Mycobiota of maize and maize silage
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (Food - P2)
Keywords: mycotoxin, maize silage
During the last fifteen years the use of maize silage as dairy cattle feed has increased a lot in Denmark. Maize and maize silage can, however, be contaminated with several diverse mycotoxins, which potentially can affect performance of cattle or be carried over into milk and meat products. Mycotoxins in maize silage is therefore of great concern for farmers and consumers.
The growth conditions differ a lot before and after ensiling and these two habitats are inhabited by different fungi. The various species have different mycotoxin profiles and to get an idea of which mycotoxins may be present in maize silage we are examining the mycobiota of maize in the field and in maize silage in Denmark.
Samples of freshly harvested maize were collected late autumn 2005 (30 samples) and 2006 (71 samples). Both visibly mouldy and normal looking silage samples were collected from various stacks during 2005 to 2007. The mycobiota was examined by placing pieces of plant material on agar plates and then allowing fungi to emerge. The fungi were then isolated and identified mainly based on morphology, but the identity of Alternaria species was verified with metabolite profiling.
29 out of 30 and 60 out 71 samples examined in 2005 and 2006, respectively, contained one or more Fusarium species. The predominant Fusarium species in 2005 was F. avenaceum followed by F. graminearum, whereas the predominant species in 2006 was F. culmorum and F. equiseti. The annual differences may be due to climatic differences as the growth season was warmer in 2006. This will also explain the isolation of F. verticillioides in 2006 which is normally encountered in warmer regions.
Alternaria species were only isolated from maize in 2005. 20 of the 30 maize samples contained one or more Alternaria species. Three species of Alternaria was isolated. In total 30 Alternaria strains were isolated. The predominant species was A. infectoria (16) followed by A. tenuissima (10) and A. arborescens (4).
Investigation of 39 visibly mouldy silage samples collected in 2005 revealed Penicillium roqueforti as the predominant fungus in maize silage occurring in 15 out of 39 samples. The closely related Penicillium paneum (6 samples) often co-occurs with P. roqueforti and the two are difficult to isolate from each other. Both are known to produce mycotoxins e.g. PR-toxin and patulin. Preliminary results from 2006 and 2007 show that even healty looking silage samples can contain spores of these fungi in amounts up to 3*103 colony forming units/gram. Other mycotoxin producing fungi found were Monascus ruber (7 samples) and Byssochlamys nivea (7 samples). Species of the class Zygomycetes were also abundant (12 samples). These are not known as mycotoxin producers but some species can cause invasive fungal infections. The findings correspond well with previous surveys of filamentous fungi in silage except for the very rare findings of Aspergillus species. This may be related to climatic differences.
