A candidate gene-based association study of introgressed pod shatter resistance in Brassica napus

Abstract

Yield losses at maturity due to unsynchronized pod shattering remain a major rapeseed breeding challenge. Variation for shatter resistance in the germplasm collections is inadequate for breeding manipulations. We have recently transferred resistance to pod shattering from <em>Brassica carinata</em> to<em> Brassica napus</em>. Introgression lines (ILs) were phenotyped for shatter resistance using the pendulum machine. Introgressive breeding was successful in enhancing rupture energy in the ILs, which varied from 1.8 to 7.2 milli Joules (mJ) for Environment 1 (E1) and 2.7 to 6.5 mJ for E2 while the corresponding values for natural <em>B. napus</em> ranged from 2.2-3.5 mJ (E1) and 2.2-4.3 mJ (E2), respectively. <em>B. carinata</em> had average rupture energy of 6.3 mJ (pooled over environments). On the basis of data averaged over two environments, I2 (6.3 mJ), I3 (5.2 mJ), I8 (5.6 mJ), I22 (5.1 mJ), I32 (5.2 mJ) and I41 (5.2 mJ) appeared very promising as germplasm resources for future breeding. Significant marker trait association between candidate gene NAC NAM (no apical meristem, <em>Petunia</em>), ATAF1/2 (<em>Arabidopsis thaliana</em> activating factor) and CUC2 (cup-shaped cotyledon, <em>Arabidopsis</em>) and rupture energy explained 19% of variation for the trait. IND3 (indehescent 3) also appeared to be associated with rupture energy under E1. These polymorphisms serve as encouraging candidates for developing molecular markers useful in marker-assisted deployment of introgressed shatter resistance.