Showing papers on "Leaf spot published in 1978"

Taxonomy and biology of Pyrenopeziza brassicae sp.nov. (Cylindrosporium concentricum), a pathogen of winter oilseed rape (Brassica napus ssp. oleifera)

Abstract: Pyrenopeziza brassicae Sutton & Rawlinson sp.nov., the teleomorphosis (perfect state) of Cylindrosporium concentricum Grev., is formally described from apothecia developed in culture. The taxonomic affinities of this fungus, the cause of light leaf spot or leaf scorch of Brassicae, are discussed. Its infection, symptomatology and novel occurrence on winter oilseed rape ( Brassica napus L. ssp. oleifera ) are described, including reference to possible seed-borne transmission. Factors influencing infection, disease incidence, spore dispersal and cultivar susceptibility are discussed in relation to disease control.

Apical chlorosis and leaf spot of Tagetes spp. caused by Pseudomonas tagetis Hellmers

Abstract: An undescribed apical chlorosis caused severe losses in seedlings of Tagetes erecta and T. patula types in Sydney, Brisbane and Melbourne in 1976. Bacterial leaf spots without chlorotic haloes invariably accompanied the disease. The same bacterium was isolated from leaf lesions and chlorotic tissue and produced leaf spots and chlorosis on marigold, zinnia and sunflower with spray inoculation. Leaf spots did not develop on T. signata. Apical chlorosis developed on a diverse range of plants following wound inoculation. The pathogen was shown to be seed-borne. The pathogen was identified as Pseudomonas tagetis, cultural and biochemical characteristics described, and a neotype culture proposed. An exotoxin was produced in vitro which caused apical chlorosis in Zinnia elegans and T. patula.

Pseudocercosporella capsellae, the cause of white leaf spot and grey stem of Cruciferae in Western Canada'

Abstract: White leaf spot and grey stem, a common disease of turnip rape (Brassica campestris) and rape (B. napus) and several cruciferous weeds in Western Canada is described. The causal fungus is Pseudocercosporella capsellae. Formerly the stem symptoms on Brassica spp. were attributed to Mycosphaerella brassicicola, the cause of ring spot of B. oleracea, but a connection of this fungus with white leaf spot remains in doubt. Production of the phytotoxic red pigment "cercosporin" by P. capsellae is reported for the first time. Formation of thick-walled hyphae in stem tissue, often in the form of mycelial mats, is thought to represent an important adaptation permitting survival of the pathogen under adverse conditions.

Leaf spot of field corn caused by Pseudomonas andropogonis.

Abstract: A leaf spot of field corn was shown to be caused by the bacterium Pseudomonas andropogonis. Leaf spot symptoms were observed over 3 years in several States. Inoculation of corn by vacuum infiltration of the bacteria was necessary to reproduce field symptoms. Plant Dis. Reptr. 62: 213-216. A bacterial leaf spot disease of different cultivars of field corn was observed in early summer of 1973, 1974, and 1975. Leaves with essentially the same symptoms were obtained from South Dakota, Iowa, Kansas, Nebraska, and Michigan. The same symptoms were also seen in Wisconsin. Symptoms consisted of circular to ellipsoidal, tan to brown spots, with irregular margins. The spots were 1 to 4 mm in diameter, with one or more darker brown rings within the lesions. Some spots were surrounded by a chlorotic ring 1 mm wide. All spots tended to have a slightly sunken appearance. Occasionally the spots coalesced into irregular, somewhat elongated blotches. Water-soaking of young lesions was also seen. Bacteria were routinely isolated from the lesions. Because the symptoms did not correspond with previous reports of bacterial diseases of corn, experiments were undertaken to determine the causal bacterium and compare it with known bacterial pathogens of corn. The pathogen was subsequently identified as Pseudomonas andropogonis, previously reported to cause bacterial stripe disease of sorghum, sudangrass, teosinte, johnsongrass, field corn, broomcorn, and sweet corn (3,7,8,11). As P. stizolobii (syn. P. andropogonis), the bacterium causes leaf spot diseases of Bougainvillea, clover, and other leguminous plants (1, 3, 4). MA TERIALS AND METHODS Isolations: Bacteria were isolated from lesions by the direct puncture technique (2) onto NBY agar (9). After 3 to 5 days at 24 to 28° C, transfers from single colonies were made twice more to obtain purified clones. Eight strains were obtained in different years from various locations in the Midwest. Cultures were maintained on NBY agar, including reference strains of K. andropogonis NCPPB 933, NCPPB 934, K. stizolobii NCPPB 1024, and NCPPB 1127. Cultures were stored at 2 to 5° C and also lyophilized to serve as reference throughout this study. Bacteriological observations: Tests for oxidase, arginine dihydrolase, levan production, and fluorescence were carried out by the procedures of Lelliott, et al. (6). Sudanophilic granules were examined by the method of Hugh and Gilardi (5). Flagella of all ten P. andropogonis and two P. stizolobii strains were examined by electron microscopy after negative staining of bacteria with a 3 : 1 mixture of potassium phosphotungstate and vanadatomolybdate (10). The bacteria were treated previously with 40/0 glutaraldehyde for 10 min. Sodiumdodecyl sulfate slab gel electrophoretic patterns of total proteins were obtained for six strains, including all four reference strains; details of this procedure will be reported elsewhere. Pathogenicity tests: Inoculum for pathogeniCity tests was prepared by suspending bacteria from 2to 3-day-old plate cultures into sterile distilled water. For vacuum infiltration the suspensions were made up in 0.1\"/0 Triton X-100 (Rohm & Haas Co.). The A420 nrn was adjusted to 0.3 (approximately 4 x 108 CFU/ml) and dilutions were made as necessary. Sweet corn ('Golden Cross Bantam'), field corn (A619 x A632), and sorghum (RS626) were inoculated initially by needle puncture into the stems. White sweetc10ver (Melilotus alba) was inoculated by aerosol spray under pressure into the stomates. Corn and sorghum plants were 6 to 8 inches high (3 to 4 leaf stage) and clover plants were about 6 weeks old (4 to 6 leaf stage). 214 Vol. 62. No. 3--PLANT DISEASE REPORTER--March 1978

Postemergent Herbicides and the Biology of Drechslera sorokiniana: Influence on Severity of Leaf Spot on Poa pratensis

Abstract: HODGES, C. F., 1978. Postemergent herbicides and the biology of Drechslera sorokiniana: Influence on severity of leaf spot on Poa pratensis. Phytopathology 68: 1359-1363. The influence of four chlorophenoxy (2,4-D, 2,4,5-T, the 10-12 M concentration, but at higher concentrations, 2,42,4,5-TP, MCPP) and one benzoic acid (dicamba) D had no effect, and 2,4,5-TP remained inhibitory to disease postemergent herbicides were evaluated for their influence on development. All plants grown in soil treated with various the development of leaf spot caused by Drechslera concentrations of each herbicide and inoculated with conidia sorokiniana on Poa pratensis. Leaf spot development was in droplets of distilled water showed an increase in disease, severely inhibited on plants not previously exposed to any of except for 2,4,5-TP at concentrations of 10-6 and l0-4 M, the herbicides and leaf-inoculated with conidia in droplets of which continued to inhibit disease development. Four lesion each herbicide solution prepared at a concentration of 10-3 M types produced by D. sorokiniana were observed on the (2,4,5-TP at l0-4 M). Leaf spot development was uneffected herbicide-treated plants. These ranged from small purpleor inhibited on plants not previously exposed to the various brown necrotic areas with or without halos to enlarged herbicides and leaf-inoculated with conidia in droplets of 2,4necrotic areas with or without severe chlorotic to strawD, 2,4,5-T, and 2,4,5-TP solutions at concentrations of 10-2, colored streaking of the uninfected tissue of the leaf. The l0-9, and 10-6 M. In contrast, MCPP and dicamba at results suggest that herbicide-increased disease is, for the concentrations of 10-12, l0-9, and 10-6 M in droplets most part, independent of any stimulatory effect of the containing conidia and applied to leaves of plants not herbicides on in vitro growth of D. sorokiniana. Instead, previously exposed to the herbicides, resulted in increased herbicide-induced increases in disease may involve leaf spot severity. There was a substantial increase in leaf spot imbalances in the carbohydrate-nitrogen metabolism of P. severity on the foliage of plants spray-treated with 2,4,5-T, pratensis, and the severe chlorotic to straw-colored streaking MCPP, and dicamba, at all concentrations and then of infected leaves is suggestive of ethylene evolution in inoculated with conidia in droplets of distilled water; plants diseased tissue and (or) toxin production. sprayed with 2,4-D and 2,4,5-TP showed increased disease at Additional key words: Bipolaris, Helminthosporium, mecoprop, silvex. Drechslera sorokiniana (Sacc.) Subram. and Jain growth (6, 8, 16, 34, 41). Stimulation and inhibition of D. (Helminthosporium sativum) causes leaf spot, leaf blight, sorokiniana mycelium growth by 2,4-D also has been and root rot of grasses and cereals in the north-central reported and is formulation and concentration dependent United States (40). The diseases caused by this pathogen (20, 22). The herbicides 2,4-D, 2,4,5-TP, 2,4,5-T, MCPP, are chronic on Poapratensis L. (4, 5, 21,42) throughout and dicamba have been shown to influence germ-tube the growing season and various cultural practices have growth from conidia, mycelium growth, and production been implicated in contributing to disease development of conidia of D. sorokiniana (20). None of these (9, 17, 21, 37). The potential influence of postemergent herbicides influence conidium germination, except at l0-4 herbicides on diseases incited by D. sorokiniana, and (or) l0-3 M concentrations at which they are however, has received little attention. The use of inhibitory. Most concentrations of 2,4,5-T, 2,4,5-TP, postemergent herbicides on P. pratensis grown in MCPP, and dicamba stimulate conidia germ-tube growth monocultures is intense and includes the synthetic auxinand mycelium growth (20). MCPP and 2,4,5-T generally like herbicides 2,4-D, 2,4,5-TP, dicamba, and MCPP; inhibit sporulation of D. sorokiniana, and 2,4-D, 2,4,52,4,5-T also was used at one time. TP, and dicamba are inhibitory or stimulatory to Several reviews have established that herbicides can sporulation depending on concentration (20). stimulate or inhibit diseases incited by fungal pathogens Research on the influence of postemergent herbicides (3, 23, 24, 25). Most studies on Drechslera sp. have on Drechslera-incited diseases is limited to cereals. shown 2,4-D to have no effect on, or to inhibit, mycelium Predisposition of wheat to infection by D. sorokiniana (H. sativum) (22) and of corn to D. heterostrophus (H. 00032-949X/78/000 246$03.00/0 maydis) (32) occurs in response to 2,4-D; conversely, 2,4Copyright © 1978 The American Phytopathological Society, 3340 D reduces root rot of barley incited by D. sorokiniana (H. Pilot Knob Road, St. Paul, MN 55121. All rights reserved. sativum) (34). The research presented here was initiated

Fungicides for horticultural use

Abstract: PURPOSE:Fungicidal composition containing a specific compound as the active ingredient and having combatting effect against a broad spectrum of plant diseasis such as blast and Helminthosporium leaf spot on rice and late blight on tomatoes.

Gnomonia canker, shoot blight, and leaf spot of yellow birch.

Abstract: Describes a canker, shoot blight, and leaf spot disease of yellow birch seedlings in the northern Great Lakes region and tells how and when trees become infected by the fungal causal agent, Gnomonia setacea.

Seed-borne fungal pathogens and diseases of Japanese radish and their control in South Africa

Abstract: Severe yield losses caused by a leaf spot disease in a field of Japanese radish in the Transvaal Highveld during 1974, initiated a survey of the diseases of Japanese radish in South Africa. Those recorded were Alternaria leaf spot and wirestem (Alternaria raphani), anthracnose (Co//etotrichum higginsianum), black rot (Xanthomonas campestris), soft rot (unknown cause) and white blister (Albugo candida). A survey was also made of fungal pathogens on locally produced seeds. The most common seed-borne pathogen found, was Alternaria raphani. Other pathogens recorded were A. brassicae, A. brassicicola, A. cheiranthi, Phoma !ingam, Rhizoctonia sp. and Sclerotinia sp. Certain samples were heavily infected. Sixteen different seed treatments were evaluated for the control of pathogenic Alternaria spp. and Phoma !ingam. The pathogenic Alternaria spp. as well as Phoma !ingam were effectively eliminated from seed by the following seed treatments: soaking in hot water at 50i?½C for 25 min, and soaking in 0,5% of captab and thiram suspensions at 30i?½C for 24 h respectively.

General and Horizontal Resistance Against Leafe Spot Diseases in some Sorghum Hybrids and Varieties

Abstract: The disease garden technique of identifying and of evaluating varietiesfor their resistance was modified. Test varieties were exposed to the pathogens of potential diseases under natural field conditions prevailing during the crop season alongwith standard indicators for comparison. The disease intensity was recorded using a standard 0–5 disease index scale. The varieties with mean disease index–1 and 2 with respect to that of 4 and 5 of the standard indicators were considered to possess high and moderate resistance against the leaf spot disease in question.

Economic Control of Cercospora Leaf Spot and Rust in Rainfed Peanut Production

Abstract: An investigation was made of the relative importance of leaf spot (C. arachidicola and C. personata) and rust (Puccinia arachidis) in limiting groundnut yields under rainfed conditions in N. Thailand, together with aspects of the control of both diseases. Rust was first observed in N. Thailand in 1972. When left uncontrolled, it reduced yields as much as Cercospora leaf spot. When both diseases were controlled yield increases of 76% were obtained. When sprays were applied for the control of 1 disease and not the other, the yield increase was only 65% of that obtained by controlling both diseases. A combination of the fungicides Benlate (benomyl 50% WP) and Manzate D [mancozeb] gave the best control of both diseases. Benlate alone controlled leaf spot but not rust, while Manzate D controlled rust and not leaf spot. Daconil [chlorothalonil] and zineb gave only partial control of both diseases. For groundnuts sown at the beginning of the wet season, commencement of spraying could be left until 6 or 7 wk after sowing. Spraying at 10-day intervals gave 8.3% higher yield than did spraying at 15-day intervals. Whereas yields continued to increase with each additional application at 10-day intervals from 60 to 90 days after sowing, the results suggested that spraying beyond 80 days might not be economic, since a yield increase of 37 kg/ha would be required to cover the cost of each application (1977 prices). It may be recommended that 4 applications of Benlate + Manzate D be made at 10-day intervals between days 50 and 80 after sowing for the effective protection to commercial crops in N. Thailand.ADDITIONAL ABSTRACT:When both leaf spot (C. arachidicola and C. personata) [Mycosphaerella arachidis and M. berkeleyi] and Puccinia arachidis were controlled, yield increase of 76% were obtained in N. Thailand. A combination of Benlate (benomyl) and Manzate D (zinc + maneb) was best against both diseases, Benlate controlling only leaf spot and Manzate D only rust. Four applications are recommended at 10-day intervals, between days 50 and 80

Methods of screening rices for varietal resistance to Cercospora leaf spot

Abstract: Autoclaved rice stem nodes with prune juice provide a favorable medium for the isolation of Cercospora oryzae, the fungus causing Cercospora leaf spot or narrow brown leaf spot, and for the mass production of spores spraying of spores in late afternoon resulted in good infection on plants in the field. As shown by artificial inoculation, rice at different stages of growth is susceptible to C. oryzae. An incubation period of 20 days is necessary before the first few lesions appear and 30 days before the maximum number of lesions is reached. The slow growth of the fungus causes the late appearance of the disease, generally observed in the field. A method of artificial inoculation for screening varieties for resistance and a disease scale of 0 to 9 units, based upon the number of lesions, are suggested

Drug-resistance of Cucumber Angular Leaf Spot Bacterium, Pseudomonas lachrymans (Smith et Bryan) Carens

Abstract: Angular leaf spot of cucumber, caused by Pseudomonas lachrymans has become epidemic since many years ago, in every part of Japan. To facilitate chemical control of the disease, we have investigated the resistance of the causal bacterium to several antibiotics and HgCl2. In this paper, results of experiments on minimal inhibitory concentration (MIC) of 13 antibiotics and Hg2+ against 165 isolates of Pseudomonas lachrymans were described. These isolates were collected from various districts of Japan, and the distribution pattern of drug-resistant bacteria was investigated. Pseudomonas lachryymans isolates: During the period from 1973 to 1977, 165 isolates of Pseudomonas lachrymans were obtained from various districts of Japan. Among them, 110 isolates were generously provided by Dr. A. Ohuchi, National Institute of Agricultural Sciences. Drugs: Following 13 antibiotics which had been commonly used for agricultural and medical purposes, and HgCl2 were tested. Dihydrostreptomycin (DHSM) Kasugamycin (KSM) Kanamycin (KM) Oleandomycin (OL) Chloramphenicol (CP) Spectinomycin (SPC) Gentamicin (GM) Aminobenzylpenicillin (ABPC) Carbenicillin (CBPC) Oxytetracycline (OTC) Novobiocin (NB) Rifampicin (RFP) Nalidixic acid (NA) HgCl2 (Hg2+) Each drug except CP, RFP and NA, was dissolved in sterilized distilled water at the concentration of 8,000ƒÊg/ml, only DHSM was at 128,000ƒÊg/ml. CP and RFP were first dissolved in small amounts of propylene glycol and dimethyl sulfoxide respectively, and diluted by sterilized distilled water at the concentration of 8,000ƒÊg/ml. NA was dissolved in 0.1N NaOH (1/5 volume), then 4/5 volume sterilized distilled water was added to make the final concentration of 8,000ƒÊg/ml. Medium: Peptone broth agar (PBA) of the following formula was used. For the multiplication of test bacteria, peptone broth (PB: only agar was excluded from