*Corresponding author: santiago.tamagno@udl.cat

Wheat (Triticum aestivum L.) spikes commonly present a lanceolate shape depicting the maximum fertility in central spikelets, whereas basal ones are typically sterile or rudimentary, not achieving full development. This is frequently observed under agronomic growing conditions, leading to the assumption that basal spikelets are constitutively sterile.

Evidence from studies impairing growth during stem elongation shows that spike floret survival drastically decreases, suggesting that assimilates supply to the spike plays a key role in spikelet fertility. However, it is not known whether high resource availability per plant could prevent floret mortality in basal spikelets.

We present data from two field experiments assessing spike fertility in the four most basal spikelets of the spike from the main shoot and tillers. Experiments comprised a collection of genotypes with different years of release and another with different tillering habits under contrasting sowing densities (agronomic densities vs. isolated plants) to generate a condition of high assimilate supply to the spike. As expected, under agronomic conditions, most basal position was sterile in 12 out of 14 cases and all cases in the tillers.

However, in the isolated condition in each experiment, sterility in basal spikelets was absent and less frequent in spikes from main shoots and tillers. Modern genotypes had a higher number of grains per spikelet than their older counterparts and low tillering habit genotypes showed the least response in spikelet fertility.

Regardless of the growing condition and experiment, the fertility of spikelets in the spike showed an acropetal gradient depicting the typical lanceolate shape, suggesting a constitutive trait in wheat spikes. Yet, fertility in basal spikelets does not seem to be a constitutive trait, as they became fertile when resources were increased.

Further understanding of fertility in these positions will be instrumental in increasing grains per spike and wheat potential yield.