JSON无法读取未定义的属性“img”

这是json文件

[
    {
        "teachers": {
            "img":"assets/home/img.png"
        }
    }        
]

homeds: Home[];

constructor(
    public navCtrl: NavController, 
    public navParams: NavParams, 
    public dataService: DataProvider,
    public loadingCtrl: LoadingController
) {
    this.dataService
        .fetchData()
        .subscribe((data) => {
            this.homeds = data
        })
}

<ion-col width-50 *ngFor="let home of homeds">
    <img src="{{ home.teachers.img }}" alt="">
</ion-col>

当我运行这个代码时

运行时错误 无法读取未定义的属性“img”

我做错了什么?