Advances in Research

In the 20th century, global warming led to a 0.5 ⁰C increase in air temperature; projections for the 21st century estimate a rise of 1.5–4.5 ⁰C and higher temperatures are expected to become more common in the future. A rise in temperature above 33 °C has resulted in decreased rice production in various regions of the world. Heat stress affect the rice growth and development at different stages of crop growth. Heat Stress (HS) has a considerable negative effect on the potential for seed germination, leading to reduced seed viability and ineffective germination. During the tillering phase, high temperatures can lead to a reduction in both tiller number and biomass. Study reported that the optimum temperature for tillering is 25 °C during the day and 20°C at night. Tillers increased with increasing temperature in the range of 15 °C to 33 °C. Study found that temperatures above 33 °C damaged tillering. High temperatures can lead to reduced fertility in rice spikelets. This reduction is primarily due to impaired pollen sterility, issues with anther dehiscence, and failed stigma germination. High temperatures lead to spikelet infertility by decreasing pollen viability, restricting anther dehiscence, and preventing the germination of pollen tubes. In rice, the reproductive phase—which starts with panicle initiation and lasts until physiological grain maturity—is the most vulnerable stage to abiotic stresses. During anthesis, high temperatures significantly impede the dehiscence of anthers leads to spikelet sterility. High temperatures also adversely affect seed set and weight gaining, particularly shortly before or during anthesis. High temperatures interfere with the processes of pollen germination and tube growth by altering the balance of ions (such as Ca2þ), affecting carbohydrate metabolism. Elevated temperatures hinder spikelet differentiation, exacerbating spikelet degeneration and decreasing their overall number.