Oral presentations
M ´ethodes de lutte et gestion des r ´esistances: nouveaux d ´efis dans la gestion des risques Me. 14:00 Durable strategies to deploy plant resistance in agricultural landscapes
F. Fabrea, E. Rousseaua, L. Mailleretbet B. Mourya
aINRA, UR 407 Pathologie V´eg´etale, 84000 Montfavet, France;bINRA, UR 880 URIH, 06903 Sophia Antipolis, France
frederic.fabre@avignon.inra.fr
The deployment of resistant crops often leads to the emergence of resistance-breaking pathogens that suppress the yield benefit provided by the resistance. Here, we theoretically explored how farmer main leverages (resistant cultivar choice, resistance deployment strategy, landscape planning, cultural practices) can be best combined to achieve resistance durability while minimising yield losses due to plant viruses. Assuming a gene-for-gene type of interaction, virus epidemics are modelled in a landscape composed of a mosaic of resistant and susceptible fields, subjected to seasonality, and of a reservoir hosting viruses year round. The model links the genetic and the epidemiological processes shaping at nested scales the demo-genetics dynamics of viruses. The choice of the resistance gene (characterized by the equilibrium frequency of the resistance-breaking virus at mutation-selection balance in a susceptible plant) is the most influential leverage of action. Our results showed that optimal strategies of resistance deployment range from mixture (where susceptible and resistant cultivars coexist) to pure strategies (with only resistant cultivar) depending on the resistance characteristics and on the epidemiological context (epidemic incidence, landscape connectivity). We demonstrate and discuss gaps concerning virus epidemiology across the agro-ecological interface that must be filled to achieve sustainable disease management.
M ´ethodes de lutte et gestion des r ´esistances: nouveaux d ´efis dans la gestion des risques Me. 14:20 BioMolChem’, un outil pour ´evaluer l’ ´etat de d ´efense apr `es ´elicitation ou non, de cultivar ou de g ´enotypes r ´esistants aux maladies: du g `ene au champ
M.-F. Corio-Costeta, C. Lambertb, S. Cluzetc, D. Merdinogludet M.-C. Dufoure
aINRA, UMR SAVE, BP 81, BP 81, 33883 Villenave D’Ornon Cedex, France; bUniversit´e de bordeaux, Gesvab, 33882 Villenave D’Ornon Cedex, France;cUniversit´e de bordeaux, Gesvab, ISVV, 33882 Villenave D’Ornon Cedex, France;dINRA, Colmar, BP 20507,, 68021 Colmar, France;eINRA, UMR SAVE, 33883 Villenave D’Ornon Cedex, France
coriocos@bordeaux.inra.fr
Les stimulateurs de d´efenses des plantes, ou les vari´et´es r´esistantes aux maladies s’av`erent des m´ethodes alternatives d’int´erˆet pour limiter les intrants chimiques, dans le cadre du plan Ecophyto 2018. Afin d’´evaluer le potentiel d’´elicitation des d´efenses de la vigne au laboratoire et au champ, nous avons d´evelopp´e une triple approche appel´ee ”BioMolChem”: - des tests biologiques qui permettent d’´evaluer l’efficacit´e des d´efenses de la vigne vis `a vis des deux principaux bioagresseurs que sont l’o¨ıdium (Erysipne necator) et le mildiou (P. viticola), - des suivis mol´eculaires par q-RT-PCR qui permettent de connaˆıtre les niveaux d’expression (sur-expression ou r´epression) d’une vingtaine de g`enes impliqu´es dans les d´efenses de la vigne et de formaliser des patrons d’expressions, corr´el´es ou non avec le niveau de protection, selon les produits ´eliciteurs ou les g´enotypes ´etudi´es, - des analyses biochimiques par HPLC de ph´enylpropano¨ıdes (polyph´enols, stilb`enes), qui conduisent `a quantifier et `a identifier des mol´ecules d’int´erˆets, corr´el´es ou non `a l’expression de g`enes codant pour des enzymes impliqu´es dans leur biosynth`ese. Cet outil a ´et´e test´e sur des feuilles de vigne (cv. Cabernet-sauvignon) apr`es ´elicitation par diff´erents ´eliciteurs (benzothiadiazole, phosphonates), sur des g´enotypes r´esistants `a l’o¨ıdium et au mildiou, issus d’un croisement entre M. rotundifolia et Vitis vinifera poss´edant diff´erents QTLs de r´esistance `a l’o¨ıdium et au mildiou (Run 1, Rpv1, Rpv2, Run2) et au vignoble sur le c´epage Merlot trait´e avec diff´erents ´eliciteurs. Les r´esultats obtenus nous ont permis de valider l’outil ”BioMolChem” et montrent qu’il existe des corr´elations entre le niveau d’expression de g`enes de type Pathogenesis related (PR) prot´eines, les niveaux d’expression de g`enes codant pour des enzymes impliqu´es dans la voie de biosynth`ese du tryptophane, certains impliqu´es dans la biosynth`ese des stilb`enes et flavonoides et l’efficacit´e de protection. De mani`ere similaire, il existe des corr´elations entre la pr´esence de certaines mol´ecules connues et inconnues, et l’efficacit´e de protection. `A noter que lors de ces exp´eriences, si le resv´eratrol, une phytoalexine bien connue da la vigne, s’av`ere un bon marqueur de stimulation des d´efenses, elle n’est pas un bon marqueur de protection. Ainsi aujourd’hui dispose t’on d’un outil qui nous permet de mieux comprendre quel est l’´etat de d´efense et de protection de la vigne, tant au niveau du laboratoire, qu’au niveau du champ. M. C. Dufour, C. Lambert, J. Bouscaut, J. M. M´erillon and M. F. Corio-Costet (2012) Benzothiadiazole-primed defense responses and enhanced differential expression of defense genes in Vitis vinifera infected with biotrophic pathogens (Erysiphe necator and Plasmopara viticola). Soumis `a Plant Pathol.
M ´ethodes de lutte et gestion des r ´esistances: nouveaux d ´efis dans la gestion des risques Me. 14:40 Association mapping for yellow rust resistance in UK winter wheat
P. Bansept-Baslera, R. Baylesa, L. Boydb, S. Griffithsbet D. O’Sullivana
aNIAB, Huntingdon Road, CB3 0LE Cambridge, UK;bJohn Innes Centre, Norwich Research Park, Colney Lane, NR4 7UH Norwich, UK
pauline.bansept@niab.com
Yellow rust (YR) caused by Puccinia striiformis f.sp tritici is a major wheat disease in the United Kingdom and can cause extensive yield loss. The most cost effective strategy to control the disease is to grow resistant varieties. Despite the constant evolution of yellow rust and the development of new races overcoming the latest plant resistances, UK breeding programs succeeded over the past 30 years to regularly bring new resistant varieties to market. However, little is known about the genetic basis and the diversity of resistance used by UK breeders. The study proposes to investigate the genetic architecture of yellow rust resistance present in the UK gene pool using linkage disequilibrium analysis. Based on resistance data available from the UK Cereal Pathogen Survey, we assembled a collection of 330 winter wheat elite varieties, mainly from the UK. To complement historical disease resistance data, we evaluated the collection at seedling and adult plant stages against current UK yellow rust isolates in 2010 and 2011, as we aim to uncover loci useful in breeding to control the current races. The lines were genotyped with DArT markers and molecular markers linked to YR resistance loci. The panel was genotyped at 1809 marker loci and the combined genotype and phenotype datasets used in association analysis. In total, 230 marker-trait associations were detected in the experiments using current YR races, explaining between 2 and 15.8% of the resistance response. In addition to 96 rye-wheat polymorphic markers associated with Yr9 on the 1B/1R translocation, 26 associations were significant using the Bonferroni correction for multiple comparisons. Among these 26, the most significant markers were detected on 2B, 3B and 7B. Using a classical QTL approach with two UK doubled haploid populations, we confirmed the link between the high associations on 2B (wPt-0950 and wPt-9350) and on 7B (wPt-0752 and wPt-4814) with Yr7 and Yr6 respectively. As illustrated with Yr6, Yr7 and Yr9, the chromosomal assignment of many associated markers coincide with those of known major genes or previously identified genomic regions. It confirmed the usefulness of association genetics to localize loci responsible in YR resistance and also the potential for linked DArT markers to be converted into diagnostic markers for marker assisted selection. Additionally, associations were detected in regions where no known gene have been located up to date, particularly on the A genome, chromosomes 1A, 5A, 6A and 7A, which could lead to the identification of new resistance genes. Finally, comparison between the seedling and adult plant tests highlighted potential valuable adult plant resistance on chromosomes 2D, 3B and 5B. A majority of the significant associations were to DArT markers not assigned to any map location, making SCAR conversion/mapping of associated DArTs a key next step.
M ´ethodes de lutte et gestion des r ´esistances: nouveaux d ´efis dans la gestion des risques Me. 15:00 Natural and acquired fenhexamid resistance in Botrytis spp.: What’s the difference?
A. Billarda, S. Azeddinea, J. Bacha, C. Lanena, P. Solignaca, P. Lerouxa, H. Lachaiseb, R. Beffac, S. Fillingeraet D. Debieua
aINRA UR BIOGER-CPP, avenue Lucien Br´etigni`eres Bat13, 78850 Thiverval-Grignon, France; bBayer SAS, CR La Dargoire, 14-20 rue Pierre Baizet, 69009 Lyon, France; cBayer CropScience AG, Industriepark H¨ochst building, 65926 Frankfort, Allemagne
daniele.debieu@versailles.inra.fr
Antifungal compounds such as ergosterol biosynthesis inhibitors are widely used to control crop diseases. Among them, one of the most recent, the hydroxyanilide fenhexamid, is efficient principally against Botrytis cinerea, the major causal agent of grey mould. Fenhexamid is a new type of ergosterol biosynthesis inhibitor affecting the sterol C4 demethylation processes due to its specific interaction with one of the four proteins of the enzymatic complex, the 3-ketoreductase. Our regular monitoring conducted on French vineyards allowed the identification of the first isolates of B. cinerea with acquired resistance. Two types of resistant isolates named HydR3- and HydR3+ were distinguished by their resistance level. This acquired resistance is due to point mutations in the erg27 gene leading to target modifications. These modifications induce a reduced in affinity of fenhexamid towards its target, the 3-ketoreductase. Because of their high resistant level, the HydR3+ strains have to be considered relative to the risk of resistance phenomenom occurrence in vineyards. Fitness studies conducted in vitro on isogenic mutants showed altered ”overwintering” capacities of HydR3+ mutants suggesting that they probably do not impact fenhexamid’s field efficacy. While B. cinerea’s acquired resistance could be explained only by target modifications, as in most cases of fungicide resistance, the situation is different for the related species Botrytis pseudocinerea naturally resistant to fenhexamid. We show that erg27 polymorphism only slightly contributes to resistance whereas fenhexamid detoxification by a cytochrome P450 named cyp68.4 is the major mechanism responsible for the resistance. This is the first case of a functional validation of fungicide detoxification involved in resistance.