• Nature of Plant Phytoalexins:
• Definition: Phytoalexins (coined by Müller and Börger, 1940) are low-molecular-weight antimicrobial secondary metabolites biosynthesized de novo by plant cells in response to pathogen attack or elicitor treatment.
• Chemical Classification: Phytoalexins are primarily phenolic compounds (e.g., isoflavonoids such as pisatin in pea, phaseollin in bean, medicarpin in alfalfa; stilbenes like resveratrol in grapes) and terpenoids/sesquiterpenoids (rishitin in potato, gossypol in cotton).
• Conclusion: Phytoalexins produced in response to infection are predominantly phenolic compounds (Option 1).

Correct option: (1) Phenolic compounds