ARS | Publication request: Presence of the potato late blight resistance gene RB does not promote adaptive parasitism of phytophthora infestans

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 6, 2011
Publication Date: August 14, 2011
Citation: Halterman, D.A. 2011. Presence of the potato late blight resistance gene RB does not promote adaptive parasitism of phytophthora infestans. Potato Association of America.

Technical Abstract: The gene RB is derived from the wild potato species S. bulbocastanum and confers partial resistance to late blight, caused by the oomycete pathogen Phytophthora infestans. In order to investigate whether a single strain of P. infestans can adapt to overcome this partial resistance source, we subjected RB containing leaflets to multiple rounds of infection with P. infestans, with cultures isolated from a lesion used to infect the next leaflet (a passage). A parallel line of passages was done using susceptible leaflets as hosts. At the end of the experiment, P. infestans strains passaged through resistant or susceptible leaflets were compared for infection efficiency and lesion size. Variants of the P. infestans effector family IPI-O, some of which are recognized by the RB protein to elicit resistance, were cloned and sequenced to determine whether variation occurred during selection on the partially resistant host. Our results show that after 20 rounds of selection, no breakdown in RB resistance took place. In fact, the strain that was continually passaged through the partially resistant host produced smaller lesions on susceptible leaflets and had a lower infection frequency than the strain passaged through susceptible cultivar Katahdin. No changes within IPI-O coding regions were detected after selection on the hosts with RB. Our results indicate that continual exposure to the RB gene can reduce P. infestans virulence and that interaction with this gene should not promote adaptive parasitism of the US8 strain of this pathogen.