Phoma stem canker disease on oilseed rape (Brassica napus) in China is caused by Leptosphaeria biglobosa ‘brassicae’

This document is the Accepted Manuscript version of the following article: Ze Liu, Akinwunmi O. Latunde-Dada, Avice M. Hall, Bruce D. L. Fitt, ‘Phoma stem canker disease on oilseed rape (Brassica napus) in China is caused by Leptosphaeria biglobosa ‘brassicae’’, European Journal of Plant Pathology, Vol. 140(4): 841-857, December 2014. The final publication is available at Springer via: http://dx.doi.org/10.1007/s10658-014-0513-7 © Koninklijke Nederlandse Planteziektenkundige Vereniging 2014Phoma stem canker of oilseed rape (Brassica napus) is a globally important disease that is caused by the sibling ascomycete species Leptosphaeria maculans and L. biglobosa. Sixty fungal isolates obtained from oilseed rape stems with phoma stem canker disease symptoms collected from four provinces in China in 1999, 2005 and 2006 were all identified as Leptosphaeria biglobosa, not L. maculans, by PCR diagnostics based on species-specific primers. There were no differences in cultural characteristics (e.g. pigmentation and in vitro growth) between these L. biglobosa isolates from China and those of 37 proven L. biglobosa isolates from Europe or Canada. In studies using amplified fragment length polymorphism (AFLP) markers, Chinese L. biglobosa populations were genetically more similar to European L. biglobosa populations than to the more diverse Canadian L. biglobosa populations. Sequencing of gene fragments of β-tubulin, actin and the internal transcribed spacer (ITS) region of rDNA from L. biglobosa isolates from China, Europe, Australia and Canada showed a closer taxonomic similarity of Chinese L. biglobosa to the European L. biglobosa ‘brassicae’ than to Canadian L. biglobosa ‘canadensis’ or to the Australian L. biglobosa ‘occiaustralensis’ or ‘australensis’ subclades. These results suggest that the Chinese L. biglobosa population in this study is in the same subclade as European L. biglobosa ‘brassicae’ populationsPeer reviewe

Etude génétique de deux interactions race-cultivar chez le pathosystème Leptosphaeria maculans (Brassica napus)

* INRA, centre de Versailles, unité de pathologie végétale 78026 Versailles Diffusion du document : INRA, centre de Versailles, unité de pathologie végétale 78026 Versailles Diplôme : Dr. d'Universiténon disponibleLeptosphaeria maculans est un ascomycete filamenteux responsable de la necrose du collet des cruciferes, maladie dommageable sur colza (brassica napus l. ). Depuis peu, des interactions specifiques sont decrites sur les cultivars de colza westar, quinta et glacier, discriminant les souches de l. Maculans en 3 pathogenicity groups (pg). Cette etude s'est proposee, en un premier temps, de caracteriser le determinisme genetique de deux interactions tant du cote de l'agent pathogene que de la plante. Par une analyse de tetrades, deux genes d'avirulence, avrlm1 et avrlm2, responsables des interactions incompatibles pg3-quinta et pg2-glacier sont mis en evidence. En parallele, l'analyse des descendances issues des croisements entre quinta, glacier et un cultivar sensible indique la presence de loci majeurs dominants de resistance, rlm1 et rlm2, correspondants a avrlm1 et avrlm2. Ces resultats demontrent pour la premiere fois chez le pathosysteme l. Maculans/b. Napus l'existence de relations gene-pour-gene. Dans un second temps, l'efficacite des resistances de quinta et glacier a ete eprouvee en conditions naturelles durant deux annees consecutives. Le bon niveau de resistance de quinta est correle a la predominance des souches pg3 dans la population locale du parasite. A l'oppose, la sensibilite de glacier est expliquee par l'absence de souches pg2. Enfin, en vue du clonage ulterieur du gene d'avirulence avrlm1 par marche chromosomique, une carte genetique de l. Maculans a ete initiee. La segregation d'avrlm1, mat, spp et 89 marqueurs rapd a ete examinee chez 88 descendants en vrac. Un groupe de liaison majeur associe avrlm1 avec 4 autres marqueurs, ad1-1,52 et j19-1,20 encadrant le locus a 4,8 cm et 1,5 cm. En complement, pour faire coincider a terme les cartes genetique et physique, les caryotypes des souches parentales ont ete etablis par pfge. L'hybridation de ad1-1,52 sur les electrocaryotypes suggere qu'avrlm1 est porte par le chromosome v du parent pg

Genetic characterization of AvrLm1, the first avirulence gene of Leptosphaeria maculans

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Colonization of winter oilseed rape tissues by A/Tox(+) and B/Tox(0) Leptosphaeria maculans (phoma stem canker) in France and England

The colonization of winter oilseed rape plants and epidemiology of phoma stem canker differed between A/Tox(+) and B /Tox(0) Leptosphaeria maculans. In France and England, where plant colonization was investigated during two and three growing seasons, respectively, there was a difference in timing of leaf infection; A/Tox(+) L. maculans was predominant on leaves in the autumn (October/ November) but there was an increase in the incidence of B/Tox(0) in the winter (January/ February). In May, June and July both species could be isolated from all external parts of the plant (root to the upper stem) and all crown (stem base) tissues, although they differed in their distribution. At the root and crown, A/Tox(+) L. maculans was predominant and was located throughout the cortex, wood and pith tissues, but the rarer B/Tox(0) was located mainly in the cortex. Approximately equal numbers of A/Tox(+) and B/Tox(0) isolates were obtained from the upper stem - there was a greater proportion of B/Tox(0) isolates than at the crown. In England, after harvest in 1999 and 2000, pseudothecia on the lignified tap root and crown tissues produced predominantly A/Tox(+) ascospores (94%), while pseudothecia higher up the stem produced more B/Tox(0) ascospores (60%) than A/Tox(+) ascospores (40%). The timing of the onset of leaf spotting, earlier in the season for A/Tox(+) than B/Tox(0) L. maculans, and the predominance of mycelium of A/Tox(+) at the crown are consistent with the assumption that A/Tox(+) is more likely to cause the most damaging stem cankers than B/Tox(0) L. maculans. Identification as A/Tox(+) or B/Tox(0) by cultural characteristics differed only slightly (2.3%) from identification by molecular techniques.Peer reviewe

Perspectives d'amelioration de la résistance du colza au phoma.

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