"If parties have to contest on their own symbol why we went for the merger? Only an 'ullu' (fool) can talk such things," Prasad told reporters here.
He said such speculative talks were part of "sinister design to spread confusion."
The RJD President, who is among six chosen in a committee that would suggest name, flag and symbol of the new identity to its head Mulayam Singh Yadav, said they were treading cautiously.
"There is no point in showing haste and we are treading cautiously after giving much thoughts on every issue," Prasad said on arrival here from Delhi.
The RJD President said SP chief Mulayam Singh Yadav who has been made head of the new party would complete rest of the formalities soon.
Earlier, Bihar Chief Minister Nitish Kumar had also dispelled uncertainty over flag and symbol and had said all formalities related to the formation of the new political outfit will be completed by its president Mulayam Singh Yadav.
"Mulayam Singh Yadav has been made the president of new political party (post-merger of Janata Parivar members) and he will complete all formalities," Kumar told reporters.
The opposition BJP had mocked the Janata Parivar members for hastily announcing the merger without taking a decision on its flag and symbol.
Asked as who would be face of the new party in Bihar poll, Prasad said in a lighter vein "we will ask you all (mediapersons) about it when time comes."
On BJP making fun of merger of six parties, Prasad said "they are under fear on our joining hands and are doing so to impress Prime Minister Narendra Modi."
The RJD chief said Congress, CPI, CPIM and other secular parties would be included in fight against BJP in Bihar poll.
He claimed they would win the coming Bihar poll by two-thirds majority and speed up downfall of BJP in the country which started with Delhi election.
Samajwadi Party, JD(U), RJD, INLD, JD(S) and Samajwadi Janata Party formally decided to merge at a meeting on April 15.
The merger came almost two decades after the then Janata Dal disintegrated in the 90s.

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