what chemical compound give the first mentioned root vegetable its sharp taste?
Glucosinolate, myrosinase, and isothiocyanate
Radish
Radishes owe their sharp flavor to the various chemical compounds produced by the plants, including glucosinolate, myrosinase, and isothiocyanate
when did radishes become a food source for humans They were domesticated in Asia prior to Roman times. how are they consumed? They are mostly eaten raw as a crunchy salad vegetable with bite. are there other varieties? Yes, they differ based on the  seasons when they are grown and a variety of shapes, lengths, colors, and sizes, such as red, pink, white, gray-black, or yellow radishes, with round or elongated roots that can grow longer than a parsnip. what are parsnips? It is a root vegetable closely related to carrot and parsley; all belong to the family Apiaceae.
wiki:5330967
Radish [SEP] Introduction
The radish ("Raphanus raphanistrum" subsp. "sativus") is an edible root vegetable of the family Brassicaceae that was domesticated in Asia prior to Roman times. Radishes are grown and consumed throughout the world, being mostly eaten raw as a crunchy salad vegetable with bite. There are numerous varieties, varying in size, flavor, color, and length of time they take to mature. Radishes owe their sharp flavor to the various chemical compounds produced by the plants, including glucosinolate, myrosinase, and isothiocyanate. They are sometimes grown as companion plants and suffer from few pests and diseases. They germinate quickly and grow rapidly, common smaller varieties being ready for consumption within a month, while larger "daikon" varieties take several months.