The indicator plant used for citrus greening is –

✅Explanation:Sweet orange is a highly sensitive indicator plant for citrus greening disease. When infected, it develops characteristic symptoms like yellowing, leaf drop, and stunted growth.
📌Other Options Explanations:While other citrus varieties can also be infected with citrus greening, sweet orange is particularly susceptible and is often used for early detection and diagnosis.

🛑Additional Information :
-Citrus greening disease (Chinese: huánglóngbìng; lit. 'yellow dragon disease') is a disease of citrus caused by a vector-transmitted pathogen.
-The causative agents are motile bacteria, Candidatus Liberibacter spp.
-The disease is vectored and transmitted by the Asian citrus psyllid (Diaphorina citri) and the African citrus psyllid (Trioza erytreae), also known as the two-spotted citrus psyllid.
-Sweet orange is used as an indicator plant.