Citrus Black Spot disease investigation
It is estimated that the Citrus Black Spot (CBS) disease costs Australian growers approximately $80 million per year through export restrictions, disease management costs and fruit damage. While CBS has been present in Australia for over 100 years, it has only recently been reported in Florida.
The need to manage CBS in Australia, and reduce spread in Florida, provides an ideal opportunity for collaboration between Australia and Florida.
A collaborative research project between the University of Queensland and University of Florida has been looking at alternative management options for CBS. These include:
- examining methods to manage CBS pathogen inoculum on leaf litter or orchard floors
- gaining a better understanding of seasonal dynamics of the CBS pathogen and a related fungus that may demonstrate antagonism to the CBS pathogen
- investigating CBS-resistance in sour orange as a potential opportunity for improved breeding approaches.
Trials conducted in the 2014/15 season have provided a better understanding of the different fungal structures present in orchard leaf litter over time. Ascospores are considered the most important life cycle stage with respect to the infection process of CBS.
Spores of the fungus causing CBS are liberated from leaf litter in orchards and infect leaves and fruit, therefore treating leaf litter has the potential to reduce spore numbers. Cheap and effective methods for treating leaf litter, such as application of dolomitic lime, mulch and urea to increase the natural biodegradation of the leaf litter, are being investigated.
The susceptibility of CBS-inoculated leaves of sour orange and other citrus varieties and subsequent analysis of DNA extractions from these leaves will assist to determine the level of infection by CBS.
This project hopes to provide a better understanding of the presence of different stages of the life cycle of the CBS pathogen and how it may improve timing of management practices for this disease.
Fruit-based assays have recently been developed to investigate the possible antagonism of the CBS pathogen by a related fungus. If antagonism is demonstrated, there is potential to develop a biocontrol agent from this related fungus as a non-fungicidal means of control of CBS.
Determining the nature of CBS resistance in a selection of sour orange and other citrus varieties has the potential to allow future improvements in Australian citrus breeding programs.
Project name: Joint Florida and Australia citrus black spot research initiative
Project number: CT13021
This project has been funded by Horticulture Innovation Australia Limited using the Citrus levy with co-investment from The Citrus Research and Development Foundation c/o The University of Queensland and funds from the Australian Government.