasm were also observed. SEM observations revealed alterations in P. u. sporangiiferum cell wall structure and the presence of penetration holes apparently due to digestion by the BNR. P. u. sporangiiferum was also parasitised by both BNR isolates on capsicum seed coats, with parallel growth, hook formation and coils commonly observed. The above observations indicated that mycoparasitism is a possible mode of action of BNR against P. u. sporangiiferum.     

Virus Diseases of Pepper (Capsicum annuum L.) in Ethiopia

Viruses occurring in hot pepper (Capsicum annuum L.) in Ethiopia during 1984–1986 were identified and their symptomatology, host range, serology, morphology and transmission described. Potyviruses were found to cause severe infections of pepper wherever the crop was observed. Disease incidence and yield loss in most surveyed areas were estimated at 40–100 % and 15–50 %, respectively. Besides potato Y and pepper veinal mottle viruses, a new potyvirus with distinctive properties was found widely distributed in Shewa and Welega Provinces. The virus, tentatively designated Ethiopian pepper mottle virus (EPMV), was shown to have an unusually narrow experimental host range and filamentous particles about 700–750 nm in length, and to be nonpersis-tently transmitted by aphids but not transmissible through pepper seeds. Cucumber mosaic virus was detected in some locations, but appeared to be of minor significance.     

Viruses and the Advantage of Sex in Anthoxanthum odoratum: A Review

Abstract The nature of the selective forces responsible for the maintenance of sexual reproduction in populations remains controversial. Theoreticians have proposed a variety of mechanisms to explain how sex is adaptive, including varying environments, sib competition, mutational damage, and pathogens. In a well-studied population of the short-lived, perennial grass Anthoxanthum odoratum in a mown North Carolina field, significant fitness advantages for sexual vs. asexual offspring have been shown. Evidence from two recent experiments implicates barley yellow dwarf luteovirus (BYDV), a single-stranded RNA virus, as a cause of the short-term advantage for sex in this population. When planted in sites close to parents, asexual offspring were twice as frequently infected as sexual offspring. In other sites, infection was more frequent among common than rare genotypes. Viruses possess a unique combination of features which make them plausible candidates to favor sexual reproduction in plants. Viruses are pervasive, have subtle but significant fitness effects, have the potential for rapid mutation and evolution, and are spread by vectors whose behaviors are host frequency dependent. The ecological and evolutionary consequences of viruses in plant populations deserve further study.