Ability Of Clones Research Articles

742. Human Artificial Chromosome (HAC) Vector Provides Long-Term Therapeutic Transgene Expression in Normal Human Primary Fibroblasts

Top of pageAbstract Human artificial chromosomes (HACs) are segregating freely from host chromosomes through a set of cell divisions. Accordingly, the host genome is not disrupted and the expression of the transgene could be sustained for a prolonged period without suffering the effects of its surrounding sequence on the host genome. These are the ideal properties required for vectors in gene therapy, and therefore HACs are potentially useful to ensure both safety and duration of gene expression in therapeutic gene delivery. We constructed a novel human chromosome 21-derived HAC (21|[Delta]|pqHAC) vector, which devoid of most expressed genes by telomere truncation at the genomic regions proximal to the centromere in both p and q arms, and inserted human erythropoietin (EPO) gene, which is a growth factor for erythroid cells and widely used for the clinical treatment of anemia in renal insufficiency, into the HAC (EPO-21|[Delta]|pqHAC) as a model of therapeutic transgenes. Although low transfer efficiency of intact HACs to the cells has hampered the studies using normal human primary cells, the major targets for ex vivo gene therapy, we successfully demonstrated the introduction of EPO-21|[Delta]|pqHAC vector into normal primary human fibroblasts (hPFs) with micro cell-mediated chromosome transfer (MMCT). However, the mitotic stability of EPO-21|[Delta]|pqHAC vector in normal hPFs and the growth ability of the resultant hPF clones to obtain graft cells for transplantation remained to be elucidated. Here, we studied the hPF clones harboring the EPO-21|[Delta]|pqHAC vector cytogenetically and demonstrated that the structurally defined, extra artificial chromosome was highly maintained in normal hPFs under non-selective condition at a constant copy number mostly in a single copy per cell without accompanying aberration of host chromosomes. Mitotic-loss rates were determined, and the level of stability of EPO-21|[Delta]|pqHAC vector was comparable with those reported for the other top-down and bottom-up artificial chromosomes in human fibro-sarcoma cell line HT1080 cells. These hPF clones proliferated from a single colony up to 3.8x107 cells and then their growth stopped, suggesting that cell senescence occurred and the introduction of the EPO-21|[Delta]|pqHAC vector did not cause immortalization. We also showed the long-term expression of human epo gene in the hPFs carrying the EPO-21|[Delta]|pqHAC vector. In conclusion, this study shows the potential application of the 21|[Delta]|pqHAC vector in hormone-replacement gene therapy, which might ensure safety with no lesion of host chromosomes and provides long-term therapeutic transgene expression. This also implies that utilization of the HAC vector offers novel options for ex vivo gene therapy.

Combining ability analysis and correlation between breeding values in true potato seed

AbstractTrue potato seed (TPS) requires the selection of appropriate parents for developing hybrid offspring. Parents for routine crossing schemes need to be selected according to their combining ability. Hierarchical and factorial mating designs provide a mean values to assess the general combining ability (GCA) of clones included in crossing schemes. Furthermore, specific combining ability (SCA) may be investigated using the factorial mating design. The aim of this research was to determine the combining ability of clones included in early and intermediate TPS breeding populations developed by the Centro Internacional de la Papa (CIP). Likewise, correlations between breeding values (or additive genetic correlation, pA) were calculated. Two hierarchical mating designs (in both the early and intermediate populations) and one factorial mating design (in the intermediate population) were evaluated in two contrasting Peruvian locations (La Molina ‐ coastal desert, and San Ramon, warm humid tropics). Plant and tuber characteristics were recorded in these experiments. Significant GCA was observed for tuber yield in all experiments. The male's pA between plant vigour after transplanting and tuber yield was significant, thereby suggesting that offspring with early vigorous growth are high yielding. Plant vigour was also correlated with tuber set, but only among the breeding value of female parents, which suggests that high tuber yield could be achieved because offspring with early, vigorous growth have many tubers. High tuber yielding hybrids can be obtained by choosing parents with significant GCA, whose tuber yield can also be further enhanced if the crosses have a significant SCA.

Evaluation of Clonal Variability in Shoot Coppicing Ability and in vitro Responses of Dalbergia sissoo Roxb

Summary Clonal variations were observed amongst 12 clones of Dalbergia sissoo belonging to four states (U.P, Uttaranchal, Haryana and Rajasthan) of India, representing four different geographical zones in respect of ex vitro shoot coppicing ability and in vitro responses. Coppicing ability of shoot hedges of clones exhibited significant variation which ranged from average of 13.81 coppiced shoots (Clone 40, Uttar Pradesh) to 9.29 (Clone 64, Haryana). Comparative analysis of clones from different regions in respect to their coppicing ability revealed that clones from U.P had higher coppicing ability whereas those from Haryana proved to be least coppicers. Regional variations were also exhibited in the in vitro multiple bud induction ability on nodal explants excised from shoot hedges of clones (mean number of buds induced and percentage of cultures forming multiple buds). Regional as well as inter clonal variations were recorded in the shoot proliferation efficiency as well as rootability of microshoots of these clones as well as their optimal plant growth regulator requirements. BAP alone (2.5 μM) was sufficient for inducing multiple buds on cultured nodal explants of Uttaranchal and Uttar Pradesh region clones. On the contrary, clones from Rajasthan and Haryana had higher optimal requirement of BAP and in addition, they required media to be supplemented with auxin (NAA) for induction of multiple buds on explants. Correlation analysis between shoot coppicing ability of clones and in vitro performances of explants of these clones cultured on 2.5 μM BAP indicates a positive correlation. Observation lays credence to our view that these characters are genetically controlled and shoot coppicing can be used as a marker character in optimizing in vitro performance of clones. Using the information generated by this paper in vitro production of elite planting material can be maximized by ameliorating plant growth regulator requirement in the medium.

The biological basis for the use of an anti-androgen and a 5-α-reductase inhibitor in the treatment of recurrentprostate cancer: Case report and review

Although many prostate cancer cases relapse to a hormone-insensitive state, endocrine therapy involving androgen depletion by orchiectomy or by treatment with LHRH-analogue as well as blockade of the androgen receptor (AR) with anti-androgens remains a primary treatment option. Quality of life (QOL) however, is a prime consideration of men choosing such an approach. In this report we discuss a synergistic combination of 150-mg bicaltumide (Casodex) and 5 mg finasteride (Proscar) in the treatment of a 69-year-old patient with a relapsed (biochemical failure) Gleason score 7 prostate cancer, initially treated with external beam radiation therapy. A successful clinical outcome as evidenced by undetectable serum PSA, bone scan density and overall general well-being was accomplished with minimal side effects. Experiments using an established hormone-dependent prostate cancer cell line (LNCaP) showed that the combination of bicaltumide-finasteride at the same ratio as used clinically, produced synergistic effects on the inhibition of cell proliferation and AR expression/phosphorylation. A more complete inactivation of the AR on this regimen may have had the effect of constraining the ability of the AR to mutate, and/or diminishing the ability of androgen independent clones to evolve. Thus, passage to androgen independence may have been slowed or arrested.

Variation in survival and growth of cuttings in two clonal propagation methods for hybrid aspen ( [formula omitted

Cloning hybrid aspen ( Populus tremula L.×P. tremuloides Michx.) in vitro is costly. Inexpensive propagation methods for the species are needed. Two cloning methods and 10 clones of hybrid aspen were tested in a greenhouse environment. In the stock plant method greenwood cuttings were obtained from the same stock plants at 4 weeks intervals. In the successive method cuttings were taken from newly rooted cuttings and the cut stems were grown as normal saplings. The stock plant method produced new cuttings distinctly faster than the successive method. Significant differences among the clones were found in terms of growth and ability to produce new, vigorous cuttings. Except for the initiation of stock plants, which were obtained from micropropagation, all of the cloning was done in an air-conditioned growing room at low light intensities. Both of the methods can be successfully applied for propagating greenwood cuttings of hybrid aspen. The ability of different clones to be multiplied varies so much that selection of the best clones for production is essential.

Relating cultivar resistance to sugarcane yield using breeding selection trial analyses; orange rust and yellow spot

Plant breeders in the Australian sugar industry conduct yield assessment trials each year to assess the yielding ability of clones in the sugarcane breeding programme. Several endemic diseases impinge on the yield of these clones and the tested clones vary greatly in disease susceptibility. In this study, resistance to the diseases orange rust and yellow spot was assessed in final stage trials in the Northern Queensland programme. Clonal yielding ability was related to disease resistance. The results indicate that both diseases, but particularly yellow spot, influenced the yield (tonnes cane/ha and tonnes sugar/ha) of clones in northern breeding trials in 2000. Yield loss estimates were calculated, as well as the relationship between resistance and yield. There was a high level of resistance to orange rust in clones in these trials but much less resistance to yellow spot; the resistance index or orange rust was 2.2 while for yellow spot it was 5.5. Yield loss resistance index values of 5.0 and above for orange rust suggest there is adequate resistance in clones to minimise losses from this disease. In contrast, the yield loss resistance index for yellow spot (tonnes cane/ha) was below 5.0, therefore, it is concluded that during the 2000 harvest season, there was inadequate resistance to minimise losses. The information gathered from this research will be used to determine the level of leaf disease resistance needed in commercial cultivars to optimise yielding ability. Such decisions should improve the efficiency of selection and the performance of commercial cultivars in the Australian sugar industry.

Ability of pneumococcal serotypes and clones to cause acute otitis media: implications for the prevention of otitis media by conjugate vaccines.

The relative abilities of pneumococcal serotypes and strains (clones) to cause acute otitis media (AOM) were investigated by comparing the serotypes and genotypes of pneumococci recovered from cases of AOM (n = 149) in children <2 years of age with those from nasopharyngeal carriage (n = 288) in age-matched controls from the same region. The odds ratio (OR) for association of pooled vaccine serotypes with AOM was found to be slightly elevated over unity, although this was not significantly different from that of pooled nonvaccine or vaccine-related serotypes. Comparing individual serotypes, 19F and 23F had 2- to 2.5-fold higher ORs, although these were not markedly different from the ORs of nonvaccine serotypes. None of the major clones had an OR that was significantly greater than the average, and the differences in ORs among serotypes and clones were much less than those for invasive disease, suggesting little variation in their ability to cause AOM. We conclude that serotype replacement may reduce the long-term efficacy of these vaccines against AOM.

Copper resistance of the evergreen dwarf shrub Arctostaphylos uva-ursi: an experimental exposure

The copper (Cu) resistance of Arctostaphylos uva-ursi was tested in a pot experiment (lasting 8 weeks) using rooted cuttings originating from an area near the Harjavalta Cu–Ni smelter, SW Finland. The fine roots were moderately infected by arbutoid mycorrhizae. The plants were exposed to five Cu levels (1, 10, 22, 46 and 100 mg l −1) given repeatedly together with a nutrient solution. The critical Cu concentration in the nutrient solution inhibiting the growth of A. uva-ursi was below 10 mg l −1 Cu (EC 50 value for biomass production 3.3 mg l −1 Cu). This concentration was clearly lower than the value we have found earlier for other dwarf shrubs under similar experimental conditions. Most of the Cu given accumulated in the roots and old stems. The results suggest that A. uva-ursi cuttings were relatively sensitive to Cu despite the ability of the adult clones to grow in Cu-contaminated soil. The adult clones extend their roots into the less toxic deeper soil layers, which may facilitate the avoidance of heavy metals.

Effects of donor cell type and genotype on the efficiency of mouse somatic cell cloning.

Although it is widely assumed that the cell type and genotype of the donor cell affect the efficiency of somatic cell cloning, little systematic analysis has been done to verify this assumption. The present study was undertaken to examine whether donor cell type, donor genotype, or a combination thereof increased the efficiency of mouse cloning. Initially we assessed the developmental ability of embryos that were cloned from cumulus or immature Sertoli cells with six different genotypes (i.e., 2 x 6 factorial). Significantly better cleavage rates were obtained with cumulus cells than with Sertoli cells (P < 0.005, two-way ANOVA), which probably was due to the superior cell-cycle synchrony of cumulus cells at G0/G1. After embryo transfer, there was a significant effect of cell type on the birth rate, with Sertoli cells giving the better result (P < 0.005). Furthermore, there was a significant interaction (P < 0.05) between the cell type and genotype, which indicates that cloning efficiency is determined by a combination of these two factors. The highest mean birth rate (10.8 +/- 2.1%) was obtained with (B6 x 129)F1 Sertoli cells. In the second series of experiments, we examined whether the developmental ability of clones with the wild-type genotype (JF1) was improved when combined with the 129 genotype. Normal pups were cloned from cumulus and immature Sertoli cells of the (129 x JF1)F1 and (JF1 x 129)F1 genotypes, whereas no pups were born from cells with the (B6 x JF1)F1 genotype. The present study clearly demonstrates that the efficiency of somatic cell cloning, and in particular fetal survival after embryo transfer, may be improved significantly by choosing the appropriate combinations of cell type and genotype.

W135 in Africa: origins, problems and perspectives

Serogroup A meningococci have been the major cause of epidemic meningococcal disease in Africa throughout the last 100 years. The reasons for this unusual pattern of behaviour have remained unclear and there remain significant debates and logistic difficulties around the appropriate use of plain A/C polysaccharide vaccination to control African meningococcal disease. Since the Hajj pilgrimage of 2000 serogroup W135 organisms (of the ST-11 clonal complex) have emerged as a further significant cause of epidemic meningococcal disease in Africa. Whilst advances in molecular biological and genetic techniques have yielded increasing insights into meningococcal epidemiology there remain many unanswered questions about the reason for the emergence of a serogroup W135 clone capable of epidemic behaviour and in particular its relation to past use of group A/C polysaccharide. The high cost and short supply of quadrivalent (A,C,Y, W135) vaccine to protect against W135 disease has added to what was already the significant burden of controlling serogroup A meningococcal disease. The ability of virulent meningococcal clones to acquire new capsule types raises further concerns about the future nature of meningococcal disease in Africa and the strategies of vaccination use and development necessary to contain it.

Relating cultivar Pachymetra root rot resistance to sugarcane yield using breeding selection trial analyses

Plant breeders conduct a range of yield trials each year to estimate the yielding potential of sugarcane clones progressing through the breeding program. Only the highest-yielding clones are selected for further testing with very small numbers being released as commercial cultivars. Disease susceptibility varies greatly amongst the tested clones and a number of diseases influence the yield of clones in various stages of the selection process. Disease resistance testing is an important routine aspect of the breeding program. All clones for northern Queensland are screened for disease resistance, while selected clones from other areas are tested for resistance to Pachymetra root rot. Two new terms are introduced: resistance index (RI) and the yield loss resistance index (YLRI). Analyses were conducted relating yielding ability of clones in stage 3 trials to Pachymetra resistance. Pachymetra root rot on average reduced tonnes cane per hectare by 15.8% and tonnes sugar per hectare by 10.2%. There was a slight positive effect on commercial cane sugar. YLRI5 for tonnes cane was 3.5 and for tonnes sugar 5.7. With a RI of 3.7, the current breeding strategy for northern Queensland appears appropriate. The data reported here will be valuable for refining selection strategies to improve breeding efficiencies. These analyses could be undertaken each year using data from all breeding trials throughout Queensland, not only with Pachymetra root rot, but also with other diseases normally endemic in cane fields. The advantage of this technique is that with a minimum of further expenditure, ongoing estimates of disease-induced yield losses can be obtained with the information guiding the selection program.

Overexpression of an ectopic H19 gene enhances the tumorigenic properties of breast cancer cells.

The maternally expressed H19 gene is transcribed as an untranslated RNA that serves as a riboregulator. We have previously reported that this transcript accumulates in epithelial cells in approximately 10% of breast cancers. To gain further insight on how the overexpression of the H19 gene affects the phenotype of human breast epithelial cells, we investigated the oncogenic potential of RNA that was abundantly expressed from MDA-MB-231 breast cancer cells stably transfected with the genomic sequence of the human H19 gene. The amount of H19 RNA did not affect cell proliferation capacity, timing of cell cycle phases or anchorage-dependent ability of H19-transfected clones in vitro. But in anchorage-independent growth assays the H19-recombined cells formed more and larger colonies in soft-agar versus control cells. To explore this phenotypic change, we analysed tumour development after subcutaneous injection of H19-recombined cells into scid mice. Results showed that H19 overexpression promotes tumour progression. These data support the hypothesis that an overload of H19 transcript is associated with cells exhibiting higher tumorigenic phenotypes and therefore we conclude that the H19 gene has oncogenic properties in breast epithelial cells.

Human immunedeficiency virus type 1 (HIV-1) disease progression may be due to defects in the expression of the TCR/CD3 complex as well as to a T CD4+ cell deficit

The loss of T CD4+ cells leading to impairment of the immune system is the major cause of disease progression during HIV infection. More recently, the use of highly active anti-retroviral therapy (HAART) has raised important questions regarding the immune system restoration. Idiopathic CD4+ T lymphocytopenia syndrome (ICL) is similar to AIDS, except for the presence of HIV. Despite this similarity, ICL patients have a longer survival time than AIDS cases without HAART. The impairment of TCR/CD3-directed CD4+ T cell immune responses may be responsible for HIV disease progression. We think that the reduction of opportunistic infections which lead to death after HAART, is due to the ability of these memory clones to restore enough clones of the TCR/CD3 complex with fair capacity and diversity to confront frequent pathogens.

Adaptive Changes after Human Immunodeficiency Virus Type 1 Transmission

Primary HIV-1 infection (PHI) is associated with a period of viremia, the resolution of which generally coincides with the development of both humoral and cellular immune responses. In this study replication-competent quasispecies were derived from virus isolated from an individual before and after seroconversion. Virus was also isolated from the presumed donor. Phenotypic and genotypic analysis of biological clones identified transmission of an R5/M-tropic phenotype. However, the ability of clones derived from the recipient to replicate in primary macrophages and PBMCs was restricted after transmission. This apparent selection process was supported by analysis of molecular clones derived from the isolated virus. Analysis of the ratio of synonymous and nonsynonymous substitutions predicted the existence of selective pressure soon after transmission, coincident with the development of HIV-1-specific antibodies. An Env trans-complementation assay demonstrated that the infectivity of a clone derived from the recipient after seroconversion was enhanced in the presence of a selected neutralizing antibody, indicating that the developing humoral immune response may have at least in part contributed to the selective pressure identified.

Oct4 distribution and level in mouse clones: consequences for pluripotency

Somatic cell clones often fail at a developmental stage coincident with commencement of differentiation. The transcription factor Oct4 is expressed during cleavage stages and is essential for the differentiation of the blastocyst. Oct4 expression becomes restricted to the inner cell mass and epiblast. After gastrulation Oct4 is active only in germ cells and is silent in somatic cells. Here, Oct4 and an Oct4-GFP transgene were used as markers for which gene reprogramming could be directly related to the developmental potential of somatic cell clones. Cumulus cell clones initiated Oct4 expression at the correct stage but showed an incorrect spatial expression in the majority of blastocysts. The ability of clones to form outgrowths was reduced, and the outgrowths had low or even undetectable levels of Oct4 RNA or GFP. The quality of GFP signals in blastocysts correlated with the ability to generate outgrowths that maintain GFP expression and the frequency of embryonic stem (ES) cell derivation. Abnormal Oct4 expression in clones is either directly or indirectly caused by reprogramming errors and is indicative of a general failure to reset the genetic program. The abnormal Oct4 expression may be associated with aberrant expression of other crucial developmental genes, leading to abnormalities at various embryonic stages. Regardless of other genes, the variations observed in Oct4 levels alone account for the majority of failures currently observed for somatic cell cloning.

Activity of telithromycin against 26 quinolone-resistant pneumococci with known quinolone-resistance mechanisms

NCCLS agar dilution was used to test activity of telithromycin compared to clarithromycin, penicillin G, ciprofloxacin, levofloxacin, sparfloxacin and moxifloxacin against 26 pneumococci with defined quinolone resistance (type II topoisomerase and efflux) mechanisms. Thirteen strains were penicillin susceptible, six intermediate and seven resistant. Clarithromycin resistance (mef and/or erm) was seen in eight strains. Ciprofloxacin MICs (mg/L) were 8-64 compared to 1-32 (levofloxacin), 0.5 . or = 32 (sparfloxacin) and 0.125-4 (moxifloxacin). Telithromycin MIC50 and MIC90 values (mg/L) were 0.016 and 0.25, with only one strain having an MIC of 2 mg/L.

Dynamics of penicillin-susceptible clones in invasive pneumococcal disease.

In a 10-year period, 1987-1997, there was a >4-fold increase in the rate of pneumococcal bacteremia in Sweden. Invasive pneumococcal isolates (n=1136), which were obtained from 18 Swedish clinical microbiology laboratories from 1987 through 1997, and other national and international isolates were serotyped, and their clonal relationships were determined by molecular typing. The increase in invasive pneumococcal disease in Sweden during this period was associated particularly with an increase in isolates of serotypes 1 and 14. A 3-fold increase of type 14 was seen from 1987 through 1992, and a 10-fold increase of type 1 occurred from 1992 through 1997. One dominating penicillin-susceptible clone of type 14 was responsible for the increase of type 14 during the first 5 years. This clone also was found in Canada and the United States and was shown by multilocus sequence typing to correspond to a previously identified hyper-virulent clone. A novel penicillin-susceptible clone of type 1, which was not found among invasive isolates from 1987 or 1992, was responsible for the increase of serotype 1 during the last 5 years. These results illustrate the ability of virulent penicillin-susceptible pneumococcal clones to emerge and spread rapidly within a country.

Recognition of viral hemagglutinins by NKp44 but not by NKp30.

Natural killer (NK) cells destroy virus-infected and tumor cells without prior antigen stimulation. The NK cell cytotoxicity is regulated in large part by the expression of NK cell receptors that are able to bind major histocompatibility complex (MHC) class I glycoproteins. NK cells also express lysis triggering receptors specific for non-MHC ligands, including NKp30, NKp44, NKp46 and CD16. However, the nature of their ligands, recognized on target cells, is undefined. We have recently shown that the NKp46 protein, but not the CD16 protein, recognizes the hemagglutinin (HA) of influenza virus (IV) and the hemagglutinin-neuraminidase (HN) of Sendai virus (SV), and that the recognition of HA from IV requires the sialylation of NKp46 oligosaccharides. We have also demonstrated that binding of NKp46 to HA of IV is required for lysis of cells expressing the corresponding glycoproteins by a substantial subset of NK clones. Here we show that NKp44, but not NKp30, can also recognize the HA of both IV and SV and that the recognition of IV HA requires the sialylation of the NKp44 receptor in a similar way to that of NKp46. SV infection of 721.221 cells expressing MHC class I proteinsresulted in the abrogation of the inhibition by NK clones expressing high levels of NKp44. In addition, the binding of NKp44 to HA improves the ability of some NK clones to lyse IV infected cells.

H+,K+-ATPase (proton pump) is the target autoantigen of Th1-type cytotoxic T cells in autoimmune gastritis

Background & Aims: The proton pump H+,K+-adenosine triphosphatase (H+,K+-ATPase) of parietal cells is the major humoral autoantigen in both human and experimental autoimmune gastritis (AIG) characterized by an inflammatory infiltrate in the gastric mucosa and loss of parietal cells. The aim of this study was to detect H+,K+-ATPase–specific T cells in the gastric mucosa of patients with AIG and to define their functional properties. Methods: In vivo–activated T cells from the infiltrates of the gastric mucosa of 5 patients with AIG were isolated and cloned. The ability of gastric T-cell clones to proliferate and to produce cytokines in response to H+,K+-ATPase, as well as their expression of B-cell help, perforin-mediated cytotoxicity, and Fas-Fas ligand–mediated apoptosis in target cells, were assessed. Results: A proportion (25%) of the CD4+ clones from the gastric corpus of AIG patients proliferated in response to porcine H+,K+-ATPase. Most of these clones (88%) showed a Th1 profile, whereas a few secreted both Th1 and Th2 cytokines. Virtually all of the H+,K+-ATPase–specific clones produced tumor necrosis factor α and provided substantial help for B-cell immunoglobulin production, and most of them expressed perforin-mediated cytotoxicity against antigen-presenting cells and induced Fas-Fas ligand–mediated apoptosis in target cells. Conclusions: Activation of proton pump–specific Th1 cytotoxic/proapoptotic T cells in the gastric mucosa can represent an effector mechanism for the target cell destruction in AIG.GASTROENTEROLOGY 2001;120:377-386

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.