Abstract:
The growing season is critical for most of Sri Lankan traditional rice (SLTR) accessions. The effect of planting date (PD) during the two main growing seasons (Yala and Maha) on agronomic traits and yield in SLTR remains unclear, and the responsive genetic factors are uncharacterized. This study aimed to evaluate the effects of days to flowering (DF) on yield in response to growing season and characterize key genes responsible for flowering. Ten SLTR accessions (4132, 5530, 4387, 4237, 4290, 4145, 4772, 4731, 6412, 2170) and an improved variety (Bg 300) were cultivated under twelve PDs at one-month intervals in Ibbagamuwa, IL1a agro-ecological zone in Sri Lanka. DF, plant height (PH) at flowering, and number of spikelets per first panicle (SP) were significantly influenced by accession and planting date (p < 0.05). Regression analysis revealed a quadratic or linear relationship between DF and SP. Effect of environmental factors on DF, PH and SP were revealed. PCR was performed for selected six key genes responsible for flowering time. The polymorphic information content (PIC) values were computed and hierarchical cluster analysis was performed based on flowering time gene variation. Three accessions were selected (4237, 5530 and 6412) representing the clusters to study the effect on DF and yield components through exposure to controlled short-day (SD), day-neutral and long-day (LD) photoperiods. The ANOVA revealed that DF and SP were significantly (p < 0.05) affected by photoperiod. The SD resulted in the 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 regression analysis (p < 0.05). Hd1 and Ghd7 interactions mediated late-flowering under LD while the absence of Ghd7 pathway mitigated the delayed flowering response. DTH8-mediated suppression of Ehd1 and Hd3a under LD, led to delayed flowering and a simultaneous increase in SP. Alternatively, the Ehd1-RFT1 pathway facilitated early flowering under SD conditions in the absence of Hd1.
