CEREAL RUST CORNER with Bob McIntosh

The effects of stem rust on stems and grain from a crop of Coorong triticale (right) grown at North Star, NSW, in 1982. Some off-type resistant plants (left) occured in the crop.

TRITICALE AND RUSTS

Triticale, a man-made or synthetic cereal, is a wheat-rye hybrid. The most common commercial type used in Australia has mainly the chromosomes (and genes) of durum wheat combined with those of rye. Triticale has dual roles for grazing/grain or grain only.

Triticale generally has better disease resistance than its wheat parent. The rye component of the genetic make-up gives resistance to wheat diseases. However, there are lines of triticale that are susceptible to one or more of the three wheat rusts, and breeders must be careful to avoid the release of such material.

During the early 1980s a number of short, early triticales (for example, Coorong and Satu) became susceptible to a new stem rust pathotype that evolved in southern Australia and then moved northwards. As a result of heavy losses, triticale virtually disappeared from northern NSW and Queensland. The replacement resistant varieties such as Tahara, Muir, Bejon and Abacus are too late for northern areas, and now triticale tends to be a crop for the southern zone, especially areas plagued by acid soils.

The early maturing triticales has only six pairs of rye chromosomes, one pair being replaced by an additional pair from bread wheat. It turns out that the most effective genes for stem rust resistance are located in the missing rye chromosome. That missing chromosome also carries a gene for day-length sensitivity that delays flowering.

In some countries (for example, New Zealand) certain triticales may be affected by stripe rust. The pathotype involved has not increased in Australia, but its evolution by mutation in existing pathotypes must be carefully monitored by the National Cereal Rust Control Program.

Region North