Reduction of MLO1 expression in petunia increases resistance to powdery mildew

Cultivars of Petunia hybrida have been found to be susceptible to Podosphaera xanthii and other powdery mildew species. We examined whether powdery mildew resistance could be obtained through the knockdown of the petunia gene MLO1 by RNAi. Transformation of petunia with an MLO RNAi construct resulted in transgenic plants in which PhMLO1 expression was significantly reduced, but not completely silenced. The growth of Podosphaera xanthii on plants with reduced PhMLO1 expression was delayed and limited in extent compared to control plants. Powdery mildew resistance was found to be heritable in T1 progeny. The reduction in PhMLO1 expression was also associated with lower seed production, reduced germination frequency, and reduced plant height in T1 progeny. The knockdown of PhMLO1 increased resistance to powdery mildew in petunia, but pleiotropic effects on plant growth and development were also observed.