PATULIN-PRODUCING PENICILLIUM SPECIES ISOLATED FROM NATURALLY INFECTED APPLES IN SOUTH-AFRICA

Penicillium expansum, a well-known post-harvest pathogen, causes 'blue mould rot' in apples and produces patulin, a toxic secondary metaboli te. Patulin is regarded as a mutagen and exhibits immunotoxic, neuroto xic and gastrointestinal effects in rats. No information exists regard ing the identity and patulin-producing ability of fungi occurring in S outh African apples. This study was conducted, in collaboration with a local processing facility, to quantify and identify the fungal specie s from naturally infected apples. The ability of the isolates to produ ce patulin in artificially inoculated apples, as well as in yeast extr act sucrose (YES) liquid medium, was also tested. Few fungal species o ther than Penicillium, of which P. expansum was the most prominent, we re isolated from three apple cultivars examined. The number of colony forming units and the levels of patulin produced varied widely between apple cultivar and sample origin. The P. expansum isolates produced s ignificant levels of patulin in YES medium (43-2176 mu g ml(-1)), whil e production by P. roqueforti var. carneum, P. corylophilum, P. funicu losum, P. rugulosum and P. fellutanum varied (<0.1-1705 mu g ml(-1)). This is the first report of patulin production by the last four specie s. The application of Koch's postulates revealed that, amongst the Pen icillium spp. tested, only P. expansum had the ability to infect apple s and to produce patulin at levels ranging between 0.2-130 mu-g g(-1). Patulin levels were the highest in artificially inoculated apples of three cultivars (Starking, Golden Delicious and Granny Smith) when P. expansum isolates originating from Granny Smith apples were used as in oculum.