Virulence in Puccinia triticina for durum wheat cultivar creso and other durum wheat cultivars carrying resistance gene Lr14a in France

diseases notesInternational audienceDurum wheat cv. Creso has been mentioned as having durable resistance to leaf rust (2–4). However, an average final disease level of 70S on the modified Cobb scale was scored on Creso across three locations in inoculated field trials in France during 2009. A mixture of two durum wheat leaf rust isolates commonly found in France was used for the inoculation, one was virulent on Lr23 and the other was avirulent on this gene, their identical avirulence/virulence formula for other genes was Lr1, 2a, 2b, 3, 3bg, 3ka, 9, 11, 13, 15, 16, 17, 19, 24, 25, 26, 27+31/Lr2c, 10, 14a, 14b, 20, 21, 33, and 44. On cv. Llareta Inia and breeding line Somateria, both of which carry the resistance gene Lr14a, the average final disease level was, respectively, 95S and 80S. Creso, Llareta Inia, and Somateria displayed average final disease levels of, respectively, 0, 10S, and 1 in field trials inoculated with race CBG/BP in 2009 at two locations in Mexico (Ciudad Obregon and El Batan). Race CBG/BP, virulent on Lr3, 10, 11, 14b, 20, 23, 27 + 31, and 33, is the most widely virulent race identified so far in Mexico where Lr14a remains effective for durum wheat. Virulence for Lr14a in durum wheat leaf rust populations was already mentioned to be present in France since 2000 (1). It has been suggested that the resistance of Creso, which has remained durable in Italy since 1975 (4), could be due to a gene close to but different from Lr14a. Alternatively, the fact that Creso's reaction was significantly lower than those of Llareta Inia or Somateria could indicate the presence of another gene, of minor effect, in addition to Lr14a. Whatever the genetic basis of the Creso resistance may be, it has been overcome by common French pathotypes and its usefulness in breeding, at a regional if not global level, has become questionable

Low diversity and fast evolution in the population of Puccinia triticina causing durum wheat leaf rust in France from 1999 to 2009, as revealed by an adapted differential set

No internationally agreed differential set is available for characterization of virulences in populations of Puccinia triticinacausing wheat leaf rust on durum wheat. In a first step, 73 potentially differential host genotypes were tested with 96 durumleaf rust isolates collected in France. A differential set, adapted to the local epidemiological context and useful for comparisonwith international studies was selected, including French commercial cultivars, Thatcher lines with Lr genes, and internationalcultivars. In the second step, a sample of 310 isolates collected in France from 1999 to 2009 was characterized onthis set. Diversity was very low, as only five pathotypes were distinguished. Genotyping of a subset of 76 isolates accordingto 20 SSR markers confirmed this low diversity, with 73 isolates belonging to a single dominant genotype. Population wasstrongly shaped by cultivars, and the findings explain the successive breakdown of resistance sources deployed in Frenchdurum wheat cultivars. The gene Lr14a, suggested to be an efficient source of resistance in several European and Americancountries, was overcome by pathotypes frequent in France since 2000. Postulation of resistance genes in the commercial cultivarsled to a proposed simplified version of the differential set. This study, providing new information about leaf rust resistancegenes present in the French durum wheat germplasm, highlights the need to diversify sources of resistance toP. triticina in this germplasm. The results are also discussed in terms of relatedness and intercontinental migration of P. triticinaon durum wheat

Récurrence interannuelle d'un champignon parasite obligatoire d'une culture annuelle

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Testing differences between pathogen compositions with small samples and sparse data

BGPI : équipe 5The structure of pathogen populations is an important driver of epidemics affecting crops and natural plant communities. Comparing the composition of two pathogen populations consisting of assemblages of genotypes or phenotypes is a crucial, recurrent question encountered in many studies in plant disease epidemiology. Determining if there is a significant difference between two sets of proportions is also a generic question for numerous biological fields. When samples are small and data are sparse, it is not straightforward to provide an accurate answer to this simple question because routine statistical tests may not be exactly calibrated. To tackle this issue, we built a computationally-intensive testing procedure, namely the Generalized Monte Carlo Plug-In test with Calibration (GMCPIC test), which is implemented in an R package available at http://dx.doi.org/10.5281/zenodo.53996. A simulation study was carried out to assess the performance of the proposed methodology and to make a comparison with standard statistical tests. This study allows us to give advice on how to apply the proposed method, depending on the sample sizes. The proposed methodology was then applied to real datasets and the results of the analyses were discussed from an epidemiological perspective. The applications to real data sets deal with three topics in plant pathology: the reproduction of Magnaporthe oryzae, the spatial structure of Pseudomonas syringae, and the temporal recurrence of Puccinia triticina

Caractérisation de sources de résistance à la rouille brune chez le blé dur

National audienceUne pépinière comprenant 184 variétés et lignées issues des ressources génétiques françaises, Européennes, Nord-Africaines, et CIMMYT/ICARDA a été phénotypée pour sa résistance dans des essais au champ avec inoculation contrôlée (un seul pathotype par essai) de rouille brune, dans 4 lieux en France et deux lieux au Mexique, en 2009 et 2010. De plus, ces 184 lignées et variétés ont été phénotypées pour leur résistance en serre à 9 pathotypes de rouille brune. Les gènes Lr27+31 et Lr3 sont efficaces en France, mais vu qu'ils sont déjà contournés au Mexique, il est peu probable qu'ils constituent une source de résistance durable en France. Les gènes Lr61, LrCamayo, Lr19 et Lr47 sont efficaces en France et au Mexique, et peuvent constituer des sources de résistance intéressantes. Certaines lignées ont montré un niveau très élevé de résistance dans tous les lieux, probablement du à un gène majeur de résistance non identifié. Quatre variétés françaises, ainsi que plusieurs lignées "slow rusting" du CIMMYT ont montré un niveau intéressant de résistance partielle dans tous les environnement testés. Une analyse de génétique d'association, conduite à l'aide de 1300 marqueurs DArT et 34 variables de phénotypage, a mis en évidence deux QTLs et un locus correspondant à un gène majeur : i) un QTL sur le chromosome 2B, associé à wPt-1064, wPt-6477 and wPt-0408 ii) un QTL sur le chromosome 6B, associé à wPt-8059 et wPt-7065 iii) un gène majeur sur le chromosome 7B, associé à wPt-0465, wPt- 3700 et wPt-9515, qui correspond au gène Lr14a. Ce gène est surmonté en France, mais il reste efficace au Mexique