QualitySettings.anisotropicFiltering  

// Disable all anisotropic filtering

QualitySettings.anisotropicFiltering = AnisotropicFiltering.Disable;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        QualitySettings.anisotropicFiltering = AnisotropicFiltering.Disable;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        QualitySettings.anisotropicFiltering = AnisotropicFiltering.Disable