S13 - Session P3 - Genotypic variability of lettuce root system in response to P availability

Authors: Francois Lecompte *, Loïc Pagès, Amira Beroueg

Concerns about the medium-term evolution of phosphorus (P) resources and the impact of excessive P fertilization on the environment lead to the search for genotypes having a good P use efficiency. We evaluated the effect of P availability on the aerial growth and root architectural traits of 14 genotypes of the genus Lactuca , including wild species and ancient and modern cultivars. We identified substantial genotypic variation in most of the investigated traits. A limitation in P tended to increase the dominance of the taproot over the lateral roots. Despite a limited genotype x P interaction, we were able to observe compromises in the adaptations to low P of the different traits according to the genotypes. P use efficiency was mainly associated with traits related to the taproot. This pre-eminence of the taproot in the adaptation of Lactuca genotypes to low P contrasts with other species which rely more on lateral roots to adapt to P stress. Finally, by comparing total masses of observed and simulated root systems, we investigated the ability of the Archisimple root architecture model to represent the effects of genetic variability and P availability on lettuce root growth. A discussion is proposed regarding the experimental conditions required to compare the efficiency of highly contrasting genotypes, and about the root traits to be selected for a greater P use efficiency in modern varieties of lettuce.