How to get value of Select Box (which is a component) in react js?

I have created SELECT drop down reusable component, which I am using in a form at different page by importing that component. How do i get the value of selection on submit of form?

    import React from 'react';
    export default class Combobox extends React.Component {    
        render() {
            retu (

            <div className="combobox-wrapper">
                <select className="form-control">
                {
                    this.props.combolist.map(function(item, i) {
                      retu (
                        <option key={i} value={item.name}>{item.name}</option> 
                      ) 
                    })
                  }
                </select>
            </div>
        );
        }

    }

    import React from 'react';
    import Combobox from '../components/Combobox';
    export default class Home extends React.Component {
    submit(event){
            //how to get combobox (Select list) value here
    } 
    render() {
           var comboList = [{name: 'Self'},{name: 'Mother'},
               {name: 'Father'},{name: 'Domestic Partner'}];
            retu (
                <div>
                    <div className="col-lg-10 col-md-10 col-sm-10 marginTop20">
                    <form ref="form" onSubmit={this.submit.bind(this)} >
                        <div className="row">
                            <Combobox combolist={comboList} />
                       </div>
        <div className="row">
                            <input type="submit" value="submit"
              className="btn btn-primary" />
                       </div>
    </form>