<b>Physio-Morphological Evaluation of Nepalese Rice Landraces Seedlings under Contrasting Nitrogen Regimes in Hydroponics</b>

Application of nitrogen (N) fertilizer in rice has been increasing and sustaining yield; however, its inadvertent use has resulted in N-induced pollution, as rice has the lowest nitrogen use efficiency (NUE) among cereals. To mitigate these effects, there is a need to assess the performance of rice germplasm for NUE. This study evaluated 20 rice landraces for twelve N-responsive traits using a two-factor factorial completely randomized design under N-optimum (8 mM N) and N-stress (0.08 mM N) in a greenhouse condition for 28 days. Significant phenotypic variability was observed across all N-responsive traits. N-stress increased root length (35.93%) and root dry weight (30.43%) while significantly reducing shoot dry weight (27.88%), total chlorophyll (35.73%), and carotenoid content (42.14%). PCA and GGE biplots showed that root traits were primary indicators of performance under N-stress conditions. Landraces such as Jungey Kanchi and Kamal exhibited promising performance under N-optimum conditions, whereas Biramphul showed excellent results under N-stress conditions. Jungey Kanchi and Mansara were identified as the most superior, stable, and N-efficient landraces based on their high mean performance and high Stress Susceptibility Index (SSI) scores. Conversely, Darmali, Pahele, and Noulo Dalley were classified as poor performers. This study highlights the potential of specific Nepalese landraces as donor parents for enhancing NUE. These findings provide a foundational benchmark for developing N-stress-tolerant rice cultivars. However, more comprehensive insights can be gained by evaluating their tolerance during subsequent stages and identifying genes associated with NUE using omics approaches.