Aus rice: a source of promising donor genotypes for low N tolerance under field conditions

Excess nitrogen (N) fertilizer application is posing a serious concern on sustainable development of the earth's environment. Although, several studies aim reduction of N fertilizer input rate in rice, the target is yet to be achieved. Exploration of genetic diversity and identification of tolerant genotypes to low N is one of the promising strategies to achieve nitrogen use efficiency (NUE) in rice. Aus sub population is reported to possess unique stress tolerance traits, an underutilized resource for NUE. Hence, in present study, we screened the Bengal and Assam Aus Panel (BAAP) under three graded N levels (0, 50 and 100 kg N ha^- 1) for two wet seasons (2021 and 2022) and one dry season (2022). Data was recorded for seven traits viz., single plant grain yield (SPGY), single plant biomass yield (SPBY), single plant straw yield (SPSY), plant height (PH), tiller number (TN), SPAD chlorophyll meter readings (SCMR) and days to 50% flowering (DFF). Existence of wide genotypic variability was noticed not only for SPGY, but also for SPBY, SPSY, PH, TN, SCMR and DFF. Heat map clustering categorized the low N tolerant genotypes and grouped SPGY, SPBY and SPSY as sensitive traits to low N. M202 noted as highly tolerant to low N in wet season but was intermediate in dry season, indicating variable response of the genotype with season. Improved varieties viz., IR64-21, M202, BINA Dhan 5, BRRI Dhan 47 found to be tolerant to low N and can be immediately used in NUE breeding programmes.