A Gamma Ray–Induced Dwarf and Early Mutant of <scp> <i>Brassica juncea</i> </scp> With Favourable Traits for Developing High‐Yielding, Dwarf/Semi‐Dwarf Genotypes

ABSTRACT Introduction of dwarfism to cereals has set a new paradigm in crop improvement programmes. To date, very little progress has been made in the development of high‐yielding dwarf/semi‐dwarf genotypes in oilseed Brassica . Previous attempts using induced mutagenesis employed in the induction of dwarfism in Brassica crops yielded limited success, and many mutants had markedly unfavourable modifications in the plant. In the present study, we characterised a gamma radiation–induced dwarf and early mutant, Trombay juncea dwarf‐1 ( tjd1 ), in Indian mustard, Brassica juncea cv. Varuna, that showed improved yield‐contributing traits like total siliquae number and number of branches. This mutant offers a prominent source of dwarfism and earliness for crop improvement in Indian mustard, B. juncea . Nature of dwarfism in tjd1 was assessed in terms of major components of plant architecture contributing to plant height. The mutant showed about 45.09% reduction in plant height compared to the parent cultivar due to the reduction in the height of the first branch, length of main fruiting axis and number and length of the internodes. At anatomical level, mutant tjd1 showed reduction in both cell size and number of cells/mm. The genetic analysis using F 1 , F 2 and BC 1 F 1 populations indicate that the dwarf plant height is controlled by a single recessive gene with incomplete dominance. The mutant responded towards auxin treatment at both seedling and late vegetative phase and also showed significant downregulation of the key genes involved in phytohormone pathways. Overall, the B. juncea mutant tjd1 will be very useful as a source for ideotype breeding to develop early and dwarf/semi‐dwarf high‐yielding genotypes.