Review bacterial blackleg disease and R&D gaps with a focus on the potato industry
Soft rot bacterial species Dickeya and Pectobacterium are listed globally in the top 10 of important bacterial plant pathogens based on their economic impact. They are comprised of a genetically diverse group of plant pathogens affecting a wide range of plant species.
Postharvest losses are greatest in poorer countries that lack refrigerated cool chain practices. In Australia, crop losses from potato blackleg disease are generally considered to be low. However, there are cases of greater losses occurring when wet and windy weather conditions prevail, or of soft rots following planting seed tubers into warmer soils.
Across other horticultural commodities, there are crops that are affected by certain of these same potato pathogens, while others have their own species or subspecies affecting them. The diverse genetics of these bacterial species or subspecies causing blackleg and soft rot disease makes it harder to easily distinguish important ones.
There are several documented cases overseas of biosecurity breaches that suggest there are significant threats for Australian horticulture amongst this group of bacteria. Accurately estimating biosecurity risks and implementing appropriate mitigation or management strategies for these bacteria will require two simultaneous undertakings: a formal study to update our knowledge of which bacteria are currently present in Australia; and access to accurate diagnostic tests which include the capability to distinguish important subspecies of these bacterial pathogens.
There will be a need for sufficient validation of these tests to estimate their reliability, sensitivity and selectively. In particular, there will be a need to ensure no interference from related environmental species in test results.
Output data from these studies will inform authorities of any need to review potato seed production guidelines and any considerations for national and regional quarantine and biosecurity.
There may be economic implications flowing from any survey results and reporting of bacterial taxa not previously recorded in Australia. In particular, export and interstate trade in seed potatoes may be adversely affected. Similarly, introduction of testing for imported products such as ornamental bulbs and tubers will increase costs to the cut-flower and nursery industries.
These considerations need to be weighed carefully against the potential benefits that comes with a greater understanding of the causes of blackleg and soft rots in Australia, and the preparedness to deal with any future incursions.