Figure 3

Viable pollen size distributions and ploidy in parental lines and cultivars of Brassica. Pollen viability was estimated using fluorescein diacetate stain and pollen diameter was measured under the microscope in μm (viable pollen only), with the expectation that pollen size would be proportional to DNA content of the pollen grain. a) B. rapa (2n = 2x = AA) pollen, expected pollen ploidy n = x = A; b) B. juncea (2n = 4x = AABB), B. napus (2n = 4x = AACC) and B. carinata (2n = 4x = BBCC) pollen, expected pollen ploidy n = 2x = AB, AC or BC respectively; c) 2n = 4x interspecific hybrid B. juncea × B. napus (AABC), B. juncea × B. carinata (BBAC) and B. napus × B. carinata (CCAB) pollen, expected ploidy for reduced pollen n = x - 3x: A-ABC, B-ABC and C-ABC respectively. The bias of the hybrid pollen size distribution to the right suggests unreduced gamete production (ploidy 4x and above) as well as a viability advantage of higher DNA contents (mean of distribution > 2x, expected ploidy distribution x - 3x).