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Virulence in the rice pathogen Xanthomonas oryzae pv. oryzae

Virulence in the rice pathogen Xanthomonas oryzae pv. oryzae. UN Millenium Goals. Cut extreme poverty in half by 2015 Total number living in extreme poverty estimated at 1.1 billion

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Virulence in the rice pathogen Xanthomonas oryzae pv. oryzae

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  1. Virulence in the rice pathogen Xanthomonas oryzae pv. oryzae

  2. UN Millenium Goals • Cut extreme poverty in half by 2015 • Total number living in extreme poverty estimated at 1.1 billion • Disease resistance and strategies for resistance deployment are major contributions to agricultural security and agricultural development • Contribution to this goal would be one motivation for many agricultural experiments in the tropics

  3. R1 R1 R1 R2 R2 R2 Virulence and aggressiveness, in the world of plant pathologists • Virulence: ability to infect plants with a particular R gene • Aggressiveness: relative ability to infect plants for which a pathogen is virulent X X X X X Pathogen genotype with virulence corresponding to R1 and more aggressive Pathogen genotype lacking virulence but still more aggressive Pathogen genotype with virulence corresponding to R1

  4. Costs of virulence and costs of avirulence Parameterization of host-pathogen interactions based on work of Kurt Leonard

  5. 30 9 Virulence Detected 20 7 Resistance rating 10 5 Virulence frequency (%) 3 0 1 1 2 3 4 5 6 7 8 9 10 Years after initial planting Boom and Bust Cycle

  6. Blast R gene Breakdown Release 1965 1970 1975 1980 1985 1990 For rice blast, single R genes do not offer long-lasting protection Adapted from Lee and Cho, International Rice Research Conference, Seoul, 1991

  7. Analysis of virulence in populations of Xoo between 1993 and 2003 • This is work from Kim Webb’s dissertation, advised by Jan Leach, and in collaboration with others including I. Ona, J. Bai, and C. Vera Cruz • Data for virulence over such a long time period is quite rare for a bacterial plant pathogen • The manuscript describing this work is currently in preparation

  8. Race frequency over timeRace 9A/C “overcomes resistance”

  9. Disease incidence and severity over time

  10. Increases in virulence and aggressiveness over time

  11. Temperature alters the effects of the R gene

  12. Homogeneous and heterogeneous rice populations • In this experiment, experimental plots of rice were adjacent to each other • The likely rate of inoculum between plots is not known precisely, but is probably important • Effectively, selection is based on fitness in multiple host genotypes • For more information on rice research, see the website of the International Rice Research Institute: http://www.irri.org/

  13. Rice blast management through variety mixtures Here advances in resistance are combined with concepts about host mixtures to produce an effective solution to a disease problem Zhu et al. 2000 Nature

  14. Effects of susceptible host abundance on disease severity for two pathogens with different life histories Cox et al. 2004 Phytopathology

  15. Example 3 - SIR model (sort of) • Suppose a pathogen is transmitted by root-to-root contact • Resistance of a root might be root-age specific (thus, roots can move from one class to another with age) • For a real example, see the work of Chris Gilligan and colleagues Photo courtesy of Scott Bontz

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