Breeding durum wheat for a sustainable future will need to exploit its genotype-specific differential interactions with plant-probiotic micro-organisms.

In natural populations of plants, the ability to interact with beneficial rhizosphere micro-organisms like mycorrhizal fungi, associative N2 fixers, or biocontrol agents (globally named plant-probiotic micro-organisms, PPM) is a very well conserved genetic trait. In fact, during their evolution, terrestrial plants have not achieved the ability to grow independently of their own PPM, and all investigated natural plant genotypes show the biological need to find specific micro-organisms in their habitat to successfully complete their growth cycle. Selection of modern varieties has typically been performed in standardized, high fertility systems with a primary focus on yield. Under such conditions, rhizosphere microbial communities are faced with an environment that differs substantially from the one in which plants and plant-microbial interactions originally evolved. Benefits incurred through interactions between plants and PPM have been made obsolete by the excess provision of nutrients in readily plant-available forms. Studies comparing allelic diversity within landraces and modern varieties concluded that allele richness declined in modern varieties, and alleles contributing to PPM interactions were among the ones lost. In fact, wheat cultivars developed prior to 1950 were more reliant on mycorrhizal symbiosis than modern wheat cultivars. On the same way, landraces of mycorrhizal wheat grown in low-P soils produced a higher yield than modern varieties grown under the same conditions. The main present day challenges in agriculture can be summarized as the necessity to use scarce and increasingly costly fertilizer inputs more efficiently, while also raising productivity on poorer soils. Meeting these challenges will require to reintroduce genes regulating plant-PPM interactions into the gene pool of modern varieties. Despite the considerable effort devoted to the identification of suitable donors, and of genetic factors associated with these beneficial traits, progress in developing improved varieties has been slow and has so far largely been confined to modifications of traditional breeding procedures. Molecular biology, combined with Mendelian and quantitative genetics in quantitative trait locus (QTL) mapping and marker-assisted selection (MAS) are more and more used for revealing and evidence the inheritance of root association with PPM, and some examples will be given in this comunication. However, not much can be found in PPM literature about durum wheat. MAS for enhanced root-PPM association is not yet part of routine cultivar improvement programs, but this selection criterium begins to be used in experimental breeding schemes. In order to contribute to an efficient set-up of breeding programs for better durum wheat-PPM interactions, we are developing tools for the detection of plant genotypes best interacting with selected PPM, and we propose to narrow the gap between basic sciences and applied breeding, through a more interdisciplinary research. For example, if MAS for PPM-root interactions would be integrated into breeding programs that are already practicing MAS for other traits, this would avoid the necessity of additional selection methodologies purely for the determination of beneficial microbial-root associations.