摘要:

SUMMARYA technique was developed and deployed in central Illinois to trap and assay aphid alatae for incidence of soybean mosaic virus (SMV) transmission among naturally occurring transient aphid populations downwind of a field of infected soybean. In a 2‐yr study, 1709 alate aphids were trapped alive and assayed, 4.2% of which transmitted SMV. Five species of aphids accounted for more than 93% of the transmissions:Aphis craccivoraKoch,Macrosiphum euphorbiae(Thomas),Myzus persicae(Sulzer),Rhopalosiphum maidis(Fitch), andRhopalosiphum padi(L.). At least 55 additional species were assayed, five of which transmitted only once. Others did not transmit. Because virus infection during the early growth stages of soybean increases the loss of yield and the percentage of seed‐borne virus, vector species that tend to fly middle to late spring are, from an economic point of view, more important in the spread of SMV.R. maidisflew in mid‐ to late summer and in autumn.R. padiwas not abundant at any time of year and its transmission efficiency was low.M. persicaetended to fly in mid summer. Two species (A. craccivoraandM. euphorbiae) which had major flights in late spring and early summer and relatively high transmission efficiencies are potentially important in the economic spread of SMV in central Illinois. A third species,Aphis citricolaVan der Goot, may also be important because it flies in late spring and laboratory data suggest it is a relatively efficient vector of SMV.A. citricolawas not assayed by our technique because we trapped in the morning and this species appears to fly later in th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02988.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYSome preliminary associations are reported between monthly totals of cereal aphids (Metopolophium dirhodum, Rhopalosiphum insertum, R. padiandSitobion avenae) caught in suction traps and weather data. Catches at 1.2 and 12.2 m during the summer and autumn flight peaks from 1969 to 1979 were compared with combinations of prior monthly totals of rainfall and accumulated day‐degree temperatures. The best models fitting these results are reported and proposed for testing against future data. The possible relevance of these models, for forecasting whether measures for the control of barley yellow dwarf virus in autumn‐sown cereals are necessary in any year, are discus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02989.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYTraps containing a sex attractant of the pea moth (Cydia nigricana) were used to monitor numbers of male moths in individual fields in south‐eastern and eastern England from 1976 to 1978 at 16 or more sites/yr. Data concerning catches at different sites on several occasions over the flight season, and dates on which a ‘threshold catch’ was achieved were examined, and were related weakly to site locations within areas. Area spray warnings, based on trap catches at a few sites within a large area, provide a less reliable indication of the need to spray than on‐site monitoring (two traps) in each pea field. On‐site monitoring may be improved by specialist interpretation of tra

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02990.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYBark canker caused by the fungusPhytophthora palmivorahas caused the death of many cocoa trees over 15 years old in Papua New Guinea in recent years. Cankers are significantly associated with channels made by the larvae of bark‐damaging insects, which provide the major entry point for the pathogen. The combination of canker and insect damage may limit the economic life of cocoa to less than 15 years in affected area

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02991.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYSeveral lines of circumstantial evidence collectively indicated that poor early growth of apple (‘replant disease’) might be associated with the effects of soil‐borne pythiaceous fungi. This hypothesis was supported by pathogenicity tests. All isolates tested ofP. sylvaticumand certain isolates of seven otherPythiumspp. significantly reduced the growth of apple seedlings. The growth reductions caused by certainPythiumisolates were of comparable magnitude to the growth increases occurring after chloropicrin‐fumigation of apple orchard soils. ThePythiumisolates most virulent to apple were of low virulence to a clonal cherry rootstock.Reappraisal of the nature of the disease as a non‐specific soil malaise is consistent with established features of the pathology ofPythiumspp. The disease, however, is an ill‐defined ‘poor growth phenomenon’ with no diagnostic symptoms and conclusive evidence thatPythiumspp. are widely causal is likel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02992.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYObservations on plots of spring barley cv. Golden Promise during May‐July 1973–79 showed that escalation of mildew commenced in mid‐June 1976, in late June in 1973 and 1974, in early July in 1978 and 1979, and failed to develop in 1975 and 1977. By mid‐July there was 40% infection in 1976, and 13–21% infection in 1973, 1974, 1978 and 1979. Less than 2% mildew occurred in 1975 and 1977.Using as a basis the method of mildew forecasting formulated by Polley&King (1973), it was found that once mildew was established in the crop there was moderately good association between the incidence of high mildew risk according to the Polley weather criteria and the major peaks of spore concentration above the crops. It was not possible to correlate these two features during May and early June each year because of a lack of inoculum, but it is considered that the failure of mildew to develop during the entire growing seasons of 1975 and 1977, in spite of frequent high risk periods, was due in part to low atmospheric humidity during the early part of the season. The relative number of accumulated Polley factors satisfied on days when the relative humidity approx. 1 m above ground was 78% or more (at 0900 GMT) during the period mid‐May to mid‐June, separated the low mildew years of 1975 and 1977 from the moderate ones of 1973, 1974, 1978 and 1979, and the severe mildew year of 1976. This procedure may provide a practical means of forecasting the level of mildew build‐up during the later growth stages of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02993.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYThe viability of axillary buds and the growth and potential yield of lateral shoots at nodes of red raspberry (Rubus idaeus) infected naturally byDidymella applanataorBotrytis cinereawere measured on excised nodes, decapitated nursery canes or on canes from fruiting plantations. In comparison with lesion‐free nodes, buds at infected nodes were smaller and fewer of them were capable of growth when excised and ‘forced’, although the difference in growth between infected and uninfected nodes decreased during late winter. After February, those buds at infected nodes which were capable of forced growth did so as early and with a similar growth rate as those at lesion‐free nodes. In April, 70% of buds at infected nodes were capable of growth compared with 94% of those at lesion‐free nodes.When nursery canes of cv. Mailing Delight were decapitated above infected nodes the emergence of lateral shoots from the terminal infected node did not differ significantly from that at lesion‐free nodes. On a range of farm sites in Scotland the emergence of shoots at infected nodes in the cropping region of canes was significantly poorer than from uninfected nodes but substantially better at infected nodes of cv. Glen Clova than at those of cvs Mailing Jewel and Mailing Orion. It is suggested that cv. Glen Clova is relatively tolerant of spur blight and cane botrytis. The length and potential yield of laterals which developed at infected nodes in the cropping region of canes in these three cultivars did not differ significantly from those at lesion‐free nodes. In all tests there was no significant difference in growth at nodes infected byD. applanataandB. cinereawhich may indicate a common mechanism for suppre

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02994.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYIn New Zealand, all garlic (Allium sativum) plants tested were infected by a virus with flexuous filamentous particles 700–800 nm long. This virus, called garlic yellow streak virus (GYSV), infected only two of 12 species tested and was transmitted to garlic by the aphidMyzus persicaein a non‐persistent manner. In garlic sap, GYSV was infective at a dilution of 10‐4but not 10‐3, after heating for 10 min at 60°C but not 65°C, and after 2 days but not 3 days at 25°C.The yield of virus, purified from naturally infected garlic, was 3–4 mg/kg fresh leaf. Preparations hadA260/A280= 1.28 andAman/Amin= 1.08. The virus particles had a sedimentation coefficient of 149S and a buoyant density in CsCl of 1.334 g/cm3. Mol. wt estimates for the virus nucleic acid were 2.95 × 106by electrophoresis in polyacrylamide gels and 3.46 × 106from the sedimentation coefficient (41.4S) in linear‐log sucrose density gradients. Two polypeptides were detected in virus preparations; one (mol. wt 30 500) was possibly a breakdown product of the other (mol. wt 33 000). GYSV was serologically distantly related to onion yellow dwarf and leek yellow stripe viruses but was considered to be a separate virus because it differed from th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02995.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYIn Ghana, field resistance to cocoa swollen‐shoot virus (CSSV) in young, bearing trees was assessed by monitoring natural spread by mealybug vectors from adjacent graft‐inoculated line sources. Apparent rates of virus spread were estimated by regressing proportions of infected trees on time from inoculation. In some hybrids between parents derived from Upper Amazonian material, spread was only 25–40% that in currently recommended varieties. This resistance is the most effective, feasible measure to reduce economic losses and the resistant hybrids could be made available quickly for large scale use.The results from trials in which virus spread most rapidly were the easiest to interpret. Spread of CSSV is erratic, necessitating large experiments, and in trials with equal replication the largest plots gave the greatest precision. Neighbouring plot adjustment proved unsatisfactory as it improved precision but appeared to reduce acc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02996.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYDifferences in amounts of infection following seed inoculation, by the mealybug vector (Planococcoides njalensis(Laing)) of cocoa swollen‐shoot virus were used as a short‐term test of virus resistance in a range of cocoa progenies. The test results were highly correlated with virus resistance as measured in field trials. The best assessment of seed inoculation experiments allowed for progeny‐dependent variation in the latent period of the virus. Experiments in which estimates of progeny means varied significantly with replicate sometimes gave poor agreement with known field perfor

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1981.tb02997.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY