Ion-select don´t selected default value when charge the page

This is my html code

<ion-item class="input-item item-has-value">
                    <ion-label position="floating">Tipo Trabajo</ion-label>
                    <ion-select formControlName="idTipoTrabajo" cancelText="Cancelar" okText="OK">
                        <ng-container *ngFor="let subitem of tipoTrabajoList">
                            <ng-container *ngIf=" == item.idTipoTrabajo">
                                <ion-select-option [value]="">{{ subitem.nombre }}</ion-select-option>

and this charge the page in your page.ts

		this.generalForm = new FormGroup({
			idJobType: new FormControl([this.item.JobType], Validators.compose([

When you change pages, a selected value does not return to the item. How can I do when loading the page, can I show the “item” of value “by default”?

The result is already compiled in this way.

@angular/core = 7.2.15
@ionic-native/core = 5.15.0
@ionic/angular = 4.11.0
@angular/cli = 7.3.9