Pod drop in Brassica napus is linked to weight-adjusted pod-retention resistance

- Pod retention-resistance, the force it takes to dissociate canola pods at the pedicle-rachis junction, and pod drop differed among Brassica napus genotypes in a series of field experiments.
- Variance component analysis showed that the relative importance of factors that affected pod-retention resistance was different from those that affected pod drop.
- A significant negative correlation between weight-adjusted pod-retention resistance and pod drop (Pearson R = −0.63) was found among 19 commercial canola genotypes.
- Weight-adjusted pod retention resistance or the weight-adjusted pedicle attachment strength adjusted for pod-weight appears to play an important role in pod drop and requires further investigation.
- Pod retention resistance can be used as a predictor of pod drop in selecting for canola genotypes with reduced seed loss.

Canola (Brassica napus L.) often experiences high seed losses prior to and during harvest operations. Pod drop and pod shatter are responsible for pre-harvest seed losses in canola although relatively little is known about the significance of pod drop to total pre-harvest seed losses in canola. This research describes a method to measure the predisposition for pod drop among canola genotypes that was developed and tested across different sites from 2013 to 2015. This method, referred to as pod-retention resistance, consists of the use of a force gauge to quantify the force required to break the pod pedicle at the pedicle-rachis junction. Two sets of field experiments were used, the first developed and modeled the factors that influence pod-retention resistance, pod drop and seed shatter. A second set of experiments was used to validate these findings on a broader range of genotypes and determine whether a relationship between pod retention resistance and pod drop could be determined. Results showed that the pod-retention resistance was significantly greater for pods on the proximal half of the rachis compared to the distal half of the rachis. Several factors contributed strongly to variation in pod retention resistance (rachis position, genotype and site) and pod drop (site, rachis position and genotype). The relative importance of individual factors varied between pod retention resistance and pod drop suggesting no relationship between the two. However, weight-adjusted pod retention resistance, i.e., average pod retention resistance corrected for the average weight of dropped pods, was strongly correlated with pod drop, particularly in the validation experiments. This method could be used by canola breeders to select for and develop genotypes with reduced predisposition for seed losses via pod drop.