Origin
Rosabrook is derived from a single backcross of the variety Denmark with an F1 hybrid of Denmark and an accession from Italy with seedling resistance to RLEM.
Breeding and selection was conducted by Dr Phil Nichols of DPIRD. Its release follows extensive field testing in six trials throughout high rainfall regions of southern Australia as part of the National Annual Pasture Legume Improvement Program. Trials were conducted without use of insecticides to allow the improved RLEM resistance of Rosabrook to be expressed.
Rosabrook is named after the locality of Rosa Brook in south-western Western Australia.
Varietal characters
Rosabrook flowers about 142 days after an early May sowing in Perth, the same time as Denmark, a few days later than Mt Barker and Karridale, and a few days earlier than Leura (Table 1).
Fresh leaves of Rosabrook contain low levels (around 0.15% of dry matter) of the oestrogenic compound, formononetin (Table 1). This indicates a very low potential to cause ewe infertility or difficult lambing.
Laboratory measurements indicate that Rosabrook is more hardseeded than Denmark, Leura, Karridale and Mt Barker and has a similar level of hardseededness to Goulburn and Coolamon (Table 1). This makes Rosabrook well suited to permanent and semi-permanent pastures with occasional cropping. It is not suited to 1:1 crop/pasture rotations.
There is no information at present on relative tolerance of Rosabrook to herbicides commonly used on subterranean clover pastures.
| Variety | Days to first flowering | In areas where variety is suited | Hardseededness* | Formononetin | |
|---|---|---|---|---|---|
|
| (Perth sown early May) | Flowering begins | Seed formation | 0 = all soft 10 = all hard | (% of dry matter) |
| Rosabrook | 142 | Early Oct | Late Nov | 3 | 0.15 |
| Denmark | 142 | Early Oct | Late Nov | 1 | 0.00 |
| Coolamon | 133 | Late Sept | Mid-late Nov | 3 | 0.00 |
| Goulburn | 141 | Late Sept | Mid-late Nov | 3 | 0.00 |
| Leura | 147 | Early-mid Oct | Early Dec | 1 | 0.00 |
| Karridale | 139 | Late Sept | Late Nov | 1 | 0.25 |
| Mt Barker | 137 | Late Sept | Late Nov | 0.5 | 0.00 |
*Based on proportion of hard seeds remaining at the break of season
Disease and pest resistance
Emerging seedlings of Rosabrook suffer less damage from RLEM than other late flowering subterranean clovers (Table 2). This is most evident at low to moderate RLEM densities, but this advantage is less at high RLEM densities. Work by CSIRO has demonstrated that RLEM feed less and produce less progeny on subterranean clovers with cotyledon resistance. There is no information to date on RLEM damage ratings of Rosabrook in winter and spring, nor on its levels of susceptibility to lucerne flea and blue green aphids. Insecticides should be used at sowing to maximise seedling establishment of Rosabrook and whenever RLEM, lucerne flea or aphid densities are high.
Rosabrook is resistant to Race 1, the most widespread race, of clover scorch disease (Kabatiella caulivora), and Race 2, which is prevalent on the Esperance sandplain. Rosabrook has resistance to races 173 and 177 of root rot caused by Phytophthora clandestina, two widespread and virulent races across southern Australia (Table 2).
Rosabrook has not been screened for resistance to other diseases, but there have been no reports of susceptibility to leaf rust (Uromyces trifolii-repentis), cercospora leaf spot (Cercospora zebrina), or powdery mildew (Oidium sp.).
| Variety | RLEM | Clover scorch | Phytophthora root rot | ||
|---|---|---|---|---|---|
|
| cotyledon | Race 1 | Race 2 | Race 177 | Race 173 |
| Rosabrook | 3 | 2 | 4 | 1 | 2 |
| Denmark | 7 | 1 | 3 | 2 | 2 |
| Coolamon | 7 | 0 | 2 | 2 | 4 |
| Goulburn | 7 | 3 | 2 | 1 | 6 |
| Leura | 7 | 4 | 6 | 3 | 9 |
| Karridale | 7 | 3 | 3 | 3 | 9 |
| Mt Barker | 7 | 7 | 7 | 4 | 8 |
Field performance
Over all sites and seasons, regenerating seedling densities of Rosabrook were 28% greater than Denmark and 49% more than Mt Barker (Figure 1). These higher seedling densities translated into 23% greater winter herbage production than Denmark and 32% more than Mt Barker (Figure 1). The increased RLEM seedling resistance of Rosabrook is likely to be at least partly responsible for its excellent early season performance, which occurs at the time of greatest feed shortage. Spring herbage production was 5% more than Denmark and 9% more than Mt Barker (Figure 1). Rosabrook is an excellent seed producer and maintained seed bank densities 28% greater than Denmark and 51% more than Mt Barker (Figure 1).
Use of Rosabrook
Rosabrook is a replacement for Denmark with greater RLEM resistance and improved early season herbage production. It is suited for use on well-drained, moderately acid (pHCa 4.5 – 6.5) soils in areas of Western Australia with more than 650 mm mean annual rainfall, corresponding to a growing season length that extends to late November. It is suited to permanent and semi-permanent pastures with occasional cropping. It is not suited to 1:1 crop/pasture rotations.
Rosabrook can be mixed with Narrikup or Coolamon in the drier part of its target zone. Napier, Rouse or Yanco can be added to the mixture for paddocks with patches subject to waterlogging.
Rosabrook should be inoculated with Group C rhizobial inoculant prior to sowing.
Seed availability and PBR status
Seed of Rosabrook can be purchased through Seed Force agencies.
Rosabrook is protected under the Plant Breeders Rights Act 1994. Under the Act sale of Rosabrook seed can only be carried out by agreement with the licensee, Seed Force Pty Ltd. However, this does not restrict sale of produce, such as hay or silage, provided seed was legally purchased.
For seed sales information visit seedforce.com.au
