Pesticides on Yeasts Colonizing Leaves

All aerial plant surfaces are inhabited by diverse assemblages of microorganisms, including bacteria, fi lamentous fungi, yeasts, and algae. These organisms have profound effects on plant health and thus impact on the ecosystem (Lindow and Brandl, 2003). The yeasts form a major component of the population on leaves (Inácio et al., 2002). Leaf surfaces are colonized by members of several genera of saprophytic yeasts that provide a natural buffer against plant pathogens (Fokkema, 1988). Furthermore, the yeasts, as eukaryotic cells, are considered to be good models for the assessment of the toxicity of many chemical compounds, among them pesticides (Ribeiro et al., 2000). Various insecticides and fungicides are applied to protect crops, vegetables, fruits, and nuts from insects and fungal diseases. These agrochemicals differ from each other by their chemical composition, physico-chemical properties, and mode of action. Insecticides generally target the nervous system, the growth, and development, or energy production of the pest (Brown, 2005), while fungicides act mainly on essential fungal functions such as respiration, sterol biosynthesis or cell division (Leroux, 2003). However, when these compounds are used in plant protection, they can also affect non-target microorganisms associated with the plant phyllosphere. The effect of a particular pesticide on phyllosphere microorganisms depends on the specifi c chemical properties of the pesticide and the concentration at which the pesticide is used, the type of indigenous phyllosphere microorganisms present, and the environment in which the organisms grow (Walter et al., 2007). Many pesticides are non-specifi c in their mode of action, and little is known about their impact on the microbial community in the plant phyllosphere. Some agrochemicals can inhibit the growth of individual bacteria, yeasts, and fungi and/or whole populations of non-target microorganisms (Walter et al., 2007; Zhang et al., 2009). The application of the insecticide cypermethrin on the pepper plant phyllosphere caused a decrease in the abundance of fungi and a shift in the Infl uence of Pesticides on Yeasts Colonizing Leaves