Reduction of Colletotrichum acutatum infection by a polygalacturonase inhibitor protein extracted from apple

Colletotrichum acutatum, a fungal pathogen that causes soft rot in fruit, produced polygalacturonases (PGs) when grown on pectin or apple wall polysaccharides, as revealed by a clear zone around the well filled with C. acutatum medium in a radial diffusion assay. A PG-inhibiting protein (PGIP) was also extracted from healthy stored ‘Cripps Pink’ apple and its activity was tested in vitro and in vivo against an endo-PG (EC 3.2.1.15) of C. acutatum. In in vitro trials the inhibition determined by radial diffusion assay was over 62% after 24 h while in inoculated fruit the inhibition ranged from 33.9% to 54.4% after 4 days at 20 °C. The PG inhibitor extracted from healthy skin apple was a heat-denaturable protein since the halo produced by protein extracted from C. acutatum and added to boiled protein extracted from healthy skin apple tissue was 246 mm2, significantly higher than the halo produced by protein extracted from C. acutatum diluted with fresh protein extracted from healthy tissue (93.6 mm2). More investigations are required to better understand the nature of the substance responsible for C. acutatum inhibition in apple and to evaluate the possibility of manipulating the PGIP levels in fruit to reduce soft rot caused by C. acutatum.