Leaf cover dynamics highlighted old spring germplasm as promising resources to improve early vigour in oilseed rape

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Laurençon, Marianne | Alix, Elise | Carillo, Aurélien | Guichard, Solenn | Jumel, Stéphane | Moulin, Bernard | Richard-Molard, Céline | Nesi, Nathalie | Laperche, Anne

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International audience. Oilseed rape cultivated surfaces sharply decreased worldwide recently, mainly due to poorplant establishment conditions. Indeed, seedlings are affected during autumnal or springgrowth by various abiotic and biotic stresses and thus impacting yield potential. Improvingplant establishment using vigorous varieties is a promising way, especially in low-input andagroecological systems.The ability of the plant to develop rapidly, from its emergence to the 4-5 leaf stage, is calledearly vigour. It is an integrative and a complex trait, often approximated by leaf area or totalbiomass but its underlying processes remain unclear even though they are potential selectiontraits. Therefore, this study aims to identify those processes and to describe their associatedgenetic diversity.A population of 217 genetically diverse B. napus lines was phenotyped for early vigour.It included 118 winter (WOSR) and 86 spring oilseed rape (SOSR), 11 winter fodderand 2 rutabagas, with high (++) and low (00) erucic acid and glucosinolate seed content.Experiments were conducted in a tunnel in Le Rheu (France) from sowing to the 4-5 leafstage. Early vigour was estimated by the leaf area and the plant total biomass at harvest.Leaf cover dynamic was estimated each day by image analysis. Traits related to the followingbiological processes were assessed: biomass production (shoot and root biomass, specificcarbon assimilation (SCA)), plant development (leaf area, leaf surface to shoot nitrogen ratio(LASNQ)), leaf growth (area under the curve (AUC) of leaf cover dynamics, phyllochron)and nitrogen content. PCA and random forest analyses were performed to investigate therelationships and trade-offs between these processes and their contribution to early vigour.Groups of genotypes with contrasting patterns were assessed.The main processes contributing to early vigour were the specific AUC, SCA and LASNQ. Forthese traits, genetic diversity was observed and different patterns were identified betweenSOSR (++ and 00) and WOSR (++ and 00). As a whole, SOSR and specifically some SOSR++developed faster (shorter phyllochrons, higher AUC) and produced equivalent or greater totalbiomass and leaf area than WOSR. WOSR00 presented the worst AUC values. Most of thetop vigorous lines were SOSR ++. When looking more particularly at the differences betweenphenotype correlation matrices of WOSR and SOSR, it was observed that SCA was positivelycorrelated to AUC and biomass for SOSR and inversely for WOSR. On the other hand,LASNQ was positively correlated to AUC and biomass for WOSR and inversely for SOSR.These results bring more knowledge on the processes involved in early vigour and theirrelated genetic diversity. Potential selection traits were identified for early vigour. Thegermplasm characterization showed that multiple SOSR ++ lines were shown to be morevigorous than WOSR, especially WOSR00. This highlights their value to develop breedingprogram targeting plant vigour as a mean to further improve plant establishment. The nextstep will be to identify the genomic regions involved in vigour-related traits and decipher thegenetic architecture of early vigour.

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