Increased resistance to pod shatter is associated with changes in the vascular structure in pods of a resynthesized Brassica napus line

The architecture of the pod wall and dehiscence zone (DZ) was studied in populations of a resynthesized, shatter-resistant, oilseed rape line, DK142, and the commercial cultivar Apex. The dimensions of the pod wall and its component tissues were significantly larger in DK142. However, the variation in the pod architecture of Apex, DK142 and F-2 populations derive from crosses of DK142 and Apex was found to have little or no role in pod shatter. By contrast, variation in the dimensions of the DZ characters correlated strongly and positively with shatter resistance. The size of the main vascular bundle (MVBV) of DK142 as it exited the valve and joined the vascular tissue of the replum was, on average, 60% larger than in Apex, the DZ was 40% wider and there was a high preponderance of vascular tissue other than the MVBV. The variation in the size of the MVBV accounted for much of the variation in shatter resistance of all populations, including shatter-susceptible Apex. The DZ width was also found to be important in explaining the limited range of shatter values in Apex, but in populations of DK142 and F-2, where the amount of vascular intrusion into the DZ was much greater, the variation in DZ width was not important. The importance of the vascular tissue to shatter resistance was further highlighted by a novel microfracture test (MIFT). By contrast, no significant difference between DK142 and Apex in the ease of separation of the thin-walled DZ cells was detected using the MFT.