dc.description.abstract |
This study investigated the effect of interacting environmental factors on the
ecophysiology of Fusarium culmorum and F. graminearum and mycotoxin
production, and potential for controlling growth and deoxynivalenol (DON) and
nivalenol (NIV) production using antioxidants and essential oils on wheat grain. Two-
dimensional temporal profiles of growth and DON/NIV production for F. culmorum
and F. graminearum were constructed for the first time and showed that the water
activity (aw, ) ranges required for growth and DON/NIV production were different in
vitro and on wheat grain. Growth occurred over a wider aW range (0.9-0.99) while
DON/NIV production occurred over a significantly narrower range (0.95
-
0.99 a,,, ) at
both 15 and 25°C over a 40 day incubation period. Interactions between aW,
temperature, and sub-optimal concentrations of fungicides had a significant impact on
growth and competitiveness of F. culmorum in interspecific interactions with 5-6
other wheat grain fungi. This had an impact on both colonisation capacity in vitro and
in situ and affected DON/NIV production. Interactions were complex changing with
environmental or fungicide stress resulting in significant stimulation or reduction of
both fungal growth and mycotoxin production. An Index of Dominance was
developed to compare interspecific interactions between F. culmorum and other wheat
spoilage fungi and showed that competitiveness of F. culmorum increased as
temperature and a,, level approached the optimum conditions for growth and
DON/NIV production. Niche overlap indices (NOI) and niche maps were developed
for the first time and showed that interspecific competitiveness was closely related to
the number of nutritional carbon sources shared between spoilage fungi. Hydrolytic
enzyme profiles for seven different enzymes by F. culmorum, other Fusaria and
spoilage fungi showed that the most competitive species produced the highest specific
activity of N-acetyl-ß-D-glucosaminidase. Potential for control of Fusarium species
post-harvest using 23 essential oils and 8 antioxidants was investigated. Cinnamon,
clove, bay, butylated hydroxyanisole and propyl paraben (500 µg g"1) were able to
significantly reduce (>90%) the colonisation of wheat grain by three Fusarium
species and DON/NIV production. Bay essential oil was the most effective at
controlling total fungal populations and DONNIV in naturally contaminated wheat
grain. |
en_UK |