Bacterial assault on crown rot by Yang Huang

CROWN ROT caused by Fusarium graminearum Group 1 limits grain yields in many Australian cereal production areas and thus costs the Australian cereal, industry $64 million each year.

Now the development of a soilborne bacterial inoculant as seed coatings to control this intractable disease is being tested at field sites in Queensland and northern NSW at Warwick, Narrabri, Moree and Tamworth.

The pathogen infects the plant via the coleoptile, subcrown internode and crown and then extensively colonises the crown and stem, The disease is characterised by brown discolouration of the lower stem and necros is of the crown, It results in whitehead formation under water-stress conditions during grain fill. There is still a lack of an effective method to control crown rot.

Disease severity was significantly decreased by the treatment. The average yield increased by 3.5- 11 percent in wheat and 35- 50 percent in barley during the past three years of lield trials, However, caution is preceding commercial development because the promising results were variable from place to place and from cultivar to cultivar.

The differences in effectiveness of the treatments may be related to different soil and environmental conditions and cultivars, Further investigation aims to understand the reasons for differences in order to improve the protective ability by the bacterium.

Activating resistance?

A related approach was to use acibenzolar-S-methyl (BTH), manufactured by Syngenta as a foliar spray to protect wheat from crown rot Foliar application alone or after bacterial seed coating resulted in yield increases up to 10 percent with dec reased disease severity in wheat. It is not certain how foliar application of BTH protected the stems of wheat from infection by the pathogen, BTH has no apparent direct antimicrobial action against Fusarium sp. It protects wheat and several other plant species through activation of systemic resistance.

Our preliminary analysis revealed that the activity of an enzyme B1 ,3-g lucanase increased in the leaves and stems in wheat after foliar application of BTH, This enzyme has been widely reported in systemic-acquired resistance against plant disease in many plant species, Glasshouse tests also show that the protection by BTH was greatly affected by soil wetness.

More research is needed be fore the promise of the approaches can be converted into procedures for cereal growers.

Program 3 Contact: Dr Yong Huang 02 602 5595 email y.huang@agec.usyd.edu.au

Region North