Diseases Of Oilseed Rape Research Articles

Construction of cDNA Expression Library of Oilseed Rape and Identification of the Interaction Partner of PG, a Virulence Factor from Sclerotinia sclerotiorum

Sclerotinia sclerotiorum (Lib.) de Bary is the fungal agent that causes stem rot disease in oilseed rape ( Brassica spp.). To overcome plant cell wall during early pathogenesis, the fungus secretes several types of cell wall-degrading enzymes such as polygalacturonases (PGs). The activities of these enzymes determine the pathogenicity/ virulence and are crucial for the colonization on plant tissues. PGs can induce defense reactions in plants unrelated to its enzyme activities. To understand the PG signaling pathway, a PG gene was cloned from S. sclerotiorum by RT-PCR. The encoding region of the PG gene was fused to the yeast GAL4 DNA-binding domain in yeast expression vector PGBKT7 and a rapeseed ( B. napus) cDNA expression library was constructed in yeast. PG-interacting proteins were screened in the library using PG as bait by yeast two-hybrid assay. An interacting protein was isolated. Sequencing and BLAST analysis revealed that the protein contained a C2-domain and was predicted to be a Ca 2+ binding domain. The protein shared 80.24% identity in amino acids with a C2-domain protein in Arabidopsis with unknown function. The expression levels of the C2-domain protein in floral, leaf, and stem organs of oilseed rape were investigated by semi-quantitative RT-PCR. The C2-domain protein was highly expressed in leaves when inoculated with S. sclerotiorum. The comparisons of the C2-domain proteins identified in oilseed rape with that of other species suggested that aspartic acid residues involving in Ca 2+ binding were conserved.

Impact of formulation procedures on the effect of the biocontrol agent Serratia plymuthica HRO-C48 on Verticillium wilt in oilseed rape

Verticillium wilt is an important disease in oilseed rape with an increasing importance worldwide. Currently, there are no methods available to suppress the pathogen. A biological protection strategy on the basis of the plant-beneficial bacterium Serratia plymuthica HRO-C48 to control Verticillium dahliae in oilseed rape was developed. Three different techniques to apply the biocontrol agent to seeds, namely pelleting, film coating and bio-priming, were evaluated considering the influence on the control activity, cell stability during storage and practical feasibility. Neither the treatment nor the inoculum density was found to influence the abundances of HRO-C48 in the rhizosphere after 30 days. Serratia treatment using bio-priming and pelleting resulted in a statistically significant biocontrol in comparison to the non-bacterized controls. Additionally, survival of HRO-C48 differed between treatments, and was the highest using bio-priming at 20°C, and pelleting at 4°C. In conclusion, the procedure of bio-priming, which was developed in line with this study, resulted in a stable and efficient formulation of S. plymuthica on rape seed. This technology opens a possibility to develop a commercial Serratia formulation to protect oilseed against V. dahliae.

Splash dispersal of Leptosphaeria maculans pycnidiospores and the spread of blackleg on oilseed rape

The fungus Leptosphaeria maculans causes blackleg (phoma stem canker), one of the most serious diseases of oilseed rape. The role of pycnidiospores produced during asexual reproduction is poorly documented and limits the understanding of the pathogen's population dynamics. The objectives of this study were to assess rain‐splash dispersal of pycnidiospores of L. maculans from phoma leaf spots, and transmission of the disease from oilseed rape stubble carrying pycnidia. The work was conducted in still air with either a drop generator or a rain simulator. The impact of simulated incident drops on phoma leaf spots resulted in the dispersal of L. maculans pycnidiospores within splash droplets. Ninety per cent of the spores were collected within 14 cm of the source and a few were regularly observed up to 40 cm. Pycnidiospores produced on oilseed rape stubble and dispersed by simulated rain infected oilseed rape trap plants in a spatial pattern that matched the spatial dispersal of the pycnidiospores. In the field, rain‐splash dispersal of pycnidiospores could increase the pathogen population and may enhance sexual reproduction by facilitating the mating of initially spatially separated isolates of opposite mating type.

Recurring challenges from a necrotrophic fungal plant pathogen: a case study with Leptosphaeria maculans (causal agent of blackleg disease in brassicas) in Western Australia.

Blackleg disease of Brassica napus, caused by the necrotrophic fungus Leptosphaeria maculans, causes severe yield losses in Australia, Europe and Canada. In Western Australia, it nearly destroyed the oilseed rape industry in 1972 when host genotypes and conducive environmental conditions favoured severe epidemics. The introduction of cultivars with polygenic resistance and the adoption of sound cultural practices two decades later helped to manage the disease. These were abandoned by many farmers in recent years in favour of the effective but ephemeral resistance conferred by the single dominant gene-based resistance derived from B. rapa ssp. sylvestris. Recently, several cultivars carrying this gene have collapsed widely within a period of 3 years after their commercial release. An environment conducive to the disease and the association of the pathogen with susceptible hosts in Western Australia for over 80 years together have led to the proliferation of L. maculans races, amounting to half of all races delineated to date from Europe, including the United Kingdom, Canada and Australia. This review demonstrates the problems that emerge when traditional cultural practices employed, along with cultivars containing polygenic resistance to a serious necrotrophic pathogen, are discarded in preference to the exclusive deployment of effective but ephemeral single dominant gene-based resistance to the disease across Southern Australia. Single dominant gene-based resistance currently available, on its own, will not confer durable resistance to blackleg disease in oilseed rape. Return to earlier management practices, including reliance upon polygenic resistance and induced resistance, may be the best currently available options to maintain production in regions across Southern Australia predisposed to severe epidemics.

Rep-PCR based genomic fingerprinting of isolates of Leptosphaeria maculans from Poland

Leptosphaeria maculans, the ascomycete fungus which causes blackleg disease of oilseed rape, has been considered for a long time as a single species divided into ‘aggressive’ and ‘non-aggressive’ pathogenicity groups which differ in their economic importance. However, the development of accurate biochemical and molecular characterisation methods has demonstrated that the world-wide L. maculans population actually comprises at least two species. The aim of this research was to assess the ability of rep (repetitive element based)-PCR genomic fingerprinting methods, initially developed for bacterial identification, to characterise a collection of 90 isolates of L. maculans from Poland, in comparison with reference isolates from the IBCN (International Blackleg of Crucifers Network) collection. REP (repetitive extragenic palindromic)-, ERIC (enterobacterial repetitive intergenic consensus)-, and BOX primers for rep-PCR genomic fingerprinting, and primers derived from LMR1, a L. maculans specific repeated element, were tested. Rep-PCR and LMR1-based analyses were able to discriminate the different components of the species complex and to evaluate the genetic diversity within each member of the complex. These analyses suggested that Polish populations of L. maculans mainly belong to the ‘non-aggressive’ species, rather than the ‘aggressive’ species which is prevalent in Western Europe, Canada and Australia.

Effect of Coniothyrium minitans on sclerotial survival and apothecial production of Sclerotinia sclerotiorum in field‐grown oilseed rape

In two field trials with oilseed rape, Coniothyrium minitans was applied to soil as a maizemeal‐perlite preparation in order to determine its effect on sclerotial survival and apothecial production of Sclerotinia selerotiorum. The mycoparasite infected sclerotia and decreased sclerotial survival, carpogenic germination and production of apothecia. Effects were greatest when inoculum of C. minitans was applied in autumn, at the time of sowing, rather than when it was applied in spring. C. minitans survived in soil for 2 years and spread to adjacent control plots and infected sclerotia within those plots. However, despite the fact that the inoculum potential of S. selerotiorum was reduced by C. minitans treatment, no disease control was obtained either in trial 1, where disease levels were low (0‐20% of plant stems affected), or in trial 2, where disease levels were high (up to 70% of plant stems affected). Possible reasons for this failure of C minitans to control sclerotinia disease in oilseed rape, and strategies to improve its efficacy in the field, are discussed.

The incidence of three virus diseases of winter oilseed rape in England and Wales in the 1991/92 and 1992/93 growing seasons

The incidence and severity of three diseases of oilseed rape, caused by beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV) and turnip mosaic potyvirus (TuMV), were assessed in England and Wales in the springs of 1992 and 1993. In 1992, 62% of oilseed rape crops examined were found to contain BWYV, with an average of 28% plants infected; 14% of crops contained CaMV, with an average of 5% plants infected; and TuMV with 3% crops and < 1% plants infected. In 1993, BWYV was found in 42% of crops and 12% of plants infected; CaMV in 25% of crops and 7% of plants infected; and TuMV in 14% of crops and 5% plants infected. The yields of plants showing severe virus symptoms were reduced by an estimated 70 to 79%. The high incidence of CaMV and TuMV in oilseed rape crops could have important consequences for rapeseed production in the UK and also serve as a source of virus for vegetable brassicae.

Plant pathology in agriculture

PART 1 PRINCIPLES 1. What is disease? 2. What causes disease? 3. How does disease build up? 4. What effect does disease have on the crop? 5. How do we control disease? PART II PRACTICE 6. Diseases of cereals 7. Diseases of oilseed rape 8. Diseases of field peas and beans 9. Diseases of potatoes 10. Diseases of sugar beet 11. Diseases of soya beans 12. Diseases of maize 13. Diseases of field vegetables.

Studies of fungicide resistance in Pyrenopeziza brassicae, cause of light leaf spot disease of oilseed rape and other brassicas

Resistance in the light leaf spot fungus, Pyrenopeziza brassicae, to benzimidazole or dicarboximide fungicides was not detected in field isolates. Resistant mutants were, however, obtained in vitro. Benzimidazole-resistant strains were generated by mutagenesis with ultraviolet light, and dicarboximide-resistant sectors developed when the fungus was grown on media containing iprodione or vinclozolin, without prior exposure to a mutagen. The mutant isolates remained resistant after several months of subculture in the absence of fungicides. The rate of growth in culture of isolates resistant to benzimidazoles was between 10 and 20% less than that of sensitive isolates, whereas isolates resistant to the dicarboximides grew and sporulated just as well as sensitive isolates. Genetic studies showed that the resistance to benzimidazoles was probably conferred by a single gene mutation, and that the same may also have been true of resistance to dicarboximides.