Biochemical and physiological characterization for nitrogen use efficiency in aromatic rice genotypes

In a set of 78 aromatic rice genotypes, cluster analysis was performed for yield and its related traits in field under two nitrogen (N) conditions viz., application of N fertilizer (N100) and without application of N fertilizer (N0) during wet season, 2011 and dry season, 2012. Basmati370 and Ranbir basmati were selected as high nitrogen use efficiency (NUE) genotypes and Kolajoha-3 and Ratnasundari as low NUE genotypes for characterization in terms of biochemical, physiological and agronomical aspects of NUE. A total of 32 biochemical, physiological and agronomical characters were measured in the selected four genotypes, growing in field under two N levels i.e., N0 and N100 during wet season 2012. Five efficiency parameters were also studied to determine their NUE. GS activity increased under low N and the increase was more in two high NUE genotypes (41.3%) than that of two low NUE genotypes (5.43%). NR activity increased with application of N fertilizer and low NUE genotypes expressed higher NR activity (8.8% and 2.02% more in N0 and N100 respectively). Chlorophyll content recorded maximum (3.6 mg g−1) in low NUE genotypes under N100 condition, where as the chlorophyll content was minimum (0.43 mg g−1) in high NUE genotypes under N0 condition. Electron transport rate (ETR), quantum yield (ΦPSII) and Fv/Fm were not affected by N levels but there were significant variations in non-photochemical quenching (qN) (15% more in N0) and photochemical quenching (qP) (25% more in N0). Grain yield, total dry matter and N uptake by grain and straw were higher in high NUE genotypes. Higher GS activity, maintenance of sufficient chlorophyll fluorescence and chlorophyll content in case of high NUE genotypes support their higher grain yield and total dry matter content under low N conditions by efficient N uptake, and utilization of nitrogen.