Morphology and Cellular Organisation in Botrytis Interactions with Plants

Besides the ability of Botrytis species to survive saprophytically or endophytically these pathogens rapidly cause grey mould and other diseases in hundreds of mono- and dicotyledonous plants. The broad habitat range of one of these species, B. cinerea, should be perceived as having tremendous flexibility, not restricted regarding hosts and tissues. This potential is put into action by means of different infection strategies that vary along with conditions. The physical exploitation of host tissue can be best investigated by combined cytological techniques ranging from light microscopy to confocal laser video and high resolution electron microscopy. These techniques were applied to early infection phases and fungal infection organs, eventually further elucidated by molecular biological approaches. Emphasis is placed on hyphal tip swellings proven to be elaborated infection structures. Although constituting real appressoria, they might not mediate mechanical penetration in the first place. In addition, other infection mechanisms are reviewed, including enzymatic attack, and new evidence based on electron microscopy and cytochemistry is discussed, indicating chemical penetration mechanisms of cuticles not yet found in other fungal-plant interactions.