Seventeen populations of Bromus spp. were sampled from across southern Australia and accessions in the state herbaria of Western and South Australia were examined. Rigid brome (B. rigudus) differed from great brome (B. diandrus) in having shorter, sparser hairs on leaf laminae, more compact and erect panicles with shorter spikelet branches. In rigid brome, the abscission scars on the rachillae were elliptical and the lemma calluses were elongated (> 1 mm), while in great brome, these characters were circular and short (5 1 mm). Rigid brome was further differentiated into a long and short-awned biotype. Rigid brome was hexaploid, 2n = 42, and great brome an octoploid, 2n = 56. Rigid brome is widely distributed across southern Australia, often growing unrecognized in association with great brome. Rigid brome matured earlier than great brome, and there was high genetic variation (26-34% of total variation) in the time of maturity of both species. Seed production in rigid brome and great brome ranged from 1156 to 2908 and 661 to 3380 seeds per plant respectively. A short-awned ecotype of rigid brome from Geraldton, W.A., had 30% residual innate dormancy. This, together with the earlier maturity of ecotypes of rigid brome, may make it more difficult to control than a great brome when both species coexist in the field. Leaves of great brome were susceptible to rust (Puccinia bromoides Guyot), but associated ecotypes of rigid brome were rust free.

The genetic systems of Brornus diandrus Roth (great brome) and B. rigidus Roth (rigid brome) were studied in 30 populations sampled from Western Australia. Populations of B. diandrus were polymorphic and the dominant phenotype had scabrid lemmas and glabrous paleas. Polymorphs of B. rigidus had short and long awns with flat seeds and long awns with round seeds: all these phenotypes had scabrid lemmas and hairy paleas. Frequencies of the polymorphs varied between sites and years. Palea hairiness of B. diandrus is controlled by a single, dominant gene and was used as a marker gene for estimations of outcrossing frequencies and population homozygosis. B. diandrus is self-compatible and inbreeding with outcrossing frequencies less than 1%. Florets of both species were facultatively cleistogamous; there were high levels of chasmogamy in irrigated populations but most anthers had dehisced prior to exsertion. The high proportion of seed set in cleistogamous florets and similar floral biology suggested that the breeding system of B. rigidus was similar to that of B. diandrus. There was no evidence of species hybrids in the field and attempts at hybridisation failed. Populations of these species were homozygotic for a few major genotypes. Meiotic chromosomes of both species and all biotypes formed mainly bivalents and a few quadrivalents at metaphase I. This, together with the high proportion (Ͱ5 98%) of fertile pollen grains and the 3 : 1 segregation of hairy: glabrous paleas in selfed F2 progenies, indicated that inheritance in these species was disomic. The genomic formula proposed for B. diandrus is either AABBCCDD or AAAABBCC. The properties of polymorphism, autogamy and disomic inheritance within polyploidy would favour the development of tolerance to herbicides within populations, provided selected genotypes were competitive.

Seeds of Italian ryegrass perennial ryegrass wild oat winter wild oat phalaris and barnyard grass collected during the 2005/06 season were tested for dormancy and germination phenology between April and December 2006 In laboratory and outdoor environments dormancy was widespread in grass weed but not in ryegrass seeds The seeds of grass weeds had better germination in the outdoor environment than the laboratory In the outdoor environment only 15 of wild oat and winter wild oat 1963 of phalaris and 39 of barnyard grass seed germinated Protracted germination varied between species in two to seven flushes The earliest timing for effective postemergence grass control under the experimental conditions appeared to be about 6 weeks after sowing for wild oats and ryegrasses 12 weeks for phalaris and 14 weeks for barnyard grass The extended germination periods of phalaris and barnyard grass are a challenge to growers in designing a costeffective herbicide programme