Showing papers on "Leaf spot published in 1991"
TL;DR: In this article, the authors investigated the changes in glucosinolate concentration in leaves of oilseed rape following inoculation with the dark leaf spot pathogen (Alternaria brassicae).
Abstract: SUMMARY
The glucosinolates are thought to contribute to resistance to pests and diseases in members of the Cruciferae, including oilseed rape (Brassica napus) and they are known to accumulate in Brassica tissues after infestation by various pests. The present study investigated the changes in glucosinolate concentration in leaves of oilseed rape following inoculation with the dark leaf spot pathogen (Alternaria brassicae). Fourth and sixth leaves of the single-low cultivar Bienvenu (low in erucic acid) and the double-low cultivar Cobra (low in erucic acid and glucosinolate) were removed at intervals up to twenty days after inoculation and analysed for glucosinolate content using HPLC. Glucosinolates accumulated in inoculated leaves of both cultivars but the accumulation was greater for cv. Bienvenu, especially in sixth leaves. Among the glucosinolates, aliphatic compounds accumulated rapidly in cv. Bienvenu, but later declined. Indolyl and aromatic glucosinolates accumulated in both cultivars, but at a slower rate than the aliphatic glucosinolates. There were differences in the extent to which individual glucosinolates accumulated after inoculation. Disease symptoms were initially more extensive on cv. Cobra than on cv. Bienvenu but were similar on corresponding leaves of the two cultivars by the end of the experiment. However, sixth leaves had significantly less lesioning than fourth leaves. Glucosinolate accumulation in infected oilseed rape may restrict the spread of existing fungal infection or inhibit subsequent attempted infections, especially in younger leaves.
147 citations
TL;DR: The results obtained show that bacterial antagonists of sclerotial fungi can be used as seed inocula to improve plant growth through disease suppression and reduce disease and fungal wilt.
Abstract: Bacteria isolated on nutrient agar and King's medium B from sunflower leaves, crown and roots inhibited in vitro growth of the leaf spot and wilt pathogens Alternaria helianthi, and Sclerotium rolfsii, respectively, and also the root rot pathogensRhizoctonia solani and Macrophomina phaseolina. Antagonistic bacteria from leaves were mainly actinomycetes and pigmented Gram-positive bacteria, while those from roots and crowns were identified asPseudomonas fluorescens-putida, P. maltophilia, P. cepacia, Flavobacterium odoratum andBacillus sp. In soil bioassays, when used as seed inoculum in the presence ofS. rolfsii, P. cepacia strain N24 increased significantly the percentage of seedling emergence. Bacterial strains which exhibited broad spectrum in vitro antagonistic activity were tested for colonisation of sunflower roots, when used as a seed inoculum. Good colonisers (104 to 106 bacteria/g root) were consistent in their ability to reduce disease and fungal wilt. A seedling having a primary root length < 5 cm with fewer lateral roots, necrosed cotyledons or crown and a wilted shoot indicated its diseased status. On an average, only 30% of seedlings were diseased when treated with the antagonistic strains, in the presence of the pathogen, while 60% of the seedlings were diseased in the presence of the pathogen alone. In microplots treated with strain N24, only 1 to 3% of the seedlings were wilted, while 14% of the seedlings were wilted in the presence of the pathogen alone. The results obtained show that bacterial antagonists of sclerotial fungi can be used as seed inocula to improve plant growth through disease suppression
64 citations
TL;DR: Gray leaf spot of maize (Zea mays L.), caused by Cercospora zeaemaydis Tehon & Daniels, is a limiting factor in some areas where continuous minimum tillage practices are followed.
Abstract: Gray leaf spot of maize (Zea mays L), caused by Cercospora zeaemaydis Tehon & Daniels, is a limiting factor in some areas where continuous minimum tillage practices are followed The inheritance of reaction to this pathogen was studied using a diallel of 14 elite inbreds The 91 single crosses were grown in field nurseries in Montgomery and Wythe counties, Virginia, in 1987 and 1988 using randomized complete-block designs
48 citations
TL;DR: Botryosphaeria obtusa, which causes black rot of apple fruit and frogeye leaf spot, produced phytotoxins in culture, infected fruit, and spore germination fluids.
Abstract: Botryosphaeria obtusa, which causes black rot of apple fruit and frogeye leaf spot, produced phytotoxins in culture, infected fruit, and spore germination fluids. Mellein was the most abundant toxin isolated from the culture fluid. Other toxins isolated were tyrosol, 4-hydroxymelein, 5-hydroxymellein, and 4-hydroxybenzaldehyde. Seventeen apple cultivars and eight weed species were used in a leaf bioassay to determine phytotoxicity of the toxins. The apple cultivars, Supergold and Silverspur, were highly sensitive to all toxins. Only three apple cultivars showed moderate resistance to most toxins (...)
47 citations
TL;DR: Three soybean cultivars were evaluated for yield losses resulting from frogeye leaf spot caused by Cercospora sojina Hara at two locations in Nigeria that have a high natural infestation of C.Sojina .
44 citations
TL;DR: Epidemic components of leaf spot caused by Cercospora zebrina were evaluated in repeated experiments on two clones of Trifolium repens Tillman', which vary in response to infection by clover yellow vein virus (CYVV).
Abstract: Epidemic components of leaf spot caused by Cercospora zebrina were evaluated in repeated experiments on two clones of Trifolium repens Tillman', which vary in response to infection by clover yellow vein virus (CYVV). CYVV-free and CYVV-infected plants of clones T7 (low virus titer, virtually asymptomatic) and T17 (high virus titer, symptomatic) were grown at 28/23 or 22/17 C and monitored for 17 days after inoculation with C. zebrina (...)
29 citations
TL;DR: The post-inoculation temperature and humidity conditions most favourable for development of Phoma black stem and leaf spot and Leptosphaerulina leaf spot diseases on lucerne were determined and the severity of petiole disease was much less affected than that of leaf disease by an increase in the period of high-humidity incubation.
Abstract: The post-inoculation temperature and humidity conditions most favourable for development of Phoma black stem and leaf spot (Phoma medicaginis) and Leptosphaerulina leaf spot (Leptosphaerulina trifolii) diseases on lucerne (Medicago sativa) were determined using controlled-environment cabinets. P. medicaginis caused more severe leaf disease at day/night temperatures of 21/16 and 18/13°C compared with 15/10°C; petiole disease was most severe at 21/16°C compared with 18/13°C, and least severe at 15/ 10°C. L. trifolii generally caused more severe leaf disease at 18/13°C compared with 21/16°C or 15/10°C, but the most severe petiole disease occurred at 21/16°C with least at 15/10°C Leaf disease caused by either P. medicaginis or L. trifolii was always more severe with the longest period (168 h) of high-humidity incubation and, generally, increased with increasing periods of high humidity. The severity of petiole disease was much less affected than that of leaf disease by an increase in the period of high-humidity incubation.
25 citations
TL;DR: The teleomorph enables the fungus to survive the period between host crops, and the ascospores are the primary inoculum for infecting winter oilseed rape.
23 citations
TL;DR: The systemic fungicides exhibited some curative properties because of their effects in suppressing previous infections, and defoliation and yields did not differ significantly among the different fungicide treatments.
23 citations
TL;DR: It is concluded that the complex of the components may be a pathogenicity factor of B. zeicola race 3 for rice and maize plants.
21 citations
TL;DR: Late leaf spot reduced the potential yield (harvested and dropped pods) of Florunner peanut by 37% in 1986 and 46% in 1987 and in non-treated plots, the abscission of pods was initiated later but progressed fast...
Abstract: Late leaf spot, induced by Cercosporidium personatum (Berk. & Curt.) Deighton, causes serious yield losses of peanut (Arachis hypogaea L.) in the southeastern United States. A two-year study was conducted to observe progress of late leaf spot and to evaluate subsequent effects of late leaf spot on accumulation of dry matter, leaf area index (LAI), and pod production of Florunner peanut in fungicide-treated and non-treated plots. Disease severity, which is an expression of both disease-induced defoliation and necrotic leaf area, was used as an indicator of disease progression in the field. The leaf dry weight, LAI, and the dry weight of the total biomass were significantly different at 93 days after planting (DAP) in 1986, and at 78 DAP in 1987 between fungicide-treated and non-treated plots. Late leaf spot reduced the potential yield (harvested and dropped pods) of Florunner peanut by 37% in 1986 and 46% in 1987. In non-treated plots, the abscission of pods was initiated later but progressed fast...
TL;DR: A strong negative interaction between rust and early leaf spot, and a close correspondence between rust intensification andRhizoctonia blight development were indicated.
Abstract: Spontaneous epidemics of rust, early leaf spot, late leaf spot, andRhizoctonia blight simultaneously developed in a groudnut plot. Geostatistical techniques were used to describe and compare the spatial patterns of epidemics.Rhizoctonia blight exhibited a strong aggregative structure, contrasting with leaf spots and rust. The latter disease developed a general epidemic, in combination with local intensification. A strong negative interaction between rust and early leaf spot, and a close correspondence between rust intensification andRhizoctonia blight development were indicated.
TL;DR: Two double-cross populations were used to evaluate the efficiency of independent, alternate, and simultaneous selection practiced from the F2 to F8 for resistance to anthracnose and angular leaf spot of common bean.
Abstract: Two double-cross populations were used to evaluate the efficiency of independent, alternate, and simultaneous selection practiced from the F2 to F8 for resistance to anthracnose and angular leaf spot of common bean (Phaseolus vulgaris L.). Seven resistant and high-yielding lines were selected from each of the four environments used during this study. These lines and the seven parents involved in two populations were evaluated in an 8 × 8 lattice design with three replications in two cropping seasons. Pathogen inoculum was used to create the three test environments: anthracnose alone, angular leaf spot alone, and anthracnose and angular leaf spot together. All entries were also evaluated in a fourth, disease-free environment. Selection for resistance to anthracnose and angular leaf spot was effective in both populations. Mean disease scores of all selected lines for anthracnose were lower than that of angular leaf spot irrespective of selection environment. Among the three stress environments, yields were higher in the anthracnose environment. However, lines selected alternately for anthracnose and angular leaf spot were usually higher yielding, and the highest yielding line in both populations originated from this selection environment. The mean yield of selected lines was higher and the highest yielding line originated from the population involving a parent (G 1805) belonging to the Mexican highland race ‘Jalisco’. Positive association existed between seed yield of protected and pathogen-inoculated environments. No association was found between resistance to anthracnose and angular leaf spot.
TL;DR: This paper confirms the existence of variation in virulence within the cool temperature biotype of Stemphylium vesicarium, the causal agent of a lucerne leaf spot disease, within the winter-active cultivar Sequel.
Abstract: This paper confirms the existence of variation in virulence within the cool temperature biotype of Stemphylium vesicarium, the causal agent of a lucerne leaf spot disease. The new strain shows high levels of virulence on an experimental line of lucerne (SS2) that was developed by selecting for resistance to S. vesicarium within the winter-active cultivar Sequel. The experimental line UC1250 (semi-dormant), which was bred for resistance in the U.S.A. and was resistant upon initial testing in Australia, remained relatively resistant to the new race, as did a selection (TS2) made from cv. Trifecta (semi-dormant). UC1249 (winter-active), which was also selected for resistance to S. vesicarium in . the U.S.A., was relatively susceptible to the new race.
TL;DR: Rainfed soybean crops in the northern coastal region of New South Wales were surveyed from 1985 to 1987 for the prevalence and severity of diseases, but only rust, black leaf blight and bacterial pustule (Xanthomonas campestris pv. glycines) were present each season.
Abstract: Rainfed soybean (Glycine max) crops in the northern coastal region of New South Wales were surveyed from 1985 to 1987 for the prevalence and severity of diseases. Sixteen diseases were recorded over the 3 seasons, but only rust (Phakopsora pachyrhizi), black leaf blight (Arkoola nigra) and bacterial pustule (Xanthomonas campestris pv. glycines) were present each season. Rust was the most significant disease, infecting 50, 20 and 6% of crops in 1985, 1986 and 1987. The severity of rust was related to rainfall and temperature after flowering, with the most severe outbreaks in the higher rainfall area of the lower Richmond Valley. Black leaf blight was also significant and occurred in 39, 10 and 27% of crops in 1985, 1986 and 1987, but in most crops severity was low. The other diseases recorded were downy mildew (Peronospora manschurica), root and stem rot (Phytophthora megasperma f. sp. glycinea), stem canker (Rhizoctonia sp.), pod and stem blight (Phomopsis spp.), anthracnose (Colletotrichum spp.), seedling blight (Rhizoctonia sp.), stem rot (Phytophthora sp.), white mould (Sclerotinia sclerotiorum), flower blight (Botrytis cinerea), leaf spot (Phoma sp.), bacterial blight (Pseudomonas syringae pv. glycinea), mosaic (soybean mosaic virus) and orange bark (not identified). All of these diseases were generally of low prevalence and severity.
TL;DR: Three growth models (logistic, Gompertz, and Weibull) were fitted to the severity values by nonlinear regression and resulted in disease progress curves that were almost symmetrically sigmoidal.
Abstract: The progress and spread of dark leaf spot (Alternaria brassicicola) in three cultivars of cabbage (Brassica oleracea var. capitata) were characterized in two seasons. The intensification of disease in time at each of six points along a gradient from a line source of diseased plants resulted in disease progress curves that were almost symmetrically sigmoidal. Three growth models (logistic, Gompertz, and Weibull) were fitted to the severity values by nonlinear regression. The shape parameter (c) for the Weibull function averaged 3.61 (ranged from 2.40 to 6.36) (.)
TL;DR: Effects of leaf susceptibility and seed treatment with the systemic fungicides tebuconazole or difenoconazole on Altenaria macrospora in Pima cotton were examined and no significant differences in disease control were detected between the two fungicides.
Abstract: Effects of leaf susceptibility and seed treatment with the systemic fungicides tebuconazole (Raxil) or difenoconazole (Dragon) on Altenaria macrospora in Pima cotton were examined under glasshouse conditions and in the field. In the absence of fungicide, the susceptibility of cotyledons to Alternaria-induced shedding increased with seedling age. Effects of seed treatment with fungicide were evident even on the third true leaves, and persisted up to 39 days after planting. Disease suppression was determined both by the fungicide and also by the susceptibility of the host tissue: seed treatment suppressed Alternaria-induced shedding of cotyledons for 18 days, but not 29 days after planting In a field trial, disease progress was delayed by 20-24 days in plots planted with treated seeds. The effect persisted for up to 86 days after planting. Alternaria-induced defoliation at later stages of the season was not affected by the seed treatment. No significant differences in disease control were detected between the two fungicides.
TL;DR: Parallel veins of orchardgrass leaves were examined in relation to width of leaf spots incited by Stagonospora arenaria and found that veins with large vascular bundles alternated regularly with veins having small vascular bundles.
Abstract: Parallel veins of orchardgrass leaves were examined in relation to width of leaf spots incited by Stagonospora arenaria Trials of 12 greenhouse-inoculated plants and 12 naturally infected, field-grown single-cross lines that ranged widely in mean leaf spot size gave similar results Veins with large vascular bundles (enlarged metaxylem vessels present) alternated regularly with veins having small vascular bundles (enlarged metaxylem vessels absent) Vascular bundles usually were connected to the lower and/or upper epidermis by girders of lignified sclerenchyma and/or girders of thin-walled cells ()
TL;DR: When leaf spot diseases are severe, early harvest of alfalfa has been recommended to preempt defoliation, preserve yield and quality, and prevent accumulation of pathogen-infested leaf debris.
Abstract: When leaf spot diseases are severe, early harvest of alfalfa (Medicago sativa) has been recommended to preempt defoliation, preserve yield and quality, and prevent accumulation of pathogen-infested leaf debris. Effects of debris on incidence of all leaf spots taken together (percentage of leaves with lesions caused by species of Leptosphaerulina, Stemphylium, Phoma, and/or Cercospora), frequency of leaf spot pathogens (percentage of diseased leaflets infected by each pathogen), and yield were evaluated during five periods of alfalfa growth in each of 2 yr among untreated plots (10.0×4.1 m) and plots in which naturally infested debris was either removed or added immediately after each harvest (...)
TL;DR: The paper discusses the disease in Zimbabwe against the background of work reported from other countries on its effect on yield and on its epidemiology and control.
Abstract: Leaf spots caused by Alternaria macrospora and A. alternata are common in cotton crops around the world. Both species are, however, usually considered to be minor pathogens of Upland cotton (Gossypium hirsutum) but A. macrospora causes premature defoliation with resulting yield loss in cultivars of G. barbadense in Israel and in the USA. A. macrospora is also able to cause defoliation in Upland cotton if the crop is. predisposed to infection by environmental or physiological stress. In Zimbabwe the main predisposing factor is potassium deficiency. The paper discusses the disease in Zimbabwe against the background of work reported from other countries on its effect on yield and on its epidemiology and control.
TL;DR: Asparagus fern grown under conditions of low light (particularly a reduced photoperiod), high relative humidity, and temperature became severely infected and disease severity decreased with increasing age of fern at time of inoculation.
Abstract: Light intensity, photoperiod, relative humidity, and temperature during fern growth and fernage at timeof inoculation, and wetnessduration, light intensity, and temperature during infection period were examined to establish their effect on severity of Stemphylium leaf spot on asparagus. Plants were inoculatedwith a conidialsuspension of two isolates of Stemphylium sp. from asparagus. Disease assessments based on percentage stem area necrosis,percentagediebackof stem,and percentage infection of cladode tissue were made 10–14 days after inoculation. Asparagus fern grown under conditions of low light (particularly a reduced photoperiod), high relative humidity, and temperature became severely infected. Disease severity decreased with increasing age of fern at time of inoculation. Two days of wetness following inoculation were sufficientfor maximum diseasedevelopment; plants held at low temperature (14°C) had higher levels of infection than those held at 20 or 26°C. Light intensityduring the infectio...
01 Jan 1991
TL;DR: A necrotic leaf spot of Brazil wood trees is reported as caused by Pestalotiopsis maculans, which appears to be the first report of such a disease.
Abstract: A necrotic leaf spot of Brazil wood trees is reported as caused by Pestalotiopsis maculans. This appears to be the first report of such a disease.
TL;DR: The late appearance of gray leaf spot in West Africa implies that the disease may have little effect on yield, and area under the disease progress curve was largest for ICSV 1001 BF in 1986 and for IS 18696 in 1987 and 1988.
Abstract: The development of gray leaf spot on sorghum, caused by Cercospora sorghi, was monitored between 1986 and 1988 for a total period of 5 wk each year. The top four leaves of tagged plants infected by natural inoculum were rated weekly for disease severity on a 1–6 scale. Symptoms of gray leaf spot first appeared either shortly before or several days after anthesis. Thereafter, the progress of the disease was slow and symptoms became more severe toward physiological maturity. Final disease severity ratings on the fifth week in 1986 were 3.3, 3.6, and 3.9 for the sorghum lines ICSV 1001 BF, ICSV 16-3 BF, and ICSV 20-1 BF, respectively. In the following years, disease ratings on the fifth week were 4.8, 5.6, and 6.0 in 1987 and 2.4, 3.6, and 5.5 in 1988 for ICSV 1001 BF, ICSV 16-3 BF, and IS 18696, respectively. Area under the disease progress curve was largest for ICSV 1001 BF in 1986 and for IS 18696 in 1987 and 1988. The late appearance of gray leaf spot in West Africa implies that the disease may have little effect on yield
TL;DR: A new disease of perilla (Perilla frutescens) broke out in Oita Prefecture in 1990 and the causal fungus was identified as Corynespora cassiicola (Berk. & Curt.) Wei by the similarity to the description of Ellis (1971).
Abstract: A new disease of perilla (Perilla frutescens) broke out in Oita Prefecture in 1990. The symptoms of the disease appeared on leaves and stem as brown spot. Corynespora sp. was isolated from infected lesions. Conidia were hyaline to pale brown, obclavate to cylindrical, curved, broad at the base, formed on conidiophores singly or in chain. Conidiophores were pale to mid brown and erect. No stromata were observed. The optimum temperature of mycelial growth lied at 27.5-30°C. The fungus was pathogenic to 17 species including tomato, cowpea, sesame and others among 18 tested plants in inoculation experiments. Based on these morphological and pathological characters, the causal fungus was identified as Corynespora cassiicola (Berk. & Curt.) Wei by the similarity to the description of Ellis (1971).