| Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most important disease of potato (Solanum tuberosum L.) because it affects foliage, tuber yield and storage ability. Previous work demonstrated that the wild diploid potato species S. bulbocastanum is highly resistant to all known genotypes of P. infestans. In this study, we transformed and expressed the RB gene from S. bulbocastanum (Rpi-blb1) into conventionally bred, late blight resistant breeding lines to evaluate the effect of pyramided late blight resistance genes. All RB potato transformation events were confirmed by Polymerase Chain Reaction (PCR) and RB expression was detected by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR). Foliar host plant resistance was characterized using detached leaf bioassays (DLB), greenhouse whole plant bioassays (WPB) and an inoculated field trial. A set of four P. infestans genotypes (US-8, US-22, US-23 and US-24) were used to evaluate foliar resistance in the DLB and WPB experiments, whereas only the US-22 genotype was used in the field. The results of the greenhouse whole-plant bioassays and detached leaf bioassays were varied. However, the highest level of resistance was demonstrated in conventionally bred, late blight resistant lines, which also contained the RB gene from S. bulbocastanum. The results from the field trial were more explanatory and proved that pyramiding resistance genes is an effective strategy to increase the level of late blight resistance. |
