Diverse alleles of Photoperiod-H1 directly and indirectly affect barley yield-related traits under contrasting photoperiods and PHYTOCHROME C backgrounds.

This article investigates the direct, pleiotropic effects of the Photoperiod-H1 (PPD-H1) gene on barley spike fertility and grain yield, independently of its known influence on flowering time. Using near-isogenic lines (NILs) differing in PPD-H1 alleles (photoperiod-sensitive Ppd-H1 and photoperiod-insensitive ppd-H1) across two PHYTOCHROME C (PHYC) genetic backgrounds and under contrasting photoperiods (12 h and 24 h), the study found that under a 24 h photoperiod—where flowering time differences were minimized—the ppd-H1 allele increased grain number by enhancing spike fertility through greater resource allocation to juvenile spikes and improved floret development efficiency. These effects were consistent regardless of PHYC background and were primarily due to increased fertile florets per spike rather than changes in spike number. The findings support a true pleiotropic role of the ppd-H1 allele in improving barley yield components beyond its impact on flowering time.