using static System.Console;

​

public class Program {

    public static void Main() {

        var array = new string[1, 6] {{"texto", "", "", "", "", ""}};

        if (array.ContainsInFirstCol("texto")) {

            WriteLine("achou");        

        }

    }

}

​

public static class ArrayExt {

    public static bool ContainsInFirstCol(this string[,] array, string search) {

        for (int row = array.GetLowerBound(0); row <= array.GetUpperBound(0); row++) {

            if (array[row, 0].Contains(search)) {

                return true;

            }

        }

        return false;

    }

}

​