Botrytis cinerea: Molecular Aspects of a Necrotrophic Life Style

Abstract

Pathogenic fungi have developed a wide range of strategies to infect and colonize plants. Traditionally they are grouped into the major classes necrotroph/ hemi-biotroph/biotroph, according to major criteria like their source of nutrition (living vs dead cells), their ability to infect young and healthy tissue or a preference to older or senescent ones, the formation of specialized infection structures (haustoria), and more recently the type of plant defence reaction they provoke (e.g. jasmonate vs salicylic acid pathway). In many cases these criteria do not allow unequivocal decisions for the grouping of pathogens, as pointed out in the recent review by Oliver and Ipcho (2004). As an example, they list references grouping Phythophthora infestans in all three classes, and other references naming Magnaporthe grisea a necrotroph or a hemi-biotroph. Detailed cytological analyses only recently brought unequivocal evidence about the true biotrophic nature of the early infection stage of M. grisea (Kankanala et al. 2007), but still the exact mode of the switch to necrotrophic growth is unclear. Thus it needs much more detailed structural and physiological studies to fully understand the nature of a specific fungus–host interaction; and the question remains whether the old classification system is still helpful, because of the large degree of variation observed in nature.