An indigenous rice variety of Tamil Nadu known for its medicinal properties is:

Karuppu Kavuni
Mapillai Samba
Seeraga Samba
Thooyamalli

The correct answer is Karuppu Kavuni.

Karupu Kavuni is a traditional rice variety from Tamil Nadu, India. It is known for its medicinal properties, including its ability to lower blood sugar levels and reduce the risk of heart disease. Karuppu Kavuni is also a good source of fiber and antioxidants.

Mapillai Samba is another traditional rice variety from Tamil Nadu. It is a long-grain rice that is known for its taste and its ability to cook up fluffy and light. Mapillai Samba is not known for its medicinal properties.

Seeraga Samba is a short-grain rice variety that is popular in Tamil Nadu and other parts of South India. It is known for its nutty flavor and its ability to cook up sticky and delicious. Seeraga Samba is not known for its medicinal properties.

Thooyamalli is a long-grain rice variety that is grown in Tamil Nadu and other parts of South India. It is known for its white color and its ability to cook up fluffy and light. Thooyamalli is not known for its medicinal properties.

In conclusion, Karuppu Kavuni is the only indigenous rice variety of Tamil Nadu known for its medicinal properties.