Showing papers on "Leaf spot published in 1993"

Quantitative trait loci controlling resistance to gray leaf spot in maize.

Abstract: Gray leaf spot (GLS) (caused by Cercospora zeae-maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type-of-gene action for GLS resistance in segregating families of three single-cross populations of maize using restriction fragment length polymorphisms (RFLPs) (.)

Effect of levels of corn residue on the epidemiology of gray leaf spot of corn in Ohio.

Abstract: The effect of soil-surface residue level (0, 10, 15, and 85% soil coverage) on the progress of gray leaf spot of corn, caused by Cercospora zeae-maydis, over time was studied in Ohio during two environmentally different growing seasons. Area under the disease progress curve (AUDPC) was calculated and analyzed with analysis of variance followed by orthogonal polynomials (.)

Olive scab: a review1

Abstract: Olive scab or leaf spot, caused by the fungus Spilocaea oleagina, is widespread in the Mediterranean region. Losses arise mostly from defoliation of severely infected trees, with consequently reduced yield. Symptoms are mainly confined to leaves and appear as dark brown, circular, zonate spots surrounded by yellow haloes (‘peacocks eye’). S. oleagina shows a typical subcuticular growth, forming flat colonies within the cutinized layer of the thick epidermal cell wall. This habit has been associated with a defence reaction of the host involving mobilization and breakdown of the phenolic glucoside oleuropin and inhibition of pectolytic enzymes produced by the pathogen. The disease is particularly severe in densely planted groves of susceptible olive cultivars and in nurseries. Infections may occur throughout the year, except during hot and dry summers, when favourable temperatures (opt. 16–21°C) and rains occur. Conidia, formed at the apex of short ampulliform conidiophores, are usually carried by rain droplets, but recent data show that humid air currents and insects also contribute to limited aerial dissemination. Usually, the incubation period is about 2 weeks; however, if infection is followed by a hot season, it may last several weeks. Spots already formed in spring may stop growing in summer and resume their growth and sporulation in autumn. Chemical control schedules include fungicide (especially copper) treatments during the main infection seasons (spring and autumn).

Gray leaf spot disease of maize: rating methodology and inbred line evaluation.

Abstract: Development of gray leaf spot (GLS) of maize (Zea mays), caused by Cercospora zeae-maydis, was evaluated in seven inbreds in 1990 and 19 inbreds in 1991 in field plots with naturally infested corn debris. In 1990, nine ratings over 35 days were made beginning 9 August. In 1991, 10 ratings over 43 days were made beginning 17 July. Individual plants were assessed by two methods: 1) a disease index (DI) score was assigned on a 1-5 scale (1=no lesions, 5=all leaves dead); and 2) disease severity (DS) was expressed as diseased leaf area divided by the total area multiplied by 100, assessed on the ear -1 leaf and all leaves above it. The mean of ratings over time and the area under the disease progress curve (AUDPC) rankings for seven inbreds were similar both years (.)

Prevalence of sorghum diseases in Nigeria

Abstract: A survey was conducted in farmers’ fields in Nigeria during the 1990 cropping season to determine the prevalence of sorghum diseases in the four major sorghum‐growing climatic zones (Sahel, Sudan, northern Guinea, and southern Guinea). The foliar diseases anthracnose (Colletotrichum graminicola) oval leaf spot (Ramulispora sorghicola) sooty stripe (Ramulispora sorghi) and grey leaf spot (Cercospora sorghi) were widely distributed. Anthracnose was predominant throughout the areas surveyed with ≥40% leaf area covered or destroyed by lesions in 70% of the surveyed fields. The incidence of other foliar diseases was low. Among the panicle diseases, long smut (Tolyposporium ehrenbergii) incidence was ≤10% in ≥20% farmers’ fields in the sahelian zone. Head (Sporisorium reilianum) covered (Sporisorium sorghi) and loose (Sphacelotheca cruenta) smuts were common, but their incidence varied from 1 to 10% in the Sahel, Sudan, northern Guinea and southern Guinea zones. Survey results based on ELISA indicated ...

Enterobacter pyrinus sp. nov., an Organism Associated with Brown Leaf Spot Disease of Pear Trees

Abstract: A new species, Enterobacter pyrinus, which was isolated from brown leaf spot lesions on pear trees, is described on the basis of the characteristics of seven strains. These bacteria are gram-negative, facultatively anaerobic, straight rods (0.6 to 1.0 by 1.6 to 2.3 μm) that are motile and peritrichous. As determined by DNA hybridization (hydroxyapatite method), these seven strains were 97.5% related in both 60 and 75°C reactions, with no evidence of sequence divergence, indicating that they are members of a single species. E. pyrinus is most closely related to Enterobacter gergoviae (46%) and to Enterobacter agglomerans hybridization group XI (37%). E. pyrinus is differentiated from E. gergoviae by its growth in KCN broth, acid production from myo-inositol, and lack of acid production from raffinose. The type strain of E. pyrinus is strain KCTC 2520 (= CDC G6570 = ATCC 49851).

Evaluation of Streptomyces for biocontrol of Bipolaris sorokiniana and Sclerotinia homoeocarpa on the phylloplane of Poa pratensis

Abstract: Several species of Streptomyces were evaluated for their ability to control Sclerotinia homoeocarpa (dollar spot) and Bipolaris sorokiniana (leaf spot) on the phylloplane of Poa pratensis (Kentucky bluegrass). Species evaluated included S. diastaticus (S32), S. galbus (S35), and S. hygroscopicus (isolates S13, S28). All evaluations were conducted on the upper epidermis of intact attached leaves of P. pratensis, and antagonism was measured as the ability of Streptomyces isolates to prevent chlorophyll loss from leaves inoculated with B. sorokiniana or S. homoeocarpa during pathogenesis. Only S. hygroscopicus (S13) effectively prevented infection and subsequent chlorophyll loss from leaves inoculated with B. sorokiniana or S. homoeocarpa. Isolate S28 of S. hygroscopicus showed erratic antagonism of both pathogens, depending upon how the isolate was prepared for use. Streptomyces diastaticus and S. galbus were antagonistic to S. homoeocarpa only in whole culture form.

Disease progress, defoliation, and spatial pattern in a multiple-pathogen disease complex on white clover

Abstract: Disease progress, host growth and defoliation, and spatial patterns for a multiple pathogen, leaf spot disease complex on white clover (Trifolium repens) were monitored in four 6-wk growth periods during 1990-1991 in a natural, 10-ha pasture of white clover and tall fescue (Festura arundinacea) in North Carolina. The disease complex comprised summer blight (Rhizoctonia solani), black spot (Pseudomonas andropogonis), Stagonospora leaf spot (Stagonospora meliloti), Cercospora leaf spot (Cercospora zebrina), Curvularia leaf spot (Curvularia trifolii), anthracnose (Colletotrichum trifolii), sooty blotch (Polythrincium trifolii), and rust (Uromyces sp.) []

Phaeoramularia fruit and leaf spot of citrus with special reference to Kenya.

Abstract: Fruit and leaf spot of citrus caused by Phaeoramularia angolensis was first observed in Angola and Mozambique in 1952. The disease has now spread to 15 countries, south of Sahara, and recently to Yemen, in the Arabian Peninsula. All citrus species are affected with grapefruit, with orange being the most susceptible. P. angolensis infects foliage, fruit and stems. Severe infection causes leaves to abscise, fruit to ripen prematurely and drop, and young shoots to die back. Total loss of yield of marketable fruit is not uncommon in severely diseased orchards. In most of the countries where the disease is prevalent control is effected by extensive use of fungicides. Because of strong traditional trade links and the wind‐borne nature of the fungal spores the fungus is a potential threat to citrus production in the Middle East, Indian subcontinent and the Far East (which is the centre of diversity of citrus). This paper discusses the disease in Kenya against the background of work reported elsewhere. I...

Additional Genes for Resistance to Frogeye Leaf Spot Race 5 in Soybean

Abstract: Frogeye leaf spot (caused by Cercospora sojina Hara) is a common foliar disease of soybean (Glycine max L. Merr.) in the southeastern USA. Three major dominant genes (Rcs 1 , Rcs 2 , and Rcs 3 ) have been identified that confer resistance to frogeye leaf spot. Our objective was to determine the inheritance and possible allelism to Rcs 3 of genes for resistance in «Lee», «Stonewall», and «Ransom», Lee, Stonewall, and Ransom were all intercrossed, crossed with «Davis», which has Rcs 3 , and crossed with known susceptibles. F 2 plants of crosses were inoculated with a spore suspension of race 5 of C. sojina, placed in a moist chamber for 2 to 3 d, and identified as susceptible or resistant based on leaf symptoms 14 d after inoculation

The influence of disease complexes involving Leptosphaeria (Septoria) nodorum on detection of resistance to three leaf spot diseases in wheat

Abstract: In controlled inoculation studies with Septoria nodorum and Pyrenophora tritici-repentis, estimates of the relative proportion of each pathogen demonstrated differences in the responses of cultivars to pathogen mixtures that were not apparent from measurements of diseased leaf areas. Under field conditions estimates of the relative proportion of S. nodorum, P. tritici-repentis and S. tritici varied between field screening locations in Western Australian but also between lines within locations. Lines with known resistance to P. tritici-repentis and S. tritici, but susceptible to S. nodorum, could not be distinguished from susceptible lines on the basis of leaf area diseased or grain weight depression when S. nodorum was present in the disease complex. Such conditions, while suitable for the selection of combined resistance to these pathogens, were unsuitable for identifying resistance to individual pathogens. As symptoms were similar, the proportion of diseased leaf area sporulating with each pathogen provided a means of measuring the variation in disease development induced on lines varying in resistance. Knowledge of the components of disease and their relative importance were essential in understanding varietal response information under mixed infections of these leaf spot pathogens.

Field evaluation of mungbeans for resistance to Cercospora leaf spot and powdery mildew

Abstract: Cercospora leaf spot, caused by Cercospora canescens and powdery mildew, caused by Erysiphe polygoni are two of the most important fungal diseases of mungbeans. Nearly 4000 accessions of the global mungbean collection at the Asian Vegetable Research and Development Center were screened for resistance to these two pathogens. Less than 4% and 12% of the accessions showed resistance to Cercospora leaf spot and powdery mildew, respectively. The level of resistance to Cercospora leaf spot varied and highly resistant lines were not found. A few lines were rated highly resistant to powdery mildew over several years but others were rated moderately resistant or susceptible in other years.

Physiologic leaf spot of winter wheat

Abstract: A leaf spot of unknown etiology damages winter wheat in the northwestern United States. The symptoms are similar to Septoria leaf blotch and tan spot, but the causal agents of these diseases are not present. Leaf spot symptoms are described. Dominant microbial colonists of the spots were Cladosporium herbarum, C. macrocarpum, C. cladosporioides, and Alternaria species. Leaf spot symptoms could not be induced on fresh leaf tissues with any of the inoculation or incubation procedures examined (.)

Bacterial blight of kiwifruit in California

Abstract: Flower bud rot, blossom blight, and leaf spot of kiwifruit (Actinidia deliciosa) have been observed in numerous commercial orchards in California since 1986. As the diseased flower buds develop, petals become yellow-orange, then brown, and the entire bud falls from the vine. Fruit may be small, misshapen, or fail to set. The bacterial pathogens Pseudomonas syringae and P. viridiflava, in addition to the saprophyte P. fluorescens, consistently have been isolated from both symptomatic and asymptomatic vines throughout the spring. In pathogenicity tests, P. viridiflava caused significantly more flower bud rot and blossom blight, but not leaf spot, than P. syringae. P. fluorescens was not pathogenic

Sources of resistance to foliar diseases of groundnut and their stability in West Africa

Abstract: Three foliar pathogens, early (Cercospora arachidicola [Mycosphaerella arachidis]) and late (Cercosporidium personatum [M. berkeleyi]) leaf spots and rust (Puccinia arachidis) are a major constraint to groundnut production in West Africa, although their severities vary from location to location. A total of 424 germplasm lines was screened for resistance to these pathogens in Niger and Burkina Faso and resistant lines were identified. Some sources of resistance to early leaf spot reported in India showed variable reactions in West Africa. Differential reactions to early leaf spot at different locations indicated that there may be physiological races of the pathogen. Sources of resistance to late leaf spot and rust selected at the ICRISAT Centre (India) were also resistant in West Africa. Multiple disease resistance was evident in lines ICG 1707, ICG 6330 and USA 63.

Influence of crop management practices on physiologic leaf spot of winter wheat

Abstract: The response of physiologic leaf spot to winter wheat management practices was examined in the semiarid Pacific Northwest. Winter wheat cultivars exhibited large differences in susceptibility. The dominant cultivar (Stephens) produced in the region was the most susceptible cultivar evaluated. The disease became less severe as the date of seeding was delayed and as the rate of nitrogen fertilization increased. Leaf spot severity was reduced and grain yield increased with foliar application of urea+calcium chloride, but not with application of urea+micronutrients. The disease was more severe in annual wheat than in rotations of wheat with fallow or peas

Occurrence of antimicrobial activities of bacteria from soybean leaf spots.

Abstract: Bacteria were isolated from leaf spots of field grown soybeans during two growing seasons. The leaf spots yielded up to 4 different species and a total population size of about 107–108 bacteria/cm2. The majority of the 192 isolates belonged to the species Pseudomonas syringae pv. glycinea (55%), causing leaf spots of bacterial blight on soybeans, and Erwinia herbicola (22%). The remaining isolates included bacteria from other genera, but occurred occasionally. The determination of biological activity of the isolates demonstrated that a high percentage of strains from the group Erwinia/Enterobacter produced biological active substances against Escherichia coli (69%) and against Chlorella pyrenoidosa (88%). The majority of P. syringae pv. glycinea strains failed to do so. None of the isolates affected the growth of Geotrichum candidum. The E. herbicola strains showed clear antagonistic properties against a wide range of isolated bacteria. Four E. herbicola strains inhibited the growth of nearly all other E. herbicola isolates and 6 other strains were active against most of the P. syringae pv. glycinea isolates. However, antagonistic interactions among strains isolated from a distinct leaf spot were very rarely.

Integrated management of foliar diseases of groundnut (Arachis hypogaea L.) in India.

Abstract: Field experiments for the integrated management of early leaf spot (ELS) and late leaf spot (LLS) diseases of groundnut were conducted during 1988 to 1990 rainy seasons. All treatments had significantly lower disease severity of ELS and LLS than unsprayed sole crop. Corresponding to the significantly lower severity of both the diseases in various treatments, monetary returns were also significantly higher than that of unsprayed sole crop. The severity of both diseases was significantly different among treatments, between varieties, and due to their interactions. Almost the same trend was followed for monetary returns. The treatments, application of a mixture of fungicides (carben‐dazim 0.05% + mancozeb 0.2%) at 40, 55 and 70 d.a.s., groundnut intercropped with pigeonpea + two sprays of fungicides at 55 and 70 d.a.s., and groundnut intercropped with pigeonpea + one spray each of neem leaf extract, fungicides and cell‐free culture filtrate of Penicillium islandicum at 40, 55 and 70 d.a.s., respecti...

Evaluation of plant extracts for the control of fungal diseases of mulberry

Abstract: Antifungal activity of leaf extracts of Azadirachta indica, Calotropis gigantea, Catharanthus roseus, Eucalyptus sp., Parthenium hysterophorus and Pongamia pinnata was tested against Cerotelium fici and Cercospora moricola causing leaf rust and leaf spot diseases in mulberry, respectively. A. indica was more effective inhibiting spore germination of C. fici by 91.2 per cent, whereas extracts of Eucalyptus sp. and C. gigantea proved highly toxic to C. moricola inhibiting conidial germination by 91.5 and 91.3 per cent, respectively. Under field conditions also, leaf extracts of Eucalyptus sp. and C. gigantea showed promising results reducing leaf spot disease incidence by 63.6 and 56 per cent, respectively. Extract of P. pinnata showed poor fungitoxicity against both the fungi tested.

Comparison of Greenhouse Methods for Assessing Resistance to Bacterial Leaf Spot in Plum

Abstract: Four greenhouse leaf inoculation methods for screening Japanese plum (Prunus salicina L. and hybrids) for resistance to Xanthomonas campestris pv. pruni (Smith) Dye were compared for repeatability, ability to differentiate among plant genotype responses, and correlations with field ratings. Clonally propagated trees were inoculated artificially in a greenhouse by immersing leaves in 2.5 × 108 cfu/ml inoculum (DIP), rubbing the adaxial side of leaves with a slurry of 2.5 × 108 cfu/ml inoculum and Carborundum powder (CARB), infiltrating leaves with 5 × 10 5 cfu/ml inoculum using a needle- less syringe (INFS), and infiltrating with 5 × 10 6 cfu/ml inoculum (INF6). No greenhouse method was superior in all assessment categories. The CARB method was most repeatable (t = 0.78) but had a low Spearman's correlation (rS = 0.29), indicating that greenhouse rankings did not correspond closely with field rankings. The INF6 method was unsuitable because it did not differentiate between plant genotypes. The DIP method appeared most suitable, having moderate repeatability (t = 0.46) for four observations per leaf and moderate Spearman's correlation with field performance (rS = 0.56). The INF5 method may be appropriate for identifying bacterial spot resistance that is associated with resistance in the leaf mesophyll. Field evaluation of fruit tree breeding germplasm is expensive due to large plant size and prolonged juvenility (Hansche, 1983). Therefore, selection methods that allow roguing of undesirable genotypes before field planting are beneficial. Resistance to bac- terial diseases can be assessed in this manner, and many methods have been used on various crops. Greenhouse systems for Prunus have included immersing leaves under vacuum (Daines and Hough, 195l), infiltrating with by high pressure sprays (Civerolo and Keil, 1976; Du Plessis, 1986), and infiltrating with needleless syringe (Du Plessis, 1988; Hammerschlag, 1988; Randhawa and Civerolo, 1985). The desirability of any one system of disease inoculation and assessment depends on its accuracy, precision, and correlation with field performance. Partitioning the total variance of random variables in experiments that compare plant genotypes allows determination of some of these factors (Campbell and Madden, 1990; Gomez and Gomez, 1984). The purpose of this study was to compare four greenhouse leaf inoculation and assessment systems for Xanthomonas campestris pv. pruni on Japanese-type plums for repeatability (precision), correlation with field ratings (accuracy), and ability to differentiate among genotypes.

Comparative Morphology and characterization of colletotrichumisolates occurring on Cocoa in Malaysia

Abstract: Isolation from cocoa leaves showing symptoms of shot-hole, blight or irregular leaf spot and from cherelles and pod rot yielded Colletotrichum gloeosporioides. No distinct differences in cultural and morphological characteristics were noted between the various isolates. The fungus was found to grow and sporulate well at 3()C. Cocoa LeafExtract Agar (CllA) was the best medium for mycelial growth while Potato Dextrose Agar appeared to favour sporulation. Both cocoa leaves and injured pods were liable to infection by C. gloeosporioides. Three week old cocoa seedlings and cherelles were noted as the most susceptible stages.

Chemigation and ground-spray applications of cyproconazole for control of late leaf spot of peanut

Abstract: In field experiments conducted during 1990 and 1991, chemigation applications of biosynthesis inhibiting fungicide cyproconazole (0.112 kg a.i./ha) were equal to or bether than ground-spray applications of cyproconazole or chlorothalonil (1.26 kg a.i./ha) late leaf spot, caused by Cercosporidium personatum, on peanut (Arachis hypogae) cultivars Florunner and Southern Runner. Late-season leaf spot epidemics and resulting defoliation were severe in nontreated plots in both years. All fungicide treatments provided similar levels of control in 1990 (.)