Abstract
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 antioxidant 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.
Highlights
Blackleg is one of the most important bacterial diseases of potatoes and leads to severe economic losses in agriculture globally, whereby climate change will strengthen this problem in the future (De Boer & Rubio, 2016)
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
The pathogenicity of the bacteria is based on a set of enzymes such as pectinases, cellulases, proteases and xylanases that are secreted all into the plant tissue and coordinately degrade the major cell wall polymers leading to soft rot and/or blackleg symptoms (Toth & Birch, 2005)
Summary
Blackleg (blg) is one of the most important bacterial diseases of potatoes and leads to severe economic losses in agriculture globally, whereby climate change will strengthen this problem in the future (De Boer & Rubio, 2016). The pathogenicity of the bacteria is based on a set of enzymes such as pectinases, cellulases, proteases and xylanases that are secreted all into the plant tissue and coordinately degrade the major cell wall polymers leading to soft rot and/or blackleg symptoms (Toth & Birch, 2005). Major part of these enzyme mixtures are pectolytic enzymes, above all pectate lyases (PL), exo-polygalacturonate lyase, pectin lyase, pectin methyl esterase and polygalacturonase (Collmer & Keen, 1986; Barras et al, 1994). PL isoenzymes that depolymerize pectate and pectin are predominant in this frame and act in a synergistic manner (Bartling et al, 1995)
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