04568naa a2200169 a 450000100080000000500110000800800410001902000220006010000110008224500960009326000090018952040390019865300230423765300160426065300170427677301050429310844902012-04-20       2012    bl uuuu     u00u1 u    #d  a978-953-51-0157-41 aEpagri  aMagnaporthe oryzae Genetic Diversity and Its Outcomes on the Search for Durable Resistance.  c2012  aRice is one of the most important cereal crops, feeding more than 50% of the world population. In some places in Asia, this cereal is responsible for more than half of the total calories intake. Also in Brazil this crop is essential to supply food and is one of the crops responsible for great economic incomes for the Brazilian southern states. If we consider that the world populations will continue to raise for approximately another 30-40 years (until 2040-2050), so the absolute demand for food will also increase and it would be necessary for the agriculture in all parts of the world to make improvements in order to support the demand. This required increase in crop production will occur in a context of mounting water scarcity, decreasing area and environmental degradation of arable land (that is partially caused by agriculture), increasing pollution, inevitable emergence of new races and biotypes of pathogens and pests, and possible adverse effects of climate change (Collard & Mackill, 2008). Plant breeding will play a key role in this coordinated effort for increasing food production. Given the context of current yield trends, predicted population growth and pressure on the environment, traits related to yield stability and sustainability should be a major focus of plant breeding efforts (Collard & Mackill, 2008). Meanwhile, if this requirement must be attended under environmental conditions of sustainability, this means that this increase in food production must be done under conditions of the best use of environmental goods and services while not damaging these resources (Pretty, 2008), and this represents an unprecedented challenge to scientists and farmers. In front of this, studies about genetic background are essential for rice culture, to surpass actual productivity levels and mainly for adaptation of modern cultivars to actual environmental conditions. Rice blast disease is the most important and destructive disease for rice crop, and is caused by ascomycete Magnaporthe oryzae. The disease is spread worldwide occurring in almost all rice-producing areas and can be very destructive when environmental conditions are favorable. Disease occurrence and severity vary by year, location and even within a field depending on environmental conditions and crop management practices. Yield loss estimates from other areas of the world have ranged from 1-50%. It is estimated that each year this disease destroys enough rice to feed more than 60 million people. The economic losses are nearly unmeasurable, but some data suggests values over $ 70 billion of dollars. The fungus M. oryzae presents genetic diversity and is able to recombine by parasexual reproduction, and this causes difficulties on develop resistant cultivars, being also responsible for the short living resistance of released cultivars. Because of the narrow genetic basis of the elite lineages used for crosses, one of the main troubles in rice breeding is the search for resistance gene sources and how to use them in order to prevent great losses in the crop. Obviously it is necessary to apply a correct culture management in order to use obtained resistance as long as possible. In this way, we present a shortly state-of-the-art about the pathogen and its epidemiology, what is reported about resistance to the disease, and something about our experience of breeding and management of these disease. We also explain that in our view, the most promising alternative is the use of cultivars with stacking resistance genes allied to a constant follow up on about pathogen genotype frequency by molecular tools. So, emerging of new pathogen races able to overcome resistance could be identified early and some decisions can be made in order to avoid the cultivars to lose their resistance to the disease over the time. Knowledge about the pathogen population genetic structure could also be useful in order to guide breeding actions related to which and how many resistance genes to exploit for develop the new rice cultivars.  aDisease resistance  aMagnaporthe  aOryza sativa  tIn: CALISKAN, M. The Molecular Basis of Plant Genetic Diversity. Croatia: In Tech, 2012. p. 332-356.