End-of-day Far-red Lighting with a Low Daily Light Integral Increases Stem Length But Does Not Promote Early Leaf Expansion for Petunia ×hybrida Seedlings

Greenhouse production of high-quality young annual bedding plants (plugs) at northern latitudes often requires supplemental lighting to compensate for a low natural daily light integral (DLI), but radiation interception by plugs is limited leaf area index. Some species show an increase in response growth under ratio red far-red (R:FR), and early may allow more effective capture seedlings reduction wasted radiation. Thus, the objective this study was examine effects end-of-day (EOD-FR) treatments varying intensity, R:FR (600–700 nm/700–780 nm), duration on expansion plug quality petunia ( Petunia × hybrida ) ‘Wave Purple’ ‘Dreams Midnight’. Seedlings were grown 128-cell trays common greenhouse environment simulated winter DLI (∼5.3 mol·m −2 ·s −1 received one four EOD-FR treatments, control conditions (no or lighting), (target photosynthetic photon flux density 70 μmol·m ). The provided 3 weeks cotyledon emergence included following: 10 30 minutes with ∼0.8 (EOD FL ), 20 ∼0.15 10:30 EOD 20:30 , respectively), 240 20:240 Destructive data collected 14 21 days after emergence. that did not any compared treatments. Stem length generally increased treatments; greater elongation observed when decreased from 0.8 0.15, treatment minutes. However, 0.15 minutes, intensity promote further stem resulting similar lengths both cultivars . Results indicate DLIs, applied first seedling does expansion, decreases petunia. As responses vary based taxa, incident radiation, DLI, future research examining EOD-FR–induced morphological changes warranted.