**Core Concept**
Thromboangiitis obliterans, also known as Buerger's disease, is a non-atherosclerotic, segmental inflammatory disease of the small and medium-sized arteries and veins of the limbs, leading to ischemia and gangrene.

**Why the Correct Answer is Right**
Thromboangiitis obliterans is a significant cause of lower extremity ischemia in young smokers. The disease is characterized by inflammation of the blood vessels, leading to thrombosis and subsequent ischemia. The disease predominantly affects the small and medium-sized arteries and veins of the limbs, with a strong association with smoking. The disease often presents with claudication, pain at rest, and eventually gangrene in the affected limb. The patient's age, occupation as a farmer, and smoking habit make him more susceptible to this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Atherosclerosis is a common cause of peripheral artery disease, but it is more prevalent in older individuals and is not as strongly associated with smoking as thromboangiitis obliterans.

**Option B:** Raynaud's disease is a condition that affects blood flow to the fingers and toes, and while it can cause ischemia, it is not typically associated with gangrene.

**Option D:** Myocardial infarction is a condition that affects the heart and is not directly related to the development of gangrene in the foot.

**Clinical Pearl / High-Yield Fact**
Thromboangiitis obliterans is a disease that predominantly affects young smokers, particularly those with a history of heavy smoking. Early recognition and cessation of smoking are crucial in preventing disease progression and amputation.

**✓ Correct Answer: C. Thromboangiitis obliterans**