Potato blackleg (blg) caused by Pectobacterium species leads to great economic losses in agriculture worldwide. In this study, three breeding clones with varying degree of disease tolerance, i.e. tolerant (t), moderately tolerant (mt) and susceptible (s) to blg were evaluated in field trials for several disease related factors. The s-clone L 696 with its high portion of oversized tubers showed increased lenticel swellings and had a weak defense potential in its tuber tissue coinciding with low

more »

... ntioxidant capacities and reduced necrosis formation 48 h after incubation with Pectobacterium atrosepticum (Pba). The t-clone B 165, however, was outstanding in its tuber soft rot resistance and antioxidant levels and generated the best extent of necrosis after incubation with Pba among the genotypes. Moreover, B 165 expressed significantly higher (P < 0.05) polyphenol oxidase (PPO) and peroxidase (POD) activities in the external sprout basis (ESB) of its sprouting tubers, and histochemical analyses revealed embedding of lignin in ESB-tissue sections. Together with PPO, POD and phenols, this lignin forms a barrier that provided high protection of B 165-sprouts against Pba invasion and seems to be a key factor for blg tolerance. The mt-clone P 92388 with its medium-sized tubers had also a lower risk for infections. Hence, the oversized tubers and strong lenticel swellings can be seen as major risk factors for potato blg disease.