Showing papers on "Leaf spot published in 2003"
TL;DR: This review summarizes the knowledge on pathogenic strategies employed by the fungus to plunder the host and strategies employ by potential host plants in order to ward off an attack.
Abstract: SUMMARY
Alternaria species are mainly saprophytic fungi However, some species have acquired pathogenic capacities collectively causing disease over a broad host range This review summarizes the knowledge on pathogenic strategies employed by the fungus to plunder the host Furthermore, strategies employed by potential host plants in order to ward off an attack are discussed
Taxonomy:Alternaria spp kingdom Fungi, subkingdom Eumycotera, phylum Fungi Imperfecti (a non-phylogenetic or artificial phylum of fungi without known sexual stages whose members may or may not be related; taxonomy does not reflect relationships), form class Hypomycetes, Form order Moniliales, form family Dematiaceae, genus Alternaria Some species of Alternaria are the asexual anamorph of the ascomycete Pleospora while others are speculated to be anamorphs of Leptosphaeria
Host Range: Most Alternaria species are common saprophytes that derive energy as a result of cellulytic activity and are found in a variety of habitats as ubiquitous agents of decay Some species are plant pathogens that cause a range of economically important diseases like stem cancer, leaf blight or leaf spot on a large variety of crops Latent infections can occur and result in post-harvest diseases or damping-off in case of infected seed
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588 citations
TL;DR: DNA fingerprinting of resistant isolates revealed that the mutations occurred in just five genetic backgrounds, suggesting that field resistance to the Q(o)I fungicides in Pyricularia grisea is due to a small number of ancestral mutations.
Abstract: Gray leaf spot caused by Pyricularia grisea is a highly destructive disease of perennial ryegrass turf. Control of gray leaf spot is dependent on the use of preventative fungicide treatmen...
214 citations
TL;DR: Lab experiments demonstrated the ability to induce germination and vegetative growth of BacB from a spore formulation, without shaking or fermentation equipment, which shows promise for optimizing Bacillus sp.
108 citations
TL;DR: It is suggested that plant adaptations that reduce water retention on leaves may also reduce disease incidence, but the selective advantage of these traits will vary among habitats.
Abstract: Many foliar pathogens require free water to germinate; therefore, disease pressure should favor plants that are able to repel water. For a suite of 18 sympatric clover species (Trifolium and Medicago, Fabaceae), we evaluated leaf traits affecting leaf wetness and susceptibility to infection by the fungal pathogen Stemphylium sp., causal agent of Stemphylium leaf spot. Spore germination increased with time in free water, and the relative susceptibility of host plants to infection was proportional to the duration of water retention on leaves. Larger leaves captured more water and retained it longer. Unexpectedly, trichomes and leaf wettability did not affect water capture. For clovers planted within natural clover populations at two sites, infection was threefold greater at the wetter site. At the drier site, water retention on the leaf surface was an important predictor of infection rates across host species, but persistent fog and dew at the wetter site reduced the importance of rapid leaf drying. Our results suggest that plant adaptations that reduce water retention on leaves may also reduce disease incidence, but the selective advantage of these traits will vary among habitats.
102 citations
TL;DR: It is concluded that systemic suppression of foliar diseases induced by compost amendments is a rare phenomenon and inoculation of compost-amended potting mixes with biocontrol agents such as T(382) that induce systemic resistance in plants can significantly increase the frequency of systemic disease control obtained with natural compost amendments.
Abstract: Composts can induce systemic resistance in plants to disease. Unfortunately, the degree of resistance induced seems highly variable and the basis for this effect is not understood. In this work, only 1 of 79 potting mixes prepared with different batches of mature, stabilized composts produced from several different types of solid wastes suppressed the severity of bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae compared with disease on plants produced in a nonamended sphagnum peat mix. An additional batch of compost-amended mix that had been inoculated with Trichoderma hamatum 382 (T382), which is known to induce systemic resistance in plants, also suppressed the disease. A total of 11 out of 538 rhizobacterial strains isolated from roots of radish seedlings grown in these two compostamended mixes that suppressed bacterial leaf spot were able to significantly suppress the severity of this disease when used as inoculum in the compost-amended mixes. The most effective s...
92 citations
TL;DR: Citrus is affected by four diseases caused by Alternaria spp.
Abstract: Citrus is affected by four diseases caused by Alternaria spp. Brown spot of tangerines, leaf spot of rough
lemon, postharvest black rot of fruit occur widely in citrus areas of the world and are caused by different pathotypes
of A. alternata. Mancha foliar occurs only on Mexican lime in western Mexico and is caused by A. limicola. Tangerine
and rough lemon pathotypes produce host-specific toxins that affect membranes and respiration, respectively. Black
rot is always associated with wounds and is caused by most citrus-associated isolates of A. alternata that produce
endopolygalacturonase. Alternaria brown spot is a serious disease of susceptible tangerines and their hybrids in
semi-arid Mediterranean climates as well as in more humid areas. Conidia, produced on lesions on mature and
senescent leaves and stems under humid conditions, are dispersed by wind, and infect all juvenile tissues of susceptible
cultivars when temperature and leaf wetness conditions are favorable. Commercially acceptable cultivars resistant
to brown spot are being developed. Disease severity can be reduced by planting disease-free nursery stock on
wider spacings, pruning tree skirts, and reducing irrigation and nitrogen fertilization. However, fungicides such as
dithiocarbamates, triazoles, strobilurins, iprodione, or copper fungicides are used in most areas for disease control. A
disease-forecasting model, the Alter-Rater, has been developed in Florida to assist in timing fungicide sprays.
88 citations
TL;DR: Induced resistance by C3 was not host or pathogen specific; foliar application of heat-killed C3 cells controlled B. sorokiniana on wheat and also was effective in reducing the severity of brown patch, caused by Rhizoctonia solani, on tall fescue.
Abstract: Kilic-Ekici, O., and Yuen, G. Y. 2003. Induced resistance as a mechanism of biological control by Lysobacter enzymogenes strain C3. Phytopathology 93:1103-1110. Induced resistance was found to be a mechanism for biological control of leaf spot, caused by Bipolaris sorokiniana, in tall fescue (Festuca arundinacea) using the bacterium Lysobacter enzymogenes strain C3. Resistance elicited by C3 suppressed germination of B. sorokiniana conidia on the phylloplane in addition to reducing the severity of leaf spot. The pathogen-inhibitory effect could be separated from antibiosis by using heat-inactivated cells of C3 that retained no antifungal activity. Application of live or heat-killed cells to tall fescue leaves resulted only in localized resistance confined to the treated leaf, whereas treatment of roots resulted in systemic resistance expressed in the foliage. The effects of foliar and root applications of C3 were long lasting, as evidenced by suppression of conidial germination and leaf spot development even when pathogen inoculation was delayed 15 days after bacterial treatment. When C3 population levels and germination of pathogen conidia was examined on leaf segments, germination percentage was reduced on all segments from C3-treated leaves compared with segments from nontreated leaves, but no dose–response relationship typical of antagonism was found. Induced resistance by C3 was not host or pathogen specific; foliar application of heat-killed C3 cells controlled B. sorokiniana on wheat and also was effective in reducing the severity of brown patch, caused by Rhizoctonia solani, on tall fescue. Treatments of tall fescue foliage or roots with C3 resulted in significantly elevated peroxidase activity compared with the control.
77 citations
TL;DR: It was demonstrated that septoria leaf spot had a considerably higher impact on grain yield than mildew, and the optimal fungicide dose increased almost linearly with N rate above a minimum N rate, but with a large dependency on price relations.
Abstract: The effects of nitrogen (N) rate and timing on need for fungicide application in winter wheat (Triticum aestivum) were investigated in 3 years of field experiments on loamy sand soils in Denmark. A two-factor completely randomized experimental design was used, comprising seven combinations of different N fertilizer rates and application times, and five doses of fungicide (co-formulation propiconazole and fenpropimorph). Two different varieties of winter wheat with high susceptibility to powdery mildew (Blumeria graminis) were used, Florida in the first season and Pepital in the last two seasons. The severity of powdery mildew and septoria leaf spot (mainly Septoria tritici) varied between seasons from slight to moderate with powdery mildew dominating in the first season and septoria leaf spot in the last season. The severity of both powdery mildew and septoria leaf spot assessed as the Area Under the Disease Progress Curve (AUDPC) was increased by application of N in all years, and more so by early applied N. Grain yields increased with increasing N rate and fungicide dose. However, the observed grain yields did not reveal any N×fungicide interactions. Regression models were therefore fitted, relating grain yield to rate and timing of N fertilizer and to AUDPC of powdery mildew and septoria leaf spot, and relating AUDPC to rate and timing of N fertilizer and to fungicide dose. They demonstrated that septoria leaf spot had a considerably higher impact on grain yield than mildew. The optimal fungicide dose and N rate were defined as those giving the highest economic return. The regression models were used to estimate the effect of N rate and timing on optimal fungicide dose, and the effect of fungicide application on optimal N rate. The optimal fungicide dose increased almost linearly with N rate above a minimum N rate, but with a large dependency on price relations. Early applied N caused a higher demand for disease control. The fungicide applications in the model were mainly driven by the need to control septoria leaf spot, whereas powdery mildew gave a poor net return for control. The estimated optimal N fertilizer rate for untreated diseased crops was 60 kg N/ha lower than for crops without disease. The use of fungicides with an efficacy twice that of the EBI-fungicides used in this experiment would increase the optimal N rate by c. 20 kg N/ha.
76 citations
TL;DR: These genotypes from the primary and secondary common bean gene pools resistant to Andean and Mesoamerican races of P. griseola offer a potential for developing broad and durable ALS resistance.
Abstract: Angular leaf spot (ALS) is one of the most devastating diseases of common bean (Phaseolus vulgaris L.) in tropical and subtropical countries. The causal fungus, Phaeoisariopsis griseola(Sacc.) Ferr. is highly variable and a diverse source of resistance genes is required to manage this disease. We evaluated a common bean core collection,primary and secondary gene pools and lines derived from inter-specific crosses of P. vulgaris and P. coccineus or P. polyanthus (secondary gene pool) for resistance to angular leaf spot. Of the 1441 accessiones in the core collection, only 2.2% were resistant to both Andean and Mesoamerican races of P. griseola, 28% were resistant only to Andean and 9% to Mesoamerican races. Of the 32 resistant accessions, 68%originated from Bolivia, Colombia,Guatemala and Mexico. More accessions from these countries should be examined for P. griseola reaction. Very few wild P. vulgaris accessions (4%), were resistant to ALS. In contrast, high levels of resistance (62%) were found in the secondary gene pool. Among the 1010 lines from inter-specific crosses, 109 lines were highly resistant. These genotypes from the primary and secondary common bean gene pools resistant to Andean and Mesoamerican races of P. griseola offer a potential for developing broad and durable ALS resistance.
66 citations
TL;DR: The ability of antibiotic-producing streptomycetes to colonize alfalfa plants and influence the activities of a fungal plant pathogen and a mutualistic symbiont was investigated and careful selection of Streptomyces isolates for use in biological control of plant diseases will limit the potential negative impacts on rhizobia.
66 citations
TL;DR: Fungicide applications may be reduced in cases of low powdery mildew severity combined with low crop susceptibility to this disease, as this low susceptibility was found to be obtainable with split N application strategies, as the severity of both powdery Mildew and septoria leaf spot increased with increasing leaf N concentration.
Abstract: Data from a two-factorial experiment carried out during 3 years were used to analyse the effects of crop nitrogen (N) status on disease development, and the effects of N supply and disease on light interception (IPAR) and radiation use efficiency (RUE) in winter wheat (Triticum aestivum). The factors in the experiment comprised seven strategies of N fertilizer application including different N rates and timing of application, and five doses of fungicide application for control of the leaf diseases powdery mildew (Blumeria graminis) and septoria leaf spot (Septoria tritici). Light interception was estimated from weekly measurements of crop spectral reflectance. The increase of crop dry matter was mainly affected by N fertilizer and disease through effects on IPAR. Early N application increased IPAR and thus dry matter growth more than later N application. A split N strategy may ensure both high N uptake and high growth rates of the crop. Only septoria leaf spot significantly reduced RUE. Septoria leaf spot was found to be up to nine times more detrimental to grain yield than powdery mildew for similar severity levels. Fungicide applications may therefore be reduced in cases of low powdery mildew severity combined with low crop susceptibility to this disease. This low susceptibility was found to be obtainable with split N application strategies, as the severity of both powdery mildew and septoria leaf spot increased with increasing leaf N concentration. A similar but smaller correlation was obtained between disease severity and canopy size. Measurements of canopy size using spectral reflectance may be used as a simple indicator of general crop susceptibility to disease, whereas measurements of leaf N concentration may be used as input into decision support systems for fungicide application.
TL;DR: A polymerase chain reaction (PCR)-based method was developed and evaluated and found to be reliable for the extraction of M. oryzae DNA from infected perennial ryegrass tissue.
Abstract: Gray leaf spot caused by Magnaporthe oryzae is a serious disease of perennial ryegrass in the midwestern United States. Symptoms of gray leaf spot can be confused with those caused by other fungal diseases that also are common during periods of high temperatures and ample moisture. Because turf managers must select appropriate fungicides for remedial treatment, accurate and timely identification of the pathogen is essential for efficient and effective disease management. We developed and evaluated a polymerase chain reaction (PCR)-based method to detect M. oryzae in infected perennial ryegrass tissue. The method utilizes a commercially available kit that is used for isolation and amplification of plant DNA from leaf tissue. The kit protocol was modified and found to be reliable for the extraction of M. oryzae DNA from infected perennial ryegrass. Primers were designed to amplify a 687-bp fragment of the Pot2 transposon that is found in multiple copies in the genome of the pathogen. The protocol amplified amounts of purified DNA as low as 5 pg and consistently and specifically detected M. oryzae in single diseased leaf blades as well as in field samples of infected perennial ryegrass. The total time required for detection was approximately 4 to 8 h.
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01 Jan 2003
01 Jan 2003
TL;DR: The spread of the disease during the 1990s in several countries and regions, and the important socio-economic consequences are discussed, as well as the methods, developed in the last decade, to identify the species of Mycosphaerella that cause leaf spot diseases in banana.
Abstract: By the end of the 1980s, black leaf streak disease caused by Mycosphaerella fijiensis was present in all continents where bananas or plantains were grown, although distribution in some regions was limited to a few countries. In this presentation, the spread of the disease during the 1990s in several countries and regions, and the important socio-economic consequences are discussed. From 1990 to 1999, new records of black leaf streak disease were reported from six countries in Africa, eight in Asia, eight in Latin America and the Caribbean, and one from Australasia/Oceania. M. fijiensis has also spread within countries to ecological niches that were previously occupied by M. musicola, the causal agent of Sigatoka disease, thus threatening the survival of this pathogen. This presentation also discusses the methods, developed in the last decade, to identify the species of Mycosphaerella that cause leaf spot diseases in banana.The methods were used to confirm the synonymy of M. fijiensis var. difformis and M. fijiensis, and have provided the opportunity to study the genetic diversity of pathogen populations among isolates from different geographical regions. Resumen Propagación, detección e impacto de la Sigatoka negra y otras enfermedades foliares causadas por Mycosphaerella de bananos en la década de los 90 Al finales de la década de los 80, la Sigatoka negra, causada por Mycosphaerella fijiensis, ya se encontraba presente en todos los continentes donde se cultivan bananos y plátanos, pero su distribución en algunas regiones estaba limitada a unos pocos países. En esta presentación, se discutirá brevemente la propagación de la enfermedad durante los 90 abarcando varios países y regiones, y su impacto socioeconómico. De 1990 a 1999, se reportaron nuevos registros de la enfermedad desde seis países en Africa, ocho en Asia, ocho en América Latina y el Caribe, y solo un informe de un país en Australasia/Oceania. M. fijiensis también ha estado progresando en los países para llegar a los nichos ecológicos que anteriormente estaban ocupados solo por 21 Session 1 R.A. Romero Chiquita Brands, San José, Costa Rica MyLsd 17x24 25/06/03 15:15 Page 21
TL;DR: Although the pathogen produces highly toxic compounds, there have been no definitive reports of ill health in animals that have grazed pastures with natural levels of leaf infection of P. semeniperda.
Abstract: Pyrenophora semeniperda (anamorph Drechslera campanulata) causes a minor leaf spot and seed infection of at least 36 genera of annual or perennial grasses and has been recorded on several dicotyledonous species. The fungus causes distinctive ‘ring spot’ leaf lesions, 1–4 mm in size with a light-coloured centre and dark-brown margin. It also produces prominent black stromata up to several centimetres long from germinating seeds. Thus, although it is a relatively uncommon fungus, it is unlikely to be overlooked. The current world distribution is in temperate grasslands and cereal growing areas of Argentina, Australia, Canada, Egypt, New Zealand, South Africa and the United States of America: there are no definite records from Europe or Asia. Reports of its epidemiology are reviewed to show that the fungus is unlikely to be more than a minor leaf and seed disease. It is readily seed-borne on a wide range of cereals and grasses that are traded internationally, so there have been many opportunities for it to spread beyond the limits of its natural distribution. There are no reports of economic losses associated with P. semeniperda. Although the pathogen produces highly toxic compounds, there have been no definitive reports of ill health in animals that have grazed pastures with natural levels of leaf infection of P. semeniperda.
TL;DR: There was no correlation between BacB density and Cercospora leaf spot disease severity, indicating that neither antibiosis nor parasitism is likely an important mechanism of disease control.
TL;DR: Results indicate that P. aeruginosa may be a potential biocontrol agent for gray leaf spot of perennial ryegrass turf, and the bacterium proved effective against gray leaf spots maintained as fairway and rough heights.
TL;DR: The functional relationships among temperature and leaf wetness duration and gray leaf spot incidence and severity were determined and may be used as part of an integratedgray leaf spot forecasting system for perennial ryegrass turf.
Abstract: Gray leaf spot is a serious disease of perennial ryegrass (Lolium perenne), causing severe epidemics in golf course fairways. The effects of temperature and leaf wetness duration on the development of gray leaf spot of perennial ryegrass turf were evaluated in controlled environment chambers. Six-week-old Legacy II ryegrass plants were inoculated with an aqueous conidial suspension of Pyricularia grisea (approximately 8 × 104 conidia per ml of water) and subjected to four different temperatures (20, 24, 28, and 32°C) and 12 leaf wetness durations (3 to 36 h at 3-h intervals). Three days after inoculation, gray leaf spot developed on plants at all temperatures and leaf wetness durations. Disease incidence (percent leaf blades symptomatic) and severity (index 0 to 10; 0 = leaf blades asymptomatic, 10 = >90% leaf area necrotic) were assessed 7 days after inoculation. There were significant effects ( α = 0.0001) of temperature and leaf wetness duration on disease incidence and severity, and there wer...
01 Jan 2003
TL;DR: It is indicated that colonization of roots by H. chaetospira could induce systemic resistance in Chinese cabbage and reduce the incidence of bacterial leaf spot and Alternaria leaf spot.
Abstract: The root endophytic fungus Heteroconium chaetospira isolate OGR-3 was tested for its ability to induce systemic resistance in Chinese cabbage against bacterial leaf spot caused by Pseudomonas syringae pv maculicola and Alternaria leaf spot caused by Alternaria brassicae of the foliar diseases Chinese cabbage seedlings planted in soil infested with an isolate of H chaetospira were incubated in a growth chamber for 32 days The first to fourth true leaves of the seedlings were challenge-inoculated with P syringae pv maculicola or A brassicae Chinese cabbage planted in soil infested with H chaetospira showed significant decreases in the number of lesions of bacterial leaf spot or Alternaria leaf spot when compared to the control plants not treated with H chaetospira The results indicated that colonization of roots by H chaetospira could induce systemic resistance in Chinese cabbage and reduce the incidence of bacterial leaf spot and Alternaria leaf spot
TL;DR: Three new molecular markers were identified that are linked to to the angular leaf spot resistance gene block in Ouro Negro cultivar and the utility of RAPD markers linked to common bean resistance genes, previously identified in the literature, was restricted.
Abstract: Molecular markers were used to study the organization of rust, anthracnose and angular leaf spot resistance genes in common bean (Phaseolus vulgaris) Ouro Negro cultivar A segregant population of 154 recombinant inbred lines (RIL´s) from the crossing between Ouro Negro and Ruda cultivars was inoculated under controlled conditions with seven races of Uromyces appendiculatus, three of Colletotrichum lindemuthianum and four of Phaeoisariopsis griseola DNA samples of each RIL were amplified by polymerase chain reaction using 70 decamer primers Segregation analysis of rust, anthracnose and angular leaf spot resistance suggested specific resistance inheritance to each physiologic race Genetic linkage analysis revealed the grouping of different rust and anthracnose resistance genes in the same linkage group Angular leaf spot resistance genes also were mapped together, but in another linkage group The utility of RAPD markers linked to common bean resistance genes, previously identified in the literature, was restricted Only five out of 38 molecular markers tested were validated on the RIL´s population as linked to rust and anthracnose resistance genes Three new molecular markers (OBA16669 and OAB16583 to 104 cM in coupling and OAD93210 to 139 cM in repulsion) were identified that are linked to to the angular leaf spot resistance gene block in Ouro Negro cultivar
01 Jun 2003
TL;DR: A detached leaf disk assay was developed for screening sour cherry (Prunus cerasus) cultivars for resistance to cherry leaf spot (Blumeriella jaapii) and a disease scoring scheme to categorize disease severity in sour cherry trees was developed.
Abstract: A detached leaf disk assay was developed for screening sour cherry (Prunus cerasus) cultivars for resistance to cherry leaf spot (Blumeriella jaapii). This assay was used to characterize the events occurring in cv. Montmorency (susceptible) and cv. GiSelA 6 [GI 148-1] (resistant) host-pathogen interactions, and to develop a disease scoring scheme to categorize disease severity in sour cherry trees. Forty-three seedlings grown from seeds collected in Russia were screened for resistance using the scoring scheme. Cross infection studies were also carried out with leaf spot isolates from four other Prunus species. These studies were made possible by the development of a new method of culturing B. jaapii isolates, using cherry fruit agar. This method enabled large amounts of inoculum to be produced within 2 weeks rather than a couple of months as required previously. In ‘Montmorency’, disease symptoms were first observed 4 days postinoculation (dpi), with the appearance of small white spots on the und...
TL;DR: This is the first report of highly virulent isolates of Alternaria spp.
Abstract: Alternaria leaf spots of gerbera (Gerbera jamesonii H. Bolus ex J. D. Hook) were observed on plants from different greenhouses on commercial plants in Bulgaria. The symptoms of the disease on the leaves were characterized by the development of brown, small, scattered dots, which gradually enlarged and coalesced to form large, oval, circular or irregular, brown to black lesions with concentric rings. Affected plants showed lower vitality, suppressed development and fewer, smaller, distorted in shape flowers. Alternaria isolates, obtained from infected leaf tissues were grown in pure culture and the morphological characteristics of the colony and sporulation apparatus were determined. DNA, extracted from the fungal isolates was subjected to polymerase chain reaction (PCR) with primers ITS1/ITS4, amplifying the internal transcribed spacer (ITS) regions. The resulting products were sequenced and compared for homology with other species in the GeneBank. The isolates showed 94% homology of the ITS region with either Alternaria alternata, A. arborescens, A. tenuissima, A. longipes, A. lini or A. smyrnii. None of the studied isolates was amplified with the A. alternata specific primers AAF2/ AAR3, indicating that they are pathogenic varieties of it or belong to another species. Pathogenicity tests on 10 gerbera cultivars revealed that all of them were susceptible to Alternaria leaf spot. Additional tests on nine other crops (Solanum lycopersicum, Calendula officinalis, Capsicum annuum, Celosia argantea, Pelargonium spp., Petunia hybrida, Nicotiana tabacum, Cucurbita moscata and Raphanus sativus var. radicina) and on tomato or pepper fruits, potato tubers and carrot roots also indicated that all tested plant species were potential hosts of the disease. This is the first report of highly virulent isolates of Alternaria spp. in Bulgaria that cause leaf spots on gerbera in greenhouses.
TL;DR: Biological control of Septoria leaf spot of hybrid poplars was investigated using disease-suppressive Streptomyces strains, which significantly reduced leaf disease in all treatments by 64 to 78% compared with the controls.
Abstract: Biological control of Septoria leaf spot of hrhrid poplars was investigated using disease-suppressive Streptomyces strains. Field experiments were conducted in 1998 and 1999 on potted trees placed in a hybrid poplar plantation near Rosemount, MN, and on field-planted trees in 1998 at St. Paul. At both locations, one resistant and three susceptible hybrid poplar clones were sprayed with Streptomyces spore suspensions and exposed to natural field inoculum of Septoria musiva. In the 1998 potted-tree experiment, strains GS-93-3, 93, and Mycostop in Tergitol Triton X-100 solutions applied every 7 days significantly reduced leaf disease by 29 to 83% compared with the controls. In the I999 potted-tree experiment, Streptomyces strain mixtures in Tergitol solution applied every 5 days significantly reduced leaf disease by 50 to 87% compared with the controls. In the 1998 plantation experiment, strains GS-93-3, 93, or Mycostop in Tergitol solution applied weekly, bi-monthly, or monthly significantly reduced leaf disease in all treatments by 64 to 78% compared with the controls.
TL;DR: The apparent unimportance of this plant pathogen as a cause of leaf disease in relation to its poor adaptation to dew periods and dew period temperature is discussed, along with the importance of its seed borne characteristics.
Abstract: Infection processes of Pyrenophora semeniperda on seedling and adult wheat leaves and wheat ears were investigated. Almost 100% germination of conidia occurred on seedling leaves, compared with 20–30% on adult leaves. Appressoria formed over the anticlinal epidermal cell walls and haloes always accompanied infection. Sometimes papillae formed within the leaves as a resistance mechanism. Infection hyphae ramified through the intercellular spaces of the mesophyll resulting in cellular disruption. The infection processes on floral tissues were similar to those observed on leaves; however, no infection occurred on anther, stigmatic or stylar tissues. Infection of ovarian tissue occurred both with and without appressoria formation. Hyphae grew mainly in the epidermal layers and appeared unable to breach the integumental layer as no growth was observed in endosperm or embryo tissues. The optimum dew period temperature for conidial germination was 23·6°C, compared with 19·9°C for lesion development, 20·4°C for the production of infection structures on seedling leaves and 23·7°C for floret infection. Leaf disease development occurred in a logistic manner in response to dew period, with maximum infection observed after 21 h compared with > 48 h in seeds. An initial dark phase during the dew period was necessary for infection and temperature after the dew period had an effect, with significantly more numerous and larger lesions being formed at 15°C compared with 30°C. Seedling leaves were found to be more susceptible than older leaves, under both field and controlled environment conditions. Infection of wheat seeds following inoculation of ears, or after harvest burial of inoculated disease-free seeds, was demonstrated. In the latter, 3-week-old seedlings were slightly stunted, whereas older plants were unaffected. The apparent unimportance of this plant pathogen as a cause of leaf disease in relation to its poor adaptation to dew periods and dew period temperature is discussed, along with the importance of its seed borne characteristics.
TL;DR: Based on morphological and pathological studies of the isolated fungi, it was shown that Pestalotiopsis longiseta, P. acaciae, and P. crassiuscula were found to be new pathogens of the disease.
Abstract: In June 1996, a leaf spot disease widely occurred in Japanese persimmon (Diospyros kaki) orchards in Tottori Prefecture, Japan. The main diagnostic symptom was ring spot on the leaves and calyxes of young fruits; in severe cases, lesions developed on more than half of the area of the leaf, resulting in early defoliation. Based on morphological and pathological studies of the isolated fungi, it was shown that Pestalotiopsis longiseta, P. glandicola, P. acaciae, and P. crassiuscula were responsible for the diseases. These fungi, except P. longiseta, were found to be new pathogens of the disease.
TL;DR: The monoclonal antibody recognition system is highly sensitive to P. grisea and can be used effectively for the rapid diagnosis of gray leaf spot of perennial ryegrass turf.
Abstract: An immuno-recognition assay using a monoclonal antibody was developed to detect Pyricularia grisea, the causal agent of gray leaf spot of perennial ryegrass (Lolium perenne). In vitro assays with isolates of P. grisea from perennial ryegrass, tall fescue (Festuca arundinacea), St. Augustinegrass (Stenotaphrum secundatum), crabgrass (Digitaria sanguinalis), finger millet (Eleusine coracana), wheat (Triticum aestivum), triticale (× Triticosecale rimpaui), and rice (Oryza sativa) showed positive reactions; however, the strength of the reactions differed among isolates. Reactions were more intense with isolates from perennial ryegrass, wheat, and triticale. All P. grisea isolates from perennial ryegrass collected from various regions of the United States showed positive reactions. P. grisea was detected at antigen dilution rates of 0.5×, 0.25×, 0.13×, 0.06×, and 0.03×. Dot-blot assays with Bipolaris sorokiniana, Colletotrichum graminicola, Curvularia lunata, Microdochium nivale, Pythium aphanidermatum, Rhizoctonia solani, or Sclerotinia homoeocarpa isolated from turfgrasses were negative. In vivo assays of symptomatic leaves of perennial ryegrass plants inoculated with P. grisea also showed positive reactions, and those inoculated with B. sorokiniana, P. aphanidermatum, R. solani, or S. homoeocarpa were negative. Intensity of reaction between the monoclonal antibody and P. grisea was proportional to disease severity in perennial ryegrass inoculated with P. grisea; however, there was no reaction in dot blots of leaf tissue collected during the latent period. P. grisea was detected in perennial ryegrass samples from golf course fairways affected by gray leaf spot in Connecticut, Massachusetts, Maine, New Jersey, Pennsylvania, and Rhode Island using this procedure. The monoclonal antibody recognition system is highly sensitive to P. grisea and can be used effectively for the rapid diagnosis of gray leaf spot of perennial ryegrass turf.