By Professor Robert F Park and Dr Colin R Wellings, University of Sydney Plant Breeding Institute, Cobbitty
The Cereal Rust column in the last issue of Ground Cover discussed the concept of pathotypes in cereal rust pathogens. Pathotypes (also referred to as races or strains) are variants within rust pathogens that differ in their abilities to overcome resistance genes in cereal cultivars.
In Australia, new pathotypes of the three wheat rust pathogens arise mainly by random mutation, or less commonly by introduction from overseas. Over the past 10 years, annual Australia-wide surveys of the three wheat rust pathogens have detected 39 new pathotypes, of which 38 are regarded as mutants, and one an exotic introduction.
Importantly, only nine of these pathotypes were of potential danger to wheat cultivars being grown at the time they were detected. Warning the agricultural community of the occurrence of new pathotypes with the ability to attack previously resistant cultivars is an important function of the annual rust surveys.
Providing a simple name for a new pathotype that conveys something of its features is important in getting a clear message across to the wider community. For example, in 1968, influenza type A strain H3N2 killed about 40,000 people. The virus was commonly referred to as the "Hong Kong flu".
Similarly, important rust pathotypes are given both technical and colloquial designations:
Australia and reached epidemic levels that led to significant yield losses and widespread fungicidal spraying. This pathotype was commonly referred to as the "WA pathotype".
These common names for pathotypes also bring certain problems. Wheat breeders are very passionate about their work, and having a rust pathotype named after one of your cultivars could well be viewed as a dubious honour.
Similarly, naming pathotypes after regions may also seem a dubious honour. However, these names convey important messages that are more easily understood by the wider community than from a series of pathotype numbers.
A case in point is the "WA pathotype" of stripe rust. This name is still relevant for several reasons. It remains the only stripe rust pathotype present in WA.
Although it is now present in eastern Australia, the name reinforces that it is pathogenically very different to the pathotypes that have prevailed in eastern Australia over the past 25 years.
The name further reminds us of the ability of rust pathogens to migrate between the western and eastern cereal growing regions.
The announcement of a new rust pathotype can cause a level of fear among the agricultural community. The appearance of several new pathotypes capable of overcoming the resistance of many wheat cultivars has been met with headlines to the effect that we are losing the battle of resistance breeding.
Whilst these new pathotypes have presented additional and unwelcome challenges to wheat breeders, there are still many sources of rust resistance available that are currently being actively incorporated into breeding programs. Ensuring this genetic resource gets into growers" paddocks is the responsibility of the industry as a whole.
Rust resistance research has to serve, and will continue to serve, the interests of winter cereal crop protection while there remains an industry willingness to commit to the task.
(Dr Wellings is on secondment from the NSW Department of Primary Industries)
GRDC Research Code: US315.
For more information: Robert Park, 02 9351 8806, email@example.com