Characterization, establishment and persistence under grazing of nitrous oxide‐induced octoploid Phalaris aquatica L.

Abstract

AbstractThe increased seed size of induced polyploid forms has been an important component of improved seedling vigour of small‐seeded pasture species. Nitrous oxide was used to produce an octoploid form of the F3 generation of a cross between the closely related tetraploid cultivars, Uneta and Australian phalaris (Phalaris aquatica L.; 2n=28). A high degree of recovery of octoploid plants (30%) was attained by nitrous oxide treatment. Increases in seed weight, glume length, stomatal guard cell length and pollen grain diameter of 13–84% were recorded in glasshouse‐grown plants of the octoploid compared with the tetraploid parent population. In a field experiment the superior establishment of the octoploid compared with the tetraploid was interpreted as evidence of the better establishment capacity of the octoploid from deep placement of the seed. However, there was a greater loss of octoploid seedlings over summer, and a greater reduction in the basal area of the sward under continuous grazing than in the tetraploid. Although the octoploid swards produced significantly less phalaris dry weight than the tetraploid in exclosures, the total herbage dry weight of the two types was not significantly different in three of four cuts taken over 2 years. This result supports the view that the more erect, sparsely tillered growth habit of the octoploid phalaris is conducive to the productivity of other sward components.