Genetic characterization of tetraploid wheats and evaluation of their mycorrhizal affinity

Genetic diversity of domesticated wheats has been significantly reduced compared to that of their wild progenitors, through a long selection procedure for those phenotypic traits which led the wild plants to better suit the human needs. Tetraploid wheat landraces were largely cultivated until the first decades of the twentieth century, being progressively abandoned from the early 1970s and replaced with improved, genetically uniform semidwarf cultivars as a consequence of the Green Revolution. Nevertheless, since the current climate change is affecting grain yields worldwide and threatening food securety, sources for specific adaption to drough and heat are urgently needed. In this context, addressing the research towards the study of the level and the structure of genetic diversity in tetraploid wheats, linked to the dection of specific chromosomic traits of interest, has become very important. The relatively high level of genetic variation in modern crops could be obtained through the genetic drift and introgressions between or among the domesticated crops and their close wild relatives. In particular, landraces, characterized by a wide variability in terms of morphological, phenological and quality traits, provide a large source of genetic variability. Many researches have showed their specific adaptation to local environmental conditions according to their place of origin, and, very recently, their ability to form mycorrhizal symbiosis. Positive advances have been reported regarding the mutualistic relationship between the plant and the mycorrhizal fungus, revealing better performance for the host in terms of nutrient uptake and protection from salinity, lack of water, and excess phytotoxic elements. Mycorrhiza studies and the recent progress in research in this sector have shown a possible solution for environmental sustainability: AMF represent a valid alternative to overcome the loss of biological fertility of soils, reduce chemical inputs, and alleviate the effects of biotic and abiotic stresses. However, the actual role of the single wheat genotype in establishing this type of association is still poorly investigated. In this work, the genetic diversity and population genetic structure of a collection of 265 accessions of eight tetraploid Triticum turgidum L. subspecies were investigated using 35,143 single nucleotide polymorphisms (SNPs) screened with a 35K Axiom® array. Neighbor joining algorithm, discriminant analysis of principal components (DAPC) and Bayesian model-based clustering algorithm implemented in STRUCTURE software revealed clusters in accordance to the taxonomic classification, reflecting the evolutionary history and the phylogenetic relationships among Triticum turgidum L. subspecies. Starting from these results, 130 accessions have been inoculated with the AMF species Funneliformis mosseae (F. mosseae) and Rhizoglomus irregulare (R. irregulare), and a genome wide association study (GWAS) was conducted to identify genetic markers in linkage with chromosome regions involved in this symbiosis. 5 Six clusters of genetically related accessions were identified, showing a different mycorrhizal colonization among them. GWAS revealed four significant quantitative trait nucleotides (QTNs) involved in mycorrhizal symbiosis, located on chromosome 1A, 2A, 2B and 6A. The results of this work enrich future breeding activities aimed at developing new grains on the basis of genetic diversity on low or high susceptibility to mycorrhization, and, possibly, maximizing the symbiotic effects.