Disguising the leaf surface: the use of leaf coatings for plant disease control

The ability of fungal pathogens to develop resistance to fungicides and to overcome genetic resistance in their hosts, coupled with growing public concern for the environment, means that there is an urgent need for novel methods of disease control. The leaf surface provides the first barrier that fungi must overcome in order to gain access to the leaf, but it also provides chemical and physical cues that are necessary for the development of infection structures for many fungal pathogens. Film-forming polymers can coat the leaf surface, acting not just as an extra barrier to infection, but also disguising the cues necessary for germling development. Kaolin particle films can envelop the leaf in a hydrophobic particle film barrier that prevents spores or water from directly contacting the leaf surface and as a result, can suppress infection. Adhesion of fungal spores to the leaf surface, which is important to keep spores on the leaf surface and for appropriate development of the fungus on the leaf surface, can be inhibited, leading to reduced infection and lesion development. Polymer and particle films have been shown to provide disease control in the field, while research on agents that inhibit spore adhesion on leaf surfaces is still in its infancy. There is an urgent need for research on the practicality of using these novel methods under field conditions and on ways of integrating them into current crop protection programmes.