High seed retention of Indian ricegrass PI 478833

Abstract

Reduction of Indian ricegrass [Oryzopsis hymenoides (Roem. and Schult.) Ricker] seed shattering losses is of interest because it would result in more economical seed harvest. PI 478833, a genotype with glumes closely surrounding the seed, was compared with 'Paloma' for glume pair angle and seed retention parameters. Our objective was to determine its suitability as a source of seed shattering resistance for genetic transfer to an Indian ricegrass variety. Regrowth from a 19 June 1989 clipping of 'Paloma' and PI 478833 with and without supplemental irrigation was evaluated in late July. Irrigation did not affect glume pair angle or percentage intact seed (number of seeds/number of mature florets). Though Paloma and PI 478833 glume pair angles averaged 66% and 44%, respectively, percentage intact seed was 13% higher for Paloma than PI 478833 because Paloma's more indeterminate flowering pattern allowed it to replace its shattered florets more quickly than PI 478833. In a second experiment we observed individual florets of Paloma and PI 478833 for 7 weeks starting 5 September 1989. Floret opening occurred mostly during daylight hours and on warm days. Shattering events occurred when a storm followed a period of floret opening. Duration of seed retention from glume opening to shattering averaged 91% longer for PI 478833 than Paloma. After 7 weeks 83 and 35% of Paloma and PI 478833 florets had shattered, respectively. In a third experiment seed retention index (seed yield/forage dry weight) on 15 September 1989 was 0.45, 0.19, and 0.11 for PI 478833, 'Nezpar', and Paloma, respectively. PI 478833's acute glume pair angle and resultant increased seed retention make it a valuable source of shattering resistance for introduction into bred Indian ricegrass varieties.