Independent genetic factors control floret number and spikelet number in Triticum turgidum ssp

Abstract

Wheat grain yield is a complex trait resulting from a trade-off among many distinct components. During wheat evolution, domestication events and then modern breeding have strongly increased the yield potential of wheat plants, by enhancing spike fertility. To address the genetic bases of spike fertility in terms of spikelet number per spike and floret number per spikelet, a population of 110 recombinant inbred lines (RILS) obtained crossing a Triticum turgidum ssp. durum cultivar (Latino) and a T. dicoccum accession (MG5323) was exploited. Being a modern durum and a semi-domesticated genotype, respectively, the two parents differ for spike architecture and fertility, and thus the corresponding RIL population is the ideal genetic material to dissect genetic bases of yield components. The RIL population was phenotyped in four environments. Using a high-density SNP genetic map and taking advantage of several genome sequencing available for Triticeae, a total of 94 QTLs were identified for the eight traits considered; these QTLs were further reduced to 17 groups, based on their genetic and physical co-location. QTLs controlling floret number per spikelet and spikelet number per spike mapped in non-overlapping chromosomal regions, suggesting that independent genetic factors determine these fertility-related traits. The physical intervals of QTL groups were considered for possible co-location with known genes functionally involved in spike fertility traits and with yield-related QTLs previously mapped in tetraploid wheat. The most interesting result concerns a QTL group on chromosome 5B, associated with spikelet number per spike, since it could host genes still uncharacterized for their association to spike fertility. Finally, we identified two different regions where the trade-off between fertility related traits and kernel weight is overcome. Further analyses of these regions could pave the way for a future identification of new genetic loci contributing to fertility traits essential for yield improvement in durum wheat.

Keywords: QTLs; T. dicoccum; durum wheat; florets; spike architecture; yield.

Figure 1

Fertile florets developing in the Latino and MG5323 parental lines. (A–E) An average of six fertile florets develop within the central spikelets in the Latino parental line. (F–H) An average of four fertile florets develop within the spikelet of the MG5323 parental line. (I) Overview of a mature Latino’s spikelet; the seventh floret is always unfertile. (J) Overview of a mature MG5323’s spikelet; the fourth floret is always unfertile. Scale bars indicate 200 micron.

Figure 2

The frequency distribution for all traits of data collected from single and multi-environment BLUPs (light blue for F19, green for F20, red for F21, orange for P20 and black for MEnv, multi-environments data).

Figure 3

Pearson’s correlation analysis between all spike and floret related traits and heading date using multi-environment BLUPs. Level of significance at P <0.05, ** P <0.01, *** P <0.001 and non-significant (ns).

Figure 4

Schematic representation of QTL groups anchored on the durum wheat reference genome. (A) QTL groups related to spike traits; (B) QTL groups referred to floret traits. Part of the chromosomes are represented by including some markers surrounding the QTL group; SNP marker IDs are on the right, whereas their positions on the durum wheat reference genome are reported in Mbp on the left. The name of flanking markers of the best QTL in each group is in bold. QTL names are according to Table 2 . The traits are denoted as: FRT, total floret number; NFRT, net floret number; SPK, total spikelet number; NSPK, net spikelet number; SPW, spike weight; SD, spike density; SPL, spike length; HD, heading date. Environments abbreviations: F19, F20 and F21 for Fiorenzuola d’Arda field experiment, P20 for Pisa field trial in 2020 and BL for multi-environment data analysis. Known genes are reported. Complete information of this figure is on Tables 2 and 3 , Supplementary Tables 6 , 7 .