Showing papers on "Leaf spot published in 2009"
TL;DR: Although these leaf pathogens appear to be of minor economic importance, they are morphologically similar to two serious eucalypt canker pathogens, namely T. gauchensis and T. zuluensis, which predominantly cause stem cankers, but could also be found occurring in leaf spots on their own, or in association with some of the other species treated here.
Abstract: A common leaf spot disease occurring on Eucalyptus cladocalyx and E. lehmannii in the Western Cape Province of South Africa is known from literature to be caused by the fungus Coniothyrium ovatum, which is a pathogen native to several eucalypts in Australia. Recent collections have shown that Australian material identified as C. ovatum is morphologically and phylogenetically distinct from the South African specimens, and that all these taxa would be better accommodated in the genus Teratosphaeria. South African specimens previously identified as C. ovatum were found to represent two species that co-occur in the same leaves and even spots and are described here as T. juvenalis and T. verrucosa. Furthermore, a fresh collection of T. ovata from E. phoenicea in Australia, is distinguished morphologically and phylogenetically from similar, newly described taxa such as T. veloci on E. miniata, and Readeriella dimorpha, which is also placed in Teratosphaeria. Although these leaf pathogens appear to be of minor economic importance, they are morphologically similar to two serious eucalypt canker pathogens, namely T. gauchensis and T. zuluensis, which predominantly cause stem cankers, but could also be found occurring in leaf spots on their own, or in association with some of the other species treated here. Further research is, therefore, required to develop molecular detection techniques for these taxa to enable researchers to rapidly distinguish the minor pathogens from the more serious quarantine pathogens that co-occur on leaves.
77 citations
TL;DR: It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen.
Abstract: Quantitative resistance to Leptosphaeria maculans in Brassica napus was investigated in field and controlled environments using cultivars Darmor (with quantitative resistance) and Eurol (without quantitative resistance). In field experiments, numbers of phoma leaf spot lesions in autumn/winter and severity of stem canker the following summer were assessed in three growing seasons. There were no differences between Darmor and Eurol in number of leaf lesions in autumn/winter. However, stem cankers were less severe on Darmor than Eurol at harvest the following summer. In controlled-environment experiments, development of leaf lesions at different temperatures (5–25°C) and wetness durations (12–72 h) was investigated using ascospore inoculum; symptomless growth of L. maculans along leaf petioles towards the stem was quantified using quantitative PCR and visualized using GFP-expressing L. maculans; growth of L. maculans within stem tissues was investigated using GFP-expressing L. maculans. There were more leaf lesions on Darmor than Eurol, although there was no difference between Darmor and Eurol in L. maculans incubation period. There were no differences between Darmor and Eurol in either distance grown by L. maculans along leaf petioles towards the stem or quantity of L. maculans DNA in leaf petioles, but L. maculans colonized stem tissues less extensively on Darmor than Eurol. It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen.
63 citations
TL;DR: There appears to be a trade-off for coffee farmers in the Blue Mountains of Jamaica, West Indies: vegetation complexity may attract beneficial insect-eating birds that can reduce insect damage, but it is also associated with the prevalence of fungal leaf symptoms.
Abstract: The effects of overstory trees and birds on coffee pests are poorly understood. This study documents (a) the effect of bird exclusion on foliage-dwelling arthropod abundance and insect-caused leaf damage, and (b) the relationships between vegetation complexity and insect abundance, leaf damage, and prevalence of fungal leaf symptoms on coffee farms in the Blue Mountains of Jamaica, West Indies. Overall arthropod abundance was reduced inside bird-proof exclosures, and this corresponded to reduced insect-caused leaf damage. The reduction in leaf damage increased with greater shade, but fungal leaf symptoms increased with greater shade and proximity to non-coffee habitat patches. There appears to be a trade-off for coffee farmers in our study region: vegetation complexity may attract beneficial insect-eating birds that can reduce insect damage, but it is also associated with the prevalence of fungal leaf symptoms.
58 citations
TL;DR: Analysis of the genetic variation between isolates using Amplified Fragment Length Polymorphism (AFLP) showed significant concordance with host plants and Multilocus sequencing of a subset of isolates showed that such isolates were similar to S. vesicarium.
Abstract: Stemphylium vesicarium (teleomorph: Pleospora herbarum) is the causal agent of brown spot disease in pear. The species is also able to cause disease in asparagus, onion and other crops. Saprophytic growth of the fungus on plant debris is common. The objective of this study was to investigate whether isolates of S. vesicarium from different hosts can be pathogenic to pear. More than hundred isolates of Stemphylium spp. were obtained from infected pear fruits, dead pear leaves, dead grass leaves present in pear orchard lawns as well as from necrotic leaf parts of asparagus and onion. Only isolates originating from pear orchards, including isolates from dead grass leaves, were pathogenic on pear leaves or fruits in bioassays. Non-pathogenic isolates were also present in pear orchards. Stemphylium vesicarium from asparagus or onion, with one exception, were not pathogenic to pear. Analysis of the genetic variation between isolates using Amplified Fragment Length Polymorphism (AFLP) showed significant concordance with host plants. Isolates from asparagus or onion belonged to clusters separate from the cluster with isolates from pear or grass leaves collected in pear orchards. Multilocus sequencing of a subset of isolates showed that such isolates were similar to S. vesicarium.
47 citations
TL;DR: This is the first report on the chemical structure of a toxin produced by the pathogen that causes Curvularia leaf spot on maize, identified as methyl 5-(hydroxymethyl) furan-2-carboxylate.
Abstract: Curvularia lunata, a causal agent of Curvularia leaf spot of maize, was shown to produce a toxin in vitro and in planta based on TLC and HPLC-MS analyses. The purified toxin was able to induce symptoms on maize plants similar to those of natural infection. The toxin was identified as methyl 5-(hydroxymethyl) furan-2-carboxylate through UV, ESI-MS, FT-IR, 1 H-NMR, and 13 C-NMR spectral analyses. Host specificity tests showed that this toxin was non-host specific. This is the first report on the chemical structure of a toxin produced by the pathogen that causes Curvularia leaf spot on maize.
47 citations
TL;DR: The disease resistance against Fusarium wilt and Alternaria leaf spot in cotton strains would serve as good breeding materials for producing fungal disease resistant cotton varieties.
Abstract: Problem statement: The present investigation described a simple
and reproducible protocol for transgenic cotton regeneration and characterization
of chitinase (Chi II) gene expression against two different fungal pathogens in
cotton. Approach: Transgenic cotton (Gossypium hirsutum cv. SVPR2)
plants were produced by pCambia-bar-Chi II (13.8 kb) under the control of the
CaMV 35S promoter, harbored in the strain LBA 4404 Agrobacterium tumefaciens by
using shoot tip explants. Results: Finally, from the 10 experiments,
21.8% of transformation frequency was recorded. Segregation ratio of 3:1 was recorded
in the T0 plant seeds. Polymerase chain reaction and southern blotting analysis
were used to confirm the integration of Chi II transgene in the T0 plants genome
of putative transgenics. Quantitiave and qualitative (SDS-PAGE) analyses were
also carried out to confirm the expression of chitinase enzyme in T0 plants. Further,
randomly selected transgenic plants (T0) were analyzed for disease tolerance by
evaluating them with spores of Fusarium oxysporum and Alternaria macrospora. All
the selected PCR positive plants showed enhanced disease resistance against Fusarium
wilt. The plants selected randomly showed an enhanced survival rate compared with
the control when they were grown in earthen pots inoculated with 1×105 spores 100-1 g of soil mixture. Another four randomly selected plantlets were sprayed with spores of Alternaria macrospora in order to test their tolerance to Alternaria leaf spot disease. After 20 days of culture, the number of lesions per leaf and the lesion length per leaf spot in non-transferred leaves increased. In the case of transgenic plantlets, lesion formation was completely absent. Conclusion: The disease resistance against Fusarium wilt and Alternaria leaf spot in cotton strains would serve as good breeding materials for producing fungal disease resistant cotton varieties.
45 citations
TL;DR: Penthiopyrad has excellent potential for management of late leaf spot and stem rot of peanut, and may complement current SBI and QoI fungicides.
Abstract: BACKGROUND: Management of early leaf spot (Cercospora arachidicola Hori.), late leaf spot [Cercosporidium personatum (Berk. & MA Curtis) Deighton] and stem rot (Sclerotium rolfsii Sacc.) of peanut (Arachis hypogaea L.) in the southeastern USA is heavily dependent upon sterol biosynthesis inhibitor (SBI) and quinone outside inhibitor (QoI) fungicides. Effective new fungicides with different modes of action could improve overall disease control and extend the utility of the current fungicides. Penthiopryad is a pyrazole carboxamide fungicide being evaluated for use on peanut. Field experiments were conducted from 2004 to 2007 to determine the effect of a range of rates (0–0.36 kg AI ha−1) of penthiopyrad on leaf spot and stem rot and the relative efficacy of penthiopyrad and current fungicide standards chlorothalonil, tebuconazole and azoxystrobin.
RESULTS: Leaf spot control in plots treated with penthiopyrad at 0.20 kg AI ha−1 or higher was similar to or better than that for the chlorothalonil standard. The incidence of stem rot for all penthiopyrad treatments was usually less than that for the tebuconazole or azoxystrobin standard treatments. Pod yields for all penthiopyrad treatments were similar to or higher than those for the respective standards.
CONCLUSION: Penthiopyrad has excellent potential for management of late leaf spot and stem rot of peanut, and may complement current SBI and QoI fungicides. Copyright © 2008 Society of Chemical Industry
44 citations
Journal Article•
TL;DR: Foliar disease resistant induction of Trichoderma spp.
Abstract: The efficiency of Trichoderma spp. in inducing acquired systemic disease resistance in tomato was conducted. Systemic induce resistant reaction was evaluated on chitinolytic and β-1,3glucanolytic activities produced by tomato plant (Sida cultivar) including disease severity of bacterial and gray leaf spot. Fifteen isolates of Trichoderma spp., T1, T9, T10, T13, T14, T17, T18, T19, T20, T24, T25, T30, T35, 90 and 103 were inoculated in soil of tomato potted plants. Tomato leaves were collected on 0, 5, 8, 11 and 14 days of interval after inoculation. Crude enzymes were extracted from leaf samples and determined for chitinase and β-1,3-glucanase activities. High chitinase activity was detected from Trichoderma isolates in descending order, T1, T9, T13, T18 and T18. For β-1,3-glucanase activities, The isolates T9, T13, T14 and T17 induced to tomato plant in this enzyme activity ranking from high to low, compared to uninoculated plants. Foliar disease resistant induction of Trichoderma spp. was tested under screened house condition. The Trichoderma isolate T9 (T. harzianum), T13 (T. asperellum), T17 (T. asperellum) and T18 (T. asperellum) were evaluated by cultivation in sterilized sorghum grains and inoculated in tomato pot plants. The test plants were inoculated with As. J. Food Ag-Ind. 2009, Special Issue, S99-S104 100 bacterial suspension of Xanthomonas campestris pv. vesicatoria (XCV). The result showed that T. harzianum (T9) induced resistance with the best reduction spot numbers (69.32 %.). Other isolates T13, T17 and T18 showed reduction in bacterial spot numbers of 34.66%, 37.41% and 44.77%, respectively. On Stemphylium gray leaf spot, these 4 isolates of Trichoderma spp. reduced number of spots in parenthesis as followed, T18 (19.23%), T9 (7.52%), T13 (3.8%) and T17 (3.69%). Trichoderma spp. are shown to have potential in inducing resistant of bacterial spot and gray leaf spot of tomato which varies among the range of isolates evaluated.
41 citations
TL;DR: Groundnut (Arachis hypogaea) has an AB genome and is one of the most important oil crops in the world and wild germplasm accessions of both genome types are available for the introgression of resistance genes against three fungal diseases of peanut.
Abstract: Groundnut (Arachis hypogaea) has an AB genome and is one of the most important oil crops in the world. The main constraints of crop management in Brazil are fungal diseases. Several species of the genus Arachis are resistant to pests and diseases. The objective of our experiments was to identify wild species belonging to the taxonomic section Arachis with either A or B (or " non-A" ) genomes that are resistant to early leaf spot (Cercospora arachidicola), late leaf spot (Cercosporidium personatum) and rust (Puccinia arachidis). For the identification of genotypes resistant to fungal diseases, bioassays with detached leaves were done in laboratory conditions, with artificial inoculation, a controlled temperature of 25oC and a photoperiod of 10 h light/14 h dark, for 20-42 days, depending on the fungi species. Most of the accessions of wild species were more resistant than accessions of A. hypogaea for one, two or all three fungi species studied. Arachis monticola, considered to be a possible tetraploid ancestor or a derivative of A. hypogaea, was also more susceptible to Cercosporidium personatum and Puccinia arachidis, as compared to most of the wild species. Therefore, wild germplasm accessions of both genome types are available to be used for the introgression of resistance genes against three fungal diseases of peanut.
39 citations
TL;DR: Results of this study highlight a remarkable fungal biodiversity that can occur within a very specific niche and emphasise the importance of verifying the identity of fungal isolates in culture, as many taxa, especially those of the Capnodiales, frequently co-occur in the same niche, lesion or leaf spot.
Abstract: Eucalyptus spp. are susceptible to a large number of foliar pathogens, some of which can cause serious defoliation and die-back. In this study, a single leaf spot on a Eucalyptus leaf collected in Madagascar revealed an unusual association of microfungi with disease symptoms. Initial observations indicated that the leaf spot was associated with Mycosphaerella marksii, a common pathogen of eucalypts. However, more intensive scrutiny showed the presence of several other microfungi co-occurring in this, and other leaf spots on the leaf. A total of 41 single conidial propagules were subsequently obtained from a single lesion for morphological study and DNA sequence comparisons. Based on these data, 11 members of the Capnodiales, including one species of Pestalotiopsis (Xylariales), were observed. Of the capnodialean taxa, nine could be cultivated, which revealed one known species, M. marksii, two taxa in the Cladosporium cladosporioides species complex that were not treated here, and six new species, including Passalora intermedia, Pseudocercospora madagascariensis, Teratosphaeria hortaea, Toxicocladosporium chlamydosporum, T. rubrigenum and T. veloxum. Results of this study highlight a remarkable fungal biodiversity that can occur within a very specific niche. Furthermore, the results emphasise the importance of verifying the identity of fungal isolates in culture, as many taxa, especially those of the Capnodiales, frequently co-occur in the same niche, lesion or leaf spot.
36 citations
TL;DR: Heat treatment of strawberry nursery stock is feasible and can be used to supplement standard production practices for producing pathogen-free nursery stock and killed plants in two trials established at two locations in successive years.
Abstract: Turechek, W. W., and Peres, N. A. 2009. Heat treatment effects on strawberry plant survival and angular leaf spot, caused by Xanthomonas fragariae, in nursery production. Plant Dis. 93:299308. Angular leaf spot is an important disease in strawberry nursery production. The European and Mediterranean Plant Protection Organization (EPPO) lists Xanthomonas fragariae as an A2 quarantine pathogen. Therefore, nurseries wishing to export plants to European countries must maintain phytosanitary standards to exclude X. fragariae. To help nurseries achieve these standards, heat treatment for killing or reducing the number of viable bacterial cells in strawberry crown tissue was investigated. First, the sensitivity of bacteria to heat was determined by dispensing 1-ml aliquots of standardized cell suspensions in microcentrifuge tubes for each of four isolates of X. fragariae, including the type culture, and submerging the tubes in water at 36, 40, 44, 48, 52, and 56°C for 0, 1, 2.5, 5, 10, 15, 30, 60, 120, 240, 360, and 480 min. Bacteria were transferred to growth medium to determine the proportion surviving heat treatment. Two trials were conducted in a greenhouse to determine the sensitivity of bare-root plants to heat treatment. In the first trial, plants of cvs. Camarosa and Diamante from two different nurseries were heat treated as follows: (i) plants placed in metallic mesh cages and immersed directly into water (industry standard, direct dip); (ii) plants sealed in a plastic bag and the bag immersed in water (bagged dry); or (iii) plants wetted in warm water, sealed in a plastic bag, and then immersed in water (bagged wet). Plants were treated at 44 or 48°C for 0, 60, 120, 180, and 240 min. In the second trial, plants of cvs. Camarosa, Camino Real, Diamante, Oso Grande, Strawberry Festival, and Ventana from a single nursery were subjected to the same treatments. In both trials, plants were potted after treatment and rated for growth characteristics. Results showed that populations of bacteria exposed to 56 and 52°C were killed completely after 15 and 60 min of exposure, respectively; both treatments killed plants. Bacterial populations exposed to 44°C for 4 h or 48°C for 2 h were reduced by 10 5 or 10 6 CFU/ml. The same treatments minimally affected vegetative growth of plants bagged dry or wet, but flowering was adversely affected. These heat treatments were selected for testing of nursery stock of several cultivars in field trials established at two locations in successive years. The survival rate among cultivars was similar to that observed in greenhouse trials, and angular leaf spot developed appreciably only in non-heat-treated control plots. Heat treatment of strawberry nursery stock is feasible and can be used to supplement standard production practices for producing pathogen-free nursery stock.
01 Jan 2009
TL;DR: Integrated disease management (IDM) modules for important foliar and viral diseases of chickpea (ascochyta blight and botrytis gray mold), pigeon pea (sterility mosaic and Phytophthora blight), lentil, lentil (rust, ascochyTA blight and stemphylium blight), faba bean (as cochyta blight, chocolate leaf spot and rust), field pea, mungbean and urdbean (viral diseases
Abstract: Of the most important food legumes grown world over, chickpea (Cicer arietinum
L.), lentil (Lens culinaris Medik.), faba bean (Vicia faba L.), grasspea (Lathyrus sativus
L.) and field pea (Pisum sativum L.) are grown in cool season, while pigeonpea (Cajanus
cajan (L.) Millsp.), blackgram (Vigna mungo (L.) Hepper), mungbean (V. radiata (L.)
Wilczek), horsegram (Macrotyloma uniflorum (Lam.) Verdc.), cowpea (V. unguiculata
(L.) Walp) and soybean (Glycine max (L.) Merr) are known as warm season legumes.
Biotic stresses such as diseases, insect-pests, nematodes and weeds substantially reduce
the yield of these legumes in farmers’ fields. Among these, fungi and viruses are the
largest and most important groups affecting all parts of the plant at all stages of growth
of both cool season and warm season food legumes. According to estimates made in
India nearly 10-15% of food legumes production is lost due to diseases alone. Among fungi, diseases caused by species of Botrytis and Ascochyta are of great importance to
faba bean, lentil, chickpea and field pea. The genus Stemphylium causes foliar disease in
lentil and chickpea and Septoria species causes leaf spots in cowpea. The viruses of
major economic importance on cool season legumes belong to the Luteoviruses,
Nanoviruses, Potyviruses, Carlaviruses, Furoviruses. Perusal of the literature on diseases
of food legumes and their management reveals new records of diseases, loss estimations,
biology of causal agents, identification of host plant resistance and fungicide use. The
purpose of this paper is to review the etiology and biology of major foliar diseases of food
legumes and outline current and suggested future research on issues related to disease
management strategies globally. Integrated disease management (IDM) modules for
important foliar and viral diseases of chickpea (ascochyta blight and botrytis gray mold),
pigeonpea (sterility mosaic and Phytophthora blight), lentil (rust, ascochyta blight and
stemphylium blight), faba bean (ascochyta blight, chocolate leaf spot and rust), field pea
(powdery mildew and Ascochyta complex), mungbean and urdbean (viral diseases and
chocolate leaf spot) and cowpea (viral diseases and chocolate leaf spot) are discussed. The
IDM involves the individual component of disease management such as host plant resistance
(HPR), agronomic practices, judicious use of fungicides, pesticides for vector control,
biopesticides for pathogen control, risk forecasting that operate on different aspects of
the disease etiology, such that they complement each other and can be applied together
in farmers’ fields collectively to provide farmers with maximum economic return.
TL;DR: Resistance to northern leaf blight and gray leaf spot in a set of nine inbred popcorn lines was examined and additive and non-additive gene effects both contributed to resistance to these diseases, but that the additive gene effects were more important.
Abstract: We estimated general and specific combining abilities and examined resistance to northern leaf blight (Exserohilum turcicum) and to gray leaf spot (Cercospora zeae-maydis) in a set of nine inbred popcorn lines. These inbreds were crossed in a complete diallel scheme without reciprocals, which produced 36 F(1) hybrids. Two experiments with a square lattice design and three replications were conducted during the 2008/2009 crop season, in Maringa, PR, Brazil. The severity of northern leaf blight and gray leaf spot was assessed under natural infestation conditions. Data were examined by individual and joint analysis of variance. Individual and joint Griffing's diallel analyses were carried out for adjusted means. General combining ability and specific combining ability were significant (P < 0.10) by the F-test for northern leaf blight and gray leaf spot infestation levels. This denotes that additive and non-additive gene effects both contributed to resistance to these diseases, but that the additive gene effects were more important. Among the inbred lines, P(8) and P(9) gave the highest resistance to northern leaf blight, and P(3) and P(4.3) gave the highest resistance to gray leaf spot. The hybrids P(7.4) x P(8) and P(4.3) x P(9) could be exploited by reciprocal recurrent selection to provide genotypes with both northern leaf blight and gray leaf spot resistance. Significant interaction between general combining ability and crop season (P < 0.10) denotes the importance of environment, even though the disease levels in the hybrids were quite consistent.
TL;DR: Chloroform extract from H. arifolia can be utilized for managing rust and leaf spots diseases on groundnut and between these two fungi, P. personata was found to be more sensitive to the tested plant extracts than P. arachidis.
Abstract: Antimycotic activity of three fern extracts from Hemionitis arifolia (Burm.f.) Moore., Pteridium aquilinum (Linn.) Kuhn. and Christella parasitica (Linn.) H. Lev. were evaluated against groundnut early leaf spot and rust disease causative agents viz., Puccinia arachidis Speg. and Phaeoisariopsis personata (Berk & M.A. Cuortis) Vanarx., espectively by mycelial dry weight method. Both the fungi were sensitive to all the three fern extracts tested. Among the extracts, chloroform extract of H. arifolia was found to have maximum antifungal activity against both fungi. Between these two fungi, P. personata was found to be more sensitive to the tested plant extracts than P. arachidis. From this study it is concluded that chloroform extract from H. arifolia can be utilized for managing rust and leaf spots diseases on groundnut.
TL;DR: Bacterial isolates from maize plants showing a leaf spot disease were identified through molecular and phenotypic traits, showing that the isolates belong to Pantoea ananatis.
Abstract: Bacterial isolates from maize plants showing a leaf spot disease were identified through molecular and phenotypic traits, showing that the isolates belong to Pantoea ananatis. Maize plants inoculated with those isolates showed a pathogenic reaction. This is the first report of a disease of Mexican maize caused by P. ananatis.
TL;DR: The presence or absence of the chlorotic halo was determined to be governed by a single gene, with the presence of the halo (the susceptible phenotype) being a dominant character.
Abstract: Angular leaf spot is a common disease of cucumber (Cucumis sativus) caused by Pseudomonas syringae pv. lachrymans. Genetics of resistance to this disease was investigated using two sets of parameters: (i) disease severity, i.e. the number and size of necrotic and chlorotic lesions on the infected leaves, and (ii) presence or absence of a chlorotic halo around the necrotic spots on the infected leaves. Disease severity appears to be controlled by multiple genes and the heritability of the resistance was estimated to be 53%. The presence or absence of the chlorotic halo was determined to be governed by a single gene, with the presence of the halo (the susceptible phenotype) being a dominant character. A RAPD marker linked to the gene conferring the chlorotic halo was identified. Genetic distance between this marker, OP-AO07, a polymorphic 420 bp amplicon in the DNA of the susceptible plants, and the locus encoding the chlorotic halo was estimated to be 13 cM.
01 Jan 2009
TL;DR: This study showed that mutations causing QoI fungicide resistance were present in almost all recently obtained R. collo-cygni isolates from across Europe.
Abstract: Summary Ramularia collo-cygni first appeared as a major pathogen of barley in Scotland during 1998 and was found to be easily controlled by the fungicide azoxystrobin (Amistar). This type of fungicide was therefore recommended for Ramularia leaf spot disease control. However, during 2002 there was a sharp decline in the efficacy of azoxystrobin, when used to control Ramularia leaf spot. It was therefore assumed that fungicide resistance had developed, although it was not confirmed by either bioassay or sequencing. This study showed that mutations causing QoI fungicide resistance were present in almost all recently obtained R. collo-cygni isolates from across Europe.
Journal Article•
TL;DR: In the field trials, seed treatment with a spore suspension of Trichoderma and Pseudomonas fluorescens reduced the disease incidence significantly and significantly increased seed germination, seedling growth and seedling vigor.
Abstract: 3 Abstract: Helminthosporium (Bipolaris) causes a leaf spot disease in Chrysalidocarpus lutescens (cane palm) in Sri Lanka. The losses could reach 90% of production during rainy weather conditions. Field experiments were carried out to test the efficacy of treatment of seeds of C. lutescens against Helminthosporium infection. In the fungal growth tests the isolates T.harzianum 1, T.harzianum 2, T.viride 1,T.viride 2 and T.viride 3 inhibited growth of the pathogen by 79.18, 69.03, 83.75, 82.99, 74.11% respectively. Isolates of Trichoderma harzianum and Trichoderma viride obtained from soil and having antagonistic activity against Helminthosporium were used in the field experiments. In the field trials, seed treatment with a spore suspension of Trichoderma completely eliminated the disease while Trichoderma and Pseudomonas fluorescens reduced the disease incidence significantly. The seed treatments also significantly increased seed germination, seedling growth and seedling vigor.
TL;DR: The results together suggest that the CWP from P. oligandrum can be retained on the leaf surface and induce expression of disease resistance genes, thereby reducing Cercospora leaf spot on sugar beet.
Abstract: After a cell wall protein fraction (CWP) of Pythium oligandrum was sprayed on sugar beet leaves, we screened leaves for induced expression of defence-related genes and for resistance against Cercospora leaf spot. In a western blot analysis, the CWP was primarily retained on the surface of leaves without degradation for at least 48 h after spraying. In northern blot analyses, four defence-related genes (β-1, 3-glucanase, acidic class III chitinase, 5-enol-pyruvylshikimate-phosphate synthase and oxalate oxidase-like germin) were expressed more rapidly in CWP-treated leaves compared to control leaves treated with distilled water (DW). When CWP was applied to a suspension of cultured cells of sugar beet, an oxidative burst was observed that did not occur after the DW treatment. In growth chamber trials after inoculation with Cercospora beticola, the severity of Cercospora leaf spot was significantly reduced in CWP-treated plants compared to the DW-treated controls. In a field experiment, CWP treatment was also effective against the disease. CWP did not reduce growth rate of the pathogen in plate tests. The results together suggest that the CWP from P. oligandrum can be retained on the leaf surface and induce expression of disease resistance genes, thereby reducing Cercospora leaf spot on sugar beet.
TL;DR: Soybean germplasm line S99-2281 will be useful as an elite parent in soybean breeding programs to develop productive soybean cultivars with broad resistance to frogeye leaf spot and resistance to multiple nematode species.
Abstract: Soybean (Glycine max (L.) Merr.) germplasm line S99-2281 (Reg. No. GP-361, PI 654356) was developed at the University of Missouri-Delta Center and released by the University of Missouri Agricultural Experiment Station. It is an F 4 plant selection composited in the F 5 generation from the cross of N90-516 × S92-1069. S99-2281 is a productive, early group V (relative maturity 5.2) soybean line with broad resistance to soybean cyst nematode (Heterodera glycines Ichinohe) HG types (races), southern root knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood), and reniform nematode (Rotylenchulus reniformis (Linford and Oliveira)). It also carries the Rcs3 gene for resistance to all known races of frogeye leaf spot, caused by Cercospora sojina K. Hara. In combined analyses over 3 yr, S99-2281 yielded 3 and 7% more than 'Manokin' in southeast Missouri trials (15 tests) and in Uniform Group IVs Tests-Southern States (39 tests), respectively. It will be useful as an elite parent in soybean breeding programs to develop productive soybean cultivars with broad resistance to frogeye leaf spot and resistance to multiple nematode species.
TL;DR: Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has increased in incidence and severity during the last 3 years in Ohio and caused substantial economic losses for the firs...
Abstract: Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has increased in incidence and severity during the last 3 years in Ohio and caused substantial economic losses for the firs...
Journal Article•
TL;DR: McMullen et al. as mentioned in this paper reported that three important fungal leaf spot diseases, tan spot, Stagonospora nodorum blotch and Septoria tritici blotch, commonly occur in North Dakota and can cause reduced test weights and yield losses of up to 50 percent.
Abstract: Three important fungal leaf spot diseases, tan spot, Stagonospora nodorum blotch (SNB) and Septoria tritici blotch (STB), commonly occur in North Dakota and can cause reduced test weights and yield losses of up to 50 percent. Among these, tan spot, caused by Pyrenophora tritici-repentis, is the most destructive leaf spot disease found in all wheat classes throughout the growing season across North Dakota. SNB and STB also are common in wheat in North Dakota each year, but symptoms generally appear after fl ag leaf emergence. Marcia McMullen Extension Plant Pathologist, Department of Plant Pathology
TL;DR: This newly discovered disease could potentially have a dramatic effect on the aesthetic quality and salability of this landscape ornamental.
Abstract: Tiger grass [Thysanolaena maxima (Roxb.) Kuntze] is a popular ornamental grass grown throughout landscapes in South Florida. In the summer of 2006, a leaf spot was observed on tiger grass in the landscape and a commercial nursery in Homestead, FL. The causal agent of the leaf spot was isolated and characterized morphologically and molecularly as Exserohilum rostratum (Drechsler) Leonard & Suggs. At high inoculum densities, symptoms were apparent as early as 12 h after inoculation, and caused widespread necrosis. Germinating conidia of E. rostratum and appressoria were observed in direct association with lesions. This newly discovered disease could potentially have a dramatic effect on the aesthetic quality and salability of this landscape ornamental.
TL;DR: The results indicate the potential of P. sanguineus culture filtrate as an alternative control for angular leaf spot on beans and the activities of peroxidase and polyphenol oxidase, and the content of proteins and chlorophylls, increased in plants treated with the extract.
Abstract: With the aim of developing an alternative method for the control of angular leaf spot of common bean, caused by Pseudocercospora griseola, aqueous extracts of Pycnoporus sanguineus culture filtrates were evaluated in vitro for antimicrobial activity against P. griseola, and possible induction of resistance in bean against P. griseola. The role of the defense enzymes peroxidase, polyphenol oxidase, and β-1,3-glucanase, and the content of proteins and chlorophyll, were also investigated. For the in vitro and greenhouse experiments the culture filtrate of P. sanguineus at the concentrations of 1 to 20% was used, and water, acibenzolar-S-methyl (ASM: 75 mg i.a. L-1) and fungicide (azoxystrobin: 40 mg i.a. L-1) served as control treatments. In the in vitro study, culture filtrate did not inhibit mycelial growth, sporulation and conidia germination of P. griseola. The total area under the angular leaf spot progress curve was reduced by 82 and 49% respectively, for greenhouse and field experiments in relation to the water control. The activities of peroxidase and polyphenol oxidase, and the content of proteins and chlorophylls, increased in plants treated with the extract. The results from this study indicate the potential of P. sanguineus culture filtrate as an alternative control for angular leaf spot on beans.
TL;DR: Germination, penetration and sporulation of Cercospora henningsii on cassava leaves were studied by scanning electron microscopy and emergence through stomata appeared to be random rather than a preferred route.
Abstract: Germination, penetration and sporulation of Cercospora henningsii (Allesch.) on cassava leaves were studied by scanning electron microscopy. Conidia started to germinate 9 h postinoculation producing one to two germ tubes. The germ tubes entered the leaf tissue through the abaxial surface by direct penetration of the epidermis without forming appressoria. The cassava leaf is characterized by its papillose epidermis on the abaxial surface. The penetrations occurred at smooth areas of the leaf epidermis between the papillae. The germ tubes did not enter stomata even when they passed over stomatal openings. Leaf spots started to appear 9 days after the inoculation (dpi), and the emergence of conidia occurred 14 dpi. The symptoms appeared first on the abaxial leaf surface, followed 2 days later on the adaxial. Conidia emerged in clusters through ruptured epidermis on both sides of the leaves. Conidia emerged also through the epidermal papillae and the leaf veins. Even though small groups of conidia emerged through stomata also, emergence through stomata appeared to be random rather than a preferred route. Each conidium was born on a short conidiophore with a swollen base.
01 May 2009
TL;DR: A complete 4-steps process allows, through experimental approaches, to select banana cultivars with durable resistance against Mycosphaerella leaf spot diseases.
Abstract: Mycosphaerella leaf spot diseases of banana caused by Mycosphaerella musicola (Sigatoka leaf spot, SLS) and M. fijiensis (black leaf streak, BLS) are very destructive. The cultivation of resistant banana clones appears to be the most appropriate means to combat disease because genetic resistance is usually more durable than chemical control. Since pathogen populations maintain a high level of genetic diversity and single gene resistances, such as is suspected in total or hypersensitive resistance situations, are easily overcome, the phenomenon of "partial resistance", which may be multigenic and hence more durable, is used in CIRAD breeding programmes. New hybrids of banana developed by CIRAD are routinely selected for resistance against Mycosphaerella leaf spot diseases. There are four steps in the evaluation process. Firstly, the level of resistance to M. musicola is assessed under field conditions in Guadeloupe. Secondly, the most resistant hybrids are selected for detached-leaf resistance tests to M. musicola and M. fijiensis under controlled conditions. Thirdly, the efficacy of partial resistance of selected hybrids against M. musicola is confirmed in the field in the French West Indies and against M. fijiensis in the field in Mayotte. Finally, the durability of the hybrids' partial resistance is assessed by measuring disease severity in experimental plots for several years. This complete 4-steps process allows, through experimental approaches, to select banana cultivars with durable resistance against Mycosphaerella leaf spot diseases. (Resume d'auteur)
Journal Article•
TL;DR: A new methodology has been developed for indirect assessment of severity as a direct function of yield loss in terms of occurrence or intensity but not yield or yield loss per se and may help in building simple decision rules for management early in the season.
Abstract: A survey was undertaken during 1996-1997 in different commercial perennial ornamentals in gardens and nurseries at Bolpur, Santiniketan and Sriniketan of Birbhum District, West Bengal, India, to study the fungal diseases of some commercial ornamentals. The leaf spot of Ficus religiosa (c.o. Alternaria sp.) is the first record. Fifteen fungal diseases have been formally described from West Bengal for the first time on these twelve ornamentals. Monthly dynamics was determined for occurrence, intensity and severity of these diseases. The diseases (referred as pathogens) that were the highest and fastest during warm and wet (rainy) months were: Alternaria alternata on Polyanthes tuberosa; Alternaria alternata and Septoria chrysanthemella on Chrysanthemum indicum; Colletotrichum gloeosporioides and Alternaria sp. on Dracaena deremensis; Alternaria sp. and Cercospora hibisci-manihotis on Hibiscus rosa-sinensis; Colletotrichum gloeosporioides on Calathea ornata; Alternaria sp. on Ficus religiosa; Cercospora jasminicola on Jasminum sambac; Lasiodiplodia theobromae and Diplocarpon rosae on Rosa multiflora. On the other hand, Cercospora sp. on Pothos scindapsus aureus; Alternaria alternata and Cercospora gerberae on Gerbera jamesonii; Glomerella cingulata on Ficus elastica; Alternaria tenuissima on Bougainvillea glabra were at their highest and fastest during hot and dry (summer to pre-rainy) months. A generalized 0-9 point scale was prepared and used to determine severity (= Percent Disease Index, PDI). Strongly predictive equations for severity in terms of intensity in all cases but one viz. Alternaria leaf spot of Dracaena deremensis in terms of occurrence were developed. Such relationships helped prior assessment of severity before the disease reaches the predicted level. Thus, although crop losses were neither determined nor sought to be predicted, a new methodology has been developed for indirect assessment in terms of severity as a direct function of yield loss in terms of occurrence or intensity but not yield or yield loss per se. These findings may help in building simple decision rules for management early in the season as soon as the disease appears in one case, and when some intensity has been achieved in all other cases. Where validated this approach may be a useful tool in plant protection, especially supervisory management and appropriate IPM.
TL;DR: A new bacterial disease of citrus was recently identified in Florida and is here named bacterial brown leaf spot (BBLS) of citrus, indicating that this wide-host-range bacterium is a weak, opportunistic pathogen of citrus.
Abstract: A new bacterial disease of citrus was recently identified in Florida and is here named bacterial brown leaf spot (BBLS) of citrus. BBLS-infected citrus leaves from the field displayed circular, brownish, flat lesions with slightly raised and water-soaked margins surrounded by a chlorotic halo. Based on Biolog carbon source metabolic “fingerprinting”, fatty acid analysis, and sequence analysis of partial 16S rDNA, gyrB, and rpoD genes, the causal agent of the disease was identified as Burkholderia andropogonis. Pathogenicity of these B. andropogonis isolates taken from multiple citrus leaves with BBLS was tested by various inoculation methods on three species of citrus as well as on carnation, corn, and sorghum. All isolates infected carnation, corn, and sorghum with varying degrees of pathogenicity. Variation among citrus isolates in pathogenicity was also observed in high titer (108 CFU/ml) inoculations of citrus leaves, ranging from a hypersensitive-like response to canker-like lesions. When th...
TL;DR: This report is the first of Alternaria leaf spot of basil caused by A. alternata, which was recorded in a greenhouse in Okinawa Prefecture, Japan during 2004.
Abstract: An outbreak of black mottle and dieback on basil (Ocimum basilicum L.; Lamiaceae) was recorded in a greenhouse in Okinawa Prefecture, Japan during 2004. The causal agent was identified as Alternaria alternata (Fr.) Keissler based on morphological characters and growth temperature. This report is the first of Alternaria leaf spot of basil caused by A. alternata.
TL;DR: There was little effect of agronomic practices on LS severity, but cropping sequence and tillage system affected the mean percentage fungal isolation (MPI), whereas only tillage affected the percentageFungal occurrence.
Abstract: A survey of commercial common wheat crops was conducted in eastern Saskatchewan (2000 to 2002) to determine the effects of agronomic practices on the leaf spot (LS) disease complex and causal pathogens, and to determine the impact of LS on crop productivity. Leaf spots had a negative impact on grain yield, but did not affect market grade consistently. There was little effect of agronomic practices on LS severity, but cropping sequence and tillage system affected the mean percentage fungal isolation (MPI), whereas only tillage affected the percentage fungal occurrence. A previous noncereal crop, which had in most cases been preceded by a cereal, resulted in a higher MPI of Pyrenophora tritici-repentis (Ptr), the most common pathogen, and a lower MPI of the septoria leaf blotch fungi Mycosphaerella graminicola (Mg) and Phaeosphaeria nodorum (Pn). Levels of Ptr tended to be lower after 2 yr of noncereals, grown mostly under zero tillage. Overall, the MPI of Ptr increased with a reduction in tillage, being mo...