Set selected option after dynamically load select


I have 2 select in ionic 2 and i am able to dynamically populate the second based on the value selected in first. but i cannot set the selected default option after the population. i tried:

     <ion-select  (ionChange)="setCity($event)">
     <ion-option selected >City1</ion-option>
     <ion-option >City2</ion-option>

 < ion-item>
    <ion-select >
        <ion-option  *ngFor ="let location of locations[city]" 
             [selected] = location.selected >

  in .ts

  this.locations = {'City1':[{ zone: 'Zone1', selected: true},{zone:'Zone2', selected: false}],
              'City2': [{zone: 'Zone3', selected: false} {zone:'Zone4', selected: true}]}

   setCity(event){ = event;

thanks all

Maybe relevant.