We analysed nine traits of the root system of 223 genotypes of Triticum turgidum (2n = 4x = AABB) subspecies dicoccoides, dicoccum, turgidum, durum and polonicum, finding a large intra and interspecific variability in both the number and size of roots, as well as in their spatial distribution. We studied the presence of an incomplete MITE (Miniature Inverted-repeat Transposable Element) inserted in the TtDro1B gene, which is present in some genotypes of dicoccoides, dicoccum, and turgidum, but not in polonicum and the 97.9% of the durum accessions. Comparison between genotypes shows that genotypes with the MITE element have smaller and shallower roots. Since Aegilops is considered to be the donor of the wheat B genome, the presence of the same MITE element was analysed in 55 accessions of the species Aegilops speltoides, searsii, bicornis and longissima, and in no case was it detected. We propose that after the emergence of T. turgidum subsp. dicoccoides, the insertion of the MITE element probably occurred in a single plant. Subsequent domestication resulted in genotypes of dicoccum with and without the MITE element, which after selection gave rise to the subspecies turgidum, and durum and polonicum, respectively. The MITE element can be used to differentiate turgidum from the durum and polonicum with high reliability.

Durum wheat (Triticum turgidum, 2n = 4x = AABB) includes several subspecies with differential characteristics in their root system architecture (RSA). Subspecies durum has longer and more vertical roots, while subspecies turgidum has smaller and shallower roots. The homeologous genes TtDro1A and TtDro1B of both subspecies have been identified and found to differ in their sizes, sequences and the proteins they encode. To determine whether there is a relationship between the level of expression of these two genes and the angle adopted by the roots of durum wheat seedlings, their expressions has been studied by RT-qPCR, both in the primary seminal root and in the other seminal roots. The results of the analyses showed that the TtDro1A gene is expressed 1.4 times more in the primary seminal root than in the other seminal roots. Furthermore, this gene is expressed 2.49 to 8.76 times more than TtDro1B depending on root type (primary or seminal) and subspecies. There are positive correlations between the expression ratio of both genes (TtDro1A/TtDro1B) and the mean of all root angles, the most vertical root angle and the most horizontal root angle of the seedlings. The higher the expression of TtDro1B gene, the lower the root growth angles.