FilterMode.Point  

renderer.material.mainTexture.filterMode = FilterMode.Point;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Awake() {
renderer.material.mainTexture.filterMode = FilterMode.Point;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Awake():
renderer.material.mainTexture.filterMode = FilterMode.Point