Determination of Seed Size, Seed Set, and Yield Parameters

Inflorescences were covered with microperforated plastic bags to collect seeds. To determine single seed mass, aliquots were weighed and seed number per aliquot was counted. Seed area was determined using ImageJ (https://imagej.nih.gov/ij/) using the particle analysis function with a consistently applied threshold on all microscope images of seeds taken with identical magnification and exposure time within experiments (Herridge et al., 2011). For seed size distributions, the percentage of seeds within bins at 0.002-mm² intervals was determined and a running average over six bins was plotted. For controlled pollination, preanthesis flowers (Smyth et al., 1990; stage 12) were emasculated using forceps. One day after emasculation, the pollen from the donor genotype was applied to the stigma of the recipient genotype. Seed development and seed set were determined by dissecting developing siliques and dehisced siliques, respectively (Groszmann et al., 2008; Kay et al., 2013). For the grafting experiment, the bolt harvest index was determined as the seed mass as a proportion of total bolt biomass (seed mass/total bolt dry mass including seed).