Anatomy of Seed Dispersal Mechanisms in High and Low Seed Shattering Cultivars of Orchardgrass

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Abstract
In orchardgrass (Dactylis glomerata L.), seed shattering is a common feature that can be a serious economic problem. To obtain information for breeding improvement programs in seed retention, the mechanism that leads to seed shattering in orchardgrass was histologically determined in two cultivars, Hallmark and Marta, chosen for their different shattering levels. Two abscission layers were identified in both cultivars at the first stage of floral development. A primary abscission layer was located in the rachilla supporting the fertile floret; a secondary layer extended across the pedicel near thebase of the glumes. In Hallmark, seed shattering may occur from the soft dough stage onward because of the disintegration of the cells in the primary layer. In this cultivar the secondary layer remains intact. In Marta, the disintegration of cells in the primary layer gradually occurs over a longer period and seed shattering begins about 30 d after Hallmark and lasts until autumn. In both cultivars the deterioration process observed in the primary layer was probably the consequence of the action of one or more hydrolytic enzymes. During autumn, spikelet dispersion in Martalso occurs because of breakage of the secondary layer. The rupture of this layer was assumed to be mechanical because there was no evidence of cell disintegration.

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