National repository of EMS induced mutants of an upland rice cultivar Nagina 22: progress update on characterization and utilization.

Abstract The Indian initiative for creating mutant resources in rice has generated 87,000 mutants in the background of a popular drought- and heat-tolerant upland cultivar, Nagina 22 (N22), through EMS mutagenesis. So far, 541 macro-mutants from this resource have been identified, maintained in the mutant garden and characterized in detail based on 44 descriptors pertaining to distinctness, uniformity and stability (DUS) of rice and other agronomic parameters. The similarity index of the mutants was more than 0.6 for nearly 90% of the mutants with respect to DUS descriptors, further establishing the validity of the mutants. The available high-quality sequence resource of N22 has been improved by reducing the gaps by 0.02% in the coding sequence (CDS) region. This was made possible using the newly synthesized whole-genome data of N22 which helped to remove 9006 'Ns' and replace 12,746 existing nucleotides with the accurate ones. These sequence and morphological details have been updated in the mutant database 'EMSgardeN22'. Further, 1058 mutants have been identified for low-P tolerance, tolerance to sheath blight, blast, drought, heat, higher photosynthetic efficiency and agronomic and root traits from this resource. A novel herbicide-tolerant (imazethapyr) mutant earlier identified and characterized from this resource is now being used in introgressing the herbicide-tolerant trait in eight major rice varieties in India. Further, robust and simpler screening systems have been tested for studying low-P tolerance of the mutants. A grain-size mutant, heat-tolerant mutant, drought-tolerant mutant, stay-green mutant and low-P tolerant and water-use efficient high-root-volume mutants have been characterized at morphological and molecular levels. A brief account of all these mutants, the entire mutant resource and the elaborate trait-based screenings is presented in this chapter.