Showing papers on "Leaf spot published in 1987"

Studies on watercress chlorotic leaf spot virus and on the control of the fungus vector (Spongospora subterranea) with zinc

Abstract: SUMMARY Watercress chlorotic leaf spot virus (WCLV) caused a yellow leaf spot disease of watercress at Pickering, Yorkshire. The virus was mechanically transmitted to and maintained in Chenopodium quinoa, C. amaranticolor and Petunia hybrida in which it caused systemic symptoms. It could not be mechanically transmitted, however, from infected C. quinoa to Chrysanthemum, Gynura aurantia, potato, tomato, watercress or nine other species of Cruciferae. WCLV could be partially-purified after extraction in weak (0.05–0.1 M) but not strong (0.5 M) phosphate or tris/HCl buffer after clarification with diethyl ether and acidification to pH 3.9–4.0. Preparations were non-infective if treated with 5% (vlv) ethanol or n-butanol or if stored at — 12°C for 1 day or heated for 10 min at 54°C. Preparations were non-infective after treatment with RNase or proteinase K but not after treatment with DNase. The virus was present in roots of diseased watercress plants which also contained the watercress crook root disease fungus Spongospora subterranea f. sp. nasturtii. Tests showed that WCLV was transmitted by S. subterranea zoospores and that it persisted in the resting spores of the fungus. The crook root disease was controlled by adding 0.3–0.5 μg Zn/ml to the inlet water supply to the crop. The water that had flowed through the crop contained 0.05–0.10 μg Zn/ml. Although this increased the zinc content of the watercress from 8–9 in untreated beds to 16–48 μg Zn/g in treated beds, this was below the tolerance recommended by the Food Standards Committee. A method is described of obtaining accurate dilutions of solutions of zinc sulphate (20% w/v ZnSO4.H2O) in the water supplying the crop using solutions of the red dye Ariavit Amaranth.

A computer simulation model for Cercospora leaf spot of peanut

Abstract: Knudsen, G. R., Spurr, H. W., Jr., and Johnson, C. S. 1987. A computer simulation model for Cercospora leaf spot of peanut. Phytopathology 77:1118-1121. A computer simulation model was developed to predict disease delay processes, and host plant growth (increase in leaflet number) was progression of Cercospora leaf spot of peanut (causal agents: Cercospora described as a logistic process. The model was validated using independent arachidicola and Cercosporidiumpersonatum). The model was derived in weather and disease severity data from field trials with peanut cultivar part from an advisory system used for fungicide scheduling in North Florigiant, in which C. arachidicola was the predominant pathogen. Carolina and Virginia. Basic infection rate was modeled as a function of Simulated disease progress curves and periods of rapid disease increase hours of relative humidity > 95%, minimum temperature during the period were similar to those observed in field trials. The model effectively ranked of high humidity, amount of infectious tissue, and proportion of uninfected four epidemics in terms of end-of-season disease severity and area under the tissue remaining. Latent and infectious periods were treated as distributed disease progress curve. Additional key words: disease forecast, early leaf spot, late leaf spot. Early and late leaf spots of peanut (Arachis hypogaea L.), caused day. Interactions between system components in the model are by Cercospora arachidicola Hori and Cercosporidium diagrammed in Figure 1. Disease severity was expressed as personatum (Berk. & Curt.) Deighton, respectively, are among the percentage of leaflets either defoliated or having one or more most serious diseases of peanuts (13,14). The two diseases exhibit visible lesions (6,7). Plant growth, defined as increase in leaflet similarities in symptom expression, epidemiology, and resultant number, was modeled as a simple logistic function. Parameters for yield loss and are usually referred to as Cercospora leaf spot or peanut leaf spot. Cercospora leaf spot is controlled by several fungicides; the most widely used in North Carolina is chlorothalonil. Fungicides are usually applied on a 10-14-day Uninfected schedule beginning about 30-40 days after planting (12). U ec A leaf spot forecast system developed by Jensen and Boyle (7) Leaflets and Parvin et al (11) is currently used to schedule fungicide sprays Growt \" netn in North Carolina and Virginia (2,12). The forecast system uses -_ Infection < hours of relative humidity (RH) >95% and minimum temperature A during the high relative humidity period to calculate a daily index Latently Humidity, representing likelihood of disease increase. The sum of 2 days' Infectedt .Temperature indices is usually sufficient to determine a fungicide spray advisory. Leaflets \" The leaf spot advisory system is a management tool; it does not predict the effects of a control decision on subsequent disease I/Latent severity. Period A model to predict disease progress of Cercospora leaf spot , -• io would be a valuable research tool because it would provide a _ IC framework within which to evaluate effects of weather, control + Leaflets strategies, and host resistance on disease development. In this Visib l report, we describe a computer simulation model that predicts disease progression of Cercospora leaf spot over the course of a Disease 4/Infectious growing season. The model was validated in field trials in North PostPeriod Carolina and Virginia. infectious Leaf lets MATERIALS AND METHODS Model description. The computer model simulates disease Fig. 1. State-Rate diagram for a computer simulation model of Cercospora leaf spot of peanut cultivar Florigiant. Major state variables are shown in progress over the course of a growing season, with time steps of 1 rectangular boxes; other boxes represent rate variables. Flows of material This article is in the public domain and not copyrightable. It may be freely (e.g., transfer of lesions from latent to infectious state) are indicated with reprinted with customary crediting of the source. The American solid arrows. Flows of influence or information (e.g., the effect of weather Phytopathological Society, 1987. on infection rate) are indicated with dashed arrows.

Studies of fungicide resistance in Pyrenopeziza brassicae, cause of light leaf spot disease of oilseed rape and other brassicas

Abstract: Resistance in the light leaf spot fungus, Pyrenopeziza brassicae, to benzimidazole or dicarboximide fungicides was not detected in field isolates. Resistant mutants were, however, obtained in vitro. Benzimidazole-resistant strains were generated by mutagenesis with ultraviolet light, and dicarboximide-resistant sectors developed when the fungus was grown on media containing iprodione or vinclozolin, without prior exposure to a mutagen. The mutant isolates remained resistant after several months of subculture in the absence of fungicides. The rate of growth in culture of isolates resistant to benzimidazoles was between 10 and 20% less than that of sensitive isolates, whereas isolates resistant to the dicarboximides grew and sporulated just as well as sensitive isolates. Genetic studies showed that the resistance to benzimidazoles was probably conferred by a single gene mutation, and that the same may also have been true of resistance to dicarboximides.

Inheritance of Resistance To Brown Blotch, Septoria Leaf Spot and Scab in Cowpea (Vigna Unguiculata (L.)Walp.)

Abstract: Inheritance of resistance of brown blotch, scab, and Septoria leaf spot was studied in crosses of cowpeas involving resistant and susceptible parents. The observations on F1, f2 and backcross populations of different crosses indicated that resistance to brown blotch is controlled by a single recessive gene pair, resistance to Septoria is controlled by duplicate dominant genes and the resistance to scab is controlled by a single recessive gene pair. Accordingly, the gene symbols rcc for resistance to Colletotrichum capsici (brown blotch); Rsv 1 and Rsv 2 for resistance to Septoria vignae (Septoria leaf spot) and rss for resistance to Sphaceloma sp. (Scab).are being assigned.

Two new species of Phomopsis from India

Abstract: Phomopsis micheliae sp.nov. and P. gmelinae sp.nov. are described from Kerala, India. P. micheliae causes a leaf spot disease of Michelia champaca and P. gmelinae a stem canker of Gmelina arborea.

Epidemiological studies on cercospora leaf spot of sugar beet

Abstract: In the glasshouse, inoculation of sugar beet with Cercospora beticola followed by 16 h of high humidity produced visible disease only with at least four conidia per cm2 of leaf area. Disease became more severe after increasing periods of high humidity in the range of 0–24 h. In the field, spraying plants with water enhanced disease spread from a focus. Disease progress curves were sigmoid. Apparent infection rate declined towards the end of the season, possibly because of high temperature. In approximate agreement with prediction, epidemic development was delayed when initial inoculum was reduced. Reduced infection, resulting from either reduced initial inoculum or delayed inoculation, decreased the adverse effect of disease on sugar yield.

Temperature-induced suppression of alternaria leaf spot of cotton in Arizona

Abstract: Couy. r. J. 19117, ,'cmpc...tur-e-lnductd suppfcs.sioll of Al'(turia leilfspot ofcotton in Ari~on •. Plant Di$tase 71:IIJI·II40. lainn (ormation by AlurnQritl rnauosportl. the a1u$lI1 agenl of Allernan. leaf 6pot of colton (GoIIJ'pium /)Q,bluhnvJ. is innuenced by fhe tcmpcnlurc at ..-hich pia nu are held .ftcr inf«lioD. Fen)' 10 100% rwucliolU in lesion number otnlrrw on c:otlon planls inccubaled a, CIC\\'altG lcmperalurcsc:omparcd ..·;th plants m;ainl;a;Md :lr30C.lC'Sion formalion was reduced more.lbtl 7(1% .rtel upon\",: 10 4J.j C (01 2 hr. RcsullS indicate IMI daily tcmpcr.llture mu.im.a may be imponanl in limiti\". Alterun.a leaf SPOI in Arizonl and may plruallytxplain increased disease 5e\\'Crir)' in cenl 1\"11 Arizona daring counn seloSOr15 in whkh daily temptr.u I,Irt ma:o.ima .. ~ ~lIti\\,tly low. The innuc\",\"o(h'lh rernpe:ralurtOn lhe p:nho8tn in \\'ilrowaJ 1olsoRuditd. Germ tubes orA. mtJuOlportJ Upl05i~ly l)'S(\"d on potalo-duuose I,ar (I'OA) IMuNled al 42-46 C. \"fler 6 hral 42.43 5. Irwl4ll C. rt5p«li\\·dy. 7. S2. and 82% of tilt gtrm tubes lysed. Sport \\'iabililY on PO\" declined 6S% aftcr 4 hr al 46 C but r<:mainc:d sltble for 24 hr II 42 C. Results provide indir«t evidcnee thatlcrm lUbe lysis and reduced spore Vil~lil)' may be m«hanl!ims of tempcraturt-mediated reduclion in Ic!iion number. lIoll'cver. lither temperature.induced .lterations in Ihe host-pathogen inleraction may be equally important Table I. frtquency of vllriousdilily lcmptfllturt ma.Jlima al Ca$a Grande Nationill Monument.

Cytological Observations of Leaf Spot-Causing Bacteria in Susceptible and Resistant Hosts

Abstract: The studies were carried out in order to obtain more insight into the mechanisms involved in the resistant reaction.

Stigmina zilleri sp.nov., associated with brown leaf spot of broadleaf maple

Abstract: Stigmina zilleri sp.nov. is described from a brown zonate leaf spot of broadleaf maple (Acer macrophyllum Pursh) in southwestern British Columbia, Canada.

Assessment of Resistance to Leaf Spot Diseases Among Alfalfa Cultivars in North Carolina Fields

Abstract: Thal, W. M., and Campbell, C. L. 1987. Assessment of resistance to leaf spot diseases among alfalfa cultivars in North Carolina fields. Phytopathology

Somaclonal variation in hybrid poplars for resistance to Septoria leaf spot

Abstract: Tissue culture techniques have been used to obtain hybrid poplars with putative resistance to leaf spot caused by Septoria musiva from clones previously susceptible to the disease Stem internode explants were used to obtain proliferating callus cultures Adventitious bud formation and shoot proliferation were then induced Elongated shoots were excised and rooted in a peat : perlite medium under high humidity After acclimation, rooted plants were transferred to the greenhouse Variant plants were selected among the regenerants using a leaf disc bioassay that rapidly distinguishes plants with high resistance The incidence of somaclonal variation in disease resistance differed among the genotypes tested Over 500 tissue culture-derived plants tested for resistance using the bioassay have been planted in the field and are being evaluated for field performance Somaclonal variation and tissue culture have the potential to significantly change tree breeding programs by reducing the time required for selecting and improving desired traits

Foliar disease of sorghum species caused by Cercospora fusimaculans

Abstract: A Cercospora species with catenulate conidia was isolated on V-8-CaCO3 from foliar lesions on Sorghum bicolor and S. halepense, and the original scalariform lesions were reproduced on sorghum cultivar TX7078. Samples of this foliar disease were mailed from Rwanda and from Comayagua, Honduras, to the Commonwealth Mycological Institute, Kew, U.K., for pathogen identification. The pathogen was identified as Cercospora fusimaculans. Field inoculations were performed in Choluteca, Honduras. This disease, which we hereby name ladder leaf spot, is distinguishable from gray leaf spot of sorghum caused by C. sorghi by its scalariform or ladderlike elliptical lesions. Sources of resistance to ladder leaf spot and gray leaf spot are apparently independent of each other. Ladder leaf spot has been observed on sorghum in Experiment, GA, at various locations in Texas, in Tampico, Mexico, throughout Honduras, and in El Salvador, Cuba, Colombia, Venezuela, Brazil, Rwanda, Malawi, and Zambia