Genetic gains in wheat spike fertility and associated floret development attributes

Yield gains in wheat ( Triticum aestivum L.) have been historically associated with greater number of grains per area and per spike. Alternative strategies to further gains will require improving spike fertility through greater number of fertile florets or reducing grain abortion. We studied the influence of selection for yield on spike fertility and the dynamic underlying floret primordium development and grain setting in a collection of eleven cultivars from different breeding eras. Two field experiments were sown during the 2022/23 season in Spain under a high- and low-yielding environments and contrasting photothermal conditions. Floret development on three positions of the spike was monitored twice a week from the onset of stem elongation to anthesis and grain number per spike and per area were measured at physiological maturity. The maximum number of primordia initiated was similar between cultivars and independent from environmental conditions. Modern cultivars had 15% and 26% more fertile florets and grains per spike, respectively, mostly evidenced in the central and apical positions of the spike. This increase was associated with a higher floret survival rate of primordia and the development of labile florets in distal positions of spikelet. Higher grain number per area in modern varieties was explained in greater proportion (59%) by the higher number of fertile florets at anthesis than the grain setting. Moreover, greater allocation to the spike in modern varieties highlights the importance of alleviating source limitations during pre-anthesis for achieving further gains in spike fertility.