Journal of Agronomy and Field Innovations

Background: Rice (Oryza sativa L.) is the primary source of energy to nearly 50% of humans globally, and its decline directly impacts food security. Different temperature increases (ambient temperature) due to climate change are being experienced during the critical reproductive phases of the plant, necessitating the need to study the impact of heat on rice yields.
Objectives of the study: The main aim was to demonstrate the genetic variations between different rice varieties in terms of tolerance toward heat. This study also focused on finding certain parameters that could be used as an indicator to measure rice productivity during high temperatures.
Methods: Two types of rice varieties that can grow under extreme temperatures and two heat-sensitive varieties were grown using a randomized complete design with four replications. A heat stress (with temperatures of 40-30 degrees C day and night for a period of 5 days) was developed using chamber systems at the heading stage of rice and measurements for chlorophyll fluorescence (such as F0, Fm, Fv/Fm, ΦPSII, ETR, NPQ, qP) were taken for 0, 3, and 5 days.
Results: The application of heat stress caused a notable decrease in the Fv/Fm and ΦPSII ratio in all of the studied genotypes (p < 0.01), whereby the sensitive genotypes reacted more seriously to stress in comparison to tolerant ones. Moreover, NPQ increased to a greater extent in tolerant genotypes, indicating that these plants were able to perform better under heat stress conditions. The results showed that Fv/Fm on day 5 of the stress was positively correlated with the spikelet fertility (r = 0.81) and grain yield (r = 0.76) of the studied rice genotypes.
Conclusion: Chlorophyll fluorescence techniques that measure the Fv/Fm and ΦPSII ratios are helpful methods for quickly and non-destructively assessing the heat tolerance of rice genotypes under field conditions, thus confirming their applicability in breeding programmes aimed at creating heat-resistant rice.