Background/context:

Black Sigatoka disease, caused by Mycosphaerella fijiensis, is a significant threat to banana production worldwide. The disease is endemic to Papua New Guinea and parts of the Torres Strait, and the close proximity of these regions to Australia necessitates increased vigilance in surveying for disease entry into the country. Since 1981, there have been nine incursions of Black Sigatoka in north Queensland, and each time the disease has been eradicated by destruction of infected plants and/or banana replacement programs. Traditional diagnosis relies on the presence of fungal structures for microscopic identification. To assist identification in the absence of fungal structures, the centre developed a gel-based PCR assay. This assay played a major role in the surveillance and eradication strategy of the Tully 2001 Black Sigatoka outbreak.

 Aim:

The development of improved DNA assays based on real-time PCR formats will provide more reliable and robust assays for rapid and accurate identification of Black Sigatoka. To meet this objective, the team sought to: investigate sequence variability in Australian isolates of Mycosphaerella fijiensis and Mycosphaerella musicola, and compared this data with sequences from overseas isolates of these fungi, other Mycosphaerella spp. and other phytopathogens known to infect banana; screen the centre’s gel-based PCR test against DNA of worldwide isolates of Mycosphaerella fijiensis and Mycosphaerella musicola, as well as other phytopathogens infecting banana; and develop improved diagnostic assays for Sigatoka leaf diseases based on real-time PCR

Major Outcomes:

Sequence data from Australian and overseas isolates of Mycosphaerella as well as isolates of other banana foliar pathogens indicated that the regions selected for the diagnostic primers are highly conserved. Fluorescent, TaqMan® MGB probe assays for Black Sigatoka (Mycosphaerella fijiensis), Yellow Sigatoka (M. musicola) and Eumusae leaf spot disease (Mycosphaerella eumusae) have been developed. These assays have been fully validated against an extensive collection of worldwide isolates. The black and yellow Sigatoka assays have been delivered to the Mareeba laboratory and are in routine use for surveillance. The Eumusae leaf spot assay has been tested against a collection of 190 Mycosphaerella spp. isolates, however, it requires further “in field” validation before delivery to industry. Together, these assays offer the Australian banana industry, the very best diagnostic capacity for Sigatoka leaf spot disease available worldwide. 

The diagnostic test developed in this project was used during the 2001 Black Sigatoka eradication program in North Queensland’s major banana growing region. The net benefits afforded from the availability of this test have been calculated at around $17 million – a 16-fold return on the Centre’s investment in this project.

For more information contact:

Dr Juliane Henderson
Department of Primary Industries and Fisheries
Phone: +61 (0)7 3896 9341
Email: Juliane.Henderson@dpi.qld.gov.au