Characterization of Late Blight Resistance Potato Breeding Lines with the RB Gene from Solanum bulbocastanum

Late blight, caused by Phytophthora infestans, is an important disease of potato (Solanum tuberosum). Previous work has demonstrated that the wild diploid potato species Solanum bulbocastanum showed resistance to all known genotypes of P. infestans. In this study, the RB gene (also known as Rpi-blb1) from S. bulbocastanum was transformed and expressed into conventionally bred, late blight resistant breeding lines to evaluate the effect of pyramiding late blight resistance genes. All RB potato transformation events were confirmed by polymerase chain reaction and RB transcription was detected by reverse transcriptase-polymerase chain reaction. Multiple P. infestans genotypes were used to evaluate foliar host plant resistance using a greenhouse whole plant bioassay (WPB) and field trials. The results of the WPB were dependent on different pathogen genotypes. The RB lines derived from MSM171-A late blight resistant (LBR) parental line showed less foliar late blight than other RB lines. Field trials indicated most RB lines from three LBR parental lines had lower RAUDPC values than their parent and susceptible check line. Our results suggest that stacking of R-genes may be a viable strategy to obtain late blight resistant potato varieties.