The major suspects the barber Ivan Yakovlevich as the culprit. This suspicion stems from the fact that the barber finds the nose in his bread, and the nose seems to be unusually "familiar" to him, as if he recognized it.
Madame Podtotchina, while being a character in the story, is not connected to the disappearance of Kovaloff's nose in any way. She is simply a wealthy lady who is a neighbour of Kovaloff's and is known for her luxurious lifestyle and gossiping.
The story intentionally plays on the absurdity of the situation, making the reader question who could possibly be responsible for such a strange event. The focus is on the absurdity of the situation, not on pinpointing a specific culprit.