Chemicals that have been implicated in attraction of rhizobia are

Correct option is A

✅ (a) Flavonoids [Root Exudates for Signaling] • Flavonoids are phenolic compounds exuded by legume roots. • They act as chemical signals that attract Rhizobium species in the rhizosphere. • Flavonoids induce the expression of nod genes in rhizobia, initiating nodulation. • Example: Luteolin in alfalfa is a well-known inducer for Rhizobium meliloti.
❌ (b) Sugars • Sugars serve as a carbon source for rhizobia but do not initiate signaling. • Not involved in attraction or nod gene induction.
❌ (c) Peptides • Peptides are part of internal plant signaling. • No role in rhizobial attraction from soil.
❌ (d) Organic acids • Involved in nutrient solubilization and microbial metabolism, not in rhizobial signaling.