Lars Kamphuis Richard

1 Introduction 2 Advantages of using M. truncatula to study resistance to fungal necrotrophs 3 Fungal pathogens of M. truncatula 4 New pathogens and isolate validation 5 References 1 Introduction Fungal diseases in plants are almost exclusively members of the phylum Ascomycota and subphylum Pezizomycotina. All common crop plants are susceptible to fungal disease of one kind or another. Spore production and dispersal is enormously efficient in fungi, and plants crowded together in monoculture provide an ideal environment for the appearance of virulent new forms, on occasion resulting in the loss of the entire crop. Fungal pathogens are conventionally categorised into three groups: obligate biotrophs, which obtain nutrients from living host tissue; necrotrophs, which induce cell death and maceration of tissue in their hosts; and hemibiotrophs, which are necrotrophs with an initial biotrophic phase but subsequently become necrogenic. Resistance to biotrophs, which include rusts and mildews, is normally qualitative and has been intensively studied in several pathosytems. Typically the genetics of resistance follows the well established race-specific gene-for-gene recognition system (Hammond-Kosack and Parker, 2003). Resistance to necrotrophs, by contrast, is often quantitative, poorly understood and relatively few resistance genes have been characterised. These include the race-specific Hm1 gene in maize (Johal and Briggs, 1992), the Pyrenophora tritici-repentis ToxA-insensitivity tsn1 (Faris et al., 1996) and ToxB-insensitivity tsc2 (Friesen and Faris, 2004) loci in wheat, and resistance to the Fusarium graminearum mycotoxin deoxynivalenol in wheat (Lemmens et al., 2005).