Stukenbrock, E. H. & Rosendahl, S. (2005) Development and amplification of multiple co-dominant genetic markers from single spores of arbuscular mycorrhizal fungi by nested multiplex PCR. Fungal Genetics and Biology 42 : 73–80. Vandenkoornhuyse, P., Leyval, C. & Bonnin, L. (2001) High genetic diversity in arbuscular mycorrhizal fungi: evidence for recombi- nation events. Heredity 87 : 243–253. DOI: 10.1017/S0953756205242375 RICE BLAST FUNGUS ATTACKS LEAVES AND ROOTS DIFFERENTLY Rice blast, the causal agent of which is Magnaporthe grisea 2 , is one of the most destructive plant pathogens known. It has been studied in extraordinary detail from almost all conceivable standpoints (Ziegler, Leong & Teng 1994, Tharreau et al. 2000, Talbot 2003). The genome has been sequenced, and the infection process on leaves is known to comprise a series of develop- mental steps involving over 30 genes. The fungus is, however, a member of the same family as the soil-borne take-all pathogen of cereals, Gaeumannomyces graminis, which invades through roots. The development of M. grisea on roots has now been investigated in detail using strains tagged with a green fluorescent protein (GFP) and chlorazole black E staining (Sesma & Osbourn 2004). It was discovered that on roots the fungus infection developed in a different way to the process on leaves. The melanized appressoria typical of foliar infections and which build up astonishing turgor pressures in order to penetrate leaf surfaces were not developed. Instead, when growing on the root sur- face, much simpler penetration structures are devel- oped, which take the form of hyphal swellings and in turn give rise to hyphal pegs. The authors refer to these swellings as ‘hyphopodia’, a term better subsumed under ‘ appressoria ’ as the structures are functionally similar (Mibey & Hawksworth 1995), but it many be more helpful to use the terms ‘functional’ and ‘non- functional’ appressoria. Whatever label is used for the non-functional swellings, the excitement is that these are unlike the appressoria formed on leaves, but do recall the structures produced by the root-infecting G. graminis. Further, sclerotium-likes structures devel- oped on the root surface and inside the outermost layers of root tissue ; these recall the growth-cessation structures familiar from G. graminis. Once inside roots, GEF-tagging shows that M. grisea can extend into the aerial parts of the plant. The knowledge that the fungus can invade through roots is of significance for the development of control strategies which have traditionally been focussed on aerial infections. Sesma & Osbourn (2004), who are based at The Sainsbury Laboratory in Norwich, also generated strains of M. oryzae which were melanin-deficient; these could not form functional appressoria and were unable to penetrate leaves, but could still produce the smaller non-functional appressoria on roots and suc- cessfully infect them. The genetic basis for the differ- ences were investigated using an FOW1 homologue linked with infection processes in Fusarium oxysporum, a characteristic root-invader. When the gene was deleted, there was a reduction in root browning. In addition, the authors searched for evidence of gene-for- gene resistance with the host using different rice culti- vars, and found some evidence of specific disease resistance to the rice blast fungus in roots. This is a fascinating story, particularly well-illu- strated by colour photographs and also superb con- focal microscopy images, and is sure to be something lecturers in plant pathology will wish to include in future courses. Mibey, R. K. & Hawksworth, D. L. (1995) Diporothecaceae, a new family of ascomycetes, and the term ‘hyphopodium’. Systema Ascomycetum 14 : 25–31. Sesma, A. & Osbourn, A. (2004) The rice leaf blast pathogen under- goes developmental processes typical of root-infecting fungi. Nature 431 : 582–586. Talbot, N. J. (2003) On the trail of a cereal killer: exploring the biology of Magnaporthe grisea. Annual Review of Microbiology 57 : 177–202. Tharreau, D., Lebrun, M. H., Talbot, N. J. & Notteghem, J. L. (2000) Advances in Rice Blast Research. [Developments in Plant Pathology No. 15.] Kluwer Academic Publishers, Dordrecht. Zeigler, R. S., Leong, S. A. & Teng, P. S. (eds) (1994) Rice Blast Diseaese. CAB International, Wallingford. DOI: 10.1017/S0953756205252371 WHY PICKING WILD MUSHROOMS MAY BE BAD BEHAVIOUR There has been a spectacular increase in mushroom consumption in recent years in North America and western Europe. In the USA, the USDA Economic Research Service estimates that per capita annual con- sumption of cultivated mushrooms has risen from 0.3 kg in 1965 to 1.8 kg in 2001 (Lucier, Allshouse & Lin 2003). Increasing market acceptance of cultivated fruit bodies has been paralleled by a boost in the popularity of wild mushrooms, and a number of popular species are now harvested on a large-scale 2 Currently the nomenclaturally correct name for this fungus is Magnaporthe oryzae (anamorph Pyricularia oryzae), but this is not being taken up generally by researchers in the field. A formal pro- posal to typify the name in a way to maintain current is required. See ‘Identity of the causal agent of rice blast’ in Mycologcal Research News (Mycological Research 106 : 994–995, September 2002). 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