Floret development and fertility of barley as affected by <i>Photoperiod-H1</i> under contrasting photoperiods and <i>PHYTOCHROME C</i> backgrounds

The photoperiod-insensitive allele of Photoperiod-H1 (ppd-H1) increases spike fertility in barley, both indirectly by lengthening flowering time and directly when flowering time is accelerated under extra long photoperiods. To determine if the effect of PPD-H1 on spike fertility is related to the initiation or the mortality of spikelets/florets, we performed detailed analysis of the dynamics of floret development along the barley spikes. Four near-isogenic lines (NILs) combining ppd-H1 and Ppd-H1 alleles with two PHYTOCHROME C (PhyC-l and PhyC-e) backgrounds were compared under 12 h and 24 h photoperiods. The ppd-H1 line consistently showed higher survival rates of floret primordia. Fertility differences were observed within spikes, with the insensitive ppd-H1 line improving fertility in the less favoured distal florets, and even inducing more developmental progress before floret mortality in apical spikelets. The ppd-H1 allele constitutively enhanced floret primordia survival, as the effect was seen even under long photoperiods when lines had similar phenology. The dynamics of floret development affecting spike fertility resulted in a parallel effect on grain setting. Together, these results indicate that photoperiod insensitivity in barley contributes to greater yield potential by reducing floret primordia mortality and improving spike fertility.