An average of 250,000 hectares of oats is grown in Queensland annually extending from the Central Highlands to the New South Wales border Oats in this region is used primarily for grazing in the beef, dairy and sheep industries with less than 10% being harvested for grain, primarily to provide seed for sowing. The crop is grown during winter to provide quality fodder when native pastures are unproductive.
Rusts are a major constraint and the main thrust of oat improvement is rust resistance. Historically, Queensland has relied heavily on North American germplasm for its oat improvement and continues to do so. It has been extremely difficult to attract the level of funding necessary to address the rust problem domestically in what is essentially a grazing crop. All recent releases have come from breeding programs in either Texas, the northern prairie states or Canada. While most of these were released as rust resistant, from fourteen varieties commercialised since 1990 only three are currently leaf rust resistant and none resistant to stem rust.
Varieties currently resistant to leaf rust are Moola (AC Medallion), Graza 68 (AC Assiniboia) both released for sowing in 1998 and both protected by Pc68, and Barcoo (88Quaker 129), released for sowing in 1996. The leaf rust resistance of Barcoo has not been determined. Pc91 is effective in the region but has not been exposed on a commercial scale. Lines possessing this resistance are being increased for release in the near future.
Oats from Canada and northern USA are particularly well suited to grazing in this region. They generally produce vigorous early growth which maximises dry matter production from limited soil moisture. In addition, their requirement for a lengthy cumulative photoperiod for head initiation, ensures they remain suitable for grazing into late spring after which time summer growing pastures or forage crops are usually ready to graze. The majority of current commercial varieties and pending releases are from these sources.
Until quite recently oat improvement in Queensland has been given scant attention. Since 1988, a Departmental introduction and selection program has released five varieties but leaf rust resistance has been ephemeral. In recognition of the challenges posed by the rusts, Queensland Department of Primary Industries appointed its first oat breeder in 1996 to develop improved forage oat varieties with durable rust resistance. Mr Greg Platz was appointed to the position and has since been replaced by Dr Leonard Song.
Pyramiding of rust resistance genes has proven very successful for the wheat industry in this region and a similar approach was initiated for oats. Molecular marker technology is being adapted to facilitate selection. Unfortunately, breeding for rust resistance in oats is hampered by the dearth of effective resistance genes; the continual release of varieties carrying these genes as the sole source of resistance and the ubiquitous nature of the alternative host - wild oats (Avena fatua, A. ludoviciana). Wild oats can be found growing at any time of the year in this environment. Rust surveys have identified pathotypes with virulence on genes to which the population has not been exposed in A. sativa. The alternate host (Ramnus spp) does not occur.
Dr R G Rees, previously a pathologist at this Institute, initiated a breeding program to pyramid resistance genes, and progeny from these crosses are currently being evaluated for forage production. Most emphasis has been placed on Pc68, Pc91, Pc50 and a gene designated PcCul from the variety Culgoa (82 Quaker 225). Initially substantial emphasis was placed on the Pc38, Pc39 base but virulence on this combination was detected in 1995 and many promising lines were discarded. Virulence has since been detected on PcCul and an unidentified gene in the variety Cleanleaf (84 IORN 148) which proved useful for several years. Pathotypes virulent on Cleanleaf now dominate the leaf rust population.
Personal communication with Mr S Meldrum of the Plant Breeding Institute, Cobbitty suggests the most useful genes for a pyramiding program in Australia are likely to be Pc50, Pc56, Pc63, Pc64, Pc68, Pc91, PcWix and PcBet. Pc Wix is derived from a Wisconsin line and PcBet is in the South Australian variety Bettong (84 Quaker 187). Although several of these genes do not afford a high level of resistance on their own, in combination with the more effective sources, durable resistance may be achievable.
In seeking additional sources of resistance, Mr Platz visited the winter nurseries in New Zealand and made almost 200 selections from the nurseries at Palmerston North. The majority of these were from Dr Stuthman's recurrent selection program in the hope that a number of useful minor genes have been combined. Lines from the Canadian programs appeared superior agronomically. This material is currently in quarantine in Australia.
In the Queensland environment oats may be grazed several times in one season. Forage evaluation of promising lines follows two regimes:- 1) High input environments where plots are cut up to six times in a season to evaluate maximum potential forage production and 2) Limited inputs at several sites to assess performance under conditions similar to commercial application. Seldom are more than three harvests possible in this situation. Plots are harvested with a Carter Plot Forage Harvester with particular attention being given to the timing and height of the first cut. Initial harvests are done shortly after Zadoks growth stage 31 at a height slightly above the growing point on the main stem. This is usually between 12 and 20cm and ensures that subsequent regrowth will not be unduly affected. Timing of the first harvest is critical with lines that produce quick early growth.
To date no selection for forage quality has been practised. Lines are promoted on rust resistance, forage yield and appearance. Access to NIR equipment has been negotiated and once calibration is effected more emphasis will be placed on this trait.
It is a popular belief in Australia that Queensland is unsuitable for oat grain production and most of the 30,000+ tonne used annually is imported from southern and western states. Freight costs are substantial and growers are receptive to new cropping opportunities. Interstate varieties can yield well in Queensland yet lack adequate rust resistance. During screening of introduced material for forage, it became apparent that many lines had potential for grain production in this environment.
A project conducted by Mr D Hibberd under the supervision of Dr Rees identified a number of lines that performed well under Queensland conditions. Several introduced oat lines out-yielded the Australian reference varieties (in the absence of rust) and despite a sequence of drought years out-yielded both wheat and barley reference varieties. Most of these lines were drawn from Quaker Nurseries 1987- 90. The late maturing lines from northern USA and Canada yielded poorly.
Invariably the best performers were early maturing, short with strong straw and rust resistant. This is in direct contrast with most forage varieties which are late maturing and tall. The project demonstrated that lines suitable for oat grain production in Queensland were available; however, during the final year of the project, a race of stem rust with virulence on Pg-a annihilated one trial site and effectively negated commercial application of the results. All of the highest yielding lines were protected by Pg-a and consequently no variety is currently resistant to stem rust in Queensland.
Australian Oat Workers Meeting
Toowoomba hosted the annual Australian Oat Workers Meeting in September, 1997. Although the region was experiencing its fifth consecutive year of below average winter rainfall, a tour of southern Queensland clearly demonstrated to interstate visitors why varieties grown in the region are different from those in the rest of Australia and highlighted the diversity of uses for the crop. Resistance to rusts was central to discussions. We were fortunate to have Dr Bryan Rossnagel address the meeting and bring us up to date on happenings in North America.
Oats in Queensland is an important crop and durable rust resistance is essential for reliability of production. Collaboration between all players in Queensland is necessary to achieve this goal. It is vital that strong links be fostered and maintained with North American programs, in particular. The scarcity of effective resistances to both leaf and stem rusts here, and in fact, worldwide demands concerted international effort to discover or create new resistances that will enable breeders to achieve the quantum leap necessary to combat oat rusts.
Figure legend. Plots being harvested. Care is taken to limit damage to growing points at initial cut.