Alright, I found the Plant Variety Protection Office which is the starting point if you have a plant that you want rights over. From the reading it states that you'll be issued a certificate and after a year and one else has describe the same plant for a certificate then the person can apply for a patent. However this don't mean you can make other people stop growing it. It's only for legal right over the market. So anyone can grow it, just once money has exchanged hands for the crop then legal actions can be taken.
But thanks for posting the patents, I couldn't find any at the time.