Application of Thermal Imaging for Assessing Desiccation Stress Memory in Sugarcane and Sorghum Cultivars

Pre-exposure of plants to moderate stress may create a “stress memory” that enables a fast protective response to next stress event. Protocols to differentiate the crop genotypes for such traits are essential for genetic improvement of plant stress tolerance. We hypothesized that memory due to soil moisture deficit may get reflected in leaf canopy temperature responses to fluctuating ambient temperature. We conducted a factorial completely randomized block design experiment with two treatments: well-watered (WW) and water deficit stress (WS) in three and two popular cultivars of sugarcane and sorghum, respectively, with eight replications. The 30 and 15 days old plants of sugarcane and sorghum were exposed to soil moisture deficit for 25 and 10 days, respectively, followed by their recovery. For differentiating the response of plants after stress recovery (ASR), the WW and WS plants were labelled as WW_ASR and WS_ASR, respectively. After 30 days of recovery, canopy temperature responses to ambient temperature fluctuations were monitored. Warming of the canopy was faster in WS_ASR as compared to WW_ASR plants. Further, there was a difference within the WS_ASR cultivars, indicating the existence of genetic variation in recalling and responding to desiccation caused by increasing ambient temperature. These indicated that water exhaustive and non-exhaustive C₄ plants differ in their adaptive mechanisms associated with transpirational cooling of the plant canopy. The pixel-wise analysis of thermal images of plants provided a more effective differentiation of stress responses among sugarcane and sorghum cultivars compared to the conventional method of recording canopy temperature. The existence of cultivar differences suggests that the trait representing stress memory can be phenotyped with protocols optimized with the IR imaging system and may serve as a promising tool for phenotyping crop stress tolerance.