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 a culture 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 individual strains of P. infestans are not capable of rapidly overcoming RB resistance even when it is the only host available.
Highlights
The oomycete phytopathogen Phytophthora infestans is the causal agent of late blight on potatoes (Solanum tuberosum L.)
The objective of this work was to observe the local adaptation of P. infestans on a host containing a single R gene conferring partial resistance
With a growing season of approximately 120 days, a field of potatoes under constantly ideal conditions for late blight would allow for 30 P. infestans generations
Summary
The oomycete phytopathogen Phytophthora infestans is the causal agent of late blight on potatoes (Solanum tuberosum L.). Late blight infections are destructive and can spread rapidly throughout a field under favorable environmental conditions. Intensive long-term efforts have been made to identify and integrate host resistance into potato and have led to the identification of numerous resistance genes from wild potato species. Rate-reducing, host resistance results in reduced pathogen virulence as defined by decreased infection efficiency, diminished sporangia production, and a reduction in the size of necrotic lesions [9]. A promising source of long-term resistance, the durability of partial late blight resistance remains to be seen. The environmental conditions supporting adaptation to partially resistant cultivars remains uncertain since evidence suggests that pathogen populations are most likely to adapt to the most readily available host, regardless of environment or their resistance characteristics [15]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call