1.Preheat oven to 180°C/160°C fan-forced. Grease deep 20cm ring cake pan; line base and side with baking paper.
2.Beat butter and sugar in medium bowl with electric mixer until light and fluffy. Beat in eggs, one at a time. Stir in flour and combined yogurt and juice, in two batches. Stir in blueberries and rind until just combined.
3.Spread mixture into pan; bake about 1 hour. Stand cake in pan 5 minutes; turn onto wire rack over tray.
4.Meanwhile, make orange syrup. Stir sugar, juice and the water in small saucepan over heat, without boiling, until sugar dissolves. Stir in rind; simmer, uncovered, without stirring, 5 minutes.