Nanoparticulate (NP) substances have widely documented antimicrobial
properties, yet their utilisation in the biocides and pesticides industries has yet to be
fully exploited. This is particularly so in the pesticides industry, where their potential
has not yet been realised. This mini review identifies the emerging trends identified in
research characterising the in vitro antimicrobial properties of NP substances against
fungal and oomycete phytopathogens. Nanoparticulate substances for which there was
a sufficient depth of published studies on activity against fungal and oomycete
phytopathogens are covered in this review, these include chitosan, copper, magnesium,
silver and zinc. All substances displayed significant activity against a range of
phytopathogens, though silver and copper-based NPs appear to be the most potent at
relativity low (<50 ppm) concentrations. However, as particle size and shape affect the
level of exhibited toxicity, direct comparisons of activity between studies are often
difficult due to the different types of NP examined. One particularly promising NP
substance is the organic biodegradable substance chitosan which is considered
environmentally friendly. Chitosan has also been shown to stimulate plant growth and
defence in addition to possessing antifungal activity. The lack of toxicological
properties marks chitosan as having particular potential for fulfilling the regulatory
requirements for environmental fate and ecotoxicology necessary for gaining approval
as an authorised pesticide. Another distinct problem in comparing studies is the lack of
a recognised standardised growth medium/media for determining nanomaterial toxicity.
A growing body of evidence suggests that the in vitro toxicity of certain nanoparticles
is highly influenced by the properties of the growth medium, such as its pH, salinity
and components. These confounding factors will be discussed and their implications
for comparing nanomaterial efficacy highlighted while also providing suggestions for
improving characterisation of nanomaterial efficacy. Characterisation of nanomaterial
efficacy in vitro is a critical step in determining which nanomaterials should be
progressed for further testing in higher tier tests such as simulated use trials and field
trials. The aim of this chapter is to draw attention to the limitations of in vitro
characterisation and highlight how these techniques can be improved.
Keywords: Chitosan, Copper, Fungi, Growth medium, In vitro, Magnesium, Nanoparticles, Oomycetes, Phytopathogens, Silver, Zinc.
