Relationship of resistance to common scab disease and tolerance to thaxtomin A toxicity within potato cultivars

Thaxtomin A has a central and implicit role in common scab disease expression in potato. Thaxtomin A tolerance has been suggested as a possible rapid means for screening potato germplasm for disease resistance, during breeding selections. We have tested a range of genetically diverse cultivars with varying resistances to common scab disease in both pot and field based studies and measured their mean necrosis response to thaxtomin A. We found no association between resistance to common scab disease and tolerance to thaxtomin A toxicity. For example, disease resistant cultivars ‘Russet Burbank’ and ‘Atlantic’ were sensitive and tolerant to thaxtomin A toxicity respectively. Similarly; disease susceptible cultivars ‘Bismark’ and ‘Tasman’ showed susceptibility and tolerance to thaxtomin A. This demonstrates that whilst thaxtomin A is critical to disease expression, reaction to this toxin is only one component influencing resistance to common scab disease and many other anatomical, physiological or biochemical factors are critical to defence against this disease.