Reliable prediction of crop development in the field requires quantitative knowledge of relevant environmental factors. An important approach is to determine the duration when crops respond to photoperiod. The objective of this study was to investigate the continual regulation of effect of change in photoperiod on individual genotypes of a genetic population. The recombinant inbred line (RIL) population was used as experiment materials. The population consists of 94 RILs and the two parents, ‘Apex’ and ‘Prisma’. Initially, half of the pots for each recombinant inbred line were placed in long-day light (LD), while another half in short-day (SD) light. Plants were mutually transferred from LD to SD and from SD to LD environments at regular intervals. The effects of photoperiod on the recombinant inbred line population in barley (Hordeum vulgare L.) were quantified.
The results showed that the effect of photoperiod on barley development appeared linear relationship, and based on this, the time from sowing to flowering can be divided into three successive phases: a basic vegetative phase (BVP), a photoperiod-sensitive phase (PSP) and a post-PSP phase (PPP). Furthermore, a mathematic model assessing the effect of photoperiod on barley development was developed, and the lengths of each of three phases from sowing to flowering was then estimated. Based on an ecophysiological development model as a function of daily temperature and photoperiod, photoperiod sensitive parameter was calculated. These parameters were f0 (the minimum number of days to flowering at the optimum temperature and photoperiod), θ1 and θ2 (the development stages for the start and the end of the photoperiod-sensitive phase, respectively), and δ (the photoperiod sensitivity). The result showed 96 individuals (including the two parents) of the recombinant inbred line population in barley were affected by photoperiod. But there was much difference between various recombinant inbred lines. The earliest one responded to photoperiod was 9.78 days after sowing and the latest one 41.49 days; the fastest one passed photoperiod sensitive phases was 9.2 days and the slowest one until flowering. On the other hand, there was also significant difference between various development phases for the same individuals of the recombinant inbred line population. The barley growth was strongly affected by photoperiod in photoperiod-sensitive phase (PSP), but weakly in basic vegetative phase (BVP) and in post-PSP phase (PPP). The relationship between the length of various development phases of the preflowering and the photoperiod sensitive intensity was also analyzed.