SEEDBED INSPECTIONS UNDERESTIMATE THE OVERALL INCIDENCE OF RATOON STUNTING DISEASE

IN AUSTRALIA, ONLY prospective seedbeds are routinely screened for ratoon stunting disease (RSD). As seedbeds may reasonably be considered to be the healthiest cane available to a grower, it may be expected that there would be a higher incidence of RSD in commercial fields. The novel RSD diagnostic, LSB-PCR, was used to screen 154 grower seedbeds during the 2015 seedbed inspections, in addition to 24 fields that were nominated for plough-out, and 15 fields that were being assessed as part of harvest best-practice trials. While the disease was detected in 10 (6.5%) grower seedbeds, it was found in 6 (25%) plough-out fields and 5 (33%) harvest best-practice trial fields. The overall 28.2% RSD incidence in the 39 commercial fields screened is statistically significantly higher than the incidence observed in 154 seedbed inspections (p=0.0001). This paper discusses the role of possible sampling bias, sampling strategy and diagnostic technique employed in determining the incidence and impact of RSD in the Australian sugar industry, in addition to improvements in RSD management at Harwood.