摘要:

SUMMARYTotal DNA from clones ofRhopalosiphum maidiswas digested with restriction endonucleases and hybridised with a heterospecific ribosomal DNA probe. DNA banding patterns exhibited sufficient differences to distinguish five different clones, and provided greater resolving power than gel electrophoresis of allozymes. The mechanisms and applications of this marking technique are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04189.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYSuction trap catches for the period 1969 to 1984 were used to develop a forecasting system forM. dirhodum.This was achieved by using the strong relationships that exist between: a) suction trap catches ofMetopolophium dirhodumat Broom's Barn and populations of the aphid in fields near Norwich, and b) winter and spring temperatures and the time when the crop became unsuitable for this aphid.This forecasting system was tested in 1985, 1986, 1987 and 1988 and successfully forecast early in the season that it would not be necessary to apply aphicides in 1987 and 1988. The use of this forecasting system would have correctly indicated that aphicide application against this aphid was unnecessary in 9 out of the 16 seasons from 1969 to 1984.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04190.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe hydroxamic acids in the seedlings of four varieties of winter wheat were extracted initially in boiling methanol in order to avoid enzymatic hydrolysis. The increase in numbers of aphids on these varieties of wheat were recorded. HPLC analysis of hydroxamic acids in the extracts showed the presence of DIMBOA‐glucoside, DIMBOA‐aglucone and its benzoxazolinone (MBOA). There was a highly significant negative correlation between the concentration of DIMBOA‐aglucone in the seedlings and aphid performance. However, the association between aphid performance and DIMBOA‐aglucone in the tips of the seedlings was weaker. In general aphid infestation of wheat seedlings slightly increased the concentration of all the hydroxamic acid derivatives. Moreover, aphids ingested hydroxamic acids and were able to detoxify some of the DIMBOA‐aglucone they

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04191.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYDuring the mid‐1980s,Sitobion avenaebecame recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984‐85 to evaluate different control procedures againstS. avenae‐transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton‐S‐methyl or pirimicarb on one of three dates between mid‐October and mid‐November, making a factorial design.Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers ofS. avenaewere much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations ofS. avenaeto zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration ofS. avenaewere more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective.Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments.Enzyme‐linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV‐ and PAV‐like strains were present, and were most likely to have been tran

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04192.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYSpike washing and direct count methods were equally effective for sampling eggs and young larvae of millet spike worm,Raghuva albipunctella(Noctuidae: Lepidoptera) in Senegal, but spike washing is a more economical method. Most eggs (70%) were laid on emerging millet spikes and the spike apex was the preferred oviposition site. Most larvae pupated 10–30 cm from millet hills. The maximum number of pupae was found in the upper layer (<10 cm) in loamy soil and deeper (20–30 cm) in sandy soil. Ploughing fields after millet harvest reduced the population of spike worm pupae significantly, but may prove impracticable or socially unacceptable to farm

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04193.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe abundance and diversity of potential carabid predators ofSitona lineatus(L.) in field beans were monitored between 1980 and 1983. The absolute abundance of the large predatory species was determined in mark‐recapture experiments and a radio‐labelling technique was used to estimate the level of predation in the field. Using previously published population data forS. lineatus, the importance of predation in the population dynamics of the weevil was estimated. The mortality of weevil larvae due to predation varied from 0.6%– 10.5% while that of adult weevils varied from 2.6%– 23.8%. It appeared that carabids played a significant role in the population dynamics ofS. lineatusand, in years when abundant, could reduce the population of larvae and overwintering adults by more t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04194.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYWhen introduced into a mushroom crop at rates of 2, 20 or 200 larvae/tray (0.56 m2), the mushroom cecid,Heteropeza pygmaea, caused significant reductions in both yield and number of mushrooms in relation to the infestation level. The reductions were greater when the larvae were introduced at spawning rather than at casing. The yield and number of infested (unmarketable) mushrooms increased significantly in relation to the initial infestation level.Just twoH. pygmaealarvae, introduced at spawning, resulted in cecid populations that caused a 12% loss in total yield in addition to a 7% loss due to spoilage. Loss assessment in the future, therefore, should take into account both yield suppression and spoilage.There was little effect of cecid infestation on flush timing and mushroom size was only affected in the fourth flush, when a significant reduction (27%) was shown at the highest infestation rate at spawning.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04195.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYUsing an improved method for extraction of dsRNA from strawberry leaf tissue, small quantities of several dsRNA species with mol. wt greater than 1.0 × 106were detected in strawberry plants free from known strawberry viruses but affected by June yellows (JY). No such dsRNA species were detected in plants ofFragaria vescaor seven strawberry cultivars known to be free from JY. Neither JY symptoms nor these dsRNA species were detected in healthy strawberry andF. vescaplants graft‐inoculated with tissue from JY‐affected plants. It is not known whether the JY‐associated dsRNA species are those of a causal agent of JY or are a consequence of the JY condition. Nevertheless, the detection of such dsRNA species in plants affected by JY may offer a possible objective method for detecting the incipient condition in symptomless strawberry plants. However, the concentrations of dsRNA in JY‐affected plants are very low and dsRNA analysis is thought not to be sufficiently reliable for routine testing of plants. The occurrence of anomalous dsRNA species in extracts from some strawberry plants was caused by dsRNA from two‐spotted spider mites (Tetranychus urticae) infesting

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04196.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYGroundnut plants with symptoms of rosette disease contain groundnut rosette virus (GRV), but GRV is transmitted byAphis craccivoraonly from plants that also contain groundnut rosette assistor virus (GRAV). Two main forms of rosette disease are recognised, ‘chlorotic rosette’ and ‘green rosette’. GRV cultures invariably possess a satellite RNA and this is the major cause of rosette symptoms: satellite‐free isolates derived from GRV cultures from Nigerian plants with chlorotic or green rosette, or from Malawian plants with chlorotic rosette, induced no symptoms, or only transient mild mottle or interveinal yellowing, in groundnut. When the satellite RNA species from GRV cultures from Nigerian green or Malawian chlorotic rosette were reintroduced into the three satellite‐free isolates in homologous and heterologous combinations, the ability to induce rosette symptoms was restored and the type of rosette induced was that of the cultures from which the satellite RNA was derived. Thus different forms of the satellite are responsible for the different forms of rosette disease. Other forms of the satellite induce only mild chlorosis or mottle symptoms in groundnut. Individual plants may contain more than one form of the satellite, and variations in their relative predominance are suggested to account for the variable symptoms (ranging from overall yellowing to mosaic) seen in some plants graft‐inoculated with chlo

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04197.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYWhen 12 potato cultivars were inoculated with isolates (one each) of potato virus Y (PVY) ordinary (Yo), C (Yc) and tobacco veinal necrosis (Yn) strain groups, potato virus A (PVA) and potato virus V (PVV), none of them responded hypersensitively to Yn. However, with Yo, Yc, PVA and PW specific hypersensitive reactions developed depending on isolate‐cultivar combination which were all independent of each other. When field isolates of PVY thought to be Yoor Ycwere inoculated to the same 12 cultivars, two did not fit into either strain group giving hypersensitive reactions in only two cultivars instead of seven with Yoor eight with Yc. These two isolates may represent a previously unreported PVY strain group (Yz).When Yowas graft‐inoculated to seedlings of the cross Desiree × Maris Piper (hypersensitive × non‐hypersensitive for Yo), the segregation ratio obtained for non‐hypersensitive:hypersensitive reactions was close to 1:1 suggesting that a single dominant gene (Nytbr) determining Yospecific hypersensitivity may be present in cv. Desiree (simplex condition). In tests using PVV and Desiree × Maris Piper (non‐hypersensitive × hypersensitive for PVV) seedlings, the segregation ratio obtained was close to 1:5 indicating that a single dominant gene (Nv) determining PVV specific hypersensitivity may be present in cv. Maris Piper (duplex condition).Cultivars Corine, Pirola and clone G5457(4) which each carry one of the extreme resistance genes (Ry) fromSolanum stoloniferumwere graft‐inoculated with Yn, Yo, Yc, PVV and PVA. G5457(4) gave a strong localised hypersensitive reaction in all instances, while cv. Pirola did so with all except PVA to which it was immune. In cv. Corine a severe localised hypersensitive reaction developed with PVA, generalised hypersensitivity with PVV but an immune response with the three PVY strain groups. Large‐scale grafting of Ynto plants of cvs Corine and Pirola gave no evidence of selection of a strain which o

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1990.tb04198.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY