Significance of the Diversification of Wheat Species for the Assembly and Functioning of the Root-Associated Microbiome

Abstract

Wheat, one of the major crops in the world, has had a complex history that includes genomic hybridizations between Triticum and Aegilops species and several domestication events, which resulted in various wild and domesticated species (especially Triticum aestivum and Triticum durum), many of them still existing today. The large body of information available on wheat-microbe interactions, however, was mostly obtained without considering the importance of wheat evolutionary history and its consequences for wheat microbial ecology. This review addresses our current understanding of the microbiome of wheat root and rhizosphere in light of the information available on pre- and post-domestication wheat history, including differences between wild and domesticated wheats, ancient and modern types of cultivars as well as individual cultivars within a given wheat species. This analysis highlighted two major trends. First, most data deal with the taxonomic diversity rather than the microbial functioning of root-associated wheat microbiota, with so far a bias toward bacteria and mycorrhizal fungi that will progressively attenuate thanks to the inclusion of markers encompassing other micro-eukaryotes and archaea. Second, the comparison of wheat genotypes has mostly focused on the comparison of T. aestivum cultivars, sometimes with little consideration for their particular genetic and physiological traits. It is expected that the development of current sequencing technologies will enable to revisit the diversity of the wheat microbiome. This will provide a renewed opportunity to better understand the significance of wheat evolutionary history, and also to obtain the baseline information needed to develop microbiome-based breeding strategies for sustainable wheat farming.

Seed Coating with Trichoderma harzianum T-22 of Italian Durum Wheat Increases Protection against Fusarium culmorum-Induced Crown Rot

“…This is because the root exudates contain chemical compounds with low (i.e., phenols, small polysaccharides, amino acids, organic acids) and high (i.e., large carbohydrates, fatty acids, flavonoids, enzymes, tannins, steroids, terpenoids, alkaloids) molecular weights, which act as chemo-attractants of soil microbes during the interaction between plants and pathogenic and beneficial fungi [39]. Furthermore, it was demonstrated that the wheat root surface is capable of being colonized by beneficial microorganisms, including Trichoderma spp., and the amount of root exudates produced during plant-microorganism interaction is determined by the root architecture system and rhizodeposition [40].…”

“…It has been assumed that the domestication and subsequent crop selection of wild wheats, landraces, and modern cultivars led to different patterns of microbial colonization and interactions between the roots and rhizosphere [41]. In particular, landraces seem to be associated with a larger microbial diversity, which is probably the result of their increased genetic heterogeneity, and, as a consequence, their microbiome is characterized by certain microorganism families that are not found in modern varieties [40]. On the other hand, the ability to stimulate the rhizosheath and, therefore, to produce specific root exudates by Creso and Ciclope seedlings obtained from seeds treated with T-22 was associated to a greater increase in the rhizosheath/root mass ratio compared to a less evident increase in this ratio in Saragolle Lucana and Simeto [19].…”

Wheat genome architecture influences interactions with phytobeneficial microbial functional groups in the rhizosphere

“…Consequently, it is expected to affect rhizosphere microbiota as well, a hypothesis that was tested in the current work. This was made possible by the availability of current representatives with AA, BB, AABB, DD and AABBDD genomic architectures, as we do not have access to the exact same wheat species or genotypes that participated in the hybridization events (Gruet, Muller, et al, 2022). In addition, environmental conditions prevailing at the times of these hybridizations are not well documented, and here we chose a single set of soil and greenhouse features, based on their ability to sustain growth of the different wheat species tested, so as to focus comparisons on the genomic effects.…”

“…Due to several hybridization and polyploidization events, wheat genome architecture can vary drastically between wheat species, which may have an impact on root properties (Ahmadi et al, 2018; Golan et al, 2018; Gruet, Muller, et al, 2022; Iannucci et al, 2017; Pérez‐Jaramillo et al, 2016; Roucou et al, 2018; Waines & Ehdaie, 2007). Consequently, it is expected to affect rhizosphere microbiota as well, a hypothesis that was tested in the current work.…”

“…Polyploidization is thought to confer ecological benefits (Soltis & Soltis, 2000; Soltis et al, 2015). Polyploids display a patchwork of parental and new characteristics, including traits influencing plant–microbe interactions such as root exudation, root uptake patterns, and so forth (Gruet, Muller, et al, 2022; Iannucci et al, 2021; Saia et al, 2019).…”