Pre-anthesis spike growth dynamics and its association to yield components among elite bread wheat cultivars (Triticum aestivum L. spp.) under Mediterranean climate

Wheat (Triticum spp.) grain yield (GY) is highly associated with grain number per unit area (GN m-2). Biomass accumulation and partitioning are essential to understand pre-anthesis spike growth dynamics which determines spike dry matter at anthesis (SDMa) - a GN determinant. Spike growth takes place during the stem elongation period (SE), from terminal spikelet to anthesis, following leaf and spikelet initiation (LS) from sowing to terminal spikelet. In this study, bread wheat cultivars were examined under Mediterranean semi-arid conditions to determine (i) the varietal differences in pre-anthesis phase duration, (ii) whether this variability influences biomass partitioning and spike-related traits, and (iii) to what extent, the genotypic variations in pre-anthesis phase duration and spike growth are associated with yield components. A panel of Israeli commercial bread wheat cultivars were grown in the field during 2016-17 (three environments) and 2017-18 (two environments) and characterized for pre-anthesis phases, floral conditions and spike fertility via histological measurements, spike traits and dry matter accumulation and partitioning at anthesis and maturity and for yield components. Significant variability in the timing of pre-anthesis phases was detected within the tested panel. LS duration, and occasionally SE, favourably related with a better dry matter of fertile florets spike-1 (at anthesis) and SDM (at both anthesis and maturity). Two cultivar pairs Zahir-Yuval and Negev-Gedera, which flowered concurrently, revealed significant differences in the durations of LS and SE phases across the environments. Longer LS (e.g., in cultivars Zahir and Negev) exhibited increased spikelets number spike-1, whereas longer SE (e.g., in Yuval and Gedera) enhanced spike fertility through improving the survival rate of floret primordia (FSR%) of central spikelets. However, there was a trade-off for FSR at the proximal and distal spike portions, resulting reduction of final GN (or GY) in cultivars with longer SE. It is concluded that, in this panel, the duration of both LS and SE contribute to spike fertility. However, under short wheat growing cycle, LS duration seemed a stronger driver than SE for GN and yield enhancement. These highlights the novel importance of pre-anthesis phases, especially the role of LS in wheat yield increment during the short growing cycle. The varietal combination with variable LS and SE duration could be implemented in the breeding pipeline and used as pre-breeding materials for GN improvement. Furthermore, the findings will improve pre-anthesis traits adoption in Mediterranean bread wheat future breeding programs.