Showing papers on "Leaf spot published in 2000"

The Role of Chitinase Production by Stenotrophomonas maltophilia Strain C3 in Biological Control of Bipolaris sorokiniana.

Abstract: The role of chitinase production by Stenotrophomonas maltophilia strain C3 in biological control of leaf spot on tall fescue (Festuca arundinacea), caused by Bipolaris sorokiniana, was investigated in vitro and in vivo. The filtrate of a broth culture of C3, with chitin as the carbon source, was separated into fractions. A high molecular-weight fraction (>8 kDa) was chitinolytic and more inhibitory than a low-molecular-weight, nonchitinolytic fraction to conidial germination and hyphal growth by B. sorokiniana and to leaf spot development. A protein fraction derived by ammonium sulfate precipitation and a chitinase fraction purified by chitin affinity chromatography also were chitinolytic and highly antifungal. The chitinolytic fractions caused swelling and vacuolation of conidia and discoloration, malformation, and degradation of germ tubes. When boiled, the chitinolytic fractions lost chitinase activity along with most of the antifungal properties. Two chitinase-deficient and two chitinase-reduced mutants of C3 were compared with the wild-type strain for inhibition of germination of B. sorokiniana conidia on tall fescue leaves and for suppression of leaf spot development in vivo. The mutants exhibited reduced antifungal activity and biocontrol efficacy, but did not lose all biocontrol activity. An aqueous extract of leaves colonized by wild-type C3 had higher chitinase activity than that of noncolonized leaves and was inhibitory to conidial germination. The addition of chitin to leaves along with the wild-type strain increased both chitinase and antifungal activity. The chitinase activity level of extracts from leaves colonized by a chitinase-deficient mutant of C3, with and without added chitin, was no higher than the background, and the extracts lacked antifungal activity. Chitinolysis appears to be one mechanism of biological control by strain C3, and it functions in concert with other mechanisms.

Quantitative trait Loci associated with resistance to gray leaf spot of corn.

Abstract: The susceptible parent FR1141, the resistant parent 061, the F1 cross, and 301 families selfed once from backcrosses to the susceptible parent were evaluated for gray leaf spot (GLS) sever...

Septoria Leaf Spot of Banana: A Newly Discovered Disease Caused by Mycosphaerella eumusae (Anamorph Septoria eumusae).

Abstract: A previously undescribed leaf spot disease of banana has been discovered in southern and Southeast Asia. The fungus identified as the causal agent of this leaf spot has a Mycosphaerella teleomorph stage and a Septoria anamorph stage. Isolation and reinoculation of the fungus to banana reproduced symptoms and confirmed its pathogenicity. Phylogenic analysis based on sequences of the internal transcribed spacer and 5.8S ribosomal DNA regions from the different leaf spot pathogens of bananas was consistent with the definition of a new species. M. eumusae (anamorph S. eumusae) is the name proposed for the causal agent and Septoria leaf spot as the name for the disease. The presence of the pathogen has been confirmed in leaf specimens from southern India, Sri Lanka, Thailand, Malaysia, Vietnam, Mauritius, and Nigeria.

RAPD and SCAR Markers Linked to a Gene Conferring Resistance to Angular Leaf Spot in Common Bean

Abstract: Keywords: angular leaf spot; common bean; random amplified polymorphic DNA (RAPD); sequence-characterized amplified regions (SCAR); resistance

Inheritance of Angular Leaf Spot Resistance in Common Bean and Identification of a RAPD Marker Linked to a Resistance Gene

Abstract: Angular leaf spot, caused by Phaeoisariopsis griseola (Sacc.) Ferraris, is one of the major diseases affecting the common bean (Phaseolus vulgaris L.) in Brazil which can lead to severe yield losses. Previous studies demonstrated that cultivar MAR-2 was resistant to race 63.39 of P. griseola. The objective of this work was to characterize the resistance to angular leaf spot in MAR-2 in an F 2 population derived from the cross with Ruda (susceptible parent), and also to identify random amplified polymorphic DNA (RAPD) markers linked to the resistance gene. Cultivar MAR-2 was crossed with Ruda, a carioca-type cultivar susceptible to angular leaf spot, to determine the inheritance of resistance. The results demonstrated that a single dominant gene present in MAR-2 was responsible for the resistance to P. griseola, race 63.39. Resistant and susceptible DNA bulks from the F 2 population were constructed to identify RAPD markers linked to the resistance gene. Amplification with primer OPE-04 generated a 500-bp fragment which distinguished the resistant from the susceptible bulk populations. Co-segregation analysis of the entire population demonstrated that the RAPD marker was linked to the resistance gene at a distance of 5.8 Cm.

Bacterial Leaf Spot of Leafy Crucifers in Oklahoma Caused by Pseudomonas syringae pv. maculicola.

Abstract: During 1995 and 1996, bacterial leaf spots severely damaged fields of kale, spinach mustard, and turnip in Oklahoma. Symptoms were small, brown, necrotic spots with irregular edges surrounded by chlorotic halos. Lesion margins were often water-soaked on the abaxial surface. The spots enlarged and coalesced, causing extensive leaf yellowing and necrosis. Nineteen strains of a fluorescent Pseudomonas spp. were isolated from symptomatic plants. LOPAT tests and carbon source oxidation using Biolog GN MicroPlates were used to classify the strains as P. syringae. Cluster analysis of carbon source oxidation profiles for the local strains and selected reference strains of P. syringae pv. maculicola and pv. tomato produced one group with 79.5% similarity. In spray inoculations, all local strains caused chlorotic or water-soaked lesions on collards, kale, cauliflower, and tomato. A few local strains caused necrotic lesions on mustard. Most local strains caused one of the three lesion types on turnip and spinach mustard. Reference strains of P. syringae pv. maculicola caused similar symptoms. All but three of the local strains produced coronatine in vitro. The local strains were thus classified as P. syringae pv. maculicola, the cause of bacterial leaf spot of crucifers. Two distinct groups of P. syringaepv. maculicola were identified by repetitive sequence-based polymerase chain reaction (rep-PCR) with both REP and BOXA1R primers. Three subgroups within each group were further identified using the BOXA1R primer. Except for two strains of P. syringae pv. tomato which were pathogenic on crucifers, the pathovars maculicola and tomato had different genetic fingerprints. The pathogen was recovered from seven of ten fields sampled during 1994 to 1996. In five of the fields with P. syringae pv. maculicola, pathovars of Xanthomonas campestris were also isolated from lesions forming a bacterial disease complex. This is the first report of bacterial leaf spot caused by P. syringaepv. maculicola on leafy crucifers in Oklahoma.

Epidemiology in relation to methods for forecasting light leaf spot (Pyrenopeziza brassicae) severity on winter oilseed rape (Brassica napus) in the UK

Abstract: Pyrenopeziza brassicae, cause of light leaf spot of oilseed rape, has a complex polycyclic life cycle. It can be difficult to control light leaf spot in winter oilseed rape in the UK since it is not easy to optimise fungicide application timing. Early autumn infections are usually symptomless and recognisable lesions do not develop until the epidemic has progressed further by the spring. Light leaf spot often has a patchy distribution in winter oilseed rape crops and estimation of disease incidence can be difficult. There is evidence that epidemics are initiated primarily by ascospores produced from apothecia that survive the summer inter-crop period on infected debris. Subsequent development of the epidemic during the winter and spring is maintained by rain-splashed conidia that spread light leaf spot from initial foci. Understanding the relative roles of ascospores and conidia in the light leaf spot life cycle is crucial for forecasting epidemic severity and developing control strategies. The current web-based regional forecast system provides an autumn forecast of the incidence of light leaf spot that can be expected the following spring. This is based on survey data which assesses the occurrence of disease the previous July, and weather factors, such as deviations from summer mean temperature and winter rainfall. The forecast can be updated throughout the autumn and winter and includes crop-specific elements so that growers can adjust risks by inputting information about cultivar, sowing date and fungicide use. Crop-specific forecasts can be confirmed by assessing the incidence of light leaf spot. Such assessments will become easier when immunodiagnostic methods for detection of the disease become available. Incorporation of information on spore biology (e.g. apothecial maturation, ascospore release and infection conditions) is considered as a component of the interactive, continuously updated, crop-specific, web-based forecasts which are needed in the future.

RAPD and SCAR markers linked to resistance gene to angular leaf spot in common beans.

Abstract: A mancha angular do feijoeiro comum (Phaseolus vulgaris), cujo agente causal e o fungo Phaeoisariopsis griseola, e uma das principais doencas desta cultura no Brasil, causando perdas de ate 70% na producao de graos.

Evaluation of the Effect of Seed Treatments, Bactericides, and Cultivars on Bacterial Leaf Spot of Lettuce Caused by Xanthomonas campestris pv. vitians.

Abstract: As a part of a broader program for management of bacterial leaf spot, the effects of lettuce-seed treatments, greenhouse application of bactericides, and cultivars were evaluated Seed artificially inoculated with Xanthomonas campestris pv vitians was treated with bactericides or heat treated and evaluated for the incidence of contaminated seed and seed germination Seed soaked in 1% sodium hypochlorite for 5 and 20 min had an incidence of contaminated seed of less than 10% Dry-heat (1 h), hot-water (50°C, 2 h), and organic-acid treatments significantly reduced seed germination Considering both the effects on incidence of contaminated seed and seed germination, the best treatments were soaking the seeds in 1% sodium hypochlorite for 5 or 20 min Copper sulfate, alone or mixed with Zineb or Dithane, failed to control the disease and caused phytotoxicity All of the other bactericides significantly reduced the severity of bacterial leaf spot However, the differences among bactericide efficacy were too small to allow comparison between the different forms of copper used, as well as the effect of adding manganese and zinc (Dithane) or zinc alone (Zineb) to the copper product Nevertheless, copper hydroxide alone, mixed with Zineb or mixed with Dithane, and basic copper sulfate reduced disease severity by 8689, 7867, 8042, and 8182%, respectively, without causing phytotoxicity For the two years of cultivar evaluation, no significant difference in mean disease severity was observed among the cultivars Based on disease incidence, the most susceptible cultivar was Bellagreen Cvs Ideal cos, Grand Teton, Great Lakes, Paris Island, Ithaca, and Optima showed intermediate susceptibility, and the least-susceptible cultivars were Waldmann's and Grand Rapids, both green-leaf type There was no significant difference between the three romaine (cos) cultivars and between the two crisphead cultivars, but a significant difference was observed between the two butterhead types, Bellagreen and Optima, which had 8004 and 4801%, respectively, of their leaves diseased at the time of harvest

Mapping quantitative trait loci (QTLs) for resistance to Cercospora leaf spot disease (Cercospora beticola Sacc.) in sugar beet (Beta vulgaris L.)

Abstract: The breeding of sugar beet varieties that combine resistance to Cercospora and high yield under non-diseased conditions is a major challenge to the breeder. The understanding of the quantitative trait loci (QTLs) contributing to Cercospora resistance offers one route to solving this problem. A QTL analysis of Cercospora resistance in sugar beet was carried out using a linkage map based on AFLP and RFLP markers. Two different screening methods for Cercospora resistance (a field test at Copparo, Italy, under natural infection, and a newly-developed leaf disc test) were used to estimate the level of Cercospora resistance; the correlation between scores from the field (at 162 days after sowing) and the leaf disc test was significant. QTL analysis was based on F2 and F3 (half-sib family) generations derived from crosses between diploid single plants of 93164P (resistant to Cercospora leaf spot disease) and 95098P (susceptible). Four QTLs associated with Cercospora resistance (based on Lsmean data of the leaf disc test) on chromosomes III, IV, VII and IX were revealed using Composite interval mapping. To produce populations segregating for leaf spot resistance as a single Mendelian factor, we selected for plants heterozygous for only one of the QTLs (on chromosome IV or IX) but homozygous for the others.

Excoriose, cane blight and related diseases of grapevines: a taxonomic review of the pathogens

Abstract: The disease of grapevines known as excoriose has been the source of a certain amount of controversy. Much of this concerns the identity of the causal agent and this has been further confounded by the taxonomic problems of the fungal pathogens associated with this disease. Many of these problems have now been resolved and it is clear that excoriose is caused by Botryosphaeria dothidea while cane blight and leaf spot is caused by Phomopsis viticola. However, although at least five different species of Phomopsis are currently known to be associated with grapevines, only P. viticola causes cane blight and leaf spot. The role played by the other species of fungi is not clear, but they may be weak pathogens, saprophytes or endophytes.

Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on leaves of oilseed rape

Abstract: Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae. Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20 degrees C, but not at 24 degrees C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12-20 degrees C, 10 h at 8 degrees C, 16 h at 6 degrees C or 24 h at 4 degrees C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16 degrees C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16 degrees C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20 degrees C and to 26 days as temperature decreased to 4 degrees C. At 8 degrees C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6 degrees C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12-16 degrees C, and decreased as temperature decreased to 8 degrees C or increased to 20 degrees C. At temperatures from 8 to 20 degrees C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by 'lesions' (both log(10)-transformed) at different temperatures.

New leaf spot disease of Cymbidium species caused by Fusarium subglutinans and Fusarium proliferatum.

Abstract: species were consistently isolated from yellow, swollen spots with reddishbrown centers and small black spots on leaves of Cymbidium plants in the greenhouse. Fusarium subglutinans caused the yellow spots and Fusarium proliferatum caused either the yellow or the black spots. We propose the name “yellow spot” for the new disease. To denote differences in their pathogenicity to orchid plants, we designate the population causing yellow spot as race Y and that causing black spot as race B of F. proliferatum.

Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England

Abstract: Models were constructed to describe the relationships between incidence of phoma leaf spot at different growth stages in autumn/winter or early spring and incidence of stem canker (basal canker or stem lesions) in summer on winter oilseed rape in southern England. Model 1, describing the phoma leaf spot/basal canker relationship, was y(1) = beta (0) + beta (1)x(1) + beta (2)(x(2) - x(1)) if x(2) > x(1), and y(1) = beta (0) + beta (0) + beta (1)x(1) if x(2) less than or equal to x(1), in which y(1) was the incidence (Ic plants affected) of basal canker at harvest,x(1) was the maximum incidence of phoma leaf spot during the period from sowing to growth stage (G.S.) 1,6-1,7 (about 100 days after sowing) and x(2) was the maximum incidence of phoma leaf spot between G.S. 1,7 and G.S. 2,0 (start of stem extension). Model 2, describing the phoma leaf spot/stem lesion relationship, was y(2) = alpha (0) + alpha (1)x(3) + alpha (2)x(4), in which y(2) was the incidence of stem lesions at harvest, x(3) was the incidence of phoma leaf spot at G.S. 3,3-3,5 (flower buds visible) and x(4) was the incidence of phoma leaf spot at G.S. 4,5-5,5 (flower buds opening). Data from field experiments with four winter oilseed rape cultivars at Boxworth or Rothamsted in the 1992/93, 1993/94, 1996/97, 1997/98 or 1998/99 seasons were used to test the models. The values of R-2 for the regression equations testing model 1 for the phoma leaf spot/basal canker relationship were 0.75, 0.93, 0.91 and 0.89 for cvs Apex, Bristol, Capitol and Envol, respectively. The values of R-2 for the regression equations testing model 2 for the phoma leaf spot/stem lesion relationship were 0.58, 0.57, 0.54 and 0.71 for cvs Apex, Bristol, Capitol and Envol, respectively. The phoma leaf spot/basal canker relationship (model 1) could also be fitted to the combined data set for all four cultivars (R-2 = 0.65), whereas the phoma leaf spot/stem lesion relationship (model 2) could not to be fitted to the combined data set for the four cultivars. The relationships between incidence and severity of stem canker were examined and the values of R-2 for the regressions of severity on incidence were 0.91 for basal canker and 0.89 for stern lesions.

Effect of 2,6-dichloroisonicotinic acid or benzothiadiazole on Alternaria leaf spot, bacterial blight and Verticillium wilt in cotton under field conditions

Abstract: In field experiments, cotton (Gossypium hirsutum/G. barbadense) plants were treated with foliar applications of the synthetic activators 2, 6-dichloroisonicotinic acid (INA) or benzo [1, 2, 3] thiadiazole-7-carbothioic acid S-methyl ester (BTH) and the severity of natural infection with Alternaria macrospora, Xanthomonas campestris pv. malvacearum and Verticillium dahliae was assessed. Percentage leaf area infected with A. macrospora was significantly (P=0.05) lower in plants following one application of INA or BTH in the 95/96 and 97/98 seasons, respectively, compared with untreated plants. There was also significantly (P=0.05) less defoliation in the treated plants. Plants treated with one application of BTH had significantly (P=0.05) lower leaf areas infected with X. campestris pv. malvacearum and decreased defoliation compared with untreated plants in the 97/98 season. The severity of foliar symptoms of Verticillium wilt was significantly (P=0.05) decreased in plants treated with one application of INA or multiple applications of BTH compared with untreated plants in four experiments conducted over four field seasons. The reduced susceptibility of the cotton plants to Alternaria leaf spot, bacterial blight and Verticillium wilt is attributed to systemic acquired resistance following application of INA or BTH.

Disease response of carrot and carrot somaclones to Alternaria dauci

Abstract: Leaf spot of carrot, caused by the fungus Alternaria dauci, is a common disease of carrot throughout the world. To assess the disease response in different genotypes an in vitro method of assay has been developed. The terminal portion of excised mature leaves from carrot are incubated under lights at 25–26°C for 6 days with spores of A. dauci. After 6 days, chlorophyll and total soluble polyphenol contents of the leaves decline to a low level, whereas in the uninoculated control leaves levels of these compounds are largely unchanged. Electron microscope studies of the effect of infection on the ultrastructure of leaves from both cv. Fancy and wild plants show disintegration of the cell wall, plasmalemma and chloroplast membranes in the region close to the invading fungus. The response to A. dauci shows characteristics compatible with the presence of a phytotoxin. Seedling hypocotyls of the carrot cv. Fancy are used as a source of explants to initiate callus tissue and regenerate embryos. Regenerant somaclone plants show variation in morphology (crown number, height, leaf number, leaf shape and flowering time) and susceptibility to the pathogen as measured by the loss in chlorophyll from infected detached leaves after a 6-day period. Potentially susceptible and resistant regenerant plants are identified by the low and high chlorophyll levels, respectively, in excised leaves 6 days after infection. Selected high- and low-chlorophyll regenerant plants and seedling-derived cv. Fancy are self-pollinated, then the seeds are used to produce a progeny generation, which is assessed for morphological changes and disease resistance as before. The response of leaves of progeny plants to infection shows that the plants derived from high-chlorophyll regenerants still show a higher chlorophyll level after infection compared with leaves derived from low-chlorophyll and control plants. High chlorophyll levels in the presence of infection in the progeny of high-chlorophyll regenerants suggest that the capacity to resist infection in the selected somaclones is inherited.

Effect of spores of saprophytic fungi on phytoalexin accumulation in seeds of frog-eye leaf spot and stem canker-resistant and -susceptible soybean (Glycine max L.) cultivars.

Abstract: Two saprophytic fungi (Mucor ramosissimus and Rhizopus sp.) were tested for their ability to induce phytoalexin production by seeds of frog-eye leaf spot and stem canker-resistant and -susceptible soybean (Glycine max L.) cultivars. Only M. ramosissimus was shown to elicit a response and qualitative differences in phytoalexin accumulation were found between the susceptible and resistant cultivars. Glyceollins I, II, and III and glycinol were isolated from the susceptible cultivar, whereas Glyceollins I, II, and III, glycinol, glyceocarpin, genistein, isoformononetin, and N-acetyltyramine accumulated in the resistant cultivar in response to the same fungal elicitor. Genistein was found to be an inducibly formed isoflavonoid instead of a constitutive metabolite in the resistant cultivar, whereas N-acetyltyramine is described for the first time as a soybean phytoalexin. All the compounds, except genistein, showed fungitoxic activity against Cladosporium sphaerospermum. Spectral data of the pterocarpan phytoalexins, genistein, and N-acetyltyramine are also given in this work.

Bacterial Leaf Spot Diseases of Leafy Crucifers in Oklahoma Caused by Pathovars of Xanthomonas campestris

Abstract: Fields of kale, spinach mustard, and turnip were severely damaged by bacterial leaf spots during 1994 to 1996. Symptoms included circular to angular necrotic lesions with yellow halos and water-soaking on the abaxial leaf surface. Yellow, mucoid strains isolated from leaf spots were identified as Xanthomonas campestris using Biolog. Four strains caused black lesions on stems of cabbage seedlings in an excised cotyledon assay, leaf spots and sunken dark lesions on petioles of spray-inoculated crucifers, and leaf spots on spray-inoculated tomato. These strains were classified as X. campestris pv. armoraciae. Most other strains from leafy crucifers and all strains from a cabbage field caused black rot in the cotyledon assay and in spray-inoculations. Many of these strains also caused leaf spots on collard and kale but not stem and petiole lesions. The strains causing black rot were classified as X. campestris pv. campestris. Cluster analysis of Biolog profiles yielded a small group that contained local strains of both pathovars, and a large group comprised of reference and local strains of each pathovar, and some local, nonpathogenic strains. Five fingerprint groups were identified by rep-polymerase chain reaction using the BOXA1R primer. Local and reference strains of each pathovar occurred in two of the groups. Two pathovars of X. campestris are involved in the leaf spot diseases. Both pathovars were recovered within several fields, and also were recovered along with Pseudomonas syringae pv. maculicola. This is the first report of Xanthomonas leaf spot caused by X. campestris pv. armoraciae in Oklahoma.

Rational Use of Fungicide Applications to Maximize Peanut Yield Under Foliar Disease Pressure in West Africa

Abstract: Foliar diseases caused by Cercospora arachidicola, Cercosporium personatum, and Puccinia arachidis are major constraints to peanut production in the world. Fungicides are among the most efficient available control methods. Field trials were conducted in 1991 and 1992 in Benin and Niger, West Africa, to evaluate the cost effectiveness of fungicide application timings and frequencies on four peanut cultivars. A combination of four timings (40, 55, 70, and 85 days after sowing) was scheduled. Early (causal organism, C. arachidicola) and late (caused by C. personatum) leaf spot were prevalent in both years, but late leaf spot was the more economically important disease as shown by high values of area under the disease progress curve. Application of fungicide reduced late leaf spot incidence and increased pod yield. Pod yield responded to an interaction of number and timing of fungicide applications. With appropriate timing two or three fungicide applications were enough to significantly increase pod yield. Properly timed fungicide sprays can result in substantial monetary gains for peanut farmers in West Africa.

Use of Azoxystrobin for Disease Control in Texas Peanut

Abstract: Field studies were conducted at 11 locations across south Texas from 1994 to 1997 to determine the activity of azoxystrobin against southern stem rot (Sclerotium rolfsii Sacc.), Rhizoctonia pod rot (Rhizoctonia solani Kuhn), early leaf spot (Cercospora arachidicola Hori) and late leaf spot [Cercosporidium personatum (Berk. & Curt.) Deighton]. Azoxystrobin at 0.22 to 0.45 kg/ha applied twice provided control of stem rot, Rhizoctonia pod rot, and leaf spot comparable to tebuconazole at 0.2 kg/ha applied four times. Peanut yield increases were evident with all fungicide treatments over the untreated check.

First Report of Gray Leaf Spot on Perennial Ryegrass in Indiana

Abstract: Pyricularia grisea, the causal agent of gray leaf spot on turfgrass, was isolated from symptomatic perennial ryegrass (Lolium perenne) leaves collected from a golf course in north-central Indiana in August 1999. Gray leaf spot is an emerging threat to stands of perennial ryegrass in the mid-Atlantic and Midwestern United States (1). Symptoms were first evident in taller (6 cm) mown, rough areas surrounding golf course fairways. Field symptoms included diffuse patches (1 to 4 m in diameter) of thin, yellow-tan turf. Within larger affected areas, some of the turf was dead and matted. Close inspection revealed the presence of typical tan-gray lesions with brown margins and fish hook-like distortion of infected leaf blade tips. Incubation of affected turf in a saturated environment at 23°C for 16 h resulted in production of numerous three-celled, pear-shaped conidia characteristic of those produced by P. grisea. A pure culture of the isolate was grown on V8-juice agar in darkness at 29°C. After 10 days, the culture was exposed to continuous light for 4 days at 23°C to induce sporulation. Conidia were washed from the colony surface with sterile distilled water. Two-week-old perennial ryegrass plants in 8-cm-diameter pots were inoculated with the conidial suspension. Typical gray leaf spot symptoms resulted after incubation of inoculated plants at 27°C for 72 h in a saturated atmosphere. Uninoculated control plants exposed to the same environmental conditions remained healthy. This is the first report of gray leaf spot on perennial ryegrass in Indiana. Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.

Changing scenario of groundnut diseases in Andhra Pradesh, Karnataka, and Tamil Nadu states of India.

Abstract: In field surveys carried out in 1999 collar rot (Aspergillus niger), stem rot (Sclerotium rolfsii [Corticium rolfsii]), bud necrosis disease (groundnut bud necrosis virus), early leaf spot (Cercospora arachidicola) [Mycosphaerella arachidis], late leaf spot (Phaeoisariopsis personata) and rust (Puccinia arachidis) were detected on groundnuts in Andhra Pradesh, Karnataka and Tamil Nadu, India.

Identification of Tropical and Temperate Maize Populations Having Favorable Alleles for Disease Resistance

Abstract: A possible use of nonelite germplasm is as a source of alleles for disease resistance. Our objective was to determine the value of tropical and temperate maize (Zea mays L.) germplasm accessions as sources of alleles to improve disease resistance of the Corn Belt hybrid FR1064 x LH185. A group of tropical populations and hybrids from the Germplasm Enhancement of Maize Project (GEM) crossed to either Mol7 or B73 (temperate inbreds), was studied. In addition, a group of temperate accessions was evaluated. Reaction to southern corn leaf blight (SCLB) [Bipolaris maydis (Nisikado & Miyake) Shoemaker = Helminthosporium maydis Nisikado & Miyake], northern corn leaf spot (NCLS) [Bipolaris zeicola (G. L. Stout) Shoemaker = Helminthosporium carbonum Ullstrup Races 2 and 3], gray leaf spot (GLS) (Cercospora zeae-maydis Tehon & E.Y. Daniels), northern corn leaf blight (NCLB) [Exserohilum turcicum (Pass.) K. J. Leonard & E. G. Suggs = Helminthosporium turcicum Pass., Races 1, 1, 2, 23N and three unidentified races] and common rust (Puccinia sorghi Schwein) was studied using Dudley's method for identifying populations with favorable alleles. All accessions had favorable dominant alleles for resistance not present in FR1064 x LH185 for common rust, GLS, and SCLB. Four accessions had a number of favorable alleles for resistance not significantly different from the best accession for all five diseases. Crosses of the accessions containing Mol7 to FR1064 and LH185 were less susceptible to SCLB, NCLB, and rust than crosses of accessions containing B73. At least seven of the best 10 populations were tropical x Mo17 crosses for SCLB, NCLB, and rust when populations were ranked for presence of favorable alleles for resistance not present in either LH185 or FR1064. Net value statistics for tropical x B73 and tropical x Mol7 accessions differed in indicating whether backcrossing or selfing from the F 1 is more desirable. Therefore, if tropical populations are crossed to Corn Belt inbreds to increase adaptation, comparisons among tropical populations should only be made when all populations being compared have been crossed to the same Corn Belt inbred.

First Report of Bacterial Spot of Lettuce Caused by Xanthomonas campestris pv. vitians in Turkey

Abstract: During spring 1999, lettuce (Lactuca sativa) plants grown at Oltu in the eastern Anatolia region of Turkey were observed with numerous lesions typical of bacterial leaf spot. Lesions on leaves were irregular, small, pale green to black, water-soaked, and 2 to 5 mm in diameter. Coalescing lesions sometimes caused defoliation of older leaves. Isolations made from diseased leaves on yeast dextrose carbonate agar yielded nearly pure cultures of a yellow pigmented bacterium typical of a xanthomonad. Five bacterial strains were purified and used for further tests. The strains reacted positively with a Xanthomonas-specific monoclonal antibody, X1, in indirect enzyme-linked immunosorbent assays (1). Fatty acid analysis identified the strains as X. campestris pv. vitians (proposed name X. axonopodis pv. vitians), with greatest similarity indices of 29 to 71% (2). Pathogenicity of strains was confirmed on 5-week-old lettuce plants (cv. Darkland) sprayed with bacterial suspensions containing 108 CFU/ml of sterile wa...

First Report of Gray Leaf Spot Caused by Pyricularia grisea on Lolium perenne in Illinois.

Abstract: Each year from 1991 to 1999, a disease matching the description of gray leaf spot (1) was observed in the central and north central regions of Illinois. Disease severity was low ( 50% blight in some areas) from 1995 to 1998. The disease was observed on Lolium perenne (perennial ryegrass) golf course fairways and sports fields. Isolations of Pyricularia grisea were made from L. perenne collected from golf courses in Bloomington, Decatur, Kankakee, Pekin, Urbana, and Moline, IL. All isolates were collected from surface-sterilized, symptomatic leaves. Cultures were maintained on one-fifth strength potato-dextrose agar (PDA) and induced to sporulate on full-strength oatmeal agar. All isolates in culture displayed vegetative and conidial characteristics similar to those previously described for P. grisea (1). Twenty-five different L. perenne germ plasms were inoculated with isolate WF9826 (Kankakee) using a suspension of 1 × 105 conidia per milliliter. The 4-week-old lawns (100 plants per 3-cm-diameter cone-tainer) of each ryegrass germ plasm were inoculated by spraying foliage with the conidial suspension until runoff. Inoculated and uninoculated lawns were enclosed in plastic bags and placed in an incubator (16 h light; 28°C) for 7 days. Disease severity was rated using a scale of 0 to 10 (10 = 100% blight). Each treatment was replicated three times, and all experiments were repeated four times. Small blue-gray, water-soaked lesions with dark brown borders were observed on leaves of all inoculated ryegrass germ plasms. Advanced symptoms included blighting of much of the leaves. The mean disease severity rating was 3.8 (range 2 to 7) for all experimental units and all 25 germ plasms. P. grisea was isolated from leaves that were inoculated with WF9826. This is the first report of gray leaf spot of perennial ryegrass caused by P. grisea in Illinois. Reference: (1) P. J. Landschoot et al. Plant Dis. 76:1280, 1992.