Local and systemic resistance to fungal pathogens triggered by an AVR9-mediated hypersensitive response in tomato and oilseed rape carrying the Cf-9 resistance gene

Abstract Tomato and transgenic oilseed rape plants expressing the Cf-9 resistance gene develop a hypersensitive response (HR) after injection of the corresponding Avr9 gene product. It was investigated whether induction of a HR conferred resistance to different fungal pathogens in tomato and oilseed rape. Induction of an AVR9 mediated HR at the pathogen infection site delayed the development of the biotrophs Oidium lycopersicum in tomato and Erysiphe polygoni in oilseed rape, but enhanced the development of the necrotrophs Botrytis cinerea and Alternaria solani in tomato and Sclerotinia sclerotiorum in oilseed rape. Interestingly, delayed fungal disease development was observed in plant tissues surrounding the HR lesion regardless of whether a necrotrophic or biotrophic pathogen was used. In tomato, AVR9 injection induced systemic expression of PR1 , PR2 and PR3 defence genes but did not induce systemic resistance to O. lycopersicum , B. cinerea or A. solani . In oilseed rape, AVR9 injection temporarily induced systemic resistance to Leptosphaeria maculans and E. polygoni , but did not induce detectable systemic expression of PR1 , PR2 or Cxc750 . These results give new insights into the potential uses of an induced HR to engineer disease resistance.