Topic 1 : How do pathogen/pest populations respond to deployment of host resistance?. Natural vs. human-managed systems Selective effects of qualitative resistance (R genes) How does evolution to virulence affect pathogens – is there a cost to virulence?
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% isolates virulent
% isolates virulent
Estimating fitness systems
Genotype A: 10 lesions/lesion/day
Genotype B: 9 lesions/lesion/day
For example: systems(Zhan et al, 2002, Local adaptation and effect of host genotype on the rate of pathogen evolution: an experimental test in a plant pathosystem. J. Evol. Biol. 15:637-647)
si = 1 - pit pj0
Fitness measured in field; aggressive-ness measured in greenhouse
Was aggressive-ness correlated with fitness?
Xi et al. , 2003, Mycol. Res. 107:1485-1492
Fig. 1. Frequency of pathotypes E97-2 and H97-2 of Rhynchosporium secalis co-inoculated over 4 cycles on two barley cultivars: (a) ‘Earl,’ susceptible to E97-2, and (b) ‘Harrington,’ susceptible to both.
E97-2 had complex virulence (to Earl, Harrington, and 5 more cvs).
H97-2 had simple virulence (to Harrington and 1 other cv, not Earl).
Bahri et al, 2009. Tracking costs of virulence in natural populations of the wheat pathogen, Puccinia striiformis f. sp. tritici. BMC Evol. Bio. 9:26.
So: if you remove a defeated R gene from commercial production, will the corresponding virulence in the pathogen population decline in frequency?
“A great advantage of the strategy is that production, will the corresponding virulence in the pathogen population decline in frequency?it does not depend upon a supply of new resistance genes….Existing resistance genes can be recycled. For example, if a gene, or gene combination, is withdrawn because the frequency of the matching virulence increases in the pathogen population it can be re-introduced when thefrequency of the matching virulence allele(s) reduces.” (Pink & Puddephat)
Morris et al, 2009. Expanding the paradigms of plant pathogen life history and evolution of parasitic fitness beyond agricultural boundaries, PLoS Pathogens 5:1, www.plospathogens.org
So if avr genes affect fitness differentially, mutations in them should differentially affect fitness, and R genes corresponding to them should be differentially durable.
Tested in field with NILs, natural inoculum. Over 3 yrs, durability of Xa7 > Xa10.