摘要:

SUMMARYWith mist blower application, copper oxychloride at 2.25 kg/ha was effective in controllingPHYTOPHTHORA colocasiaebut mancozeb at 3.6 kg/ha was not. Phytotoxicity from captafol at 1.8 and 3.6 kg/ha nullified any potential gain in yield from control of blight. Leaf removal from healthy plants to maintain four leaves per plant for 90 days, to simulate roguing of leaves for disease control, was shown to cause no loss in yield. However, regular roguing of diseased leaves over the same period in plots affected by a severe epiphytotic did not eradicate the pathogen. When roguing ceased at 90 days disease increased rapidly to epidemic proportions that seriously affected final corm yield.An attempt to reduce the effect of blight by wider than traditional spacing was unsuccessful. Under continuous epiphytotic conditions disease had the maximum possible impact regardless of spacing. Whereas plants free from competition normally bear six to seven leaves, this number was reduced by severe disease to three or four, the same number as was borne by plants under the competitive conditions of closer‐than‐traditional spacing. Instead of the traditional 20–30 000 plantdha, it was shown that density can be doubled under conditions of high leaf blight hazard and increased yields still be obt

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04762.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYScab disease of cowpea (Vigna unguiculuta) was shown to be caused bySphacelomasp. It affects all above ground parts of the plant. The first symptom of the disease, appearing within 3 to 6 days of inoculation, is puckering of the lamina. Spots on mature leaves are white with or without brown margins. Typical scab lesions on petiole, stem, peduncle and pod are white turning dark brown when chlamydospores are formed and are oblong‐elongate except for pod lesions that are ovoid. The most destructive phase is scab of the flowering axis which causes flower and, or, pod abortion or completely prevents flower formation.Inoculation of asparagus pea (V. sesquipedalis) with a cowpea isolate ofSphacelomasp. produced symptoms similar to those on cowpea. Inoculated hyacinth bean (Lablab niger) produced atypical mild lesions. The following legumes were not affected when artificially inoculated with the fungus: black gram (Phaseolus mungo), green gram (P, aureus), French bean (P. vulgaris), Lima bean (P. lunatus), groundnut (Arachis hypogaea), and soyabean (Glycine max). The characteristics of the fungus on potato dextrose agar are describe

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04763.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYTo determine the relative importance of seed tubers and stems as sources of inoculum for potato gangrene in progeny tubers, different levels of inoculum ofPhoma exiguavar.foveatawere established in field experiments by planting rotting or contaminated seed tubers and by inoculating stems shortly before haulm desiccation.The pathogen was only occasionally detected by isolation from inside green stems in June and July on plants growing from contaminated but unrotted seed. The incidence of pycnidia on desiccated stems increased with increasing concentration of inoculum contaminating seed tubers and with increasing time interval between desiccation and harvest. Stem infection was probably derived from inoculum on seed tubers spreading via the soil to the stem bases. Stem inoculation of plants growing from uninoculated or uncontaminated seed greatly increased both the gangrene potential of progeny tubers (defined as % wounds with gangrene after uniformly damaging tubers and storing them at 5°C for 12 wk), and tuber contamination (defined as % wounds with gangrene after spreading tuber‐borne soil onto test tuber slices and storing them at 5°C for 8 wk). However, when stems of plants growing from rotting or contaminated seed were cut at ground level and removed before desiccation, gangrene potential of progeny tubers was only slightly less than that of tubers from untreated plots. There was no evidence that soil inoculum or aerial spread played a significant role in disease development.Gangrene potential and contamination of progeny tubers were related to Contamination levels on seed tubers. Some transmission also occurred from rotted seed tubers to progeny. Inoculum levels around progeny tubers increased rapidly after desiccation even in plots where stems had previously been cut at soil level and removed to eliminate pycnidial development above ground as a source of inoculum. Both gangrene potential and contamination of progeny tubers were greater on cv. Ulster Sceptre than on cv. Pentland Crown. The results showed that the inoculum on seed tubers, whether from rots or surface contamination, contributed more to the contamination of progeny tubers at harvest than did the inoculum from pycnidia on stems following desiccation of the ha

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04764.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYGlasshouse studies showed that the incidence of black point caused byAlternaria alternatain durum wheat was positively correlated with both the density of the inoculum and the growth stage of the wheat plants at the time of inoculation. A curvilinear relationship of the formY=a +logXwas found between inoculum density and disease incidence. The incidence of black point was linearly related to the stage of plant growth, between anthesis and the late milk stages of development, at the time of inoculation. A better relationship between growth stage and disease incidence was found when plant growth was expressed as days after anthesis than when the Romig scale was used (R2=0.30 and 0.24 respectively). A threshold dew period of 3–6 h was required for black point symptoms to develop. The incidence of black point increased with increasing duration of the dew period until maximum disease incidence occurred after exposure to a dew period of 48

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04765.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYHibiscus latent ringspot virus (HLRV) was prevalent inHibiscus rosa‐sinensisin Ibadan, Nigeria. It was readily transmitted mechanically to 22 of 73 species from seven of 20 families, but was best propagated inNicotiana clevelandiiorHibiscus cannabinusand assayed inChenopodium murale. HLRV was readily purified from systemically infected hosts by differential centrifugation of leaf extracts clarified with 8.0% n‐butanol, followed by molecular permeation chromatography on controlled‐pore glass beads (700 Å, 120–200 mesh). The virus has isometric particlesc. 28 nm in diameter which sedimented as three components (T, M and B), with sedimentation coefficients (s°20, w) of 51; 114 and 132Sand buoyant densities in caesium chloride of 1.32, 1.49 and 1.52 g/cm3, respectively. All three components contained a single polypeptide of rnol. wt 53.6 × 103. T component particles contained only protein but M and B components also contained single‐stranded RNA of rnol. wt 2.2 × 106and 2.5 × 106, respectively. The properties of HLRV suggest affinities with nepoviruses but no serological relationship was detected between HLRV and 15 recognised or possible members of the n

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04766.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYProtein A‐coated latex (PAL) was compared with uncoated latex (L) for sensitisation with antibodies to five plant viruses: apple mosaic virus (ApMV), arabis mosaic virus (AMV), plum pox virus (PPV), potato virus Y ordinary strain (PVY°) and prunus necrotic ringspot virus (NRS V). A range of globulin concentrations was used with each antiserum and detection end points determined in serial dilutions of infective sap. When sensitised with antibodies to ApMV, PAL detected ApMV readily, whereas L did not. When sensitized with antibodies to PVY° and AMV, PAL gave higher detection end points than L. However, PAL gave little increase in sensitivity with the antisera to PPV and NRSV. Non‐specific aggregation of latex, which sometimes occurred in very dilute sap with PAL, could be dispersed by adding 0.02% Tween‐20 to the extraction buffer. Globulins of PVY° and AMV could be used at higher dilutions with PAL than with L, giving a saving in antiserum. Both types of latex sensitised with PVY° antibody globulins readily detected the tobacco veinal necrosis and C strains of t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04767.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYLive trapping at 0.9 m of alate aphid vectors of barley yellow dwarf virus (BYDV) at Aberystwyth from 1970 to 1979 showed that ten species transmitted the virus to oat test plants. Conversion of percentage infective at 0.9 m to numbers infective based on continuous trapping at 1.2 m showedRhopalosiphum padiandR. insertumto be the main vector species in most years, whilstMetopolophium dirhodumandSitobion auenaewere normally of minor importance. The data obtained suggest that epiphytotics of BYDV in autumn‐sown cereals were caused by numerous infective vectors flying late in the year and transmitting severe strains of the virus. Evidence is presented that gynoparae and males ofR. padiare involved in the autumn spread of BYDV and that three further aphid species,Anoecia corni, Metopolophium albidumandM. frisicumare BYDV vectors. The use of live and continuous trapping techniques in forecasting BYDV epiphytotics is discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04768.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYBlack raspberry necrosis virus (BRNV) induces a severe apical necrosis in black raspberry (Rubus occidentalis) but fails to induce diagnostic symptoms in red raspberry. However, BRNV infection of F1, F2and F3hybrids from the cross black raspberry × red raspberry induced mosaic symptoms of varying intensity but no typical apical necrosis.In a survey of 28 red raspberry cultivars, a few developed severe angular chlorotic leaf spots when infected with raspberry leaf mottle virus and a few others did so when infected with raspberry leaf spot virus. These reactions were determined by single dominant genes designatedLmandLsrespectively.The value of the different host reactions for controlling the effects and spread of these viruses is discussed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04769.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYFactors affecting the detection of potato leafroll virus (PLRV) by enzyme‐linked immunosorbent assay (ELISA) in tubers of field‐grown potato plants with primary or secondary infection were studied. The reactions of extracts of virus‐free potato tubers were minimised by pre‐incubating the extracts at room temperature and by careful choice of the dilution of enzyme‐conjugated globulin. PLRV was reliably detected in tubers produced by secondarily infected plants of all six cultivars tested. PLRV concentration was greater in heel‐end than in rose‐end vascular tissue of recently harvested tubers but increased in rose‐end tissue when tubers stored at 4°C for at least 5 months were placed at 15–24°C for 2 wk.PLRV occurred at greater concentration in tubers from plants of cv. Maris Piper with natural or experimentally induced primary infection than in tubers from secondarily infected plants; again PLRV concentration was greater in heel‐end than in rose‐end vascular tissue. Plants whose shoots were infected earliest in the growing season were invaded systemically and produced the greatest proportion of infected tubers; plants infected late in the season also produced infected tubers but PLRV was not detected in their shoot tops. PLRV concentration in tubers from the earliest‐infected plants was less than in tubers from later‐infected plants. PLRV was detected reliably by ELISA in tubers from progenies that were totally infected but was not detected in all infected tubers from partially infected progenies.ELISA is suitable as a routine method of indexing tubers for PLRV, although the virus will not be detected in all infected tubers produced by plants to which it is transmitted

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04770.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

SUMMARYCrimson clover latent virus (CCLV) was detected in five seed lots of crimson clover (Trifolium incarnatum) from Europe and in one from the United States of America. Ninety‐seven per cent of all crimson clover plants examined were found to be infected but were without symptoms. Keeping crimson clover plants at 32–38°C for 34 days failed to free them from CCLV. The virus was not transmitted byMyzus persicae, but was transmitted by inoculation of sap toChenopodium album, C. amaranticolorandC. quinoa. Twenty‐four other plant species from seven families were not infected. CCLV was best propagated inC. quinoain which it caused stunting and systemic chlorosis. Sap from infectedC. quinoawas infective after dilution to 10‐2but not 10‐3, after 10 min at 60°C but not 65°C, and after 20 days at 20°C.In neutral phosphotungstate, CCLV had isometric particlesc. 26 nm in diameter with a hexagonal profile. About 20 to 80A1cm,260units of purified virus were obtained from 1 kg of infectedC. quinoaorC. amaranticolorleaves by extraction in 0.5 M phosphate buffer, pH 7.5, containing 0.01 M ethylene diamine tetra‐acetate and 0.4% 2–mercaptoethanol and clarification with chloroform‐butanol followed by two precipitations with polyethylene glycol (mol. wt 6000) and several cycles of differential centrifugation. Purified virus sedimented as three components with sedimentation coefficients (s°20, w) of 52S, 101Sand 122S. The 101Sand 122Scomponents had buoyant densities in CsCl of 1.438 and 1.495 g/cm3respectively. From these values the nucleic acid content of the 101Sand 122Scomponents was estimated to be 32–35% and 40–41% respectively. The virus contained a single protein with an estimated mol. wt of 52 000 and two single‐stranded RNA species of estimated mol. wt 1.6 × 106and 2.2 × 106. CCLV was serologically unrelated to 31 other morphologically similar viruses. Although its vector is unknown, CCLV seems to have affinities with nepoviruses.The cryptogram of CCLV is R/1:2

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1980.tb04771.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY