Great Brome

Bromus diandrus var. diandrus and Bromus diandrus var. rigidus

Synonyms - Bromus sterilis.
Current authors consider B. rigidus is a form of B. diandrus.

Family: Poaceae

Names:

Great Brome

Other Names:

Brome grass
Jabbers
Ripgut Brome
Ripgut grass (USA)
Sterile Brome
Spear Grass.

Summary

A tufted, annual, softly hairy grass, up to 900 mm tall, with a drooping seed head and stiff awned seed that contaminates wool.

Description

Cotyledons:

One.

First leaves:

Sometimes tinged with purple or red. Broad.

Leaves:

Leaves rolled in the shoot.
Blade - 80-400 mm long, 5-20 mm wide. Parallel veins. Hairy. Rough. Flat or loosely folded.
Ligule - Membranous, more than 2 mm long.
Auricles - None.
Collar - Prominent and a lighter colour.
Sheath - Tubular. Hairy. Often red to purple striped, especially near the base.
67 has stomatal patterns for leaves.

Stems:

100-800 mm tall. Hairy. Erect, round and hollow with solid nodes. Droop with weight of the seed.

Flower head:

Panicle. 80-250 mm long. Erect when young but opens out and hangs to one side as it matures.

Flowers:

Spikelets - 60-100 mm long including the awn. 4-10 flowered. Seed spikelets on long slender stalks that nod to one side of the stem. Initially purplish fading to pale yellow. Persistent.
Florets - Overlapping. Rigid. Rough. Prominent nerves. Awned.
Glumes - Hairless. Outer ones awnless. Inner outer glume 15-25 mm long, upper one 20-30 mm.
Palea -
Lemma - 20-30 mm long without the awn. Lanceolate. Rough to touch. 7 prominent veins.
Awn - 35-60 mm long. Rough to touch.

Stamens -
Anthers -

Fruit:

Seeds:

1-2 mm wide, 20-30 mm long with a 20-50 mm rough bristle. Seed weight is 0.01-0.015 g/seed (68).
In pure stands seed production is fairly constant over the range of 100-1000 plants/m2 (69).
Seed production is 631-3380 per plant for Bromus diandrus var. diandrus and 1156-2908 per plant for Bromus diandrus var. rigidus (70). Overseas data indicates more realistic field seed productions at 15-60 seeds/plant for Bromus diandrus growing in a cereal crop (71, 68).

Roots:

Large fibrous root system.
Bromus diandrus roots occur mainly in the top 10 cm of soil (69).

Key Characters:

72 has a key for 23 species of Bromus.
Bromus diandrus, Bromus rigidus and Bromus sterilis are considered varieties of one species by 73.

The callus scar (abscission scar and lemma callus) at the embryo end of the seed is elliptical in Bromus diandrus var. rigidus and this gives a very sharp tip to the seed. In Bromus diandrus var. diandrus it is more rounded giving the seed a somewhat smooth tip.
The seed of Bromus diandrus var. rigidus has a smooth feel if the seed is held by the awn end and pulled between the fingers. Bromus diandrus var. diandrus feels rough due to hairs on the seed. (Eventually it will feel smooth if it is repeated and the hairs are rubbed off).
When grown under the same conditions, Bromus diandrus var. rigidus seeds are smaller, shorter, smoother, and less hairy than Bromus diandrus var. diandrus.
The panicles or seed heads of Bromus diandrus var. rigidus are shorter and more rigid than the rather lax and drooping panicles of Bromus diandrus var. diandrus.

Biology

Plant weight is 0.4-0.85 g vegetative plus 0.35-1 g DW seed per plant at maturity growing in a cereal crop (68).
The basic chromosome number of 7, B. sterilis, B. tectorum and B. scoparius are diploid, B. madritensis, B. rubens and B. hordeaceus tetraploid, B. rigidus hexaploid, and B. diandrus octoploid (67).
Bromus diandrus var. diandrus is octoploid (2n=56) and Bromus diandrus var. rigidus is hexaploid (2n=42). They form polyploid complexes (74, 75, 70) .
Bromus diandrus var. diandrus is self compatible, and inbreeding with less than 1% out crossing (76).

Life cycle:

Annual grass. Germinates with autumn rains in about 2 days and produces about 1 leaf per week. It starts tillering at 4 weeks, forms the first node at 12-13 weeks and the seed head emerges a week or two later in late winter/spring.
(Freshly harvested seed takes 34-59 days to emerge in moist conditions (77))

Physiology:

Relatively drought tolerant (78).
Very sensitive to salt spray (79) and not found close to the coast and does not tolerate partial burial by sand (80).
Leaf production occurs for 14 weeks and 10-11 leaves are produced, tillering starts after the second or third leaf is formed, panicles appear in the fifteenth week, growth stops at 0 deg C when the plants are less than 6 weeks old and at 6 deg C for older plants in Spain (81).
In WA, the time from germination to panicle emergence depended on the length of the growing season where the seed was collected (82).
Vernalisation reduced the time from germination to flowering from 54 days to 17 days in Oregon (83).
It grows relatively independently of temperature according to 84 but 85 found a good temperature relationship where it took 325-340 degree days to produce 3 leaves in two field sites of differing average temperatures and rainfalls.
Bromus diandrus RGR similar to wild oats and lower than Bromus. mollis and Bromus multiflorum (86).
Grows well in partial shade (87).
Tolerant to acid rain (88).

Reproduction:

Flowering times:

September to November in Perth.
September to November mainly in South Australia.
Plants under water stress flower earlier (78).
Bromus diandrus var. diandrus flowers later than Bromus diandrus var. rigidus (70).

Seed Biology and Germination:

Non dormant seed germinates with 40 hours of wetting at 20 deg C (82) and 95% of seed of Bromus diandrus will germinate within 27 days of shedding (89).
Prefers to germinate in dark conditions. Germination is often stimulated by cultivation that buries the seed. After ripening period is 7 days at 10 deg C and increasing to 60 days at 25-30 deg C (90). Shallow burial reduces the after ripening period (91).
After ripening period is satisfied by the end of summer but not all seed germinates with the break indicating a small induced dormancy in SA (92, 93). After ripening protects Bromus diandrus from false breaks (94). Bromus diandrus var. rigidus loses dormancy faster than Bromus diandrus var. rigidus (95).
Plants grown under water stress produce more dormant seed (78).
A short awned variety of Bromus diandrus var. rigidus from Geraldton is reported to have 30% innate dormancy (70).
Bromus diandrus seed that is dormant due to environmental conditions is viable for at least 2 years (89).
Dormant seed germinates in response to gibberellic acid, removal of palea and lemma or water leaching of seed (82).
Germination levels increase with time after seed set. In WA, 12%, 30% and 50% of seed was able to germinate in December, February and April respectively (probably on B. rigidus?) (Zaicou, 1994). 77 reports no dormancy in Australian Bromus diandrus var. diandrus 3 months after harvest but some dormancy in Bromus diandrus var. rigidus which was lost with time in storage.
Temperature
Optimum germination conditions are alternating temperatures around 10/15 deg C on a 12 hour cycle (23).
Germination in at autumn temperatures of 10/20 deg C was 56-95% in light and 95-99% in dark (93).
At 10-25 0C, around 90% of seed will germinate and only 20% at 30 0C (Gill and Blacklow, 1985). Soil temperatures vary from 21-43 0C in WA paddocks in March (Zaicou, 1994). High and fluctuating temperatures were not required to break dormancy and may sightly increase the after ripening period (94).
Temperature but not day length had a big effect on germination (96).
97 has germination by temperatures over the 0-40 deg C range.
The main flush of germination usually occurs with the first two rains of the season. In field trials, 25% of the seed bank emerged on the first rain, 20% on the second and less than 5% on the third. These figures could be almost doubled by hand watering the site (Zaicou, 1994). Thus, control of seed set for two years is required under field conditions to reduce brome to uneconomic levels.
98 found little reaction to smoked water as nearly all the seed germinated regardless of treatment.
After ripening period is less under stubble than on bare soil (93).
Germination tends to be restricted to a fairly short period in autumn after the opening rains with little germination until the following autumn (93).
Burial
Depth of burial had little effect on longevity of non dormant seed, but on dormant seed longevity was least at 1 cm and greatest at 15 cm burial depths (99).
No Bromus diandrus seed germinated after 6 months burial at 5 or 15 cm and seedling establishment was greatest when buried 5 cm with 97% emergence within a month and less than 1% emergence from 15 cm. Establishment of surface sown seed occurred over an 18 month period (89).
90 days after burial at 0.5 cm, 7cm and 20 cm in dry soil, seed had a viability of 47%, <4% and 20% respectively and in moist soil was <4% for all depths. By 150 days after burial seed at all depth by moisture treatments had a viability of <2% (100).

Vegetative Propagules:

None.

Hybrids:

There is little evidence for hybrids between Bromus diandrus var. diandrus and Bromus diandrus var. rigidus (76), but polyploidy is common.
Bromus diandrus var. rigidus and B. diandrus var. rigidus had identical zymograms, providing support for their conspecific recognition (101).
A long awned biotype of Bromus diandrus var. rigidus is common for a 100 km north and south of Perth and has only been recorded outside WA at Jerilderie, NSW in 1880 and Marion Bay, SA in 1974.

Allelopathy:

Leachate from the litter of the understorey sp. Pholistoma auritum inhibited the growth of Bromus. diandrus and wild oats (Avena fatua) ()102.

Population Dynamics and Dispersal.

Seed is dispersed mainly as a contaminant of crop seed and by attachment to animals.
Great Brome (Bromus diandrus var. diandrus) tends to occur around the outsides of cropped areas and along fence lines whilst Bromus diandrus var. rigidus tends to occur within the cropped area.
Management of the seed reserves should be a priority in infested areas (103, 104).
105 have done some modelling on spread.
Over a 2 year period Bromus diandrus had 88-100% establishment and produced 15-35 seeds per plant in the field (71) which is similar to 68 30-60 seeds/plant and much lower than the 70 values of 631-3380 seeds/plant from southern Australia.
Competition
Fast growing with high relative growth rates (106).
Increasing planting rates of wheat and barley linearly increased yield and reduced brome grass seed production (107).
Similar to slightly less competitive to wild oats (108, 109, 110). 111 found a good relation between brome seedling numbers and cereal yield and 112, 113. 114 have competition models for Bromus diandrus in wheat.
Brome competition with wheat reduced wheat plant weight and tillering by more than 50% over the first 71 days of growth (115). The effects of competition occur before the grain filling stage of wheat (112).
Competition with wheat didn't reduce brome plant number but did reduce brome seed output and increase stem height (116). Increased proportions of wheat reduced brome vegetative growth under good growing conditions in replacement series experiments (117).
Bromus diandrus more competitive than annual ryegrass and less competitive than wild oats in wheat (118) and no niche differentiation between these species (119).
Bromus diandrus competition in lupins reduced yield by decreasing the pod number per plant and was more competitive at high nutritional levels (120).
There was little effect on medic or sub clover growth when the proportion of grass was less than 40% (121).
Nutrition
Application of low P rates led to Erodium botrys dominance and higher P rates increased the brome grass in clover based pastures at Merredin WA (122).
Sulphur favours brome in clover and medic pastures, has no effect in grass or cereal swards and reduces brome in lucerne (123).
Brome reduced N and P concentrations in wheat seedlings (115). Applying Nitrogen to alleviate brome competition on cereals had little effect (115).
Grazing
Bromus diandrus is replaced by Bromus hordeaceus and Vulpia myuros under heavy grazing by sheep (124).
125 and 126 have palatability data.

Origin and History:

Mediterranean.
Introduced into Australia in the mid 1800's, rapidly naturalised and became widespread weeds. It was probably introduced in ship ballasts and as contaminants of seed, fodder, wool and on livestock.

Distribution:

ACT, NSW, QLD, SA, TAS, VIC, WA.
Belgium (127), Britain (128), becoming more common on Corsica (129), Iberian peninsula (72), recently arrive in Mexico (130), New Mexico USA (131), Portugal (132), rare in NW Russia (133), rare in Saudi Arabia(134), Spain (135, 136, 126, 137), South Africa (138).
Occurs between latitudes 23 and 44 degrees south in Australia.

Distribution of Bromus diandrus.
Courtesy Australia's Virtual Herbarium.

Distribution of Bromus rigidus
Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

It occurs in areas with more than 250 mm annual rainfall, mean July temperatures of less than 15 degrees C and a growing season of more than 4 months. It is replaced by B. madritensis and B. rubens in drier areas.

Soil:

Prefers sandy soil types. Grows on acid to alkaline sands to loams.
Principal component analysis In California indicated that Bromus diandrus infestations were associated with specific soil characteristics (139).

Plant Associations:

Crops and pastures.
Viper's bugloss (Echium. vulgare) and Twiggy Mullein (Verbascum virgatum) in NZ (140).

Significance:

It is a common pasture plant on sandier soil types.

Beneficial:

Good quality fodder in the vegetative stages of growth.
It is a host for the sterile red fungus which reduces take-all in cereals.
Used as a cover crop to prevent erosion in Olive groves in Spain (141, 138).

Detrimental:

Wool contaminant.
Contaminates grain including barley (142), cereals (143)
Seeds penetrate skin (144).
Sharp bristles may penetrate skin affecting meat and hide quality and cause infection. This has resulted in significant lamb losses.
Competitive weed of crops that is difficult to control in cereals.
Host for barley yellow dwarf luteovirus (BYDV-PAV and BYDV-RPV)(145), Eyespot of wheat (Tapesia, Pseudocercosporella herpotrichoides) (146), Sclerotium rolfsii (147), Take-all disease of cereals (138).
It is a poor host for Root Lesion Nematodes (Pratylenchus neglectus or thornei) and allows some build up of numbers (Vanstone & Russ, 2001).
Host for the Russian wheat aphid (Diuraphis noxia) (148).
Seeds lodge in hawks eyes in the USA (149).

Toxicity:

Not recorded as toxic. Under rare conditions nitrate levels may rise sufficiently to be of concern if large amounts are eaten by starved stock.
Physical injury by seed penetration may cause abscess and death of lambs.

Legislation:

None.

Management and Control:

See Great Brome Management and Control:

Related plants:

Drooping Brome (Bromus tectorum) is mainly in Victoria and NSW and not recorded in WA.
Madrid Brome (Bromus madritensis) tends to occur in drier areas.
Mediterranean Brome (Bromus lanceolatus) is not naturalised in WA and occurs mainly in Victoria and SA.
Prairie grass (Bromus catharticus)
Red Brome (Bromus rubens) tends to occur in drier areas.
Sand Brome (Bromus arenarius) is a native species.
Soft Brome (Bromus hordeaceus = Bromus mollis = Bromus molliformis)
Weedy Brome (Bromus alopecuros) Occasionally found in wheatbelt areas.
Great Brome (Bromus diandrus var. rigidus) is very similar to Bromus var. rigidus. Both species commonly grow in the same areas and Bromus diandrus var. rigidus tends to be more abundant in the northern areas and on cropped land and Bromus diandrus var. diandrus more abundant in the southern areas and on roadsides and non agricultural areas in WA.
In Bromus diandrus var. rigidus the leaf blade has shorter and sparser hairs; the seed head is more erect, tighter (more compact) with shorter spikelet branches; the tip of the seed is pointy rather than rounded; the rachillae has elliptical rather than round abscission scars; the lemma calluses are elongated and >1 mm rather than circular and <=1 mm. Bromus diandrus var. rigidus has short and long awned varieties. Leaves of Bromus diandrus var. diandrus often have rust (Puccinia bromoides) whereas Bromus diandrus var. rigidus appear resistant (70).
If you hold a fresh seed by the awn and pull it between your thumb and forefinger then Bromus diandrus var. rigidus usually feels smooth and Bromus diandrus var. diandrus feels rough.

Plants of similar appearance:

Annual ryegrass, Barley grass, Brome grass, Darnel, Fountain grass, Guildford grass, Quaking grass, Sand fescue, Silver grass, Volunteer cereals, Wild oats, Toad rush, Winter grass.

References:

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P136.

Burbidge and Gray (1970). P30. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P68-69. Photo.

Ciba Geigy 2 P35.

Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). P12. Photos.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #200.3.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P945.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P21. Photos. Diagram.

Acknowledgments:

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