The billionaire former prime minister blamed the split, without ever naming Alfano, on "differences not of policy or values but between personalities who have created a poisonous atmosphere".
Alfano, who announced the "divorce" after late-night talks on Friday, stayed away along with some 50 other defectors from a meeting today of Berlusconi's People of Freedom (PDL) party.
During a rambling speech lasting an hour and a half, the scandal-tainted Berlusconi, 77, drew frequent applause.
In a conciliatory gesture, Berlusconi added however that Alfano's grouping would be a "necessary member" of the 200-strong centre-right voting bloc.
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The PDL meeting was meant to be a happy event at which the party would be rebaptised Forza Italia ("Go Italy"), the sporty name Berlusconi used when he first launched the party in 1994.
Alfano, whose faction is to be called the New Centre Right, said his decision had been "very bitter, painful but fair".
He said yesterday he would not be part of the reborn Forza Italia because "these past few weeks have shown to what extent extreme forces have prevailed within our movement", referring to a belief by his supporters that Berlusconi was pandering to hardliners.
Berlusconi's party has been in turmoil since September when he tried to bring down Italy's uneasy left-right coalition government by withdrawing his ministers, but was forced into a humiliating climbdown when they refused to heed his orders.
The daily La Stampa described the break-up as the "first post-Berlusconi act" with an immediate consequence: "The government is saved, with a new, smaller but also more united (parliamentary) majority.