Thermal requirements, physiological growth, and Grain sterility of some rice (Oryza sativa L.) Genotypes grown in different sowing dates

The growth and development of rice are significantly impacted by high temperatures, which also increases the sterility percentage. The consequences of extreme heat can be mitigated by selecting appropriate sowing dates for rice genotypes, particularly during flowering. In a pot experiment conducted from April to November 2024, three genotypes of japonica rice and one indica genotype were cultivated using three sowing dates: April 21, May 11, and June 11. Phenology and sterility percentage were ascertained in addition to the accumulation of Growing Degree Days, calculated for every stage from seedling to physiological maturity (PM). The effect of the three different sowing dates and the response of rice genotypes were found to differ significantly. The longest growing period (143.500 days) was for the first date with a maximum amount of GDD (3262.400) needed to reach PM, whereas the third sowing date had the shortest period (114.417 days) and the lowest GDD (2595.338). High temperatures caused differences in sterility among rice genotypes, depending on the environmental conditions provided by three sowing dates; the highest and lowest sterility percentages of V1, V2, and V3 were obtained in SD1 and SD3. The Banikhellan genotype had a far higher grain production (56.001g) than the others, whilst the Indica type produced the least (29.619g). As a result, the Indica genotype Sadry had 40% sterility, whereas the Japonica rice genotypes Banikhellan, Akre1, and Akre2 displayed more tolerance, so any rice genotype's appropriate sowing date greatly depends on the timing of the flowering and pollination.