Coincidence of inductive photoperiod and early vegetative phase leads to early flowering and increased yield in selected Sri Lankan traditional rice varieties

Despite the nutritional and environmental benefits, Sri Lankan traditional rice (SLTR) is under-cultivated due to the photoperiod sensitivity in most varieties. This experiment was carried out to determine the effect of photoperiod on the days to flowering (DF) and number of spikelets per first panicle (SP) of selected SLTR varieties Masuran (5530), Heras (6412) and Hathe pas dawase wee (4237), by exposing to different photoperiods and developing a gene network model. Three week old plants were exposed to time controlled sunlight for three photoperiods of 11 hour and 45 minutes representing short-day photoperiod (SD), 12 hours, and 12 hours and 05 minutes in the photoperiod chamber, and to the prevailing natural photoperiod, which ranged from 12 hours and 14 minutes to 12 hours and 02 minutes, and 12 hours and 15 minutes to 12 hours and 03 minutes, in two locations in a completely randomized design with three replicates. DF and SP were recorded. The ANOVA revealed that DF and SP of each accession were significantly affected by photoperiod (p < 0.05). The SD resulted in significantly reduced DF in three accessions. The increased DF reduced the SP in accessions 5530 (r = -0.51) and 6412 (r = -0.53) according to the correlation analysis (p < 0.05). The photoperiod effect on SP was explained through quadratic regression models, which indicated an optimum photoperiod for the highest SP (p < 0.05). Gene network model analysis suggested distinct interactions among pleiotropic genetic factors in response to photoperiod, and tested rice accessions. Hd1 and Ghd7 interactions mediated late-flowering under long-day conditions, while the absence of the Ghd7 pathway mitigated the delayed flowering response. DTH8-mediated suppression of Ehd1 and Hd3a under long day conditions led to delayed flowering and a simultaneous increase in SP. Alternatively, the Ehd1-RFT1 pathway facilitated early flowering under short-day conditions in the absence of Hd1. Plant responses and suggested gene interactions provide valuable insights for manipulating DF and yield in breeding SLTR.