Structure and microbiology of leaf surfaces

There are now many texts dealing with the microbiology of the phylloplane (the leaf surface) especially those based on a series of conferences which started in 1971 (Preece & Dickinson, 1971; Dickinson & Preece, 1976; Blakeman, 1981; Fokkema & van den Heuvel, 1987). The subject is also covered in many general texts on microbial ecology (Campbell, 1985) and Windels and Lindow (1985) have recently produced a small specialist study on biocontrol on the phylloplane that also contains some introductory material. The reader is referred to these texts for a general treatment of the microbiology of the phylloplane, and only an outline will be given here.

The surfaces of leaves are usually hydrophobic due to the presence of cutin and wax, the quantities of which vary with the plant species or cultivar and with the environmental conditions. This impervious layer not only restricts the loss of water from the leaf but also reduces the amount of nutrients which are leached from the leaf (cf. the root, section 5.1). Nutrients may also arrive on the leaf from dust and most importantly from the deposit of pollens. Very few leaves have flat or smooth surfaces: there are often crystals of wax of various shapes and the epidermal cells have convex surfaces with channels between them (Fig. 3.1). There may also be microscopic hairs even on apparently glabrous leaves. These topographical details give many microhabitats with improved water availability or nutrients or with protection from excessive radiation, the ultra-violet component of which is particularly damaging.