In vitro cell selection techniques for enhancing disease resistance - case study: common scab resistance in Russet Burbank

Here we demonstrate the value of in vitro cell selection techniques for potato cultivar improvement using enhancement of common scab resistance as a case study. Common scab is an important disease of potato world-wide. A diversity of Streptomyces species are associated with disease, however all pathogenic species and strains produce the phytotoxin, thaxtomin A. This toxin is an essential pathogenicity factor and provides a convenient positive selection agent for in vitro cell selection to obtain disease resistant potato variants. Using such techniques we obtained many variants of Russet Burbank with enhanced resistance to common scab, interestingly some of which did not express toxin tolerance. Agronomic assessments showed many variants had impaired yield, however several variants had equivalent or even superior yield to the unselected parent cultivar and these have been progressed toward commercial exploitation. Associated studies showed many of the common scab resistant variants showed resistance to a second unrelated disease, powdery scab. Preliminary studies suggest altered suberisation within lenticels may be a possible mechanism for broad spectrum disease resistance to tuber-invading pathogens.