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Blackleg Disease (blackleg + disease)
Selected AbstractsDual control of avirulence in Leptosphaeria maculans towards a Brassica napus cultivar with ,sylvestris -derived' resistance suggests involvement of two resistance genesPLANT PATHOLOGY, Issue 2 2009A. P. Van de Wouw Blackleg disease (phoma stem canker) of Brassica napus (canola, oilseed rape) is caused by the fungus Leptosphaeria maculans. In some regions of Australia, resistance in oilseed rape cultivars derived from B. rapa subs. sylvestris (e.g. cv. Surpass 400) became ineffective within three years of commercial release. The genetic control of avirulence in L. maculans towards cv. Surpass 400 is described. When Australian field isolates were screened on this cultivar, three phenotypic classes were observed; virulent, intermediate and avirulent. Analysis of crosses between fungal isolates varying in their ability to infect cv. Surpass 400 demonstrated the presence of two unlinked avirulence genes, AvrLm1 and AvrLmS. Complementation of isolates (genotype avrLm1) with a functional copy of AvrLm1, and genotyping of field isolates using a molecular marker for AvrLm1 showed that virulence towards Rlm1 is necessary, but not sufficient, for expression of a virulent phenotype on cv. Surpass 400. Taken together, these data strongly suggest that cv. Surpass 400, with ,sylvestris -derived' resistance, contains at least two resistance genes, one of which is Rlm1. [source] Soft rot erwiniae: from genes to genomesMOLECULAR PLANT PATHOLOGY, Issue 1 2003Ian K. Toth SUMMARY The soft rot erwiniae, Erwinia carotovora ssp. atroseptica (Eca), E. carotovora ssp. carotovora (Ecc) and E. chrysanthemi (Ech) are major bacterial pathogens of potato and other crops world-wide. We currently understand much about how these bacteria attack plants and protect themselves against plant defences. However, the processes underlying the establishment of infection, differences in host range and their ability to survive when not causing disease, largely remain a mystery. This review will focus on our current knowledge of pathogenesis in these organisms and discuss how modern genomic approaches, including complete genome sequencing of Eca and Ech, may open the door to a new understanding of the potential subtlety and complexity of soft rot erwiniae and their interactions with plants. Taxonomy: ,The soft rot erwiniae are members of the Enterobacteriaceae, along with other plant pathogens such as Erwinia amylovora and human pathogens such as Escherichia coli, Salmonella spp. and Yersinia spp. Although the genus name Erwinia is most often used to describe the group, an alternative genus name Pectobacterium was recently proposed for the soft rot species. Host range:,Ech mainly affects crops and other plants in tropical and subtropical regions and has a wide host range that includes potato and the important model host African violet ( Saintpaulia ionantha ). Ecc affects crops and other plants in subtropical and temperate regions and has probably the widest host range, which also includes potato. Eca , on the other hand, has a host range limited almost exclusively to potato in temperate regions only. Disease symptoms: ,Soft rot erwiniae cause general tissue maceration, termed soft rot disease, through the production of plant cell wall degrading enzymes. Environmental factors such as temperature, low oxygen concentration and free water play an essential role in disease development. On potato, and possibly other plants, disease symptoms may differ, e.g. blackleg disease is associated more with Eca and Ech than with Ecc. Useful websites: ,http://www.scri.sari.ac.uk/TiPP/Erwinia.htm, http://www.ahabs.wisc.edu:16080/pernalab/erwinia/index.htm, http://www.tigr.org/tdb/mdb/mdbinprogress.html, http://www.sanger.ac.uk/Projects/E_carotovora/. [source] Relationship between potato seed tuber contamination by Erwinia carotovora ssp. atroseptica, blackleg disease development and progeny tuber contaminationPLANT PATHOLOGY, Issue 2 2003I. K. Toth The relationship between contamination of potato seed tubers with Erwinia carotovora ssp. atroseptica (Eca), blackleg disease development, and the incidence and level of progeny tuber contamination in field grown crops was studied in 1998, 1999 and 2000. Seed tubers were inoculated by vacuum infiltration at three levels (low, intermediate and high) with a streptomycin-resistant marker strain of Eca (SCRI1039Str) and planted in the field. Blackleg disease development was directly related to the level of seed tuber contamination. The higher the level of seed tuber contamination, the earlier in the season blackleg disease appeared and the greater the final level of disease, which continued to rise as the season progressed. High and low levels of seed tuber contamination were related to high and low incidences of progeny tuber contamination, respectively, at all sampling times. However, an intermediate degree of seed tuber contamination tended to be associated with a low level of blackleg disease, a variable incidence of progeny tuber contamination early in the season but a high incidence later in the season. The level of progeny tuber contamination, derived from seed tubers inoculated at the three different levels of Eca, was categorized into four contamination classes (< 102, 102,103, 103,104 and > 104 marker strain colony-forming units/mL peel extract). At the lowest level of seed tuber contamination, progeny tuber contamination tended to be in the two lower categories. However, as seed tuber contamination increased, the proportion of contaminated progeny tubers in the two higher categories also increased. Overall, the results suggest that progeny tuber contamination is related to seed tuber contamination and blackleg disease, and that the threshold level of seed tuber contamination remains an important factor in predicting both blackleg disease and tuber health. [source] Expression of resistance to Leptosphaeria maculans in Brassica napus double haploid lines in France and Australia is influenced by locationANNALS OF APPLIED BIOLOGY, Issue 2 2008R. Delourme Abstract Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus), worldwide, including Australia and France. The aims of these studies were first, to determine if higher levels of resistance to L. maculans could be generated in double haploid (DH) lines derived from spring-type B. napus cv. Grouse, which has a good level of field resistance to blackleg; and second, to determine whether the resistance to blackleg disease of individual DH lines responds differentially to different L. maculans field populations within and between the two countries. DH lines were extracted from cv. Grouse and tested in field experiments carried out in both France and Australia against natural L. maculans populations. Extracting and screening DH lines were an effective means to select individual lines with greatly improved expression of resistance to blackleg crown canker disease in comparison with the original parental population. However, relative disease resistance rankings for DH lines were not always consistent between sites. The higher level of resistance in France was shown to be because of a high expression level of quantitative resistance in the French growing conditions. Big differences were observed for some DH lines between the 2004 and the 2005 field sites in Australia where the L. maculans populations differed by their virulence on single dominant gene-based resistant lines derived from Brassica rapa ssp. sylvestris. This differential behaviour could not be clearly explained by the specific resistance genes until now identified in these DH lines. This investigation highlights the potential to derive DH lines with superior levels of resistance to L. maculans compared with parental populations. However, in locations with particularly high pathogen diversity, such as in southern Australia, multiyear and multisite evaluations should be performed to screen for the most efficient material in different situations. [source] | ||||||||||