ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb04999.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe performance of clones ofRhopalosiphum padiandSitobion avenaefrom England and Spain was examined on drought‐stressed tillering winter wheat in an environment chamber at 14 ± 1°C. Two different levels of drought stress and an unstressed control were established by different watering regimes which resulted in drought‐stressed plants being smaller at the end of the experiment.The effect of drought stress to plants on aphid performance was not significantly different between the clones tested. Drought stress had no effect on aphid development time, nymphal mortality, the weight of teneral adults and the number of embryos in teneral adults up to the onset of reproduction in the first F1generation. The subsequent reproductive capacity, as measured by the effective and potential fecundity, and the reproductive rate, were much reduced on drought‐stressed plants. However, there was only a small decrease in the intrinsic rate of increase (rm). Overall the clone ofR. padifrom Spain performed better than that from England, the development and prereproductive times being shorter and the fecundity higher in the Spanish clone, giving a higher rm. There were no differences in the fecundity and the rmbetween the Spanish and the English clones ofS. avenae.The proportion of the F2generation that was alate differed greatly between clones, and only the EnglishS. avenaeproduced significantly more alatae on drought‐stressed than on unstress

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05000.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryPotato tubers (cvs Cara and Bintje) were grown in compost in a glasshouse and immature tubers harvested 57, 68 and 78 days after planting. Two moisture levels were imposed after the first harvest by disconnecting the water supply to one of the treatments and allowing the soil in that treatment to dry naturally. Tubers from wetter compost (59.4% moisture holding capacity) were more resistant toPhytophthora infestansthan those from drier compost (14.7% moisture holding capacity) 78 days after planting. The potential causes of this difference were investigated. Aqueous extracts of wet compost did not inhibit the growth ofP. infestans.The susceptibility of the internal tuber tissue, from which the periderm had been removed, was different to whole tuber susceptibility. The internal tissue of tubers from wet compost was more susceptible (cv. Cara), or as susceptible (cv. Bintje) as that of tubers from dry compost 78 days after planting. Fungi were isolated from the surface of whole tubers and there were no differences between the populations of potentially antagonistic fungal genera on tubers from wet and dry compost. As the experiment progressed, the number of bacteria per gram fresh weight on tubers grown in wet compost increased, whereas that on tubers from drier compost decreased (cv. Bintje) or remained similar (cv. Cara). There were significantly (P= 0.008) more bacteria on the surface of tubers from wet compost 78 days after planting. WhenP. infestanswas co‐cultured in Petri dishes with randomly selected tuber surface bacteria, some isolates (≤ 16.7%) inhibited the growth of the fungus. The percentage of the total bacterial population that was antagonistic toP. infestanswas not significantly affected by soil moisture level (P= 0.368). The greater numbers of bacteria, of which a proportion are antagonistic toP. infestans, on the surface of tubers grown in wet compost may account for the greater resistance to tuber blight in that insta

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05001.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAn investigation into the incidence of stem base diseases and the pathogens associated with them was undertaken on winter wheat samples collected at growth stages 31 and 73–75 in 1989 and 1990. Symptoms at growth stage 31 were classified into 10 different types based on visual characteristics. AlthoughPseudocercosporella herpotrichoideswas associated mainly with eyespot lesions andRhizoctoniaspp. with sharp eyespot lesions, a significant number of isolates of each pathogen were taken from lesions classified as fusarium. Different types of fusarium lesion on stem bases at both growth stages were not associated with any one particularFusariumorMicrodochiumspecies. 98% ofP. herpotrichoidesisolates obtained from eyespot lesions at growth stage 31 in 1989, and 87% of those obtained in 1990 were identified as the sub‐speciesP. herpotrichoidesvar.acuformis, Microdochium nivalewas more common than any of theFusariumspecies at both growth stages, and was particularly prevalent in samples from Scotland at the earlier growth stage in 1989. Isolations from the top internodes at growth stage 73–75 indicated that systemic infection byFusariumspecies, although present in some stems, was of little importance.Fusariumear blight affected 0.4% of ears in 1989 and 0.5% in 1990. Glume spot lesions on the ears in 1990 were predominantly associated withFusarium

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05002.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryField trials to examine the effect of pea bacterial blight(Pseudomonas syringaepv.pisi) (Psp)on the yield of combining peas were carried out at five sites (HRI Wellesbourne, ADAS Rosemaund, ADAS Terrington, PGRO, SASA East Craigs) in the UK in 1990, 1991 and 1992. Healthy seed, cv. Solara, and seed naturally infected withPspRace 2 was sown in large plots (c.200 m2) in the open or under nets to prevent bird damage by pigeons. Despite relatively low disease severity levels (<15% leaf area) and separation by at least 12 m of cv. Consort (resistant to Race 2) between plots there was considerable spread of disease into plots sown with healthy seed. Regression analysis demonstrated a significant relationship between yield and disease. Of the disease measurements examined, disease severity on the leaves (stipules) at growth stage 208 was found to be the best predictor of yield. A model containing environmental and bird damage terms, in addition to disease, suggested that a yield loss of 0.98 t/ha would be expected for a disease severity score of 1, equivalent to 5% leaf area affected, at growth stage 208.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05003.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryDuring the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights.Results from transmission tests showed that: (i) the two main BYDV vectors wereRhopalosiphum padiandMetopolophium dirhodumduring the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during springM. dirhodumappeared to be the most important MAV vector and nearly as good a PAV vector asR. padi; (iv) during autumnR. padiwas the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infection

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05004.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA labile virus has been identified in white clover in New Zealand. The virus was mechanically transmitted to nine species of herbaceous test plants. No virus‐like particles were identified by electron microscopy in ultrathin sections or in negatively stained sap extracts, although in infectedChenopodium quinoathere were prominent membraneous inclusion bodies in the cell cytoplasm and membrane‐bound structures c. 50 nm in diameter associated with the tonoplast in cell vacuoles. Double‐stranded RNA species of approximately 6800, 3500 and 3300 bp were isolated from infected tissues. DsRNA denatured by boiling was infectious toC. quinoa, but undenatured dsRNA was not infectious. Total nucleic acid preparations from infected leaves were highly infective without boiling, indicating that most of the infectivity was single‐stranded RNA. Infectivity was recovered in the poly (A)‐faction following oligo (dT)‐cellulose chromatography, indicating that the RNA probably lacks a 3′ tract of poly (A). The labile white clover virus is tentatively named white clover vi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05005.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe localisation of plum pox virus (PPV) in stem and petiole tissues of nine susceptible apricot cultivars and GF305 peach seedling has been studied. From stem and petioles consecutive transverse sections spaced at 1 mm were made and tissue sections printed onto nitrocellulose membrane. The resulting prints were probed with a specific antibody for plum pox virus, followed by a rabbit anti‐goat antibody conjugated with horse radish peroxidase, in order to localise the virus within the tissues. In stems the virus was mainly present in xylem and pith. The possible presence of the virus in the sclerenchyma is discussed. In petioles the virus was present in epidermis and parenchymas, but not in vessels. The probable movement through the xylem and from cell to cell has been show

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05006.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA flexuous filamentous virus 750 nm in length was isolated from field‐grown melons (Cucumis meloL.) and squirting cucumber (Ecballium elateriumL.). Infection of melon seedlings of most commercial varieties resulted in a lethal wilting, but late infections gave dieback. The virus infected systemically all economically important cucurbit crops. Its coat protein consists of a single polypeptide, 34 500 D in size, encapsidating a single stranded RNA genome of 10.1 kb.Antiserum against the Italian zucchini yellow fleck virus (ZYFV) reacted specifically with the Israeli isolate in both ISEM and Western blot. The virus was aphid transmissible in a non‐persistent manner. Based on host range, host reaction and serological data, it is suggested that the virus described is an Israeli variant of Z

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05007.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryWhitefly‐transmitted geminiviruses were found to be associated with four diseases of crop plants in Burkina Faso: cassava mosaic, okra leaf curl, tobacco leaf curl and tomato yellow leaf curl. Tomato yellow leaf curl is an economically serious disease, reaching a high incidence in March, following a peak population of the vector whitefly,Bemisia tabaci, in December. Okra leaf curl is also a problem in the small area of okra grown in the dry season but is not important in the main period of okra production in the rainy season. The geminiviruses causing these four diseases, African cassava mosaic (ACMV), okra leaf curl (OLCV), tobacco leaf curl (TobLCV) and tomato yellow leaf curl (TYLCV) viruses, were each detected in field‐collected samples by triple antibody sand‐wich‐ELISA with cross‐reacting monoclonal antibodies (MAbs) to ACMV. Epitope profiles obtained by testing each virus isolate with panels of MAbs to ACMV, OLCV and Indian cassava mosaic virus enabled four viruses to be distinguished. ACMV and OLCV had similar but distinguishable profiles. The epitope profile of TobLCV was the same as that of one form of TYLCV (which may be the same virus) and was close to the profile of TYLCV from Sardinia. The other form of TYLCV reacted with several additional MAbs and had an epitope profile close to that of TYLCV from Senegal. Only minor variations within each of these four types of epitope profile were found among geminivirus isolates from Burkina Faso.Sida acutais a wild hos

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1995.tb05008.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY