So what's the specific reason this morning for the spike in Italy's implicit interest rate?

Well it is because the organisation through which investors clear or settle their bond transactions, LCH.Clearnet, has announced that those trading in Italian bonds have to deposit more cash with it to cover the risks of non-payment.

In essence, it means that LCH.Clearnet has decided that the risks of trading in Italian government debt have increased. And the important point is that by insisting that those trading in the bonds put up more "margin", that they deposit more cash with LCH.Clearnet to cover the risks, LCH.Clearnet has made it more expensive to trade in Italian debt.