# Dynamics of apex and leaf development in barley as affected by PPD-H1 alleles in two contrasting PHYC backgrounds under short or long photoperiod

## TL;DR

This study explores how PPD-H1 alleles and photoperiod conditions affect barley development, including leaf growth and flowering phases.

## Contribution

The study reveals how PPD-H1 interacts with PHYC backgrounds and photoperiod to influence barley development dynamics.

## Key findings

- PPD-H1 effects on flowering time depend on PHYC genetic backgrounds and photoperiod conditions.
- PPD-H1 influences leaf number and phyllochron, mainly affecting the late reproductive phase.
- Short photoperiods increase phyllochron in later leaves for lines with the ppd-H1 allele.

## Abstract

Barley development from seedling to flowering involves both external and internal changes, the latter requiring microscopic observation. Internal changes allow for the classification of preflowering development into three phases: vegetative, early reproductive, and late reproductive. Genetic and environmental factors influence the duration of these phases, impacting grain yield. Photoperiod-sensitivity genes PPD-H1 play a major role in flowering time, affecting adaptation; however, the effect might also be direct (beyond affecting phenology). In this paper, we aimed to assess how PPD-H1 alleles affect barley development, including the progression of growth phases, leaf emergence, tillering dynamics, and spikelet development. Two experiments (field and controlled conditions) were conducted with a factorial combination of (i) four near-isogenic lines (NILs) for PPD-H1 alleles (ppd-H1 or Ppd-H1) under two contrasting PHYC genetic backgrounds (PhyC-l and PhyC-e) and (ii) two photoperiod conditions (short and long days). As expected, longer photoperiods led to a shorter growth cycle. All subphases of time to flowering, final leaf number, and phyllochron were affected by photoperiod. The effects of PPD-H1 on flowering time depended on the PHYC genetic backgrounds and photoperiod conditions. PPD-H1 effects on flowering time were associated with leaf number and phyllochron; the interplay between leaf number and phyllochron affected mainly the late reproductive phase. We also found that although PPD-H1 did not affect the phyllochron of the first six leaves, the phyllochron of leaves appearing later, when grown under a short photoperiod, was consistently increased in lines carrying the ppd-H1 allele. Tillering dynamics exhibited variability, but PPD-H1 did not affect the final spike number under a 24-h photoperiod.