Topic 1: How do pathogen/pest populations respond to deployment of host resistance?

Topic 1: How do pathogen/pest populations respond to deployment of host resistance?

How do pathogen populations evolve in response to quantitative resistance?

How do pathogen populations evolve in response to quantitative resistance?

Potato cyst nematodes (Globodera pallida) reared several generations on PR potato cultivars had increased reproductive rate, those on S cultivars did not (Schouten and Beniers, 1997, Phytopathology, 87:862-867).

Cowger and Mundt, 2002, Aggressiveness of Mycosphaerella graminicola isolates from susceptible and partially resistant wheat cultivars, Phytopathology 92:624-630

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)

Bottom line on partial resistance

Topic 1: How do pathogen/pest populations respond to deployment of host resistance?

Host-selective toxins (HSTs)

How do fungal pathogen populations evolve in response to host resistance when HSTs are central to pathogenesis?

HC-toxin detoxified directly by maize HM1, which encodes HC-toxin reductase (Sindhu et al, 2008, PNAS 105:1762-1767)

Same ToxA gene present in Pyrenophora tritici-repentis (Ptr, cause of tan spot of wheat) and in Phaeosphaeria nodorum; high homology between ToxA genes

HSTs may be under diversifying selection

Types of natural selection

Fig. 3. P. nodorum SnToxA parsimonious haplotype network of 123 P. n. isolates

Evidence for diversifying selection in SnToxA

P. nodorum has at least 4 HSTs (Friesen et al, 2008, Plant Physiology 146:682-693)

Why does wheat have genes for sensitivity to ToxA, etc.?

Conclusions on SnToxA – evolution of a small-protein HST

What drives evolution of a secondary metabolite cluster and can we expect rapid appearance of new specificities as in P. nodorum SnTox series?

Resistance to HSTs

Conclusions for resistance breeding and resistance management where HSTs are involved