摘要:

SummaryThe fecundity of the aphidRhopalosiphum padiduring the first ten days of reproduction was measured on five wheats at three growth stages. The wheats were of UK and Iranian origin, but also involved both spring and winter wheats as well as hexaploid and tetraploid types. Aphids which had already been reared on the respective variety for at least one generation were transferred to the experimental plants. The tetraploid Emmer showed some resistance in comparison with the hexaploid UK varieties at later growth stages, whereas the Iranian variety Moghan 2 appeared relatively resistant only at the tillering stage. The other Iranian variety, Ommid, was resistant at all growth stages, and appears to be the most resistant hexaploid wheat variety toR. padiso far identified.Correlations of aphid fecundity with plant chemistry were attempted with total phenolic compounds, hydroxamic acids and amino acids. All three of these chemical groups have previously been reported as correlated with plant resistance to cereal aphids. Even just for the results at the tillering stage, no correlation could be found for phenolics or hydroxamic acids, but a multiple regression based on the levels of alanine, histidine and threonine accounted for over 95% of the variation in aphid fecundity at all 15 data points (5 wheats × 3 growth stages). No cause or effect relationship is necessarily implied

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03981.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryIn a screen of seedlings of a worldwide range of 47 cultivars ofTriticum(mainlyT. aestivum) the concentration of the hydroxamic acid DIMBOA ranged between 1 and 8 mmol/kg fresh wt. In a bioassay in which alatae of the aphidSitobion avenaewere released among replicated test seedlings, there were highly significant correlations between aphid ‘preference’ and DIMBOA levels in the seedlings. The value of these results in work leading to the production of aphid‐resistant cultivars is disc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03982.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummarySpiders were the most important group of aphid natural enemies in an irrigated perennial grass pasture. The Lycosidae and Linyphiidae were the only families encountered. An exclusion experiment found predation by spiders to be an important factor in controlling aphid numbers. Together with high temperatures, they maintained aphid numbers at a lower than expected level.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03983.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe population dynamics ofMetopolophium dirhodumwere studied on winter wheat seedlings at constant (10°C, 15°C, 20°C, 25°C and 30°C) and fluctuating (12(night)‐22(day)°C) temperatures, and during booting to early inflorescence, and anthesis to early milky ripe stage, at 19°C. The pre‐reproductive development time was decreased by increasing the temperature from 10°C to 25°C. It was significantly shorter when the aphids were feeding during booting to early inflorescence than during anthesis to early milky ripe stage but was similar when the aphids were feeding on the flag, second or third leaves. The total number of nymphs produced/apterous adult was not significantly affected by temperature from 10°C to 25°C but adult reproductive lifespan was reduced by increasing temperature from 10°C and 12–22°C to 15°C, 20°C and 25°C. The daily intrinsic rate of increase changed from 0.11 to 0.25, and the cohort generation time decreased from 31 to 12 days, with increase of temperature from 10°C to 25°C. Reproductive rate was similar when the aphids were feeding on the flag, second or third leaves during booting to early inflorescence at 19°C. The reproductive rate was higher when the aphids fed from mid‐inflorescence to mid‐milky ripe stage than from mid‐milky to early ripe stage. These results were compared with those from other studies. Predictions from a simulation model using development and reproductive rates from this study and literature were compared and the former rates resulted in a more accurate prediction of field observat

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03984.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummarySeasonal changes in numbers of conidia ofRhynchosporium secalison debris from previous barley crops infected with leaf blotch (primary inoculum) were monitored in 1985–86 and 1986–87. In 1986–87, changes in numbers of conidia on leaves of plants in the new winter barley crop (secondary inoculum) were also recorded. The greatest increases in production of primary inoculum were in early spring after rain, when temperatures were increasing after periods of sub‐zero temperatures when there was little conidial production. Subsequently, more conidia were recovered from this debris after cycles of drying and rewetting than when it remained wet. After January 1987, amounts of secondary inoculum produced on the crop were much greater than amounts of primary inoculum on debris. Most spores were produced on the basal leaves and more spores were present on the September‐sown than on the November‐sown crop. Thus, while primary inoculum was a source of disease when plants were emerging, secondary inoculum on basal leaves was the main source of disease at stem extension, especially on early

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03985.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryIndividual leaves of perennial ryegrass cv. Aberystwyth S23 of two leaf ages and at two levels of nitrogen fertilisation were point inoculated withPuccinia coronataf.sp.coronatain a growth chamber. In general, there was no significant difference in the lifespan of inoculated versus control leaves. However, the higher rate of nitrogen extended leaf lifespan more markedly in rusted than in control leaves.Uredospore production varied according to leaf age: colonies on juvenile leaves produced three times as many spores as those on mature leaves.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03986.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryIn three field experiments in 1985 and 1986, we studied the effect of the date of primary infection on the spread of beet yellows closterovirus (BYV) and beet mild yellowing luteovirus (BMW) from artificially inoculated sugar beet plants. Laboratory‐reared vector aphids,Myzus persicae, were placed on these sources of virus. There was no substantial natural immigration of vectors or viruses. In two experiments, one with BMYV in 1985 and the other in BYV in 1986, populations of vector aphids remained low and there was little virus spread, i.e.c.50 infected plants from one primarily infected source. The cause of this small amount of spread was the low number of vector aphids. In the third experiment, with BYV in 1986, large populations ofM. persicaedeveloped and there was substantial virus spread: c. 2000 infected plants in the plots which were inoculated before canopy closure. In later‐inoculated plots in the same experiment, there was much less spread:c.100 infected plants per virus source plant. Differences between fields in predator impact are implicated as the most probable factor causing differences in vector establishment and virus spread between these three experiments. Virus spread decreased with later inoculation in all three experiments.A mathematical model of virus spread incorporating results from our work has been used to calculate how the initial proportion of infected plants in a crop affects the final virus incidence. This model takes into account the effect of predation on the development of the aphid populations. The processes underlying the spread and its timing are discus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03987.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe detection by ELISA of pea seed‐borne mosaic virus (PSbMV) in pea leaves and seeds was improved by the addition of cellulase or Triton X‐100 to the extraction fluid, probably because the additives aided the release of virus particles from host materials. With leaf extracts the additives were most effective at 0.1%. In initial tests cellulase was used with macerozyme, but the latter enzyme was then shown to decrease the effectiveness of cellulase. Triton X‐100 was as effective as cellulase and the absorbance values obtained in ELISA of infected leaf extracts, diluted to 1/10 in extraction fluid containing the additive, were about six times greater than those of infected extracts diluted in normal extraction fluid. Five named isolates of PSbMV, in addition to the homologous isolate, were readily detected in infected leaves extracted in fluid containing Triton X‐100.In tests on seeds and seedlings of seven infected seed lots of pea cv. Waverex, using Triton X‐100 in the extraction fluid, PSbMV was detected in five times as many seeds as seedlings, probably mainly because in many infected seeds the virus was in the testa and not in the embryo. About 9% of infected seedlings were without recognisable symptoms 4 wk after

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03988.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTwo batches ofCicadulina mbilawere given two distinct acquisition access periods (AAP) (3 h and 50 h) on maize plants infected with maize streak virus (MSV). Infectivity assays on susceptible maize were carried out 1, 3, 10, 17, 26 and 35 days after the AAP. Transmission efficiency was significantly higher forC. mbilasubjected to the 50‐h AAP. At the same time as the infectivity assays, the amount of MSV in each leafhopper was determined by an indirect double antibody sandwich (IDAS) ELISA. There were more ELISA‐positive insects after the 50‐h AAP than after the 3‐h AAP. In the group given a 3‐h AAP, only 7% of the insects tested between day 1 and 35 were found to be positive by ELISA. In contrast, after the 50‐h AAP, the majority ofC. mbilawere positive, yet a decrease in ELISA‐positive insects was noticed from day 17 onwards. Using a calibration curve obtained with purified virus, as little as 0.15 ng of MSV per insect could be measured by the IDAS‐ELISA. A mean value of 0.36 ng of MSV perC. mbilawas found 3 days after the 50–h acquisition, whereas 14 days later there was only 0.20 ng of virus per insect. For comparison, when leafhoppers were kept on infected maize, they displayed substantial accumulation of MSV up to an average of 3.83 ng of MSV per insect after 35 days of continuous acquisition. The amount of virus per insect detected in females was usually greater than the amount detected in males. Our results suggest that MSV does not multiply inC. mbilaand contribute to the understanding of the persistence of transmission efficiency in the absence of vir

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03989.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryFlavescence dorée (FD), a yellows disease of grapevine is caused by a non cultivable mycoplasma‐like organism (MLO) transmitted in vineyards by the leafhopper vectorScaphoideus titanus.In the laboratory, FD is transmitted from broadbean to broadbean by the leafhopperEuscelidius variegatus.Total DNA from FD‐diseased broadbean was centrifuged in a bisbenzimide‐CsCl density gradient. Low density DNA was collected from the gradient, digested withHindIII, ligated into plasmid pUC18 and cloned inEscherichia coli.Trans‐formants were differentially screened by colony hybridisation with32P‐iabelled healthy and FD‐infected leafhopper DNA as probes. The selected clones were shown to carry inserts which all hybridised with FD‐diseased host DNA and not with DNA from healthy host. These32P‐labelled inserts, used as probes in dot blot hybridisation, enabled detection of FD‐MLO in field‐collected samples of grapevine. However, because of the low MLO titre in this plant, an MLO enrichment procedure using tissue from main leaf veins was necessary to ensure effi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1992.tb03990.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY