The main objective of ResPom team is to improve apple and pear resistance against pests with a major input on the three major pests of apple, Venturia inaequalis (apple scab), Erwinia amylovora (fire blight) and Dysaphis plantaginea (rosy apple aphid), either genetically or by the application of Plant Resistance Inducers (PRIs). Promotion of apple immunity is thought out as a conceptual agroecological model (see figure below), integrating not only intrinsic (genetic) and induced (PRIs) resistances and the diversity of pests, but also sources of variability such as crop management constraints, climatic factors and additional biotic factors. The main issue is to achieve a level of immunity of the cropping systems as well as a growth/immunity trade-off that guarantees the highest level of production in quality and quantity.

Working on this conceptual model implies several levels of study:

1)    Deeply investigate the molecular mechanisms underlying sustainable resistance (either intrinsic or induced). This is performed at several levels, DNA, RNA, proteins, metabolites, in order to:

i) clarify the genetic position of resistance QTLs and the mechanisms they control using the apple genetic diversity and inferred pedigrees, constructed populations or wild Malus or Pyrus progenies,

ii) deepen our knowledge of “resistance effectors” (i.e. proteins and metabolites limiting bioagressors development) and their regulation mechanisms, through functional studies, notably gene editing, in order to more accurately evaluate and optimize control methods based on apple immunity,

iii) explore the genetic variability of primary and secondary metabolism and the potential trade-off between (a) intrinsic and/or induced defenses and (b) agronomic traits (tree growth and fruit quality).

ResPom collaborates with other teams of IRHS and SFR Quasav to assess the selection pressures exerted by the various types of resistance on the bioagressors, especially V. inaequalis (Ecofun), to evaluate the role of microbiote composition in induced resistance (Emersys), to deepen metabolomic studies (SMS, SONAS), to contribute to the study of the structural organization of resistance/defense genes and its implication in gene expression (BiDefi), to refine the understanding of the epigenetic control of resistance (Valema) and to promote marker-assisted breeding (VaDiPom).

2)    Assess the effects of environmental factors including climatic conditions and cultural practices on resistance. This knowledge is a key issue for the successful deployment of new cultivars combining high level of genetic resistance with high agronomic value, and for the successful use of PRIs in practice. Genetic (G), environment (E) and management (M) interactions are investigated step by step:

i) GxE: using data generated thanks to the apple REFPOP network, genome-wide prediction is further developed for predicting adaptation and agronomic value using genome-wide marker data and eco-physiological modeling in the frame of the EU INVITE project.

ii) GxM: interaction between intrinsic and induced resistances is explored either in core collections or in dedicated segregating progenies,

iii) ExM: relationship between tree ecophysiological status (conditioned by nutrition and climatic factors) and tree responsiveness to PRIs is investigated in order to improve recommendations for tree nutrition and PRIs application in orchard.

3)    Decipher the multiple interactions between levers used in combination GxExM in order to optimize apple immunity. Studies are performed in orchards in close collaboration with the experimental unit in horticulture (UE Horti, INRAE Angers) hosting three orchards specifically dedicated to this work (including a multi-genotype orchard) and with a network of orchards in experimental stations. Different orchard management programs with integrated knowledge from axes 1) and 2) are evaluated in order to get optimized apple immunity and crop production. ResPom is also engaged in an in-depth reflection on disruptive apple cropping systems, including companion plants (attraction and feeding of natural enemies and repulsion of aphids to improve the control of rosy apple aphid) in collaboration with IGEPP (EGI team, Angers site), UE Horti, and PSH research unit at INRAE Avignon within the frame of the French Priority Research Program (PPR) CapZeroPhyto project. This should lead to the planting of a new system-orchard in the near future.