Sterility of basal spikelets in wheat. Predetermined fate or a matter of resources?

Abstract

Grains per spike in wheat (Triticum aestivum L.) are not uniformly distributed. Basal spikeletsare typically sterile (or rudimentary) under common agronomic field conditions leading to theassumption that this could be a constitutive trait. Yet, it is unknown whether high resourceavailability per plant could prevent floret mortality in basal spikelets. We present data from twofield experiments assessing spike fertility in the four most basal spikelets of spike from the mainshoot and tillers. A collection of genotypes with different years of release and tillering habitswere grown under contrasting sowing densities (agronomic densities vs isolated plants) togenerate a condition of high assimilate supply to the spike. Under agronomic densities, the fourmost basal positions presented sterility in almost all cases in the main shoot spikes andwithout exception in the tiller spikes. When plants were isolated in each experiment,sterility in basal spikelets was absent and less frequent in spikes from main shoot andtillers. Moreover, in the isolated condition, modern genotypes had a higher number ofgrains per spikelet than their older counterparts, whereas genotypes with low tilleringhabit showed the least response in spikelet fertility. These results indicate that while thepredetermined lanceolate shape of spikes leads to the sterility of basal spikelets at highdensities, this sterility can be reversed if assimilates become more available. Thus,sterility of basal spikelets in common agronomic conditions is not a constitutivecondition of the spike.