Foliar blight resistance transgene RB transcription levels correlated with blight resistance in tubers.

Millett, Benjamin P., Massimo Iorizzo, Dimitre S. Mollov, and James M. Bradeen

Late blight of potato caused by Phytophthora infestans is an important disease, resulting in multibillion dollar losses annually worldwide. Recent efforts have led to the identification and cloning of multiple late blight resistance (R) genes. One of the most promising genes, RB, identified from wild potato Solanum bulbocastanum, imparts broad spectrum foliar blight resistance. Previous studies have noted that foliar and tuber resistance to late blight are not necessarily controlled by the same R genes. The cloning of RB has provided an opportunity to directly examine this phenomenon. Tubers of 11 +RB transgenic cultivated potato lines were used in whole tuber phenotypic assays. Although all 11 lines are foliar blight resistant, all but two lines were as susceptible to tuber blight as nontransgenic controls. Two lines displayed enhanced tuber resistance. Quantitative Real-Time RT-PCR results confirmed that RB is transcribed in tubers of all lines at all time points. Interestingly, a correlation between RB transcription and tuber blight resistance was noted, with the two transgenic lines with enhanced tuber resistance showing the highest levels of transgene transcription. This correlation mimics results observed in foliar assays conducted by our laboratory, suggesting that manipulation of RB transgene transcription may be an effective means of enhancing both foliar and tuber blight resistance.