The role of pycnidiospores of Leptosphaeria maculans in the spread of blackleg disease in rape

Barbetti, MJ

doi:10.1071/ea9760911

Cited by 37 publications

(31 citation statements)

References 4 publications

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“…This was in contrast with the observations of Huang et al (2001Huang et al ( , 2003, who reported that germ tubes from A-group ascospores originated predominantly from interstitial cells. In our study, germination from interstitial cells occurred later generating severe epidemics of early seedling disease (Salisbury et al 1995;West et al 2001) and why the epidemics initiated solely by pycnidiospores develop relatively slowly (Barbetti 1976). Inoculum source differences are not expected to affect the results of our study.…”

Section: Discussionmentioning

confidence: 93%

“…The biological role of pycnidiospores is to initiate secondary infection cycles following the primary infection by ascospores (Barbetti 1976). Pycnidiospores are splash-borne and are considered to be a less important form of inoculum in some situations (Hall 1992), although they can be a significant inoculum under certain conditions (Barbetti 1976).…”

Section: Discussionmentioning

confidence: 99%

“…Under favorable conditions, ascospores germinate to infect leaves and produce lesions from which the pathogen grows down petioles into stems to initiate basal stem cankers or upper stem lesions (Hammond and Lewis 1987;Hammond et al 1985;Sun et al 2000;Zhou et al 1999). In Australia, stem canker on spring-type B. napus is initiated in late autumn or winter (or both times) by airborne ascospores released from infected oilseed rape residues from previous crops onto cotyledons and leaves of seedlings and also by pycnidiospores released from seedling lesions (Barbetti 1976;Bokor 1972;West et al 2001).…”

Section: Introductionmentioning

confidence: 98%

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Germination and invasion by ascospores and pycnidiospores of Leptosphaeria maculans on spring-type Brassica napus canola varieties with varying susceptibility to blackleg

Sivasithamparam

Barbetti

et al. 2004

J Gen Plant Pathol

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The infection processes of ascospores and pycnidiospores of Leptosphaeria maculans were studied on cotyledons of six cultivars of spring-type Brassica napus: one with resistance controlled by a single dominant gene (cv. Surpass 400), three with polygenic resistance (cvs. Dunkeld, Grouse, and Outback), and two susceptible cultivars (Westar and Q2). On all cultivars, ascospore germination, penetration, and development of symptoms on cotyledons were much earlier than that with pycnidiospores. At 2 h after inoculation ascospores began to germinate, by 4 h about 50% had germinated, and by 6-8 h 85%-90% had germinated. In contrast, pycnidiospores began to germinate 1 day after inoculation (dai) and reached only 50% germination by 3 dai. Ascospores began germinating from terminal cells and then later from the interstitial cells. Pycnidiospores germinated predominantly from one end and sometimes from both ends. Germ tubes from ascospores penetrated stomata as early as 4 h after inoculation, whereas those from pycnidiospores penetrated at 2 dai. Symptom development with ascospores was 2 days earlier than that with pycnidiospores. Symptoms on Surpass 400 were evident as early as 3-5 dai with ascospores and 5-7 dai with pycnidiospores. However, on other cultivars, symptoms were not evident until 10 dai with ascospores and 12 dai with pycnidiospores. This report is the first on differences in the infection processes by the two spore types. Ascospore and pycnidiospore attachment, germination, and penetration did not differ between resistant and susceptible cultivars, but there were major differences after penetration. Under high humidity, 80%-90% of stomata of susceptible Westar and Q2 had aerial hyphae emerging from stomatal pores. However, fewer stomata (5%-10%) had aerial hyphae on Surpass 400 by 10 dai with ascospores and 12 dai with pycnidiospores, but even these were usually poorly developed. Host differences in spring-type B. napus in relation to production of aerial hyphae have not previously been reported. In Surpass 400, rapid necrosis of guard cells occurred within a few hours of penetration by either type of spore, and subsequently one or a few cells immediately adjacent to the penetration site died. This necrosis then spread to the cells around the penetration site to form a hypersensitive response (in the form of a small, dark lesion) to both ascospores and pycnidiospores. This is the first detailed report on interactions between spring-type B. napus and L. maculans in relation to single dominant genebased resistance. Neither the cultivars with polygenic resistance nor the susceptible cultivars had such a response.

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Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Germination and invasion by ascospores and pycnidiospores of Leptosphaeria maculans on spring-type Brassica napus canola varieties with varying susceptibility to blackleg

Sivasithamparam

Barbetti

et al. 2004

J Gen Plant Pathol

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“…Canada have suggested a potential role for conidia as the cause of stem canker symptoms (Barbetti 1976;Guo and Fernando 2005). It was demonstrated by these authors that conidia, even at relatively low concentrations, caused severe disease symptoms on susceptible oilseed rape plants, provided a different cotyledon of the same seedling was co-inoculated with ascospores, suggesting that low concentrations of ascospores might induce susceptibility and increase disease severity in the presence of the sporulating anamorph of the pathogen (Li et al 2006).…”

Section: Discussionmentioning

confidence: 99%

Quantitative PCR analysis of abundance of airborne propagules of Leptosphaeria species in air samples from different regions of Poland

et al. 2011

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When airborne propagules of Leptosphaeria maculans and L. biglobosa were collected in Poland at three ecologically different sites from 1 September to 30 November in 2004 to 2008, using a Hirst-type seven-day volumetric spore trap, there were fluctuations in timing of ascospore release and diverse ratios between airborne propagules of both species depending on season, field location and weather conditions. The detection was done using the microscope as well as quantitative PCR with species-specific primers targeted against fragments of β-tubulin genes and quantified with a duallabelled fluorescent probe approach. This detection chemistry is described for the first time for L. maculans and L. biglobosa. Its advantage over the previous ITS-based SYBR-Green chemistry resides in improved sensitivity and the virtual absence of false positives in the detection of these fungi.There were significant, positive correlations between data obtained using visual assessment of ascospore numbers and DNA concentrations that were measured by qPCR. Climatic differences between the oilseed rape growing regions could have significantly affected the biological processes of pseudothecial maturation and ascospore development of the pathogens. The data suggest that regular rain events of intermediate intensity recorded in the Maritime region favoured the maturation of the pathogen more than the drier weather recorded in the Silesia or Pomerania regions. It was observed that the number of rainy days was of greater importance than the cumulative rainfall to obtain the generative sporulation of the pathogen. Accurate detection of airborne inoculum of pathogenic Leptosphaeria spp. facilitates improved targeting of disease management decisions for oilseed rape protection against phoma stem canker and stem necrosis diseases.

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“…In Australia, the major inoculum of blackleg is ascospores, in combination with pycnidiospores (Barbetti 1976;Marcroft et al 2004). In western Canada, pycnidiospores are the most important sources of inoculum in infection and disease development (Petrie 1995;Guo and Ghanbarnia et al 2011;Dilmaghani et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Insights into fighting against blackleg disease of Brassica napus in Canada

Zhang

Fernando

2018

Crop Pasture Sci.

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Abstract. Blackleg disease, caused by the ascomycete fungal pathogen Leptosphaeria maculans, is a devastating disease of canola (Brassica napus) in Australia, Canada and Europe. Although cultural strategies such as crop rotation, fungicide application, and tillage are adopted to control the disease, the most promising disease control strategy is the utilisation of resistant canola varieties. However, field populations of L. maculans display a high evolutionary potential and are able to overcome major resistance genes within a few years, making disease control relying on resistant varieties challenging. In the early 1990s, blackleg resistance gene Rlm3 was introduced into Canadian canola varieties and provided good resistance against the fungal populations until the early 2000s, when moderate to severe blackleg outbreaks were observed in some areas across western Canada. However, the breakdown of Rlm3 resistance was not reported until recently, based on studies on R genes present in Canadian canola varieties and the avirulence allele frequency in L. maculans populations in western Canada. The fact that Rlm3 was overcome by the evolution of fungal populations demands canola breeding programs in Canada to be prepared to develop canola varieties with diversified and efficient R genes. In addition, frequent monitoring of fungal populations can provide up-to-date guidance for proper resistance genes deployment. This literature review provides insights into the outbreaks and management of blackleg disease in Canada.

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The role of pycnidiospores of Leptosphaeria maculans in the spread of blackleg disease in rape

Cited by 37 publications

References 4 publications

Germination and invasion by ascospores and pycnidiospores of Leptosphaeria maculans on spring-type Brassica napus canola varieties with varying susceptibility to blackleg

Germination and invasion by ascospores and pycnidiospores of Leptosphaeria maculans on spring-type Brassica napus canola varieties with varying susceptibility to blackleg

Quantitative PCR analysis of abundance of airborne propagules of Leptosphaeria species in air samples from different regions of Poland

Insights into fighting against blackleg disease of Brassica napus in Canada

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