Phoma stem canker 

Biology

Phoma stem canker (blackleg), caused by Leptosphaeria maculans, is an important disease on oilseed rape (canola, rapeseed, Brassica napus, Brassica juncea, Brassica rapa) causing seedling death, lodging or early senescence in Australia, Canada and Europe.

Severity of phoma stem canker epidemics is affected by the pathogen population structure, oilseed rape species and cultivar resistance, climate and agricultural practices.

Infections are initiated by airborne ascospores, which are released from fruiting structures (pseudothecia) on crop debris after a period of maturation. Ascospores require high humidity or surface wetness on leaves or cotyledons for infection to occur. In susceptible plants, leaf infections appear as pale leaf spots (phoma leaf spots) from which the fungus spreads via the petiole to reach the stem. Leaf spots also produce asexual fruiting structures (pycnidia) which release spores (conidia), which can cause secondary infections in some situations.

Stem infections incubate (over winter in English conditions), eventually appearing as stem cankers at the stem base (crown) and as upper stem lesions. Infections on cotyledons and leaves early in the season produce the most damaging stem cankers at the stem base. Development of both crown cankers and phoma stem lesions higher up stems is most rapid in regions with high temperatures from flowering to harvest, such as Australia and Canada. Breeding for resistance (genetic, disease escape or tolerance), stubble management, crop rotation and fungicide seed treatments are important strategies for control of phoma stem canker in all areas. Fungicide spray treatments are justified only in regions such as western Europe where high yields are obtained, and accurate forecasts of epidemic severity are needed to optimise their use. Infection of pods can lead to seed-borne disease, which may spread the disease to completely new parts of the world.

A closely related species, Leptosphaeria biglobosa (formerly known as the B-group or Tox0 form of Leptosphaeria maculans) is similar to L. maculans (senso stricto), which was formerly called the A-group of Tox+. L. biglobosa is also a pathogen of oilseed rape although symptoms in England are normally not damaging to yield.

For more information on the L. maculans/L. biglobosa species complex and the genetics of L. maculans, visit the webpages of our collaborators, Thierry Rouxel's Laboratory at INRA, Versailles, France.

Dr Jon West

Bibliography

General Reviews

Gugel RK, Petrie GA, 1992. History, occurrence, impact, and control of blackleg of rapeseed. Canadian Journal of Plant Pathology 14, 36-45.

Hall R, 1992. Epidemiology of blackleg of oilseed rape. Canadian Journal of Plant Pathology 14, 46-55.

Howlett, BJ 2004. Current knowledge of the interaction between Brassica napus and Leptosphaeria maculans. Canadian Journal of Plant Pathology-Revue Canadienne De Phytopathologie 26, 245-252.

Paul VH, Rawlinson CJ, 1992. Diseases and Pests of Rape. Gelsenkirchen-Buer, Germany: Verlag Th. Mann.

Williams PH, 1992. Biology of Leptosphaeria maculans. Canadian Journal of Plant Pathology 14, 30-35.

West JS, Biddulph JE, Fitt BDL, Gladders P. 1999 Epidemiology of Leptosphaeria maculans in relation to forecasting stem canker severity on winter oilseed rape in the UK. Annals of Applied Biology 135: 535-546.

West JS, Kharbanda PD, Barbetti MJ, Fitt BDL. 2001 Epidemiology and management of Leptosphaeria maculans (phoma stem canker) on oilseed rape in Australia, Canada and Europe. Plant Pathology 50: 10-27.

Williams RH, Fitt BDL, 1999. Differentiating A and B groups of Leptosphaeria maculans, causal agent of stem canker (blackleg) of winter oilseed rape. Plant Pathology 48, 161-175.

Taxonomy, Identification and Genetics

Calderon, C, Ward, E, Freeman, J, Foster, SJ, McCartney, HA 2002. Detection of airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae in oilseed rape crops by polymerase chain reaction (PCR) assays. Plant Pathology 51, 303-310.

Delourme, R, Pilet-Nayel, ML, Archipiano, M, Horvais, R, Tanguy, X, Rouxel, T, Brun, H, Renard, A, Balesdent, AH 2004. A cluster of major specific resistance genes to Leptosphaeria maculans in Brassica napus. Phytopathology 94, 578-583.

Howlett, BJ, Idnurm, A, Pedras, MSC 2001. Leptosphaeria maculans, the causal agent of blackleg disease of Brassicas. Fungal Genetics and Biology 33, 1-14.

McCartney, HA, Foster, SJ, Fraaije, BA, Ward, E 2003. Molecular diagnostics for fungal plant pathogens. Pest Management Science 59, 129-142.

Mendes-Pereira, E, Balesdent, MH, Brun, H, Rouxel, T 2003. Molecular phylogeny of the Leptosphaeria maculans-L. biglobosa species complex. Mycological Research 107, 1287-1304.

Pinochet, X, Mestries, E, Penaud, A, Delourme, R, Chevre, AM, Renard, M, Brun, H, Bousset, L, Balesdent, MH, Rouxel, T, Aubertot, JN 2003. Towards a durable management of genetic resistances to Leptosphaeria maculans. Ocl-Oleagineux Corps Gras Lipides 10, 208-211.

Rouxel, T, Penaud, A, Pinochet, X, Brun, H, Gout, L, Delourme, R, Schmit, J, Balesdent, MH 2003. A 10-year survey of populations of Leptosphaeria maculans in France indicates a rapid adaptation towards the Rlm1 resistance gene of oilseed rape. European Journal of Plant Pathology 109, 871-881.

Rouxel, T, Willner, E, Coudard, L, Balesdent, MH 2003. Screening and identification of resistance to Leptosphaeria maculans (stem canker) in Brassica napus accessions. Euphytica 133, 219-231.

Epidemiology & Yield Effects

Aubertot, JN, Schott, JJ, Penaud, A, Brun, H, Dore, T 2004. Methods for sampling and assessment in relation to the spatial pattern of phoma stem canker (Leptosphaeria maculans) in oilseed rape. European Journal of Plant Pathology 110, 183-192.

Gudelj, I., Fitt, B.D.L. & van den Bosch, F. (2004). Evolution of sibling fungal pathogens in relation to host specialisation. Phytopathology 94, 789-795.

Huang YJ, Underwood CT, Fitt BDL, Todd AD, West JS, Koopmann B, Balesdent MH. 2001 Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape). Annals of Applied Biology 139: 193-207.

Huang, YJ, Fitt, BDL, Hall, AM 2003. Survival of A-group and B-group Leptosphaeria maculans (phoma stem canker) ascospores in air and mycelium on oilseed rape stem debris. Annals of Applied Biology 143, 359-369.

Huang, YJ, Toscano-Underwood, C, Fitt, BDL, Hu, XJ, Hall, AM 2003. Effects of temperature on ascospore germination and penetration of oilseed rape (Brassica napus) leaves by A- or B-group Leptosphaeria maculans (phoma stem canker). Plant Pathology 52, 245-255.

Jedryczka, M., Fitt, B.D.L., Kachlicki, P., Lewartowska, E., Balesdent, M.H., Rouxel, T. (1999). A comparison between Polish and UK isolates of Leptosphaeria maculans, cause of stem canker of winter oilseed rape. Zeitshrift fur Pflanzenkrankheiten und Pflanzenschutz 106, 608-617.

Schmit J, West J, Narcy JP, Roux J, Balesdent MH, Rouxel T, Gout L, 2002 La nécrose du collet du colza : analyse de la distribution du champignon dans la plante à l'aide d'outils moléculaires (Stem canker in oilseed rape: analysis of the distribution of the fungus in the plant using molecular tools. Ocl-Oleagineux Corps Gras Lipides 9: 79-85.

Sun, P., Fitt, B.D.L., Gladders, P. & Welham, S.J. (2000). Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England. Annals of Applied Biology 137, 113-125.

Sun P, Fitt BDL, Steed JM, Underwood CT, West JS. 2001 Factors affecting development of phoma canker (Leptosphaeria maculans) on stems of winter oilseed rape (Brassica napus) in southern England. Annals of Applied Biology 139: 227-242.

Toscano-Underwood C, West JS, Fitt BDL, Todd AD, Jedryczka M. 2001 Development of phoma lesions on oilseed rape leaves inoculated with ascospores of A-group or B-group Leptosphaeria maculans (stem canker) at different temperatures and wetness durations. Plant Pathology 50: 28-41.

Toscano-Underwood, C, Huang, YJ, Fitt, BDL, Hall, AM 2003. Effects of temperature on maturation of pseudothecia of Leptosphaeria maculans and L. biglobosa on oilseed rape stem debris. Plant Pathology 52, 726-736.

West JS, Fitt BDL, Leech PK, Biddulph JE, Huang Y-J, Balesdent M-H, 2002 Effects of timing of Leptosphaeria maculans ascospore release and fungicide regime on phoma leaf spot and phoma stem canker development on winter oilseed rape (Brassica napus) in southern England. Plant Pathology 51: 454-463.

West JS, Balesdent M-H, Rouxel T, Narcy JP, Huang Y-J, Roux J, Steed JM, Fitt BDL, Schmit J, 2002 Colonisation of winter oilseed rape tissues by A/Tox+ and B/Tox0 Leptosphaeria maculans (phoma stem canker) in France and England. Plant Pathology 51: 311-321.

Zhou Y, Fitt BDL, Welham SJ, Gladders P, Sansford CE, West JS. 1999 Effects of severity and timing of stem canker (Leptosphaeria maculans) symptoms on yield of winter oilseed rape (Brassica napus) in the UK. European Journal of Plant Pathology 105: 715-728.

Zhou, Y., Fitt, B.D.L., Welham, S.J., Evans, N. & Gladders, P. (2000). Effects of stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus) in southern England. Plant Pathology 49, 487-497.