Characterization of physiological traits in advanced rice (Oryza sativa L.) breeding lines

Abstract

A field experiment was conducted to evaluate physiological growth traits in thirty advanced rice (Oryza sativa L.) breeding lines with the objective of identifying superior genotypes based on growth efficiency. The study was carried out over two consecutive seasons, and observations were recorded at key growth stages, namely active tillering, panicle initiation, physiological maturity, and harvest. The physiological parameters assessed included leaf area index (LAI), leaf area duration (LAD), and crop growth rate (CGR), which are important indicators of canopy development, photosynthetic efficiency, and biomass accumulation in rice. Significant differences were observed among the breeding lines for all the studied physiological traits across seasons as well as in pooled analysis, indicating substantial genetic variability. Leaf area index showed an increasing trend from active tillering to panicle initiation, followed by a decline towards harvest. Among the genotypes evaluated, SP-08 and SP-72 consistently recorded higher LAI values at all growth stages compared to the quality check variety BPT-5204, while IR-64 recorded the lowest values. Similar trends were observed for leaf area duration, where SP-08 and SP-72 maintained functional leaf area for a longer duration, reflecting delayed senescence and sustained photosynthetic activity. Crop growth rate increased from active tillering to panicle initiation and declined during later stages of crop growth. The highest CGR values were recorded by SP-08 and SP-72 during both seasons and in pooled data, indicating efficient dry matter production during critical growth phases. In contrast, IR-64 exhibited lower CGR values throughout the crop growth period. The superior performance of SP-08 and SP-72 can be attributed to their enhanced canopy structure, prolonged photosynthetic duration, and efficient biomass accumulation. These physiological advantages suggest their potential for higher productivity and better resource-use efficiency. The study highlights the importance of physiological trait-based screening in rice breeding programs and identifies SP-08 and SP-72 as promising genotypes for further yield evaluation and varietal improvement.