Comparison of disease measures for assessing resistance in canola (Brassica napus) to blackleg (Leptosphaeria maculans)

1996 ◽  
Vol 74 (12) ◽  
pp. 1930-1936 ◽  
Author(s):  
Curtis B. Rempel ◽  
Robert Hall
Keyword(s):  
Brassica Napus ◽  
Disease Severity ◽  
Disease Incidence ◽  
Leptosphaeria Maculans ◽  
Stem Canker ◽  
Measurement Range ◽  
Sampling Time ◽  
Severity Of Disease ◽  
Spring Canola ◽  
Range Of Values

Disease incidence, disease severity, areas under the disease incidence and disease severity progress curves, and maximum and minimum incidence and severity of disease were evaluated as measures of resistance in canola (Brassica napus) to blackleg caused by Leptosphaeria maculans. Seven genotypes of spring canola were tested in Ontario at three locations 60, 81, and 102 days after sowing in 1990 and at two locations 55, 70, 85, and 100 days after sowing in 1991. Disease incidence was expressed as the percentage of sampled plants with basal stem canker, and disease severity was assessed as the percentage discolouration of a cross section of the stem base. Based on ease of measurement, range of values, number of significant differences among genotypes, and constancy of rank of genotypes at different locations, measures of disease severity or disease incidence in mature plants proved to be most useful. No advantage was gained by using area under the disease incidence and disease severity progress curves, or maximum and minimum incidence and severity of disease at the last sampling time. It is recommended that resistance of canola stems to blackleg be evaluated from measures of disease severity or disease incidence in mature plants. Keywords: canola, blackleg, Leptosphaeria maculans, resistance measurements.

scholarly journals Effect of Elevated CO2 Concentration on the Disease Severity of Compatible and Incompatible Interactions of Brassica napus–Leptosphaeria maculans Pathosystem

Plants ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 484
Author(s):  
Zou ◽  
Liu ◽  
Chen ◽  
Fernando
Keyword(s):  
Brassica Napus ◽  
Disease Severity ◽  
Elevated Co2 ◽  
Disease Incidence ◽  
Leptosphaeria Maculans ◽  
Co2 Concentration ◽  
Gene Interaction ◽  
Avirulence Genes ◽  
Noticeable Effect ◽  
Co2 Concentrations

Global warming by increased atmospheric CO2 concentration has been widely accepted. Yet, there has not been any consistent conclusion on the doubled CO2 concentration that in the future will affect plant disease incidence and severity. Blackleg disease, mainly caused by Leptosphaeria maculans, is a major disease on canola production globally. Brassica napus and L. maculans have a gene-for-gene interaction, which causes an incompatible reaction between canola plants carrying resistance genes and L. maculans isolates carrying corresponding avirulence genes. In this study, B. napus varieties and lines inoculated with different Leptosphaeria isolates were subjected to simulated growth conditions, namely, growth chambers with normal environments and with controlled CO2 concentrations of 400, 600, and 800 ppm. The results indicated that the elevated CO2 concentrations have no noticeable effect on the inferred phenotypes of the canola–blackleg interactions. However, the disease severity decreased in most of the B. napus–L. maculans interactions at extremely high CO2 concentration (800 ppm). The varied pathogenicity changes of the B. napus–L. maculans pathosystem under elevated CO2 concentrations at 400 or 600 ppm may be due to the genetic background or physiological differences in plants and pathogenicity differences in L. maculans isolates having different Avr gene profiles. The mechanisms by which elevated CO2 concentrations affect the B. napus–L. maculans pathosystem will help us understand how climate change will impact crops and diseases.

Effects of time and rate of application of triazole fungicides on incidence and severity of blackleg and growth and yield of canola

1995 ◽  
Vol 75 (3) ◽  
pp. 737-743 ◽  
Author(s):  
C. B. Rempel ◽  
R. Hall
Keyword(s):  
Brassica Napus ◽  
Disease Severity ◽  
Seed Weight ◽  
Disease Incidence ◽  
Growth And Yield ◽  
Growth Stages ◽  
Triazole Fungicides ◽  
Foliar Sprays ◽  
Spring Canola ◽  
Key Words:Brassica

The ability of three triazole fungicides to reduce blackleg and to increase the yield of spring canola (Brassica napus) was tested at four locations in Ontario in 1990 and 1991 in fields containing stubble infested with Leptosphaeria maculons. In test 1, triadimefon (3.46 kg ha−1), diconazole (1.41 kg ha−1) and uniconazole (2.12 kg ha−1) were sprayed on foliage at the late rosette stage, or when flowers were opening on the main raceme, or at both growth stages at half rate (split). Split applications were most effective and reduced disease incidence and severity by 9.2 and 22.6%. Yields were not increased. In test 2, the fungicides were applied at the late rosette stage at four rates. The highest rates of triadimefon (9.24 kg ha−1), diconazole (3.76 kg ha−1) and uniconazole (5.64 kg ha−1) reduced disease incidence by 12.8, 10.6 and 6.4%, reduced disease severity by 25.7, 31.8 and 24.2%, and increased yield by 17, 33 and 30%, respectively. In both tests, most treatments increased seed weight, delayed crop flowering and maturity, reduced lodging and height, and increased vigor. Triazole fungicides applied as foliar sprays can reduce blackleg and improve yield of canola. Key words:Brassica napus, canola, triadimefon, diconazole, uniconazole, blackleg

Evaluation of disease forecasting variables for sclerotinia stem rot (Sclerotinia sclerotiorum) of canola

2000 ◽  
Vol 80 (4) ◽  
pp. 889-898 ◽  
Author(s):  
M. Bom ◽  
G. J. Boland
Keyword(s):  
Soil Moisture ◽  
Disease Severity ◽  
Sclerotinia Sclerotiorum ◽  
Prediction Models ◽  
Disease Incidence ◽  
Stem Rot ◽  
Disease Prediction ◽  
Strong Correlations ◽  
Sclerotinia Stem Rot ◽  
Spring Canola

Selected environmental, crop and pathogen variables were sampled weekly from winter and spring canola crops before and during flowering and evaluated for the ability to predict sclerotinia stem rot, caused by Sclertinia sclerotirum. Linear and nonlinear relationships were examined among variables but, because no strong correlations were observed between final disease incidence and any of the variables tested, a categorical approach (e.g., disease severity) was used instead. Disease severity in individual crops was categorized as low (< 20% diseased plants) or high (> 20% disease), and differences in weekly rainfall, soil moisture, crop height, percentage of petal infestation, and number of apothecia m−2 and clumps of apothecia m−2 were significantly associated with differences in disease severity within or between years. Two disease prediction models were compared for the ability to predict low or high disease severities using petal infestation alone, or petal infestation in combination with soil moisture. The model that included petal infestation and soil moisture predicted more fields correctly than the model using petal infestation alone, but the accuracy of both was affected by the timing of soil moisture measurements in relation to petal infestation, and threshold values used in discriminating categories of soil moisture and petal infestation. Key words: Brassica rapa, Brassica napus, Sclerotinia sclerotiorum, disease prediction

scholarly journals Breakdown of a Brassica rapa subsp. sylvestris Single Dominant Blackleg Resistance Gene in B. napus Rapeseed by Leptosphaeria maculans Field Isolates in Australia

Plant Disease ◽  
2003 ◽  
Vol 87 (6) ◽  
pp. 752-752 ◽  
Author(s):  
H. Li ◽  
K. Sivasithamparam ◽  
M. J. Barbetti
Keyword(s):  
Brassica Napus ◽  
Resistance Gene ◽  
Disease Severity ◽  
Brassica Rapa ◽  
Oilseed Rape ◽  
Leptosphaeria Maculans ◽  
Blackleg Disease ◽  
Field Isolates ◽  
Western Australian ◽  
Lower Stem

Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus) grown in Canada, Europe, and Australia. Cv. Surpass 400 was released in Australia in 2000 as the most resistant cultivar to L. maculans. It carries a single dominant resistance gene from B. rapa subsp. sylvestris. This cultivar usually shows a hypersensitive response to L. maculans characterized by small, dark brown lesions that are necrotic, localized, and without pycnidia on cotyledons, leaves, and stems. However, in 2001 on a Western Australian experimental farm, a small proportion of the lesions on the lower stem and crown region of cv. Surpass 400 were typical of those observed in susceptible cultivars, which were brown, necrotic lesions with a darker margin, but they contained fewer pycnidia. Forty seedlings of cv. Surpass 400 and susceptible cv. Westar were inoculated with pycnidiospore suspensions (106/ml) of each of 18 isolates taken from lesions on cv. Surpass 400. All 18 isolates caused collapse of cotyledons of susceptible cv. Westar. Four of these isolates caused large cotyledon lesions with some pycnidia on cv. Surpass 400. Three of these four isolates were subsequently inoculated onto 60 seedlings per isolate, at each of the four cotyledon lobes of each seedling of the two cultivars. Inoculated plants were assessed for disease severity on cotyledons and transplanted to the field 14 days after inoculation. The cotyledons of inoculated cv. Surpass 400 showed characteristic large, necrotic lesions with pycnidia, while the cotyledons of cv. Westar had collapsed and contained a mass of pycnidia. Blackleg disease severity in the crown region of the stem was assessed at 2 weeks before harvest. Fifty-four percent of the cv. Surpass 400 transplanted inoculated plants subsequently developed susceptible symptoms of crown cankers on stems. These symptoms were deep, girdling, brown lesions on the plant crowns with some pycnidia. One hundred percent of cv. Westar plants were infected and dead at this stage. This confirmed the ability of these field isolates to overcome the single dominant resistance gene present in cv. Surpass 400. To our knowledge, this is the first report of breakdown of a single dominant B. rapa subsp. sylvestris gene based resistance to blackleg in oilseed rape in the field.

scholarly journals Mycovirus-Induced Hypervirulence of Leptosphaeria biglobosa Enhances Systemic Acquired Resistance to Leptosphaeria maculans in Brassica napus

2020 ◽  
Vol 33 (1) ◽  
pp. 98-107 ◽  
Author(s):  
Unnati A. Shah ◽  
Ioly Kotta-Loizou ◽  
Bruce D. L. Fitt ◽  
Robert H. A. Coutts
Keyword(s):  
Brassica Napus ◽  
Systemic Acquired Resistance ◽  
Acquired Resistance ◽  
Leptosphaeria Maculans ◽  
Stem Canker ◽  
Systemic Resistance ◽  
Phoma Stem Canker ◽  
Isogenic Lines ◽  
Related Proteins ◽  
Leptosphaeria Biglobosa

Phoma stem canker (blackleg) is one of the most important diseases of winter oilseed rape (Brassica napus) worldwide and is caused by a complex that comprises at least two species: Leptosphaeria maculans and L. biglobosa. Screening a panel of field Leptosphaeria isolates from B. napus for the presence of mycoviruses revealed the presence of a novel double-stranded RNA quadrivirus in L. biglobosa and no viruses in L. maculans. Following elimination of the mycovirus, virus-infected and virus-free isogenic lines of L. biglobosa were created. A direct comparison of the growth and virulence of these isogenic lines illustrated that virus infection caused hypervirulence and resulted in induced systemic resistance toward L. maculans in B. napus following lower leaf preinoculation with the virus-infected isolate. Analysis of the plant transcriptome suggests that the presence of the virus leads to subtle alterations in metabolism and plant defenses. For instance, transcripts involved in carbohydrate and amino acid metabolism are enriched in plants treated with the virus-infected isolate, while pathogenesis-related proteins, chitinases and WRKY transcription factors are differentially expressed. These results illustrate the potential for deliberate inoculation of plants with hypervirulent L. biglobosa to decrease the severity of Phoma stem canker later in the growing season. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

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