Title : Differential chlorophyll responses and stability indices of flood-tolerant Nigerian rice landraces under submergence stress
Abstract:
Flooding stress is a major environmental constraint limiting rice productivity in lowland ecologies. Understanding physiological mechanisms underlying tolerance is critical for breeding climate-resilient rice varieties. This study evaluated seventy-three (73) Nigerian rice landraces and two tolerant checks (L-19 SUB1 and Futia-12) for chlorophyll content and chlorophyll stability index (CSI) under flash flood and deep-water submergence conditions. The experiment was conducted at Ahmadu Bello University, Zaria, Nigeria, using a randomized complete block design with two replicates. Thirty-day-old seedlings were submerged following IRRI protocols, and chlorophyll content was measured with a SPAD-502 chlorophyll meter before and after submergence. CSI was calculated as the relative percentage reduction in chlorophyll content. Results revealed wide variability among landraces. Chlorophyll declines under flash flooding ranged from 6 – 32%, while deep-water submergence induced 34 – 82% reduction. CSI values ranged from 17 – 100% and 0–100% under flash flood and deep-water conditions, respectively. Tolerant checks (L-19 SUB1 and Futia-12) maintained high CSI values, indicating enhanced photosynthetic stability. Interestingly, some rice landraces (Bakin Iri, Mai Adda, Yar Mamman) exhibited CSI values equal to or exceeding tolerant checks, suggesting possible deep-water escape strategies through shoot elongation and sustained chlorophyll function. These findings highlight the presence of promising Nigerian rice landraces with inherent tolerance mechanisms comparable or superior to known tolerant lines. Such genotypes provide valuable genetic resources for breeding programmes targeting flood prone ecosystems.
