Characterization of apple cultivar susceptibility to Neofusicoccum parvum Brazilian strains

Due to climate change, Neofusicoccum parvum is currently emerging as a new pathogen of Rosaceae plant species. This increases the need of gaining knowledge on the pathogenicity of this fungus, particularly on apple cultivars of considerable economic importance. In this study, the virulence and temperature dependence of N. parvum isolates was assayed on 'Gala' and 'Fuji' apple fruit and wood. At 25 °C and 30 °C, 'Gala' fruits showed a higher susceptibility to all fungal strains than 'Fuji', whereas low infection severity was shown at 15 °C and 20 °C on both cultivars. Infrared spectroscopy revealed that 'Fuji' fruit tissues displayed a higher content of phenolic compounds and pectin esterification degree, as factors possibly correlated with fruit susceptibility. When strain virulence was assayed on wood, no significant difference in susceptibility was detected, as also shown by SEM analysis. The virulence of N. parvum was also tested by assaying the activity of lytic enzymes such as cellulase, polygalacturonase, polymethylgalacturonase, and xylanase.