Abstract

I will present a synthesis of the work that we carried out on apple tree in the AFEF team as part of my post-doc in 2017-2018 (Agropolis/AgreenSkills). We combined the deployment of high-throughput phenotyping methods in an apple tree (Malus domestica) core collection, and genome wide association studies, to study the genetic variability of vegetative architecture and functioning of a perennial species. Here follows a summary of our main hypotheses and findings.

• Tree architecture shows large genotypic variability, but how this affects water-deficit responses is poorly understood, thus limiting the possibility of reaching ideotypes with adequate combinations of architectural and functional traits in the face of climate change.
• We used terrestrial light detection, T-LiDAR scanning and airborne multispectral and thermal imagery to screen tree architecture, canopy shape, light interception, vegetation indices and transpiration on 241 apple cultivars, half of the trees being submitted to progressive field soil drying. GWAS was performed with single nucleotide polymorphism (SNP)-by-SNP and multi-SNP methods.
• Large phenotypic and genetic variability was observed for all traits, especially canopy surface temperature in both well-watered and water deficit conditions, suggesting control of water loss was largely genotype-dependent. Robust genomic associations revealed independent genetic control for the architectural and functional traits. Screening associated genomic regions revealed candidate genes involved in relevant pathways for each trait.
• We show that multiple allelic combinations exist for all studied traits within this collection. This opens promising avenues to jointly optimize tree architecture, light interception and water use in breeding strategies.