Showing papers on "Leaf spot published in 2002"
TL;DR: Bean rust induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens.
Abstract: Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO 2 , due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host-pathogen trophic relationships.
98 citations
TL;DR: Out of eight probability distribution functions compared, the double Gaussian model best described the frequency of disease severity levels for most diseases, and the proportion of fields with disease severity level thought to cause yield loss was calculated as 26.6%.
Abstract: To assess the prevalence and severity of sorghum diseases in western Kenya, a 2-year survey was conducted (July 1995 and 1996), in 91 and 109 farmers' fields, respectively. Fields were generally 25% in 3% of fields surveyed. Grain yield reduction from smut diseases alone was estimated to be 5%. Out of eight probability distribution functions compared, the double Gaussian model best described the frequency of disease severity levels for most diseases. Based on the best-fitting model, the proportion of fields with disease severity level thought to cause yield loss (severity rating >5 on a 1 to 9 scale, where 1 = no disease) was calculated as 26.6% for oval leaf spot, 15.3% for rust, 14.8% for anthracnose, 4.8% for ladder leaf spot, and 1.5% for leaf blight. The production environment influenced the prevalence of disease severity. Severe anthracnose, leaf blight, and ladder leaf spot were confined to fields in the humid LM1 and LM2 agro-ecological zones, rust was ubiquitous, and severe gray leaf spot was more prevalent in the dryer LM4 zone.
94 citations
TL;DR: Eight species of Brassica, including cultivated and wild allies, of the genus Brassica were evaluated under epiphytotic conditions for two years and were found completely resistant to leaf spot disease in Indian mustard.
Abstract: Development of leaf spot resistant mustard cultivars is a relevant objective in view of heavy crop losses caused by this pathogen. Thirty-eight species belonging to 9 genera, including cultivated and wild allies, of the genus Brassica were evaluated under epiphytotic conditions for two years. Inoculations were done on whole plants (in vivo) and on detached leaves (in vitro). Data on incubation period, number of lesions per leaf, lesion size and leaf area covered by lesions were recorded. Species which never produced disease symptoms throughout the growing period in pots and until 72 hours after inoculation in detached leaf assays during both years were treated as resistant, while those that produced symptoms were classified as moderately resistant, susceptible or highly susceptible depending upon incubation period, size of lesions and leaf area covered by disease symptoms. Eight species (Brassica desnottesii, Camelina sativa, Coincya pseuderucastrum, Diplotaxis berthautii, D. catholica, D. cretacea, D. erucoides, and Erucastrum gallicum) were found completely resistant, whereas others were classified as moderately resistant (12), susceptible (11) or highly susceptible (9). Since resistance is unavailable within the cultivated species, these 8 resistant wild species could be used as donor parents for introgressing resistance to leaf spot disease in Indian mustard.
82 citations
TL;DR: Foliar applications of fungicide to field plots in the autumn and winter not only decreased the incidence of crown cankers but also reduced the rate of canker development on stem bases in the spring and early summer (when severity of Crown cankers increased linearly with time).
Abstract: At Rothamsted during 1997/98, 1998/99 and 1999/2000 winter oilseed rape growing seasons, numbers of air-borne ascospores of Leptosphaeria maculans were often > 4 m−3 from autumn (September/October) to spring (April/May), while few or no ascospores were detected during the summer. Mature pseudothecia were generally not observed on debris of the previous crop until September. One-year-old debris (harvested in July 1998) had 95% discharged and 5% mature pseudothecia in August 1999, but by 15 September new pseudothecia (of which 30% were mature) were observed and the first increase in air-borne ascospores (> 4 m−3) occurred. Phoma leaf spotting appeared in untreated field plots 14–25 days after the first increase in air-borne ascospores in autumn. The fungicide mixture difenoconazole plus carbendazim decreased the incidence of new leaf lesions for 1 month after application in autumn and for 2 months in mid-winter. When L. maculans was isolated from infected leaves, the growth rate of isolates from leaves to which fungicide was applied was less than that of those from untreated leaves. Foliar applications of fungicide to field plots in the autumn and winter not only decreased the incidence of crown cankers but also reduced the rate of canker development on stem bases in the spring and early summer (when severity of crown cankers increased linearly with time). In untreated crops, when phoma leaf spots appeared early in the autumn, crown cankers developed early in the spring but only became severe enough before harvest to reduce yield greatly in 1997/98. Yield loss was associated with crown cankers that girdled more than half of the stem by harvest (mean severity > 3 on a 0–5 scale). Infections of new leaves produced after stem extension, from January onwards, led to phoma stem lesion development above the crown. In the three seasons, phoma stem lesions became moderately severe (> 2) by harvest only in untreated plots in 1997/98.
76 citations
TL;DR: The MAGGY retrotransposon was unevenly distributed in the prg pathogens, with some isolates lacking this element, some possessing six to eight copies, and others having 10 to 30 copies.
Abstract: Gray leaf spot of perennial ryegrass (prg) (Lolium perenne), caused by the fungus Pyricularia grisea (teleomorph = Magnaporthe grisea), has rapidly become the most destructive of all turf grass diseases in the United States. Fungal isolates from infected prg were analyzed with several molecular markers to investigate their relationship to P. grisea strains found on other hosts. All of the molecular markers used in this study revealed that isolates from prg are very distantly related to those found on crabgrass. Fingerprinting with MGR586 (Pot3) revealed zero to three copies of this transposon in the prg pathogens, distinguishing them from isolates pathogenic to rice, which typically have more than 50 copies of this element. RETRO5, a newly identified retroelement in P. grisea, was present at a copy number of >50 in isolates from rice and Setaria spp. but only six to eight copies were found in the isolates from prg. The MAGGY retrotransposon was unevenly distributed in the prg pathogens, with some isolates lacking this element, some possessing six to eight copies, and others having 10 to 30 copies. These results indicated that the P. grisea isolates causing gray leaf spot are distinct from those found on crabgrass, rice, or Setaria spp. This conclusion was supported by an unweighted pair-group method with arithmetic average cluster analysis of single-copy restriction fragment length polymorphism haplo-types. Fingerprints obtained with probes from the Pot2 and MGR583 transposons revealed that the prg pathogens are very closely related to isolates from tall fescue, and that they share similarity with isolates from wheat. However, the wheat pathogens had fewer copies of these elements than those found on prg. Therefore, I conclude that P. grisea isolates commonly found on other host plant species did not cause gray leaf spot epidemics on prg. Instead, the disease appears to be caused by a P. grisea population that is specific to prg and tall fescue.
68 citations
TL;DR: Genotypic differences were highly significant for all the traits studied and selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs.
Abstract: Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs.
66 citations
TL;DR: Breeders should use the most aggressive isolates of C. zeae-maydis to maximize discrimination between genotypes in gray leaf spot trials.
Abstract: The use of genetically resistant maize hybrids is the preferred means of control of gray leaf spot, caused by Cercospora zeae-maydis. One problem faced by maize breeders attempting to breed for resistance to gray leaf spot is the high degree of genotype-environment interactions observed in disease trials. In North Carolina gray leaf spot trials conducted at four locations in the western part of the state, we found consistent hybrid-location interactions over the 1995 and 1996 growing seasons. Isolates of C. zeae-maydis from those test locations were evaluated on the same hybrids used in the multilocation testing at a location in central North Carolina that does not have a history of gray leaf spot. The hybrid-isolate interactions observed in the isolate trial mirrored the hybrid-location effects seen in the multilocation testing. Most of the interactions arose from changes in the magnitude of differences between hybrids when inoculated with the isolates rather than from any change in hybrid ranking. Analysis of internal transcribed spacer-restriction fragment length polymorphisms (RFLPs) and mitochondrial rDNA RFLPs of those isolates and others revealed that both type I and type II sibling species of C. zeae-maydis, as well as C. sorghi var. maydis, are isolated from typical gray leaf spot lesions. Breeders should use the most aggressive isolates of C. zeae-maydis to maximize discrimination between genotypes in gray leaf spot trials.
50 citations
TL;DR: Combined application of the P. fluorescens formulation to seed and foliage effectively controlled leaf spot and rust, and increased the pod yield in greenhouse and field tests.
Abstract: Glasshouse and field trials were conducted to determine the efficacy of a talc-based powder formulation of Pseudomonas fluorescens strain Pf1 in controlling groundnut leaf spot ( Cercosporidium personatum ) and rust ( Puccinia arachidis ). Seed treatment with the talc-based powder formulation of the bacterium alone effectively reduced the severity of leaf spot and rust. When the treated seeds were sown in soil, the antagonist moved to the rhizosphere and multiplied well in it. Foliar application with the powder formulation effectively controlled the groundnut leaf spot and rust. P. fluorescens multiplied well in the phyllosphere after foliar application of powder formulation. Combined application of the P. fluorescens formulation to seed and foliage effectively controlled leaf spot and rust, and increased the pod yield in greenhouse and field tests.
45 citations
TL;DR: It is assumed that a possible genetic mechanism based on the imbalanced AOS metabolism contributes to formation of physiological leaf spots in spring and winter barley in Germany.
Abstract: A leaf spot disease with unknown etiology has become more pronounced in spring and winter barley in Germany in recent years. The symptoms are similar to net blotch and Ramularia leaf spots, but the causal agents of these diseases are not identified. The symptom expression varied much on cultivars. Cultivars most affected by the disease of both spring and winter barley showed a significantly higher level of superoxide (O2¯) production and lipid peroxidation (malondialdehyde), but a lower level of antioxidant potential expressed as superoxide dismutase (SOD) activity, catalase activity, and integral water-soluble antioxidant capacity (ACW) than insensitive cultivars. A high positive correlation between O2¯ production and leaf spot development between ear emergence and milk ripeness was established in the most sensitive winter barley cv. Anoa (r2 = 0.9622) and spring barley cv. Barke (r2 = 0.9434). Leaf H2O2 levels increased with the severity of leaf spots. The histochemical localization of O2¯ and ...
45 citations
TL;DR: Both mixtures and alternate applications of chlorothalonil and benomyl were effective for management of leaf spot in fields wherebenomyl alone did not provide season-long leaf spot control and neither tank mixes nor alternating sprays prevented an increase in the relative frequency of benomel-resistant isolates compared with other treatments in which benomy was used.
Abstract: Recent registration of sterol biosynthesis inhibitor and strobilurin fungicides for control of early (Cercospora arachidicola) and late (Cercosporidium personatum) leaf spot diseases of peanut (Arachis hypogaea) has renewed interest in the potential for loss of disease control due to fungicide resistance. The objectives of this study were to use the systemic fungicide benomyl, the protectant fungicide chlorothalonil, and late leaf spot of peanut as a model system to compare fungicide application strategies for fungicide resistance management. Field experiments were conducted at Tifton and Plains, GA, in 1995 and 1996 to determine the effects of alternate applications, mixtures, and alternating block applications of chlorothalonil and benomyl compared with full-season applications of two rates of chlorothalonil and two rates of benomyl alone on late leaf spot of peanut and on the proportion of the pathogen population resistant to benomyl following the various regimes. Tank mix combinations of half rates of the two fungicides and alternations of the full rates of the two fungicides provided better (P ≤ 0.05) control of late leaf spot than full-season applications of either rate of benomyl alone, and were comparable to full rates of chlorothalonil alone. Neither tank mixes nor alternating sprays prevented an increase in the relative frequency of benomyl-resistant isolates compared with other treatments in which benomyl was used. Both mixtures and alternate applications of chlorothalonil and benomyl were effective for management of leaf spot in fields where benomyl alone did not provide season-long leaf spot control.
44 citations
TL;DR: Monitoring the pathogenic variability of common bean (Phaseolus vulgaris) in Brazil is the best strategy for a breeding program aimed at developing resistant genotypes, and searching for new resistance genes to angular leaf spot must be pursued.
Abstract: Due to the increased importance of angular leaf spot of common bean (Phaseolus vulgaris) in Brazil, monitoring the pathogenic variability of its causal agent (Phaeoisariopsis griseola) is the best strategy for a breeding program aimed at developing resistant genotypes. Fifty one isolates of P. griseola collected in five Brazilian States were tested on a set of 12 international differential cultivars in the greenhouse. When inoculated plants showed symptoms but no sporulation was observed, they were transferred to a moist chamber for approximately 20-24 h. After this period of time, if no sporulation was observed, the plants were considered resistant; otherwise, they were considered susceptible. From the fifty-one tested isolates, seven different pathotypes were identified. No Andean pathotypes were identified; consequently, all isolates were classified as Middle American pathotypes. Pathotype 63-31 was the most widespread. Pathotype 63-63 overcame resistance genes present in all differential cultivars and also the resistance gene(s) present in the cultivar AND 277. This fact has important implications for breeding angular leaf spot resistance in beans, and suggests that searching for new resistance genes to angular leaf spot must be pursued.
TL;DR: A simple, rapid PCR method based on primers from the cfl gene was developed to detect coronatine-producing strains of P. syringae pv.
Abstract: Xanthomonas campestris pv. campestris, X. campestris pv. armoraciae, and Pseudomonas syringae pv. maculicola are bacterial pathogens that cause leaf spot diseases on leafy crucifers in Okl...
TL;DR: Results confirm that isolates of the A. tenuissima group can infect and colonize Amaranthus hybridus leaves in a manner consistent with other endophytic fungi, and suggest that these fungi can act as latent leaf pathogens when the host is altered by wounding.
Abstract: Blodgett, J. T., and Swart, W. J. 2002. Infection, colonization, and disease of Amaranthus hybridus leaves by the Alternaria tenuissima group. Plant Dis. 86:1199-1205. With the increased use of Amaranthus hybridus as a leafy-vegetable crop in Africa and the recent identification of Alternaria leaf spot on this host in southern Africa, the role of this potentially damaging pathogen was investigated. The goals of this study were to test the pathogenicity of the Alternaria tenuissima group, determine how these fungi infect Amaranthus hybridus leaves, and examine the colonization pattern within host tissues. Asymptomatic leaves of Amaranthus hybridus were collected from two field sites in South Africa. Eight A. tenuissima group isolates collected from these leaves were used in inoculation experiments conducted in both greenhouse and growth chamber studies. Scanning electron microscopy revealed A. tenuissima– like conidia germinating on leaf surfaces and mycelia entering leaves only through stomata of both field-collected and artificially inoculated leaves. Unwounded, inoculated leaves had no symptoms, and light-microscopy observations of both asymptomatic field-collected and unwounded and inoculated leaves revealed hyphae in mesophyll tissue growing intercellularly with no host cell penetration or host-cell response. Seven of the eight isolates produced brown to black, circular to oval, necrotic lesions only at the wound site of injured and inoculated leaves. These results confirm that isolates of the A. tenuissima group can infect and colonize Amaranthus hybridus leaves in a manner consistent with other endophytic fungi, and suggest that these fungi can act as latent leaf pathogens when the host is altered by wounding.
TL;DR: An existing PCR-based method for diagnosis of the winter oilseed rape (Brassica napus ssp oleifera) fungal pathogen Pyrenopeziza brassicae (cause of light leaf spot) was improved by the development of a pair of primers for use in nested-PCR reactions.
Abstract: An existing PCR-based method for diagnosis of the winter oilseed rape (Brassica napus ssp oleifera) fungal pathogen Pyrenopeziza brassicae (cause of light leaf spot) was improved by the development of a pair of primers (PbN1 and PbN2) for use in nested-PCR reactions. The nested-PCR technique improved the detection of P. brassicae DNA in vitro by three orders of magnitude over that achieved using the first-round PCR primers (Pb1 and Pb2). In controlled environment experiments, the nested-PCR assay detected P. brassicae within infected B. napus leaves before visible light leaf spot symptoms developed and earlier than was possible by incubating infected leaves in polyethylene bags to promote sporulation of P. brassicae. A three-primer PCR technique using the primers PbM-1-3, PbM-2 and Mt3 was developed to distinguish between the two mating types (MAT-1 and MAT-2) of P. brassicae. This technique was able to determine the mating types present within DNA extracted from infected plant tissue, including tissue infected with both mating types together.
TL;DR: To the authors' knowledge, this is the first report of C. sojina from soybean in Wisconsin and typical field symptoms appeared on each of the inoculated plant 8 days after inoculation, while the controls expressed no leaf symptoms.
Abstract: Frogeye leaf spot, caused by Cercospora sojina, is an economically important foliar disease of soybean (Glycine max (L.) Merr.) in areas where growing conditions are warm and humid. During a survey conducted in 2000 and 2001 in soybean fields in Wisconsin, reddish brown, circular to angular spots varying in diameter from 1 to 5 mm were observed on soybean leaves in four fields in Dane and Iowa counties, and in five and six fields in Lafayette and Green counties, respectively. Soybean plants were in growth stages between R3 and R5 during sampling. Disease incidence ranged from 30 to 100% with 5 to 10% of leaf area covered with leaf spot in 2000. In 2001, trace levels of the disease were detected in Dane County, but no symptomatic plants were present in the other counties. Symptomatic leaves were collected from all locations in 2000 and Dane county in 2001. Ten leaves were randomly picked from all samples for each year, placed in a 100 × 15 mm petri dish dampened with Whatman No.1 filter paper, and incubated overnight at 24°C. Fungal sporulation developed after 24 h. Fifteen spores were removed from the 10 leaves, placed on acidified potato dextrose agar (APDA), and incubated in the dark at 24°C. Cultures with dark pigmentation and associated conidia and conidiophores were observed after 3 weeks. The conidiophore, spore type, and leaf symptoms correspond to the description of C. sojina (1). Conidiophores were light-to-dark brown, one to four septate, and fasciculate. The conidiophores were also geniculate and measured 52 to 120 x 4 to 6 μm. Conidia were 0 to 10 septate, hyaline, elongate to fusiform, and measured 40 to 60 x 6 to 8 μm. Cultures were maintained on APDA, and spores for inoculations were produced on this medium. Spores from the 2000 cultures were harvested, bulked together, and used for pathogenicity tests. Pathogenicity tests were conducted in a growth chamber using a known susceptible soybean cultivar, Blackhawk. Ten-cm-diameter pots each containing 4 plants was used. Twenty plants were inoculated and 20 served as noninoculated controls. Ten-day-old plants were inoculated with a spore suspension of 3 × 105 spores/ml by spraying inoculum over the entire leaf surfaces with a spray atomizer. Control plants were sprayed similarly with sterile distilled water. Plants were incubated in an enclosed, transparent fiberglass box with a humidifier that provided 95 to 100% humidity. Lighting in the growth chamber was adjusted to 18-h light and 6-h dark during the inoculation period. Plants were removed from the box after 48 h and placed in a growth chamber with a 12-h photoperiod. The light output in the growth chamber was 300 μmol·m-2·s-1 and the temperature was maintained at 24 ± 3°C. The experiment was repeated once. Typical field symptoms appeared on each of the inoculated plant 8 days after inoculation, while the controls expressed no leaf symptoms. C. sojina was reisolated from all symptomatic plants. To our knowledge, this is the first report of C. sojina from soybean in Wisconsin. Reference: (1) D. V. Phillips. Frogeye leaf spot. Page 20 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman, J. B. Sinclair, and J. C. Rupe, eds. American Phytopathological Society, St. Paul, MN, 1999.
TL;DR: Results showed that stem extension was an important factor in influencing vertical light leaf spot spread in the model oilseed rape crop, and rain events contributed to the splash dispersal of conidia to the plant apex and the resulting infections were directed vertically by internode growth.
TL;DR: In a comparison of symptoms of the disease and morphological characteristics of the isolated fungus with other broad bean diseases, this disease represented a new, as yet undescribed disease of broad bean in Japan and is proposed the name "leaf spot of broadbean" and "Soramame hanten-byô" in Japanese.
Abstract: Farmers' fields were surveyed for a new disease on broad bean in different parts of Shimane Prefecture. The disease was found in all surveyed fields. The fungus frequently associated with diseased broad bean leaves having the characteristic leaf spot symptom was identified as Alternaria tenuissima, based on morphological characteristics. The initial lesion was brown, water soaked, circular to slightly irregular. Then the lesion enlarged and became concentric. Mature leaves had coalescing necrosis surrounded by yellowing. Older leaves of the plant were particularly affected. In a later stage of the disease, the leaves became blighted from the margin to the center and most of the diseased plants defoliated. In severely infected fields, circular to irregularly shaped lesions also appeared on stems and pods, and plants defoliated completely. All tested isolates were pathogenic to broad bean leaves. Different isolates of the fungus varied in pathogenicity on different broad bean cultivars. In a comparison of symptoms of the disease and morphological characteristics of the isolated fungus with other broad bean diseases, this disease represented a new, as yet undescribed disease of broad bean in Japan. Therefore, we propose the name "leaf spot of broad bean" and "Soramame hanten-byo" in Japanese.
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01 Jan 2002
TL;DR: These guidelines have been written with the collaboration of the Fusarium, Sigatoka and Nematology working groups of PROMUSA and INIBAP staff with the objective of helping researchers to design their trial, choose the appropriate location for the trial, and evaluate selected genotypes for resistance and tolerance to various diseases as mentioned in this paper.
Abstract: These Technical Guidelines replace Technical Guidelines 1 ('Screening of Musa Germplasm for resistance and tolerance to nematodes') and 3 ('Evaluation of Musa germplasm for resistance to Sigatoka diseases and Fusarium wilt') as far as indepth evaluations are concerned. Technical Guidelines for performance evaluations, which were also part of Technical guidelines 3, will appear shortly. These changes were made to reflect the apparition of a third disease caused by a Mycosphaerella fungus ('eumusae leaf spot disease'), to simplify the guidelines, and to group under one cover the evaluations for the main pests and diseases affecting bananas. These guidelines have been written with the collaboration of the Fusarium, Sigatoka and Nematology working groups of PROMUSA and INIBAP staff with the objective of helping researchers to design their trial, choose the appropriate location for the trial, and evaluate selected genotypes for resistance and tolerance to various diseases. Field forms are included to help data collection.[Ce guide technique remplace les guides techniques 1 et 3 ('Evaluation du materiel genetique de Musa pour la resistance aux nematodes' et 'Evaluation de la resistance des bananiers aux cercosporioses et a la fusariose') en ce qui concerne les evaluations approfondies. Le guide technique pour l'evaluation des performances, qui faisait egalement partie du guide technique 3 sera publie prochainement. Ces changements ont ete effectues pour prendre en compte l'apparition d'une troisieme maladie causee par un champignon de type Mycosphaerella ('eumusae leaf spot disease'), pour simplifier les guides techniques et pour regrouper dans un meme ouvrage les protocoles d'evaluation pour les principaux ravageurs et maladies qui affectent les bananiers. Ce guide technique a ete redige avec la collaboration des groupes de travail de PROMUSA sur la fusariose, les cercosporioses et les nematodes, ainsi que du personnel de l'INIBAP, avec l'objectif d'aider les chercheurs a concevoir un dispositif experimental, choisir un site experimental approprie et evaluer la resistance et la tolerance aux maladies des genotypes selectionnes. Des modeles de fiches d'observation sont fournis afin d'aider les chercheurs dans la collecte de donnees.][Estas Guias Tecnicas reemplazan las Guias Tecnicas no. 1 y no. 3 ('Cribado de Germoplasma de Musa con respecto a la resistencia y tolerancia a los nematodos' y 'Evaluacion de la resistencia de los bananos a las enfermedades de Sigatoka y marchitamiento por Fusarium'), en lo que respecta a las evaluaciones profundas. Pronto publicaremos las Guias Tecnicas para la evaluacion del desempeno que tambien formaban parte de las Guias Tecnicas No. 3. Estos cambios fueron realizados para reflejar la aparicion de una tercera enfermedad causada por un hongo Mycosphaerella (enfermedad de la mancha foliar causada por eumusae), simplificar las guias y agrupar bajo una cubierta las evaluaciones para las principales plagas y enfermedades que afectan a los bananos. Estas guias han sido escritas con la colaboracion de los grupos de trabajo en el marchitamiento por Fusarium, Sigatoka y Nematologia de PROMUSA y del personal de INIBAP con el objetivo de ayudar a los investigadores a disenar sus ensayos, escoger el sitio adecuado para el ensayo, y evaluar genotipos seleccionados con respecto a la resistencia y tolerancia a varias enfermedades. Se incluyen los formularios de campo para ayudar a la recoleccion de los datos.]
TL;DR: Cytological research showed variable chromosome association and also homeology between the genomes of A. hypogaea and A. glabrata and the hybrids produced had morphological characters of both parents plus floral abnormalities not seen in either parent.
Abstract: Arachis glabrata Benth, variety glabrata collector GK 10596 (PI276233; ICG 8176) belonging to section Rhizomatosae has resistance to rust, late leaf spot and viral diseases A hypogaea L cv MK 374 (section Arachis) is susceptible to rust, late leaf spot and to the viral diseases peanut stripe, peanut mottle and peanut bud necrosis Hybrids between A hypogaea cv MK 374 and A glabrata were produced after inter specific pollinations and embryo culture The hybrids produced had morphological characters of both parents plus floral abnormalities not seen in either parent It was possible to identify the hybrids by esterase isozyme analysis when still in culture Cytological research showed variable chromosome association and also homeology between the genomes of A hypogaea and A glabrata The hybrids inherited resistance to rust, late leaf spot, peanut bud necrosis and peanut stripe diseases from the pollen parent A glabrata
TL;DR: In this paper, the effects of potassium (K) application on nodulation, leaf to stem ratio, herbage yield, leaf drop, and disease severity of common leaf spot disease (caused by fungus Pseudopeziza medicaginis) in dryland alfalfa (cv. Genesis) (Medicago sativa L).
Abstract: An on-farm field experiment was conducted to investigate the effects of potassium (K) application on nodulation, leaf to stem ratio, herbage yield, leaf drop, and disease severity of common leaf spot disease (caused by fungus Pseudopeziza medicaginis) in dryland alfalfa (cv. Genesis) (Medicago sativa L). The soil of the experiment site was dark greyish clay with a pH of 7.3 (1 : 5 Calcium chloride). Topsoil (0–15 cm) had 1.03 meq 100 g−1 K and subsoil (15–30 cm) had 0.88 meq 100 g−1 K (Ammonium Acetate extracted K). The experiment was conducted in a randomized complete block design with 6 rates of K supply (0, 20, 40, 60, 80, and 100 kg K ha−1). The source of K was potassium chloride. Potassium application has a significant beneficial impact on nodulation, herbage yield, and leaf to stem ratio of alfalfa plants. There were also significant reductions in leaf drop and common leaf spot disease severity of alfalfa with K application. The adequate K rates for reducing the common leaf spot disease severity a...
TL;DR: In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetting duration at 8°C.
Abstract: In controlled environment experiments, sporulation of Pyrenopeziza brassicae was observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation (l0), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm2 leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parameters c (maximum percentage leaf area with sporulation), r (maximum rate of increase in percentage leaf area with sporulation) and l37 (days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation, l50) of P. brassicae was generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.
TL;DR: Environmental, cultural, and disease data were summarized for four different periods during the growing season and analyzed by stepwise multiple linear regression in order to determine which variables significantly contributed to gray leaf spot severity at the dough or dent growth stages of maize.
Abstract: Gray leaf spot of maize caused by Cercospora zeae-maydis is a major foliar disease in the United States and other parts of the world. Efficient management of gray leaf spot is hindered by a lack of quantitative information regarding environmental and cultural influences on disease severity. We collected environmental, cultural, and disease severity data in southern Iowa at 13 locations in 1998 and 11 locations in 1999. The independent variables that we considered included temperature, relative humidity, leaf wetness, percent maize residue cover, distance to nearest maize residue, planting date, and previous crop. A time-duration value (TDV) variable was created to represent cumulative hours of favorable temperature (22 ≤ T ≤ 30°C) and relative humidity (≥95%). Disease severity was assessed at 2-week intervals on three to eight maize genotypes differing in gray leaf spot resistance and maturity at each location. Environmental, cultural, and disease data were summarized for four different periods d...
TL;DR: To the authors' knowledge, this is the first report of gray leaf spot of perennial ryegrass turf in California and Pyricularia grisea was isolated from symptomatic leaves of plants inoculated with the fungus.
Abstract: Gray leaf spot of perennial ryegrass (Lolium perenne L.) turf was first reported in the United States in 1991. The disease epidemic was primarily confined to golf course fairways in southeastern Pennsylvania (1). Subsequently, moderate to severe outbreaks of gray leaf spot occurred in perennial ryegrass fairways and roughs in numerous locations throughout the eastern and midwestern United States. In August 2001, a serious decline of perennial ryegrass turf was observed in a bermudagrass (Cynodon dactylon (L.) Pers) baseball field in Dodger Stadium in Los Angeles, CA, that had been overseeded with perennial ryegrass. The bermudagrass turf was not affected. The perennial ryegrass turf developed necrotic lesions that resulted in blighting of leaf blades. In laboratory assays, Pyricularia grisea (Cooke) Sacc., was consistently isolated from symptomatic ryegrass blades from turf samples collected from the site. Of the 12 P. grisea isolates collected from the assayed leaf blades, five isolates were selected for a pathogenicity assay. Twenty-five 'Legacy II' perennial ryegrass plants were grown from seeds in 4 × 4 in.-plastic pots, (10 × 10 cm) which were filled to 1 cm below the rim with granular calcine clay medium (Turface MVP, Allied Industrial Material Corp., Buffalo Grove, IL). Three weeks after seeding, plants were fertilized with a water-soluble 20-20-20 N-P-K fertilizer (1.3 g/liter of water) once per week. Treatments (isolates of P. grisea and a control) were arranged as a randomized complete block design with five replications. Five-week-old plants were sprayed with an aqueous suspension of P. grisea conidia (≈5 × 104 conidia per ml of sterilized distilled water with 0.1% Tween 20) using an atomizer until the leaves were completely wet. Plants sprayed with sterilized distilled water served as the control. After inoculation, individual pots were covered with clear polyethylene bags and placed in a controlled environment chamber maintained at 28°C and continuous fluorescent light (88 μE m-2 s-1). Four days after inoculation, necrotic lesions ( 90% of the leaf blade necrotic ) were assessed. P. grisea was isolated from symptomatic leaves of plants inoculated with the fungus. Disease incidence and severity on inoculated plants were 92 to 96% and 8.8 to 10, respectively. There were no significant differences in disease incidence and severity (P = 0.05) among the isolates of P. grisea included in the test. To our knowledge, this is the first report of gray leaf spot of perennial ryegrass turf in California. Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.
TL;DR: The ability to use pyraclostrobin at 21-day intervals and maintain control of early leaf spot similar to that of application of currently available fungicides at 14- day intervals represents potential savings in time, fuel, labor, and equipment costs.
Abstract: Field tests were conducted in Tifton, Georgia, in 1998 to 2000 and in Plains, Georgia, in 1999 and 2000 to determine the efficacy of pyraclostrobin on early leaf spot (Cercospora arachidic...
TL;DR: Evaluated the behavior of corn genotypes when inoculated with P. ananas in the greenhouse reinforced those previously obtained that showed the role of the bacterium as the initiator agent of the disease.
Abstract: A leaf spot disease in maize has been reported throughout all corn producing areas in Brazil, and its incidence and severity have increased significantly. Initial symptoms are characterized by the development of dark green water-soaked leaf spots, which later turn into straw-colored necrotic lesions. Some authors associated the symptoms of this disease to those of the disease Phaeosphaeria Leaf Spot caused by fungus Phaeosphaeria maydis (f. imperf. Phyllosticta sp.). However, we reported in previous works the involvement of a bacterium, the Pantoea ananas (syn. Erwinia ananas) as the initiator agent this disease. The aim of this work was to evaluate the behavior of corn genotypes when inoculated with P. ananas in the greenhouse. The results reinforced those previously obtained that showed the role of the bacterium as the initiator agent of the disease.
TL;DR: Seasonal variations in temperature had a large effect on the length of the latent period, which increased when mean daily temperatures were less than 5 °C, and an assumption that the leaf birth rate changed around the time stem extension began (GS 2-0) improved the fit of the model.
TL;DR: In the authors' experiments it was indicated that Trichoderma harzianum suppresses pathogenic fungi at the concentration 0,5 g of Supresivit per 1 kg of the fertilizer and higher ones, and the effect on higher yields was observed.
Abstract: The biopreparation Supresivit based on spores from the fungus Trichoderma harzianum was applied as a dressing mixed with mineral fertilizers: NPK, LAV (ammonium nitrate with limestone) and DASA (ammonium nitrate and ammonium sulphate). Our experimental plots with spring barley, winter wheat, winter oil rape, maize and potatoes were fertilized with the mixtures of the biopreparation (1 g, 0.5 g and 0.1 g per 1 kg of fertilizer). There were two check variants, the first variant without any fertilization and without biopreparation, the second with fertilizer and without biopreparation. We observed the infestation of plants with pathogenic fungi and yield parameters. In our experiments it was indicated that Trichoderma harzianum suppresses pathogenic fungi at the concentration 0,5 g of Supresivit per 1 kg of the fertilizer and higher ones. The plants from treated plots had lower infestation - decreasing about 5-15% superficial infestation: tan spot of barley - yellow leaf spot on cereals and leaf blotch of ba...
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TL;DR: The management of Gerbera leaf spot disease, revealed that the fungicides Tridemorph (0.1 %), Ziram ( 0.25 %), and Mancozeb (0.25 %) were effective in inhibiting the pathogen in vitro and in controlling the disease in pot culture experiment.
Abstract: The management of gerbera leaf spot disease, revealed that the fungicides Tridemorph (0.1 %), Ziram (0.25%) and Mancozeb (0.25 %) were effective in inhibiting the pathogen in vitro and in controlling the disease in pot culture experiment. Among the plant extracts, Piper nigram and Curcuma longa at seven per cent concentration were found to be effective in controlling the disease in vitro conditions. The bioagents viz., Trichoderma viridae, Aspergillus awamori and Trichoderma hamatum were also observed to check the growth of the pathogen.
TL;DR: It is concluded that plant height could affect tan spot development in durum wheat under conditions prevalent in southern Saskatchewan, and that this is probably mediated by canopy density.
Abstract: Tan spot [caused by Pyrenophora tritici-repentis (Died.) Drechs.] is the most important leaf disease of durum wheat (Triticum turgidum L. var. durum ). Most of the durum cultivars in western Canada are of conventional height but development of shorter cultivars is desirable. Changes in microenvironment resulting from a height reduction might cause greater leaf spot development. The effect of plant height on tan spot of durum wheat was determined in five pairs of genotypes near-isogenic for plant height and five randomly selected populations, each with a semidwarf and a conventional height parent. These were grown in five environments in Saskatchewan (1996-1998 at Swift Current, 1997-1998 at Indian Head), and evaluated for tan spot reaction in a growth chamber. There was no difference in tan spot reaction under controlled conditions between short and tall genotype(s) in each pair or population, although there were differences within each height category. Under field conditions, short genotypes had either equal or greater disease than tall genotypes. Contrasts between all short and tall genotypes also showed that the tall had less disease in 1998 at Indian Head (9.8 for tall, 10.2 for short) and in all years at Swift Current (9.5 and 9.9 in 1996, 8.1 and 8.7 in 1997, 8.5 and 8.9 in 1998, for tall and short, respectively). However, there was genetic variability within populations, with some short having equal or less disease than tall genotypes. Some of these short genotypes also had a low tan spot lesion type under controlled conditions. We conclude that plant height could affect tan spot development in durum wheat under conditions prevalent in southern Saskatchewan, and that this is probably mediated by canopy density.
Journal Article•
TL;DR: Two hundred germplasm lines along with six commercial varieties of mungbean were evaluated for resistance to yellow mosaic virus, cercospora leaf spot and powdery mildew at four sowing dates spread over two seasons under field conditions.
Abstract: Two hundred germplasm lines along with six commercial varieties of mungbean were evaluated for resistance to yellow mosaic virus, cercospora leaf spot and powdery mildew at four sowing dates spread over two seasons under field conditions. Genotypic differences were observed for resistance to these three diseases. One hundred and sixty nine genotypes were identified as resistant to yellow mosaic virus. Out of these, 18 genotypes had less than 1% leaf area affected. Thirty five genotypes were found to be resistant to cercospora leaf spot. One hundred and seventy four genotypes were identified as resistant to powdery mildew. Twenty one genotypes were found to be resistant to all the three diseases.