High temperature stress prior to induction phase delays flowering initiation and inflorescence development in Phalaenopsis queen beer ‘Mantefon’

•The Phalaenopsis was treated by high temperature (HT) prior to induction phase.•HT prior to induction phase delayed both inflorescence induction and development.•HT decreased SPAD value and PSII electron transport, indicating HT stress.•CO2 uptake and sucrose contents decreased by HT stress.•HT stress lasted even during flowering initiation and inflorescence development. Temperatures above 28 °C are required to inhibit flowering and maintain vegetative growth for year-round cultivation of Phalaenopsis. However, because of seasonal variations, Phalaenopsis may be exposed to variable high temperatures (HT) above 28 °C prior to induction phase. This study was conducted to determine the effects of HT prior to induction phase on photosynthetic capacity, carbohydrates accumulation, and flowering in Phalaenopsis Queen Beer ‘Mantefon’. Twelve-month-old plants were treated with temperature at 28 (control), 31, or 34 °C for 15 and 30 days before induction phase at 20 °C. In response to HT treatment prior to induction phase, flowering initiation and subsequent inflorescence development was delayed, and other flowering characteristics (e.g. inflorescence length, inflorescence thickness, the number of flower buds, flower diameter, the number of branches) decreased. This phenomenon increased with increasing temperature and duration in some parameters [e.g. days to visible inflorescence (VI), total days to flower, inflorescence length, flower diameter]. During HT treatments, relative chlorophyll content (SPAD value) and maximum quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) significantly decreased at both 31 and 34 °C, indicating HT stress in plants. Due to the HT stress, CO2 uptake, stomatal conductance, PSII operating efficiency (Fq’/Fm’ or ΦPSII), and PSII efficiency factor (Fq’/Fv’ or qP) decreased, and non-photochemical quenching (NPQ) increased as temperature increased. Sucrose content also decreased with increase of treatment temperature. After HT treatment, the recovery aspects of SPAD value and Fv/Fm, suggest that the effects of HT stress persisted during inflorescence development. These results indicate that HT prior to induction phase can delay flowering initiation and inflorescence development of Phalaenopsis by reducing photosynthetic capacity and sucrose content.