Seed abscission and retention in Indian ricegrass

Abstract

Each spikelet of Indian ricegrass [Orysopsis hymenoides (Ram. and Schult.) Ricker] consists of a floret enclosed in a pair of glumes. As each seed matures, (1) the glumes open, (2) the lemma hairs reflex outward, and (3) the abscission layer across the rachilla fractures. This study concerned the relationship of these 3 processes to seed shattering. PI 478833 (Yellowstone Co., Mont.), had a more acute angle between the opened glumes (glume pair angle) and lower seed weight, both of which may contribute to seed retention, than ‘Paloma’ (Pueblo Co., Colo.). In Paloma and PI 478833, glume pair angle was not greater with a noret in the spikelet than without, thus the intluence of lemma hairs on opening the glumes is probably minimal. The abscission (separation) layer between the floret and rachilla of Paloma consists primarily of cells with cellulosic walls, is 1 to 2 cells thick, and lies diagonally across the rachilla. The abscission layer is distal to several layers of sclerenchyma cells with heavily lignified walls (protective layer). The abscission layer is well developed before anthesis, and it is unlikely that any genotypes lack this layer. Since lemma hairs are not related to seed retention and the abscission layer is well developed long before abscission, selection for acute glume pair angle at seed maturity may improve seed retention in Indian ricegrass, increasing harvestable seed yield.