engleski

Toxigenic Fusarium species isolated from maize in Croatia

Fungi in the genus Fusarium are the most common contaminants of maize and other cereals, which can colonise these substrates causing spoilage and production of mycotoxins. Some of Fusarium species are potent producers of trichotecenes (DON, DAS, T-2), zearalenone (ZEN) and fumonisin B1. These mycotoxins are associated with various animal and human toxicoses and carcinomas. The distribution and toxigenicity of Fusarium species isolated from non-harvested maize (left in field during winter), as well as stored maize have been studied in northern Croatia over the following years: 1999/2000 ; 2003 ; and 2005/2006. Mycological analysis of maize kernels was performed on 2% Sabouraud glucose agar (SGA) with antibiotics and sterile humid filter paper. Fusarium species were identified on the basis of macroscopic and microscopic morphology on potato-dextrose agar (PDA) and selective nutrient agar (SNA). Mycotoxin (ZEN, DON, DAS, T-2, FB1) production capacity of fusaria was examined on yeast-extract sucrose (YES) broth incubated at 25+2  C for 10 days. Isolation and detection of ZEN and trichotecenes were performed using multitoxin extraction and TLC method by Balzer et al. (1), which was modified for detection of FB1 (2). The Fusarium species constituted between 70 and 85% of the total identified microfungi isolated from non-harvested maize (N=192) and stored maize samples (N=189). Among fusaria, F. verticillioides (=moniliforme) (up to 40%) was the dominant species in all years of the study, followed by F. graminearum, F. sporotrichoides, F. poae, F. culmorum, F. oxysporum, F. tabacinum, F. tricinctum and F. stilboides (5-10%). Research conducted in 1999/2000 showed that all F. verticillioides strains isolated from non-harvested (44/44) and stored maize (22/22) were able to produce FB1 in relatively high concentrations (181-1320 mg/l) (2, 3). FB1-producers were ranged in three groups, high (881-1320 mg/l), intermediate (441-880 mg/l) and low (181-440 mg/l). Most strains were intermediate (48%) and high (21%) producers. Variability of FB1 production capacity among F. verticillioides strains could be attributed to genetic differences of regulatory genes that are involved in biosynthesis of FB1. On the other hand, in 2003 we found less FB1-producing F. verticillioides strains (11/20). The reasons may be unfavourable environmental conditions (temperature under the zero, frequent snowing, long period of coldness), as well as maize genotype. These strains produced significantly smaller amounts of FB1 (48-400 mg/l) (4). Three strains of F. verticillioides isolated from non-harvested maize during these years were able to produce ZEN in concentrations from 3.8 to 70 mg/l. Fusarium graminearum strains (4/5) isolated from non-harvested maize in 2003, produced higher amounts of ZEN (60-180 mg/l) than F. verticillioides starins (3). In 2005/2006 F. sporotrichoides (1/2) and F. oxysporum (1/1) isolated from stored maize, produced small amounts of ZEN (1.1-2.22 mg/l). T-2 production was found in 1/1 strain of F. tricinctum (1.55 mg/l) isolated from non-harvested maize in 1999/2000. When it comes to the mycotoxicological risk, maize contamination by Fusarium species is one of the greatest concerns because their toxigenic potential and accumulation of produced mycotoxins in grains intended for foods and feeds and their possible synergism in biological systems.

Fusarium; maize; toxigenicity; trichotecenes; zearalenone; fumonisin B1

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