Post-release research on the additional rust strains

Following the release of the additional strains, the impact of the rust was measured on blackberry using fungicide exclusion techniques in the field and on standardised potted plants in a shadehouse.

Although limited amount of disease developed in field experiments due to recent drought conditions, plants sprayed with water produced significantly less fruits than fungicide-sprayed plants at some of the sites.

Similarly, in one of the shadehouse experiments above and below-ground biomass was significantly reduced in plants sprayed with water only.

It is not possible to distinguish between strains of the blackberry leaf-rust fungus using morphological characters. Consequently reliable and robust molecular markers were developed to monitor establishment and persistence of the additional strains after release at four representative sites in New South Wales (NSW) and Victoria.

Alleles specific to the additional strains were found in 12.7 per cent to 100 per cent of rust samples collected at these sites one year after release. After two years, analyses indicated that rust populations sampled from two sites in NSW retained 44 and 86 per cent ancestry to the new strains.

This confirms that genes of the additional strains were successfully incorporated into the local existing rust populations, a first step towards increasing the adaptation potential of the rust fungus to improve biological control effectiveness.

Symptoms of the rust fungus, Phragmidium violaceum, on the upper surface of blackberry leaves in the field.

Symptoms of the leaf-rust fungus on the under side of blackberry leaves.