Genetic mapping of some key plant architecture traits in Brassica juncea using a cross between two distinct lines - vegetable type Tumida and oleiferous Varuna

Brassica juncea (AABB, 2n=36), commonly called mustard is an allopolyploid crop of recent origin but has considerable morphological and underlying genetic variation. An F1-derived doubled haploid (F1DH) population developed from a cross between a Indian oleiferous line, Varuna, and a Chinese stem type vegetable mustard, Tumida showed significant variability for some key plant architectural traits, including four stem strength-related traits, stem diameter, plant height, branch initiation height, number of primary branches (Pbr), and days to flowering (Df). Multi-environment QTL analysis identified twenty environmentally stable QTL for the nine plant architectural traits. Both Tumida and Varuna contain some positive QTL that can be used to breed superior ideotypes in mustard. A QTL cluster on LG A10 contained environmentally stable QTL for seven architectural traits. This region also contained overlapping environmentally stable major QTL (phenotypic variance [≥] 10%) for Df and Pbr, with Tumida contributing the trait enhancing alleles for both the traits. Since early flowering is critical for the cultivation of mustard in the Indian subcontinent, this QTL cannot be used for the improvement of Pbr in the Indian gene pool lines. Conditional QTL analysis for Pbr identified the QTL for improvement of Pbr without negative effects on Df. The environmentally stable QTL were projected on the genome assemblies of Tumida and Varuna for the identification of candidate genes. These findings provide insights into the genetics of plant architectural traits in two diverse gene pools of B. juncea and provide opportunities for improvement of the plant architecture through marker-assisted introgressions. Key MessageGenetic mapping of some key plant architectural traits in a vegetable type and an oleiferous B. juncea cross revealed environmentally stable QTL and candidate genes for breeding more productive ideotypes.