DNA technology to aid in the early detection of wheat disease

A new, highly accurate molecular test has been developed to help in surveillance of Karnal bunt, a disease which could damage a significant proportion of Australia’s wheat crop.

NSW Department of Primary Industries (DPI) scientists say weather conditions in both NSW and WA are suitable for the infection of susceptible wheat crops by the fungus Tilletia indica, which makes wheat smell like rotting fish. Wheat products from affected samples are unpalatable.

DPI plant pathologist Gordon Murray says that while Australia has a status of being free of the disease, it is essential to have highly sensitive detection tools.

“Preventing an incursion is a high priority in Australia.

“If susceptible wheat crops were infected by T. indica, Karnal bunt could develop at many locations throughout NSW, Vic., SA and WA.

“One study estimated that if an incursion occurred, between 8% and 24% of wheat production in WA alone could be affected by the pathogen, depending on the rate of spread and the amount of resources allocated to detection.

“Successful containment and eradication requires early detection”, he said.

DPI molecular biologist Dr Mui-Keng Tan has developed a new two-stage method of detection which will allow direct and immediate diagnosis of Karnal bunt from as few as ten fungal spores.

Existing protocols require the spores to germinate, and then be visually identified. This results in a delay of two weeks before T. indica can be accurately identified.

In 2004, Pakistan claimed Karnal bunt was present in Australian wheat.

At the time more than 50 ships of Australian wheat, worth more than $400 million, were en-route to markets.

Dr Tan said conventional taxonomy was labour-intensive and required spores to be identified on the basis of colour, size and appearance. About 50 spores of a species were required for a statistically-valid result.

The new protocol involves amplifying the segment of DNA common to all Tilletia species. Fluorescent probes are then used to identify and distinguish the tiny fragment of DNA that separates T. indica and its closest relative, T. walkeri. (T. indica differs from T.walkeri by just 2 out of the 612 shared nucleotides).

Plant Health Australia helped fund this proof-of-concept work.

Further research to improve the efficiency and reliability of the diagnostic protocol is being funded by the Grains Research and Development Corporation through the Cooperative Research Centre for National Plant Biosecurity.

The development of an internationally accepted protocol involves scientists from DPI and Department of Agriculture and Food Western Australia (DAFWA).

Scientists from DPI and DAFWA will seek to validate the protocol at laboratories around Australia and then at recognised international laboratories in the European Union, United States and China.

Details of the new protocol were published in Mycological Research, 110 (2006) 203-210.