Several wall-associated kinases participate positively and negatively in basal defense against rice blast fungus.

BACKGROUND: Receptor-like kinases are well-known to play key roles in disease resistance. Among them, the Wall-associated kinases (WAKs) have been shown to be positive regulators of fungal disease resistance in several plant species. WAK genes are often transcriptionally regulated during infection but the pathways involved in this regulation are not known. In rice, the OsWAK gene family is significantly amplified compared to Arabidopsis. The possibility that several WAKs participate in different ways to basal defense has not been addressed. Moreover, the direct requirement of rice OSWAK genes in regulating defense has not been explored. RESULTS: Here we show using rice (Oryza sativa) loss-of-function mutants of four selected OsWAK genes, that individual OsWAKs are required for quantitative resistance to the rice blast fungus, Magnaporthe oryzae. While OsWAK14, OsWAK91 and OsWAK92 positively regulate quantitative resistance, OsWAK112d is a negative regulator of blast resistance. In addition, we show that the very early transcriptional regulation of the rice OsWAK genes is triggered by chitin and is partially under the control of the chitin receptor CEBiP. Finally, we show that OsWAK91 is required for H2O2 production and sufficient to enhance defense gene expression during infection. CONCLUSIONS: We conclude that the rice OsWAK genes studied are part of basal defense response, potentially mediated by chitin from fungal cell walls. This work also shows that some OsWAKs, like OsWAK112d, may act as negative regulators of disease resistance

Genetic variation and population structure of the grape powdery mildew fungus, Erysiphe necator, in southern France

International audienceErysiphe necator, the causative agent of powdery mildew in grapevine, was introduced into Europe from North America during the middle of the 19th century. Our objective was to analyze the genetic variation and the population structure of the fungus in southern France. The sample comprised 101 isolates and was mainly of flag shoot origin, i.e., infection of sprouting shoots after overwintering of mycelium in buds. RAPD analysis identified different haplotypes that clustered in two genetic groups (A and B). The most frequent haplotypes of each group were found in several different locations in two areas separated by 100 km and throughout the 3 year period. Several haplotypes of both groups originated from flag shoots and were recovered over successive years indicating that there is no correlation between genetic group and overwintering mode. All isolates of group A were of mating type +, but those in group B could be either + or -. Lower genotypic diversity was detected within group A than within group B. These results were consistent with the hypothesis that group A reproduces only asexually

New rapid PCR protocols to distinguish genetic groups in Erysiphe necator

International audienceIn order to differentiate the two genetic groups (A and B) detected in populations of the powdery mildew fungus, *Uncinula necator*, we developed PCR primers to amplify two sequence characterized amplified regions (SCAR) and one sequence with a microsatellite motif (SSR). Primer pairs designed from SCARs gave a fragment for group A isolates and no fragment for group B isolates. The primer pair mO3E11 designed for the SSR sequence amplified two different sequences. The first sequence had the SSR motif and presented two alleles: one allele was present in all 49 isolates of group A tested and in two out of 34 isolates of group B, and a second allele was present in the remaining 32 isolates of group B. The other sequence did not have the SSR motif and was amplified only in the 34 group B isolates. The mO3E11 pair appears suitable for large-scale studies since it identified groups in only one PCR reaction and gave strong signals with DNA templates that can be rapidly obtained from a minute quantity of fungal material

Assessment of powdery mildew resistance of grape and Erysiphe necator pathogenicity using a laboratory assay

UMR BGPI - Equipe 4International audienceTo develop a quantitative evaluation of grapevine resistance to powdery mildew and of pathogenicity of the causal agent (*Erysiphe necator*), a spot inoculation method was developed using detached leaves of potted plants. The percentage of inoculating spots leading to a colony and the mean diameter of colonies were determined to assess the host-pathogen relationships. Significant differences were found between host cultivars and their ranking was associated with that observed in the vineyard. There was a significant interaction between cultivar and replicate during the whole experiment indicating that the physiological state of detached leaves is important. Aging of tissues was accompanied by a gain in resistance that was considerably more marked in resistant cultivars. Only partly expanded leaves of resistant cultivars that stopped expansion on the agar medium supported the development of the fungus. Significant differences between *E. necator* isolates were also demonstrated, but these variations were less marked than those due to host cultivar and leaf position. Preliminary results obtained with different isolates from the two European genetic groups (A and B) indicate that, on average, group A is less pathogeni

Tomate sous abri. Lutte biologique contre deux maladies aériennes. <em>Botrytis cinerea</em> et <em>Oïdium neolycopersici</em>

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Lutte biologique contre l'oïdium et la pourriture grise sous serre de tomate

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Tomate sous abri. Lutte biologique contre deux maladies aériennes. <em>Botrytis cinerea</em> et <em>Oïdium neolycopersici</em>

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Potential for including <em>Microdochium dimerum</em>, a biocontrol agent against <em>Botrytis cinerea</em>, into an integrated protection scheme of greenhouse tomatoes

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Tomate sous abri. Lutte biologique contre <em>Botrytis cinerea</em> et<em> Oïdium neolycopersici</em>

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