Mukherjee blessed the Gandhi-Nehru family scion by applying 'tilak' on his forhead and embraced him.
After meeting Mukherjee at his residence here, Gandhi met former Prime Minister Manmohan Singh at the party headquarters here.
Gandhi signed a set of nomination papers in the presence of Singh, senior party leaders Kamal Nath, Motilal Vora, Sheila Dikshit, Ahmed Patel, and Ashok Gehlot at the All India Congress Committee office here.
He accepted greetings from party leaders and chatted with them as they came up to him to get his signatures.
Over 90 sets of nominations are expected to be filed in support of Gandhi, whose election is a mere formality now, as there is no other candidate for the party's top post.
Gandhi will succeed his mother Sonia Gandhi, the longest serving Congress chief who has helmed the party since 1998.
Hundreds of Congress supporters thronged the party office ahead of the filing of nominations.
A large crowd of Congress workers were seen urging security guards at the premises to let them in to meet their party leader.
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