scholarly journals Host–pathogen interactions in relation to management of light leaf spot disease (caused by Pyrenopeziza brassicae) on Brassica species

2018 ◽  
Vol 69 (1) ◽  
pp. 9 ◽  
Author(s):  
Chinthani S. Karandeni Dewage ◽  
Coretta A. Klöppel ◽  
Henrik U. Stotz ◽  
Bruce D. L. Fitt
Keyword(s):  
Leaf Spot ◽  
Fungal Pathogens ◽  
Molecular Mechanisms ◽  
Brassica Species ◽  
Leaf Spot Disease ◽  
Yield Losses ◽  
Sources Of Resistance ◽  
Management Tools ◽  
Brussels Sprouts ◽  
Main Component

Light leaf spot, caused by Pyrenopeziza brassicae, is the most damaging disease problem in oilseed rape (Brassica napus) in the United Kingdom. According to recent survey data, the severity of epidemics has increased progressively across the UK, with yield losses of up to £160M per annum in England and more severe epidemics in Scotland. Light leaf spot is a polycyclic disease, with primary inoculum consisting of airborne ascospores produced on diseased debris from the previous cropping season. Splash-dispersed conidia produced on diseased leaves are the main component of the secondary inoculum. Pyrenopeziza brassicae is also able to infect and cause considerable yield losses on vegetable brassicas, especially Brussels sprouts. There may be spread of light leaf spot among different Brassica species. Since they have a wide host range and frequent occurrence of sexual reproduction, P. brassicae populations are likely to have considerable genetic diversity, and evidence suggests population variations between different geographic regions, which need further study. Available disease-management tools are not sufficient to provide adequate control of the disease. There is a need to identify new sources of resistance, which can be integrated with fungicide applications to achieve sustainable management of light leaf spot. Several major resistance genes and quantitative trait loci have been identified in previous studies, but rapid improvements in the understanding of molecular mechanisms underpinning B. napus–P. brassicae interactions can be expected through exploitation of novel genetic and genomic information for brassicas and extracellular fungal pathogens.

scholarly journals First Report of a Leaf Spot on Conyza sumatrensis Caused by Phoma macrostoma in China

Plant Disease ◽  
2012 ◽  
Vol 96 (1) ◽  
pp. 148-148 ◽  
Author(s):  
J. Liu ◽  
H. D. Luo ◽  
W. Z. Tan ◽  
L. Hu
Keyword(s):  
Leaf Spot ◽  
Fungal Pathogens ◽  
Biological Diversity ◽  
Biocontrol Agent ◽  
Continuous Light ◽  
The United States ◽  
Leaf Spot Disease ◽  
Pathogenicity Test ◽  
Dry Land ◽  
First Report

Conyza sumatrensis (Asteraceae), an annual or biennial plant, is native to North and South America. It is an invasive, noxious weed that is widespread in southern and southeastern China. It invades farm land and causes great losses to dry land crops, including wheat, corn, and beans. It also reduces biological diversity by crowding out native plants in the infested areas (3,4). During a search for fungal pathogens that could serve as potential biological control agents of C. sumatrensis, a leaf spot disease was observed in 2010 in Chongqing, China. An isolate (SMBC22) of a highly virulent fungus was obtained from diseased leaves. Pathogenicity tests were performed by placing 6-mm-diameter mycelial disks of 7-day-old potato dextrose agar (PDA) cultures of SMBC22 on leaves of 15 healthy greenhouse-grown plants of C. sumatrensis; the same number of control plants was treated with sterile PDA disks. Treated plants were covered with plastic bags for 24 h and maintained in a growth chamber with daily average temperatures of 24 to 26°C, continuous light (3,100 lux), and high relative humidity (>90%). Lesions similar to those observed in the field were first obvious on the SMBC22-inoculated leaves 3 days after inoculation. Symptoms became severe 7 to 9 days after inoculation. Control plants remained healthy. The fungus was reisolated from inoculated and diseased leaves and it was morphologically the same as SMBC22. The pathogenicity test was conducted three times. A survey of 10 southern and southeastern Chinese provinces revealed that the disease was widespread and it attacked leaves and stems of seedlings and mature plants of C. sumatrensis. Lesions on leaves were initially small, circular, and water soaked. The typical lesion was ovoid or fusiform, dark brown, and surrounded by a yellow halo. The spots coalesced to form large lesions and plants were often completely blighted. Fungal colonies of SMBC22 on PDA plates were initially white and turned dark gray. Colonies were circular with smooth edges with obvious rings of pycnidia on the surface. Aerial hyphae were short and dense. Pycnidia, black and immersed or semi-immersed in the medium, were visible after 12 days of incubation. Pycnidia were 72 to 140 μm in diameter. Conidia were produced in the pycnidia and were hyaline, unicellular, ellipsoidal, and 4.4 to 6.1 × 1.6 to 2.2 μm. To confirm identification of the fungus, genomic DNA was extracted from mycelia of a 7-day-old culture on PDA at 25°C (2). The internal transcribed spacer (ITS) gene of rDNA was amplified using primers ITS4/ITS5. The gene sequence was 524 bp long and registered in NCBI GenBank (No. HQ645974). BLAST analysis showed that the current sequence had 99% homology to an isolate of Phoma macrostoma (DQ 404792) from Cirsium arvense (Canada thistle) in Canada and reported to cause chlorotic symptoms on that host plant (1). To our knowledge, this is the first report of P. macrostoma causing disease on C. sumatrensis in China. P. macrostoma, thought of as a biocontrol agent of broadleaf weeds in Canada, has been patented in the United States. The current isolate of P. macrostoma is considered as a potential biocontrol agent of C. sumatrensis. References: (1) P. R. Graupner et al. J. Nat. Prod. 66:1558, 2004. (2) S. Takamatsu et al. Mycoscience 42:135, 2001. (3) W. Z. Tan et al. Page 177 in: Manual of Emergency Control Technology Invasive Pests in China. G. L. Zhang, ed. Science Press, Beijing, 2010. (4) C. Wang et al. J. Wuhan Bot. Res. 28:90, 2010.

scholarly journals First Report of Alternaria Leaf Spot of Almond Caused by Species in the Alternaria alternata Complex in California

Plant Disease ◽  
2001 ◽  
Vol 85 (5) ◽  
pp. 558-558 ◽  
Author(s):  
B. L. Teviotdale ◽  
M. Viveros ◽  
B. Pryor ◽  
J. E. Adaskaveg
Keyword(s):  
Alternaria Alternata ◽  
Leaf Spot ◽  
Disease Incidence ◽  
Prunus Dulcis ◽  
Leaf Spot Disease ◽  
Yield Losses ◽  
Mature Leaves ◽  
Branching Chains ◽  
Paper Towels ◽  
Industry Conference

A new leaf spot disease of almond (Prunus dulcis [Mill.] D. Webb) was observed in California in the late 1980s and was first associated with severe defoliation in the mid-1990s (1). Orchards in areas with frequent summer dews, high humidity, and little air movement sustained severe defoliation, resulting in yield losses often exceeding 50%. Symptoms occur only on leaf blades in late spring and summer. Lesions develop as small, circular, tan spots 1 to 3 mm in diameter that may enlarge to 5 to 20 mm in size. Semicircular lesions frequently develop along the leaf margins and tips. The centers of mature lesions become black with fungal sporulation. The fungi isolated from the margins of sporulating and non-sporulating lesions were identified as three species in the Alternaria alternata complex: A. alternata, A. arborescens, and A. tenuissima (2,3). Cultures grown in the dark on potato dextrose (PDA) or potato-carrot agar are grayish white to olivacious green in the former two species and dark gray and wooly in the latter species. On 5% PDA, cultures of all three species produced catenulate dictyospores that were granular to punctate (-verrucose), pale yellowish to brown or black, and had visible apical and basal pores. Conidial morphology depended on chain position; apical conidia ranged from ovoid to ellipsoid, whereas basal conidia were elliptical to obclavate. Average conidial dimensions of A. alternata and A. arborescens ranged from 20 to 28 × 8 to 10 μm. Conidia of A. alternata were produced in acropetal succession in branching chains on single, short suberect conidiophores. A. arborescens produced conidia similarly but mostly in dichotomously branching chains on short to long conidiophores. Average conidial dimensions of A. tenuissima ranged from 20 to 34 × 8 to 12 μm and they were produced in simple chains with one or two branches forming occasionally. In preliminary studies, the optimum temperature for mycelial growth on PDA for all three species ranged from 24 to 28°C. Fifty mature leaves on each of four 7- or 8-year-old almond cv. Butte trees were inoculated at 2- to 3-week intervals from mid-spring through summer in 1999 and 2000. Leaves were sprayed with aqueous suspensions containing 105 conidia per milliliter for one isolate each of A. alternata and A. arborescens and two isolates of A. tenuissima or with sterile distilled water. The shoots were covered for 72 h with plastic-lined brown paper bags containing wet paper towels. Leaves were examined for infection after 7 and 14 days. All isolates were pathogenic and produced non-sporulating lesions similar to those observed in natural infections. No symptoms were observed on noninoculated control plants. Disease incidence was low (<15%) until late June 1999 and July 2000. Inoculations in summer produced increasingly more infections, reaching incidences of 40 to 52% in September 1999 and 18 to 80% in August 2000. References: (1) J. E. Adaskaveg. 1994. Pages 5–7 in Proceedings of the 22nd Annual Almond Industry Conference. 1994. (2) J. Rotem. 1994. The genus Alternaria. Biology, Epidemiology, and Pathogenicity. APS Press, St. Paul, MN. (3) E. G. Simmons. Mycotaxon 70:325–369, 1999.

scholarly journals Molecular identification of fungal pathogens associated with leaf spot disease of date palms (Phoenix dactylifera)

All Life ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 587-597
Author(s):  
Hamed Al-Nadabi ◽  
Sajeewa S. N. Maharachchikumbura ◽  
Zameta S. Al-Gahaffi ◽  
Ahmed S. Al-Hasani ◽  
Rethinasamy Velazhahan ◽  
...  
Keyword(s):  
Molecular Identification ◽  
Leaf Spot ◽  
Fungal Pathogens ◽  
Phoenix Dactylifera ◽  
Leaf Spot Disease ◽  
Date Palms ◽  
Spot Disease

Role of foliage component and host age on severity of Alternaria leaf spot (caused by Alternaria japonica and A. brassicae) in canola (Brassica napus) and mustard (B. juncea) and yield loss in canola

2019 ◽  
Vol 70 (11) ◽  
pp. 969 ◽  
Author(s):  
H. F. D. Al-lami ◽  
M. P. You ◽  
M. J. Barbetti
Keyword(s):  
Brassica Napus ◽  
Leaf Area ◽  
Seed Yield ◽  
Leaf Spot ◽  
Yield Loss ◽  
Disease Incidence ◽  
Brassica Species ◽  
Leaf Spot Disease ◽  
Disease Development ◽  
Alternaria Leaf Spot

Studies were undertaken under controlled conditions into the effects of different foliage components (cotyledon, first, second and third leaf) at three plant ages (3, 5 and 7 weeks old) on development of Alternaria leaf spot disease, caused by Alternaria japonica or A. brassicae, in canola (Brassica napus cv. Thunder TT) and mustard (B. juncea cv. Dune). Alternaria japonica generally showed percentage disease index (%DI) values similar to A. brassicae across the two Brassica species, different foliage components and plant ages. %DI from either pathogen was greater in older plants than younger plants for the same foliage components in both cultivars. Field studies were then undertaken with canola to compare disease development from A. japonica and A. brassicae across different plant components (leaf, pod and stem) and the consequent adverse impact on seed yield. Alternaria japonica was more severe in terms of leaf area diseased (%LAD 62.6) and stem area diseased (%SAD 69.8) than pod area diseased (%PAD 25.5), whereas A. brassicae was more severe on leaves (%LAD 61.9) than on pods (%PAD 47.4) or stems (%SAD 41.0). Stem disease incidence was greater for A. japonica (%SDI 94.0) than for A. brassicae (%SDI 56.5), but pod disease incidence was greater for A. brassicae (%PDI 93.5) than for A. japonica (%PDI 86.1). For A. japonica, AUDPC values of leaf disease incidence (LDI, 283.5), leaf area diseased (LAD, 253.3) and leaf collapse (LCI, 149.5) resulted in a yield loss of 58.1%, similar to A. brassicae, where AUDPC values of LDI (277.8), LAD (247.2) and LCI (111.0) caused a yield loss of 59.4%. These findings explain observed acceleration of Alternaria leaf spot severity from A. japonica, as from A. brassicae, through the growing season as plants become more susceptible with increasing age, and as more susceptible, later developing leaves become abundant. For the first time, we demonstrate that under conducive field conditions for disease development, A. japonica can cause serious seed-yield losses of a magnitude similar to those occurring with A. brassicae.

Differentiation of Corynespora cassiicola and Cercospora sp. in leaf-spot diseases of Hydrangea macrophylla using a PCR-mediated method

2015 ◽  
Vol 95 (4) ◽  
pp. 711-717 ◽  
Author(s):  
M. T. Mmbaga ◽  
M.-S. Kim ◽  
L. Mackasmiel ◽  
N. B. Klopfenstein
Keyword(s):  
Leaf Spot ◽  
Fungal Pathogens ◽  
Pathogen Detection ◽  
Management Practices ◽  
Leaf Spot Disease ◽  
Corynespora Cassiicola ◽  
Disease Etiology ◽  
Diagnostic Pcr ◽  
Southeastern Usa ◽  
Hydrangea Macrophylla

Mmbaga, M. T., Kim M.-S., Mackasmiel, L. and Klopfenstein, N. B. 2015. Differentiation of Corynespora cassiicola and Cercospora sp. in leaf-spot diseases of Hydrangea macrophylla using a PCR-mediated method. Can. J. Plant Sci. 95: 711–717. Corynespora cassiicola and Cercospora sp. have been identified as the most prevalent and destructive leaf-spot pathogens of garden hydrangea [Hydrangea macrophylla (Thunberg) Seringe] in the southeastern USA, but they are often difficult to accurately detect and distinguish because they often occur together in a disease complex with other pathogenic leaf-spot fungi and produce very similar symptoms. This study was conducted to provide diagnostic PCR primers for detecting and distinguishing Corynespora cassiicola and Cercospora sp. among other leaf-spot pathogens of garden hydrangea. Two primer pairs showed specificity to Corynespora cassiicola and one primer pair showed specificity to Cercospora sp., and these primers did not amplify DNA from any other common fungal pathogens associated with hydrangea leaf-spot diseases. Results from this study show that DNA-based diagnostic primers provide a useful tool for pathogen detection/identification in hydrangea leaf-spot disease, which is an essential step toward understanding disease etiology and developing/applying appropriate disease-management practices in the southeastern USA.

First Report of Hemp Leaf Spot Caused by a Bipolaris Species on Hemp (Cannabis sativa) in Kentucky

2020 ◽  
Vol 21 (2) ◽  
pp. 82-84 ◽  
Author(s):  
Desiree Szarka ◽  
Bernadette Amsden ◽  
Julie Beale ◽  
Ed Dixon ◽  
Christopher L. Schardl ◽  
...  
Keyword(s):  
Leaf Spot ◽  
Cannabis Sativa ◽  
Morphological Data ◽  
Leaf Spot Disease ◽  
Yield Losses ◽  
Widespread Distribution ◽  
First Report ◽  
Common Reference ◽  
Weed Hosts ◽  
The Common

Upon reintroduction of hemp (Cannabis sativa) in 2014, reports of a leaf spot disease became increasingly common in Kentucky. Outdoor-grown plants became severely affected with necrosis and blight symptoms, and many crops were rejected by processors either as a result of leaf and bud necrosis or as a result of reduced levels of cannabidiol. Morphological data and sequences of ITS and partial 28S rDNA identified the pathogen as Drechslera gigantea. Phylogenetic analysis grouped all isolates in a clade within Bipolaris. Dicot and monocot weed hosts within symptomatic fields were also identified. We refer to the disease as Bipolaris leaf spot, but the common reference is hemp leaf spot. This is the first report of a Bipolaris pathogen infecting C. sativa. Widespread distribution, disease severity, and extreme yield losses makes this one of the most important diseases of hemp in Kentucky.

scholarly journals Screening Common Bean (Phaseolus vulgaris L.) Germplasm for Resistance against Angular Leaf Spot (Pseudocercospora griseola) Disease under Field Condition

2019 ◽  
Vol 8 (1) ◽  
pp. 30
Author(s):  
Yayis Rezene ◽  
Shiferw Mekonin
Keyword(s):  
Common Bean ◽  
Field Condition ◽  
Leaf Spot ◽  
Genetic Resistance ◽  
Angular Leaf Spot ◽  
Eastern Africa ◽  
Leaf Spot Disease ◽  
Sources Of Resistance ◽  
The Common ◽  
Pseudocercospora Griseola

Angular leaf spot (ALS) caused by the fungus Pseudocercospora griseola is one of the most destructive disease in Latin America and eastern Africa countries. The fungus, P. griseola is highly variable and a diverse sources of resistance genes is required to manage this economically important disease. The use of genetic resistance is the most practical and economic way to manage angular leaf spot of the common bean. Common bean (Phaseolus vulgarise L.) germplasm were screened for resistance against Angular leaf spot (ALS) under field conditions at Wonodogenet and Areka Research farms. Out of 300 common bean accessions evaluated only 14 (4.6%) common bean accessions were resistant to naturally epidemics of angular leaf spot disease under field condition. Therefore, all common bean germplasm that showed resistance reaction can be involved in breeding program for the improvement of the common bean.

Early and Late Leaf Spot Resistance and Agronomic Performance of Nineteen Interspecific Derived Peanut Lines1

1994 ◽  
Vol 21 (2) ◽  
pp. 99-104 ◽  
Author(s):  
M. Ouedraogo ◽  
O. D. Smith ◽  
C. E. Simpson ◽  
D. H. Smith
Keyword(s):  
Wild Species ◽  
Leaf Spot ◽  
Rating Scale ◽  
Leaf Spot Disease ◽  
Cercospora Arachidicola ◽  
Yield Losses ◽  
Breeding Lines ◽  
Pod Yield ◽  
In The Wild ◽  
Late Leaf Spot Resistance

Abstract Nineteen selected interspecific peanut lines with resistance to leaf spot [Cercospora arachidicola Hori and/or Cercosporidium personatum (Berk, and Curt.) Deighton] were field tested 3 yr for disease reaction and productivity with and without foliar fungicide protection. Measurements included severity ratings of leaf spot every 2 wk based on the Florida leaf spot disease rating scale, and pod yield. Area under disease progress curves (AUDPC) and pod yield losses were calculated. Differences among the interspecific lines in AUDPC values were significant, and one line had values equal to or lower than that of Southern Runner. One-half of the lines were equal in yield (P=0.01) to Southern Runner. Yields among lines averaged 1 to 50% higher with, as compared to without, chlorothalonil application. Yield losses of individual entries varied significantly from 1 yr to another and incongruous with the AUDPC pattern. Correlations between the AUDPC and yield loss were significant (P=0.01) for the 1989 and 1990, but not for the 1988 data. Results of the study indicate that resistance to both C. arachidicola and personatum were incorporated from the wild species parents into productive, runner-type breeding lines, and that the resistance to personatum was equal to or better than that of Southern Runner. Additional effort will be required to transfer levels of leaf spot resistance observed in the wild species parents into successful cultivars.

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