Correlations among disease severity, firmness, minerals, and cell wall composition in radish (Raphanus sativus L.) and baemoochae (xBrassicoraphanus) roots in relation to tissue maceration by Pectobacterium carotovorum

The temporal relationships between firmness, mineral content, cell wall composition and susceptibility of radish (Raphanus sativus L.) and baemoochae (xBrassicoraphanus) root to soft rot disease were investigated. Baemoochae root showed greater firmness than the radish roots. The development of soft rot disease symptoms occurred to a greater degree in the two baemoochae lines, whereas 'Chungwoonplus' and 'Daebulyung' were most susceptible among the radish roots. There was a significant correlation between firmness and severity of soft rot symptoms. 'Dongja', 'Minongjosaeng', and 'Kwandong' root showed the highest calcium, magnesium and potassium content, respectively. The relationship between soft rot disease and the calcium and magnesium content of root tissue was significant, but no clear correlation with potassium content was evident. Cell wall composition significantly correlated with disease severity, polyuronides and non-cellulosic neutral sugars (glucose and galactose), whereas cellulose and another non-cellulosic neutral sugar (arabinose, rhamnose, mannose, and xylose) were not significant. The reduction of Pcc soft rot symptoms in high-calcium and magnesium content roots was partially attributable to the decrease in maceration related to the enhancement of structural integrity of cell wall composition. Tissue firmness data also provided supporting evidence for the reduction in maceration. Growth and spread of the pathogen through the root tissues decreased due to this effect on tissue maceration.