NEW DELHI — Concerns are mounting in India for the well-being of a sacred tree under which Lord Buddha first attained enlightenment more than 2,500 years ago.

The “Bodhi tree” in Bihar state, eastern India, has been afflicted with a mystery ailment, causing it to shed its leaves. The giant peepal, or ficus religiosa, situated outside the Mahabodhi shrine is sacred to Buddhists who make pilgrimages from all around the world to worship at it. Scientists have been called in to examine the tree that began dropping large quantities of fresh leaves late last month, raising fears that it was starting to die.

“We have taken soil and leaf samples, which are currently undergoing laboratory analysis,” said Dr. A.K. Singh of the Agricultural Research Institute in the nearby town of Patna. “The concern is that the new, young leaves are falling from the canopy.”

The fate of the tree — which is 110 years old and is, according to the temple authorities, the sixth regeneration of the original tree under which Lord Buddha attained perfect insight — is a highly sensitive subject in the Buddhist world.

Last year, reports that a local mafia gang had lopped off a branch to sell to Japanese pilgrims caused several countries, including Sri Lanka, Burma, and Japan to send high-level diplomatic delegations to inspect the place where the limb had allegedly been severed.

The temple authorities vigorously denied the incident had even occurred, saying the branch was an “old cut.” Amid further wild rumors of a cover-up, inconclusive scientific tests were ordered to ascertain how recently the branch had been cut down. Dr. Singh, who was visiting the shrine yesterday, said he was quietly called in 10 days ago after local monks noticed that the tree, whose leaves are sold to pilgrims for up to $10 each, was shedding at an unusually high rate.

He is reserving his judgment until the results of the tests. “It is normal that the tree sheds its old leaves in January and February, but the new growth which comes with the summer in March shouldn’t be falling to the ground,” he said.

“The leaves we have sent for testing have shown a certain amount of yellowing, although this may be due to more benign causes such as unusually high summer temperatures or problems with water or nutrition. As yet, we cannot tell.”

In 2002, Dr. Singh was among a number of scientists who were called in to save the tree, which could live for another 20 to 50 years, after it again showed signs of sickening. An infestation of mealy bug was diagnosed, and a course of pesticide and fungicide prescribed.

Experts also discovered that the devotees’ habit of placing candles under the tree in their thousands was coating the underside of the leaves with a layer of carbon that was impeding photosynthesis.

A separate and enclosed “lamp room” was set up a safe distance away to allow the leaves to breathe more easily. The practice of placing sweets under the tree — blamed for attracting the insect infestation — was also stopped.