Variability within Clones of Potato cv. Russet Burbank to Infection and Severity of Common Scab Disease of Potato

Signi®cant variability in the level of resistance to common scab disease (to both disease incidence ± tuber surface area a€ected, and severity ± lesion depth) within potato (Solanum tuberosum) cv. Russet Burbank clonal lines and other selected processing cultivars was shown. Across two trials, cvs. Russet Nugget and Shepody and Russet Burbank clone British Columbia were consis- tently grouped within the cluster of least disease incidence whereas cv. Russet Norkotah and Vancouver unit four were grouped within the cluster showing greatest disease incidence. Russet Nugget and British Columbia were also consistently grouped within the cluster showing least disease severity, whereas Shepody and Russet Burbank clone Starks were grouped within the cluster with greatest severity scores. For some clones, consistency of rating across trials was not always apparent. Of note for the Tasmanian industry, there were di€erences within the ®ve commercial Vancouver clonal units used interchangeably, with unit 4 showing signi®cantly greater disease severity and incidence than some of the other units. However the extent of increased disease never exceeded 1.75 times the best of the other Vancouver units and the relevance of these results to the relative ®eld performance of unit 4 remains to be tested.