Possible Clues:

• Tropical crop from the Mediterranean
• One of 29 across produces grain from the Mediterranean
• It's a Tropic, and the Sign of the Goat
• Goat gets crop on south of the island
• Sign of winter wheat on island
• Sign of crop on southern side of island
• Many an ambitious person, astrologically
• A sign of Mediterranean island humour?
• That island grain is 28 across
• Sign of island growth