CONICET | Buscador de Institutos y Recursos Humanos

Abstract. The paramount importance of accumulated biomass in active-growing spikes over the number of grains per unit area has been well documented. However, it is not clear how different nitrogen (N) and radiation supplies during the active spike-growth phase alter the dynamics of floret primordia initiation and survival to establish the number of fertile florets and grains in 2- and 6-rowed barley. The objective of this paper was to evaluatehowbiomass andNpartitioned between vegetative and reproductive organs alter the development of potential grains (i.e. floret primordia), when 2- and 6-rowed barley is grown under different radiation and N levels during their active spike-growth phase. A field experiment was carried out using two near-isogenic lines differing in the spike type and grown under contrasting radiation and N levels around the active spike-growth phase. Floret primordia development and biomass and N partitioning towards vegetative and reproductive organs were analysed. The results showed significant genotyperadiationNlevel interactions on the dynamics of generation and abortion of reproductive structures. Under non-limiting N conditions, reductions in radiation levels strongly reduced the number of differentiated florets, although the effects were higher in 6- than in 2-rowed barley types. The higher theNsupply, the higher the floret development stage reached when the spikes started growing at their maximum growth rates, increasing floret survival in that way.Athreshold offloral development could not be found at any time in the crop cycle that guaranteed a fertile floret stage at heading. As it was not possible to identify a direct effect ofNon the establishment of fertile florets, the efforts for further rising yield potential in barley should be focused on processes influencing partitioning of assimilates to reproductive growth during the critical period.