Can a collecting bank debit the account of the depositor when the checks indorsed to it (bank) were forged?

Yes, because the depositor of a check as indorser warrants that it is genuine and in all respect what it purports to be. Thus, when the checks deposited had forged indorsements and the collecting bank, as a consequence of such forgery, was made to pay the drawee bank, the collecting bank can debit the account of the depositor for his breach of warranty (Jai‐Alai Corporation Of The Philippines v. BPI, G.R. No. L-­‐29432, Aug. 6, 1975).