Invasive pathogens in plant biosecurity. Case study: citrus biosecurity

Citrus (Rutaceae) The Family Rutaceae (Order Sapindales) is widely distributed with centres of diversity in southern Africa and Australia (Bayer et al 2009). The most widely used taxonomic systems for classifying citrus are Swingle and Reece (1967) and Tanaka (1977). Many species of citrus still exist in nature as wild plants or as little-altered land races. These wild species have given rise to the diversity of citrus cultivars known today. The taxonomy of citrus, and particularly cultivated forms (Bayer et al. 2009), is complicated by a long history of cultivation and wide cross-compatibility among species (Mabberley 2004). Recent work suggests that citrus comprises about 25 species (Mabberley 2004) including reunification of Eremocitrus, Fortunella, Microcitrus and Poncirus with citrus (Mabberley 1998). In a molecular analysis (Bayer et al. 2009), citrus was broadened to include Oxanthera Montrouz and Feroniella Swingle. Unless stated otherwise, classification of plants in this chapter is based on Mabberley (1997, 1998, 2004, 2008). Scott et al. (2000), Samuel et al. (2001) and Bayer et al. (2009).