The surface microbial contamination is of great interest in case of fruit because of the threat of postharvest spoilage. Apple is a valuable product from growing, commercial, as well as from nutritional points of view. Apple diseases during the growing season can be satisfactorily controlled by different plant protection technologies, but postharvest decay of apples caused by the so called storage moulds cannot be completely avoided. Cold storage — alone, or in combination with other methods — is the main technology used to successfully prolong the shelf life of apples. The origin of the moulds causing the decay of apples during storage is not well understood. In this work the surface mycobiota of apple fruit grown in Soroksár, in the orchard of the Corvinus University of Budapest was investigated.
Aspergillus strains were isolated from Hungarian mills in order to get information on the appearance of sterigmatocystin (ST) producing moulds, whose presence has never been demonstrated in Hungary. Fungal isolates were classified into nine morphotypes, sections Nigri, Nidulantes, Versicolores (two morphotypes), Circumdati, Flavi (two morphotypes), Clavati and Terrei by classical mycological assays. ST producing strains could be classified into section Versicolores. ST production of the isolates was assessed by liquid and solid phase growth experiments and compared to ST producing reference strains: Aspergillus pepii SzMC 22332, Aspergillus versicolor SzMC 22333, Aspergillus griseoaurantiacus SzMC 22334 and Aspergillus nidulans RDIT9.32. Four of our isolates marked as Km11, Km14, Km26 and Km31 showed ST production in liquid medium. ST production on solid phase corn grit substrate was measured after three weeks of incubation, and Km26 isolate proved to be the most prominent with a toxin concentration of 277.1 μg g−1, surpassing all reference strains. The toxin-producing ability of Km26 isolate was also tested in a field experiment, where corn was infected. By the end of the experiment, ST level of 19.56 μg kg−1 was measured in infected corn.
Molecular taxonomic identification of the Km26 strain was performed using internal transcribed spacer (ITS), calmodulin and tubulin sequence analyses. Based on these studies, strain Km26 was identified as Aspergillus creber.
Here we report that an ST-producing A. creber strain has appeared in Hungary, and the Km26 strain is the first known extreme ST-producing mould in this country. As a result of climate change, aflatoxin B1 producing Aspergillus flavus strains have appeared in Hungary in the last decade. As strain Km26 is the only A. creber isolate in Hungary so far, there is no sign of mass prevalence, and due to the lower temperature optimum of the species compared to A. flavus, its appearance is probably not related to climate change.
Climate change affects the occurrence of fungi and their mycotoxins in foods and feeds. A shift has recently been observed in the presence of aflatoxin producer Aspergillus spp. in Europe, with consequent aflatoxin contamination in agricultural commodities including maize in several European countries that have not faced with this problem before, including, e.g. Northern Italy, Serbia, Slovenia, Croatia and Romania. Although aflatoxin contamination of agricultural products including maize is not treated as a serious threat to Hungarian agriculture due to climatic conditions, these observations led us to examine the mycobiota of maize kernels collected from Hungarian maize fields. Using a calmodulin sequence-based approach, A. flavus isolates have been identified in 63.5% of the maize fields examined in 2009 and 2010, and 18.8% of these isolates were found to be able to produce aflatoxins above 5 μg kg−1 on maize kernels as determined by ELISA, HPLC-FL, HPLC-MS analyses and SOS-Chromotest. These data indicate that aflatoxin producing Aspergilli are present in Hungarian agricultural fields, consequently climate change with elevated temperatures could lead to aflatoxin contamination of Hungarian agricultural products, too.